U.S. patent application number 13/214575 was filed with the patent office on 2012-03-01 for universal power converter.
This patent application is currently assigned to IDEAL POWER CONVERTERS, INC.. Invention is credited to William C. Alexander.
Application Number | 20120051100 13/214575 |
Document ID | / |
Family ID | 38923734 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120051100 |
Kind Code |
A1 |
Alexander; William C. |
March 1, 2012 |
Universal Power Converter
Abstract
Methods and systems for transforming electric power between two
or more portals. Any or all portals can be DC, single phase AC, or
multi-phase AC. Conversion is accomplished by a plurality of
bi-directional conducting and blocking semiconductor switches which
alternately connect an inductor and parallel capacitor between said
portals, such that energy is transferred into the inductor from one
or more input portals and/or phases, then the energy is transferred
out of the inductor to one or more output portals and/or phases,
with said parallel capacitor facilitating "soft" turn-off, and with
any excess inductor energy being returned back to the input. Soft
turn-on and reverse recovery is also facilitated. Said
hi-directional switches allow for two power transfers per
inductor/capacitor cycle, thereby maximizing inductor/capacitor
utilization as well as providing for optimum converter operation
with high input/output voltage ratios. Control means coordinate the
switches to accomplish the desired power transfers.
Inventors: |
Alexander; William C.;
(Spicewood, TX) |
Assignee: |
IDEAL POWER CONVERTERS,
INC.
Austin
TX
|
Family ID: |
38923734 |
Appl. No.: |
13/214575 |
Filed: |
August 22, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12479207 |
Jun 5, 2009 |
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13214575 |
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11759006 |
Jun 6, 2007 |
7599196 |
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12479207 |
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60811191 |
Jun 6, 2006 |
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Current U.S.
Class: |
363/37 |
Current CPC
Class: |
H02M 5/225 20130101;
H02M 5/10 20130101; H02M 5/297 20130101; H02M 7/4807 20130101; Y02B
70/1441 20130101; H02M 2007/4815 20130101; H02M 3/33584 20130101;
H02M 5/293 20130101; H02M 3/1582 20130101; Y02B 70/10 20130101;
H02M 7/797 20130101 |
Class at
Publication: |
363/37 |
International
Class: |
H02M 5/45 20060101
H02M005/45 |
Claims
1. A Buck-Boost Converter, comprising: an energy-transfer
reactance; first and second power portals, each with two or more
ports by which electrical power is input from or output to said
portals; first and second bridge switch arrays interposed between
said reactance and respective ones of said portals, and each
comprising one bidirectional switching device for each said port of
each said power portal.
2. The converter of claim 1, wherein said bridge arrays are
symmetrically connected to said energy-transfer reactance.
3. The converter of claim 1, wherein said bridge arrays are
full-bridge arrays.
4. The converter of claim 1, further comprising a third switch
array, which is connected to said reactance in parallel with said
first and second switch arrays.
5. The converter of claim 1, wherein each said portal is shunted by
a capacitor which provides a low-impedance voltage source
thereat.
6. The converter of claim 1, wherein said reactance comprises a
transformer.
7. The converter of claim 1, wherein said reactance comprises a
parallel combination of an inductor with a capacitor.
8. The converter of claim 1, wherein said reactance is driven at a
base frequency which is less than half its resonant frequency.
9. A Buck-Boost Converter, comprising: an energy-transfer
reactance; a first bridge switch array comprising at least two
bidirectional switching devices which are jointly connected to
operatively connect at least one terminal of said reactance to a
power input, with reversible polarity of connection; a second
bridge switch array comprising at least two bidirectional switching
devices which are jointly connected to operatively connect at least
one terminal of said reactance to a power output, with reversible
polarity of connection; wherein said first switch array drives said
reactance with a nonsinusoidal voltage waveform.
10. The converter of claim 9, wherein said bridge arrays are
symmetrically connected to said energy-transfer reactance.
11. The converter of claim 9, wherein said bridge arrays are
full-bridge arrays.
12. The converter of claim 9, further comprising a third switch
array, which is connected to said reactance in parallel with said
first and second switch arrays.
13. The converter of claim 9, wherein said input is shunted by a
capacitor which provides a low-impedance voltage source
thereat.
14. The converter of claim 9, wherein said input and output are
both shunted by respective capacitors which provide low-impedance
voltage sources thereat.
15. The converter of claim 9, wherein said reactance comprises a
transformer.
16. The converter of claim 9, wherein said reactance comprises a
parallel combination of an inductor with a capacitor.
17. The converter of claim 9, wherein said reactance is driven at a
base frequency which is less than half its resonant frequency.
18. The converter of claim, wherein said bridge arrays are
symmetrically connected to said energy-transfer reactance.
19. A Full-Bridge Buck-Boost Converter, comprising: first and
second full bridge switch arrays, each comprising at least four
bidirectional switching devices; a substantially parallel
inductor-capacitor combination symmetrically connected to be driven
separately by either said switch array; one of said switch arrays
being operatively connected to a power input, and the other thereof
being operatively connected to supply a power output.
20. The converter of claim 19, wherein said power input is shunted
by a capacitor which provides a low-impedance voltage source
thereat.
21. The converter of claim 19, wherein said power output is shunted
by a capacitor which provides a low-impedance voltage sink
thereat.
22. The converter of claim 19, wherein said reactance comprises a
transformer.
23. The converter of claim 19, wherein said bridge arrays are
full-bridge arrays.
24. The converter of claim 19, further comprising a third switch
array, which is connected to said reactance in parallel with said
first and second switch arrays.
25. The converter of claim 19, wherein said reactance comprises a
parallel combination of an inductor with a capacitor.
26. The converter of claim 19, wherein said reactance is driven at
a base frequency which is less than half its resonant
frequency.
27. A Buck-Boost Converter, comprising: first and second switch
arrays, each comprising least two bidirectional switching devices;
a substantially parallel inductor-capacitor combination connected
to each said switch array; wherein a first one of said switch
arrays is operatively connected to a power input, and is operated
to drive power into said inductor-capacitor combination with a
non-sinusoidal waveform; and wherein a second one of said switch
arrays is operated to extract power from said inductor-capacitor
combination to an output.
28. The converter of claim 27, wherein said bridge arrays are
full-bridge arrays.
29. The converter of claim 27, wherein said bridge arrays are
symmetrically connected to said energy-transfer reactance.
30. The converter of claim 27, further comprising a third switch
array, which is connected to said reactance in parallel with said
first and second switch arrays.
31. The converter of claim 27, wherein said power input is shunted
by a capacitor which provides a low-impedance voltage source
thereat.
32. The converter of claim 27, wherein said power output is shunted
by a capacitor which provides a low-impedance voltage sink
thereat.
33. The converter of claim 27, wherein said inductor is implemented
by a transformer.
34. A Buck-Boost Converter, comprising: first and second switch
arrays, each comprising at least two bidirectional switching
devices; an energy-transfer reactance connected to each said switch
array; wherein a first one of said switch arrays is connected
through respective capacitive reactances to a polyphase power
input, and operated to drive power into said reactance from
multiple different legs of said power input in succession with a
non-sinusoidal waveform; and wherein a second one of said switch
arrays is operated to extract power from said reactance to an
output.
35. The converter of claim 34, wherein said bridge arrays are
full-bridge arrays.
36. The converter of claim 34, wherein said bridge arrays are
symmetrically connected to said energy-transfer reactance.
37. The converter of claim 34, further comprising a third switch
array, which is connected to said reactance in parallel with said
first and second switch arrays.
38. The converter of claim 34, wherein said power input is shunted
by a capacitor which provides a low-impedance voltage source
thereat 39. The converter of claim 34, wherein said power output is
shunted by a capacitor which provides a low-impedance voltage sink
thereat.
39. The converter of claim 34, wherein said reactance comprises a
transformer.
40. A power converter, comprising: an energy-transfer reactance
comprising at least one inductor; an input switch array configured
to drive AC current through said reactance; and an output network
connected to extract energy from said reactance; wherein said input
switch array performs at least two drive operations, in the same
direction but from different sources, during a single half-cycle of
said reactance.
41. The converter of claim 40, wherein said inductance is
implemented by a transformer.
42. The converter of claim 40, wherein said inductance is
paralleled by a capacitor.
43. A power converter, comprising: an energy-transfer reactance
comprising at least one inductor, and operating at a primary AC
magnetic field frequency which is less than half of the reactance's
resonant frequency; an input switch array configured to drive AC
current through said reactance; and an output network switch array
connected to extract energy from said reactance; wherein said input
switch array performs at least two drive operations, in the same
direction but from different sources, during a single half-cycle of
said reactance.
44. The converter of claim 43, wherein said switch arrays are
full-bridge arrays.
45. The converter of claim, wherein said reactance comprises a
transformer.
46. A power converter, comprising: an energy-transfer reactance
comprising at least one inductor, and operating at a primary AC
magnetic field frequency which is less than half of the reactance's
resonant frequency; an input switch array configured to drive
current through said reactance; and an output switch array to
extract energy from said reactance; wherein said input switch array
performs at least two different drive operations at different times
during a single cycle of said reactance, and wherein said output
switch array performs at least two different drive operations at
different times during a single cycle of said reactance.
47. The converter of claim 46, wherein said switch arrays are
full-bridge arrays.
48. The converter of claim 46, wherein said first array connects
said reactance to a power input which is shunted by a capacitor
which provides a low-impedance voltage source thereat.
49. The converter of claim 46, wherein said first array connects
said reactance to a power input which is shunted by a capacitor
which provides a low-impedance voltage source thereat.
50. The converter of claim 46, wherein said reactance comprises a
transformer.
51. A Buck-Boost Converter, comprising: an energy-transfer
reactance comprising at least one inductor; an input switch array
configured to drive AC current, with no average DC current, through
said reactance; and an output network connected to extract energy
from said reactance.
52. The converter of claim 51, wherein said switch arrays are
full-bridge arrays.
53. The converter of claim 51, wherein said reactance comprises a
transformer.
54. A Buck-Boost Converter, comprising: an energy-transfer
reactance comprising at least one inductor; a plurality of input
switch arrays, each said array configured to drive AC current, with
no average DC current, through said reactance; and a plurality of
output switch arrays, each connected to extract energy from said
reactance; said arrays having no more than two switches driving or
extracting energy from said reactance at any given time; wherein
said input switch arrays individually drive said reactance with a
nonsinusoidal voltage waveform.
55. The converter of claim 54, wherein said bridge arrays are
full-bridge arrays.
56. The converter of claim 54, wherein said switch arrays each
selectably connect said reactance to a low-impedance voltage
source/sink.
57. The converter of claim 54, wherein said inductor is implemented
as a transformer.
58. The converter of claim 54, wherein said inductance is
paralleled by a capacitor.
59. A power conversion circuit, comprising: an input stage which
repeatedly, at various times, drives current into the parallel
combination of an inductor and a capacitor, and immediately
thereafter temporarily disconnects said parallel combination from
external connections, to thereby transfer some energy from said
inductor to said capacitor; wherein said action of driving current
is performed in opposite senses and various times, and wherein said
disconnecting operation is performed substantially identically for
both directions of said step of driving current; and an output
stage which extracts energy from said parallel combination, to
thereby perform power conversion.
60. The converter of claim 59, wherein said input stage comprises a
full-bridge array of switches.
61. The converter of claim 59, wherein said wherein said input and
output stages each comprise a full-bridge array of switches, and
are symmetrically connected to said energy-transfer reactance.
62. The converter of claim 59, wherein said stages each selectable
connect said reactance to a low-impedance voltage source/sink.
63. The converter of claim 59, wherein said reactance comprises a
transformer.
64. A power conversion circuit, comprising: an input stage which
repeatedly drives current into the parallel combination of an
inductor and a capacitor, and immediately thereafter temporarily
disconnects said parallel combination from external connections, to
thereby transfer some energy from said inductor to said capacitor;
wherein said input stage drives current in different senses at
different times; and an output stage which repeatedly couples power
out of said parallel combination, and immediately thereafter
temporarily disconnects said parallel combination from external
connections, to thereby transfer some energy from said inductor to
said capacitor; wherein said output stage couples power out of said
combination during two opposite directions of current therein;
wherein said input and output stages both disconnect said parallel
combination substantially identically for both directions of
current in said combination.
65. The circuit of claim 64, wherein each said driving action is
performed using multiple different drive pulses from different legs
of a polyphase power line.
66. A Soft Switched Universal Full-Bridge Buck-Boost Converter,
comprising: an inductor with a first and second port; a capacitor
attached in parallel with said inductor; connections to a plurality
of voltage sources or sinks (portals) of electric power each with a
plurality of ports; a first set of electronic bi-directional
switches that comprise said connections between said first port of
the inductor and each said port of each said portal, with one said
switch between the first port of the inductor and each port of each
portal; a second set of electronic hi-directional switches that
comprise said connections between said second port of the inductor
and each port of each portal, with one switch between the second
port of the inductor and each port of each portal; capacitive
filtering means connected between each said port within each said
portal; control means to coordinate said switches to connect said
inductor to port pairs on each portal, with no more than two
switches enabled at any given time; said control means further
coordinating said switches to first store electrical energy in the
inductor by enabling two switches on a given input portal to
connect the inductor to said input portal, then disabling the
switches after the proper amount of energy has been stored in the
inductor; and said control means may enable further pairs of
switches on the same or other input portals so as to further
energize the inductor, and disable said switches after the
appropriate inductor energizing is complete; said control means
further enables another pair of switches on another, output, portal
to transfer some or all of the inductor energy into said output
portal, and then disables said switches after the desired amount of
charge has been transferred to said portal; said control means may
enable further pairs of switches on the same or other output
portals so as to further send charge into said output portals, and
disable said switches after the desired amount of charge has been
transferred to said portal; and if the inductor has excess energy
after discharging into the last output portal, said control means
then enables an appropriate switch pair to direct said excess
energy back into the input portal; wherein said control means may
modify the above sequence so as to achieve any required energy
transfer among the ports and portals; said inductor magnetically
storing electrical energy in the form of electric current, using
said switches; energy transfer from one or more input portals to
said inductor occurring via current flow through two or more said
ports of one or more said portals, with only one pair of ports; and
cyclically repeating said energy and charge transfers.
67. The converter of claim 66, in which after energy transfer and
capacitor charging if any, switches complementary to said first
switches are enabled, to again transfer electric energy into the
inductor, but with the inductor current in the opposite direction;
and thereafter the energy is again subsequently transferred to one
or more other portals, also by means of enabling switches
complementary to said second switches, to thereby complete a
Full-cycle operation, which is repeated as required.
68. The converter of claim 66, wherein said inductor is implemented
by a transformer with equivalent inductive capacity, which provides
galvanic isolation, and optionally current/voltage transforming.
between input and output.
69. The converter of claim 66, where one or more of the portals is
DC and power flow is unidirectional at all times, and switches
connected to said DC and unidirectional power portal may be
uni-directional in the direction to support said Unidirectional
power flow.
70. A half-bridge embodiment of the converter of claim 66, in which
only said first set of bi-directional switches are used with said
first port of said inductor, with said second port of the inductor
connected to an actual or virtual converter ground, with a virtual
ground composed of capacitive connections to the ports of said
portals.
71. A composite of n converters according to claim 66, connected at
least partially in parallel, and operating at inductor phase angles
separated by 180/n degrees; whereby the amount of input/output
filtering can be reduced.
72. A Soft-switched Ralf-Bridge Buck-Boost Converter, comprising:
first and second power portals, each with two or more ports by
which electrical power is input from or output to said portals,
first and second half-bridge switch arrays, each comprising one
bidirectional switching device for each said port of each said
power portal, an energy-transfer link reactance with one port
connected to both said switch arrays, and with the other port
connected to an actual or virtual ground, such that said actual or
virtual ground maintains at a relatively constant voltage, each of
said switch arrays being connected to a power portal with said
portal possessing capacitive reactance between the legs of said
portals configured so as to approximate a voltage source, with
power transfer occurring between said portals via said
energy-transfer reactance, said link energy-transfer reactance
consisting of an link inductor and capacitance in parallel, said
power transfer being accomplished in a first power cycle as one or
more pairs of input portal legs are singularly or sequentially
connected to said energy-transfer reactance to store energy via
increased current flow and inductance into said link inductor,
followed by one or more pairs of output portal legs singularly or
sequentially connected to said energy-transfer reactance to remove
energy via decreased current flow and inductance from said link
inductor, with any excess energy in said link inductor subsequently
returned back to one or more said input portal leg pairs, followed
by a reversal of current within said link inductor and a repeat of
the heretofore described energy transfer, to constitute a second
power cycle, from input to output portal leg pairs, but with
opposite but equal current flow in said link inductor and utilizing
switches of said switch arrays which are complimentary to said
switches used for said first cycle of said power transfer; said
first and second power cycles comprising a single voltage cycle of
the energy-transfer link reactance; said capacitance, in
conjunction with said current reversal, producing soft-switching of
said switches with low-voltage turn-off, zero voltage turn-on, and
low reverse recovery losses; said bidirectional switching devices
being capable of blocking voltage in either direction and
conducting current in either direction; wherein said power transfer
cycles are continuously repeated by said control means to produce
said power transfer on a continuing basis; and wherein control
means coordinate said switching actions to produce current and
power transfer via said power cycles as required to produce desired
output voltage and current, as may be used to drive single or
polyphase motors at variable speed and voltage, or to drive any
other electrical DC, single phase AC, polyphase AC, and/or multiple
DC loads; said capacitance, in conjunction with said current
reversal, producing soft-off-switching of said switches with
low-voltage turn-off, as current is shunted from each turning-off
switch into said substantially parallel capacitance, said switches
having soft turn-on as diodes as the link reactance voltage causes
control means enabled switches to transition from reverse to
forward bias, said switches having soft reverse blocking turn-off
as the link inductor current linearly decreases to zero after
discharging into an output port.
73. A Soft-switched Full-Bridge Buck-Boost Converter, comprising:
first and second power portals, each with two or more ports by
which electrical power is input from or output to said portals,
first and second full-bridge switch arrays, each comprising two
bidirectional switching devices for each said port of each said
power portal, a energy-transfer link reactance symmetrically
connected to both said switch arrays, each of said switch arrays
being connected to a power portal with said portal possessing
capacitive reactance between the legs of said portals configured so
as to approximate a voltage source, with power transfer between
said portals via said energy-transfer reactance, Said link
energy-transfer reactance consisting of an link inductor and
capacitance in parallel, said power transfer being accomplished in
a first power cycle as one or more pairs of input portal legs are
singularly or sequentially connected to said energy-transfer
reactance to store energy via increased current flow and inductance
into said link inductor, followed by one or more pairs of output
portal legs singularly or sequentially connected to said
energy-transfer reactance to remove energy via decreased current
flow and inductance from said link inductor, with any excess energy
in said link inductor subsequently returned back to one or more
said input portal leg pairs, followed by a reversal of current
within said link inductor and a repeat of the heretofore described
energy transfer, to constitute a second power cycle, from input to
output portal leg pairs, but with opposite but equal current flow
in said link inductor and utilizing switches of said switch arrays
which are complimentary to said switches used for said first cycle
of said power transfer; said tryst and second power cycles comprise
a single voltage cycle of the energy-transfer link reactance; said
bidirectional switching devices being capable of blocking voltage
in either direction and conducting current in either direction;
said power transfer cycles being continuously repeated by said
control means to produce said power transfer on a continuing basis;
said control means coordinating said switching actions to produce
current and power transfer via said power cycles as required to
produce desired output voltage and current, as may be used to drive
single or polyphase motors at variable speed and voltage, or to
drive any other electrical DC, single phase AC, polyphase AC,
and/or multiple DC loads; said capacitance, in conjunction with
said current reversal, producing soft-off-switching of said
switches with low-voltage turn-off, as current is shunted from each
turning-off switch into said substantially parallel capacitance;
said switches having soft turn-on as diodes as the link reactance
voltage causes control means enabled switches to transition from
reverse to forward bias; said switches having soft reverse blocking
turn-off as the link inductor current linearly decreases to zero
after discharging into an output port.
74. The converter of claim 73, further comprising an isolation
transformer.
75. A multiple power module soft-switched converter, comprising
multiple converters according to claim 73 connected in parallel
between an input portal and an output portal, and commonly
controlled to minimize harmonics in the current drawn from and
delivered to said input and output portals.
76. An electric vehicle, comprising at least one motor, at least
one electrical energy storage device, and a power converter
according to claim 1, 9, 19, 27, 34, 40, 43, 46, 51, 54, 59, or
64.
77. A solar energy system comprising at least one photovoltaic
array, at least one electrical energy storage device, and a power
converter according to claim 1, 9, 19, 27, 34, 40, 43, 46, 51, 54,
59, or 64.
78. A motor system comprising a polyphase power line connection, a
polyphase motor, and a power converter according to claim 1, 9, 19,
27, 34, 40, 43, 46, 51, 54, 59, or 64 connected therebetween as a
variable-frequency drive.
79. A multiple power module soft-switched converter, comprising
multiple converters according to claim 1, 9, 19, 27, 34, 40, 43,
46, 51, 54, 59, or 64 connected in parallel between an input portal
and an output portal, and commonly controlled to minimize harmonics
in the current drawn from and delivered to said input and output
portals.
80. A composite of n converters according to claim 1, 9, 19, 27,
34, 40, 43, 46, 51, 54, 59, or 64, connected at least partially in
parallel, and operating at inductor phase angles separated by 180/n
degrees; whereby the amount of input/output filtering can be
reduced.
Description
CROSS-REFERENCE TO OTHER APPLICATION
[0001] Priority is claimed from U.S. provisional application
60/811,191 filed Jun. 6, 2006, which is hereby incorporated by
reference.
BACKGROUND AND SUMMARY OF THE INVENTIONS
[0002] The present application relates to electric power
conversion, and more particularly to buck-boost converter circuits,
methods and systems which can convert DC to DC. DC to AC, and
AC-AC, and are suitable for applications including line power
conditioners, battery chargers, hybrid vehicle power systems, solar
power systems, motor drives, and utility power conversion.
[0003] Numerous techniques have been proposed for electronic
conversion of electric power from one form into another. A
technique in common commercial usage for operating three phase
induction motors at variable frequency and voltage off of fixed
frequency and voltage utility power is the AC-DC-AC technique of
the input diode bridge. DC-link capacitor, and the output active
switch bridge, under PWM control, is shown in FIG. 3. This motor
drive technique ("standard drive") results in compact and low-cost
motor drives, since no magnetic components are required and only
six active switches are needed.
[0004] A number of difficulties exist with the standard drive,
however. The input current, while nominally in phase with the input
voltage, is typically drawn in pulses. These pulses cause increased
electric losses in the entire electrical distribution system. The
pulses also cause higher losses in the DC link capacitor. These
losses reduce the efficiency of the drive, and also lessen the
useful life of the DC link capacitor (commonly an Aluminum
Electrolytic type), which has a limited life in an case. If the
impedance of the source power is too low, the pulses may become so
large as to be unmanageable, in which case it is necessary to add
reactance in the input lines, which increases losses, size, cost,
and weight of the drive. Also, the voltage available for the output
section is reduced, which may lead to loss-producing harmonics or
lower-than-design voltage on the output waveform when full power,
full speed motor operation is called for.
[0005] Due to the fixed DC-link voltage, the output switches are
typically operated with Pulse Width Modulation (PWM) to synthesize
a quasi-sinusoidal current waveform into the motor, using the
inductance of the motor to translate the high voltage switched
waveform from the drive into a more sinusoidal shape for the
current. While this does eliminate lower order harmonics, the
resulting high frequency harmonics cause additional losses in the
motor due to eddy current losses, additional IR (ohmic) heating,
and dielectric, losses. These losses significantly increase the
nominal losses of the motor, which reduces energy efficiency,
resulting in higher motor temperatures, which reduces the useful
life of the motor, and/or reduces the power available from the
motor. Additionally, due to transmission line effects, the motor
may be subject to voltages double the nominal peak-to-peak line
voltage, which reduces the life of the motor by degrading its
insulation. The applied motor voltages are also not balanced
relative to ground, and may have sudden deviations from such
balance, which can result in current flow through the motor
bearings for grounded motor frames, causing bearing damage and
reduced motor life. The sudden voltage swings at the motor input
also cause Objectionable sound emissions from the motor.
[0006] The output switches used in this motor drive must be
constructed for very fast operation and very high dV/dt in order to
minimize losses during PWM switching. This requirement leads to
selection of switches with drastically reduced carrier lifetimes
and limited internal gain. This in turn decreases the conductance
of each device, such that more silicon area is required for a given
amount of current. Additionally, the switches must be constructed
to provide current limiting in the event of output line faults,
which imposes additional design compromises on the switches which
further increase their cost and losses.
[0007] Another problem with the standard drive is that the DC link
voltage must always be less than the average of the highest
line-to-line input voltages, such that during periods of reduced
input voltage (such as when other motors are started
across-the-line), the DC link voltage is insufficient to drive the
motor.
[0008] Yet another difficulty with the standard drive is its
susceptibility to input voltage transients. Each of the input
switches must be able to withstand the full, instantaneous,
line-to-line input voltage, or at least the voltage after any input
filters. Severe input transients, as may be caused by lightning
strikes, may produce line-to-line voltages that exceed 2.3 times
the normal peak line-to-line voltages, even with suitable input
protection devices such as Metal Oxide Varistors. This requires
that the switches be rated for accordingly high voltages (e.g. 1600
volts for a 460 VAC drive), which increases cost per ampere of
drive.
[0009] The standard drive also cannot return power from the DC link
to the input (regeneration), and therefore large braking resistors
are required for an application in which the motor must be quickly
stopped with a large inertial or gravitational load.
[0010] Modifications to the basic motor drive described above are
available, as also shown in FIG. 3, but invariably result in much
higher costs, size, weight and losses. For example, in order to
reduce input current harmonics (distortion) and to allow for
regeneration, the diode bridge may be replaced by an active switch
bridge identical to the output switch bridge, which is accompanied
by an input filter consisting of inductors and capacitors, all of
which result in higher costs and drive losses. Also, as shown in
FIG. 3, output filters ("sine filter") are available to change the
output voltage waveform to a sinusoid, but again at the expense of
greater cost, size, weight, and losses.
[0011] AC-AC line conditioners are constructed in a similar fashion
to the standard drive with input and output filters and an active
front end, and also suffer from the above mentioned problems.
[0012] Other motor AC-AC converters are known, such as the Matrix
Converter, Current Source Converter, or various resonant AC and DC
link converters, but these either require fast switching devices
and substantial input and/or output filters, or large, lossy, and
expensive reactive components, or, as in the case of the Matrix
Converter, are incapable of providing an output voltage equal to
the input voltage.
[0013] The term "converter" is sometimes used to refer specifically
to DC-to-DC converters, as distinct from DC-AC "inverters" and
AC-AC. "cycloconverters." However, in the present: application the
word converter is used more generally, to refer to all of these
types and more.
[0014] What is needed then is a converter technique which draws
power from the utility lines with low harmonics and unit power
factor, is capable of operating with full output voltage even with
reduced input voltage, allows operations of its switches with low
stress during turn-off and turn-on, is inherently immune to line
faults, produces voltage and current output waveforms with low
harmonics and no common mode offsets while accommodating all power
factors over the full output frequency range, operates with high
efficiency, and which does so at a reasonable cost in a compact,
light-weight package.
[0015] DC-DC, DC-AC, and AC-AC Buck-Boost converters are shown in
the patent and academic literature which have at least some of the
aforementioned desirable attributes. The classic Buck-Boost
converter operates the inductor with continuous current, and the
inductor may have an input and output winding to form a transformer
for isolation and/or voltage/current translation, in which case it
is referred to as a Flyback Converter. There are many examples of
this basic converter, all of which are necessarily hard switched
and therefore do not have the soft-switched attribute, which leads
to reduced converter efficiency and higher costs. An example of a
hard switched 3 phase to 3 phase Buck-Boost converter is shown in
FIG. 4, from K. Ngo, "Topology and Analysis in PWM Inversion,
Rectification, and Cycloconversion," Dissertation, California
Institute of Technology (1984).
[0016] One proposed DC-AC Buck-Boost converter (in U.S. Pat. No.
5,903,448) incorporates a bi-directional conduction/blocking switch
in its output section to accommodate four quadrant operation, with
AC output and bi-directional power transfer. The input, however,
cannot be AC, and it uses hard switching.
Universal Power Converter
[0017] The present application discloses new approaches to power
conversion. A link reactance is connected to switching bridges on
both input and output sides, and driven into a full AC
waveform.
[0018] In some preferred embodiments (but not necessarily in the
link reactance is driven with a nonsinusoidal waveform, unlike
resonant converters.
[0019] In some preferred embodiments (but not necessarily in all),
capacitive reactances are used on both input and output sides.
[0020] In some preferred embodiments (but not necessarily in all),
the switching bridges are constructed with bidirectional
semiconductor devices, and operated in a soft-switched mode.
[0021] In some preferred embodiments (but not necessarily in all),
the input switching bridge is operated to provide two drive phases,
from different legs of a polyphase input, during each cycle of the
link reactance. The output bridge is preferably operated
analogously, to provide two output connection phases during each
cycle of the reactance.
[0022] In some preferred embodiments (but not necessarily in all),
the link reactance uses an inductor which is paralleled with a
discrete capacitor, or which itself has a high parasitic
capacitance.
[0023] The disclosed innovations, in various embodiments, provide
one or more of at least the following advantages: [0024]
high-bandwidth active control ability--more so than resonant or
voltage-source or current-source converters [0025] Design
versatility [0026] Power efficiency [0027] Optimal use of device
voltage ratings [0028] High power density converters [0029] High
power quality (low input and output harmonics with minimal
filtering) [0030] Voltage buck and boost capability [0031]
Bi-directional, or multi-directional power transfer capability
[0032] High-frequency power transformer capability, allowing for
compact active transformer and full galvanic isolation if desired.
[0033] Input-Output isolation even without a transformer, allowing
for output with no common-mode voltage [0034] Moderate parts count
resulting from absence of auxiliary power circuits for snubbing
[0035] High-bandwidth active control ability--more so than resonant
or voltage-source or current-source converters
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] The disclosed inventions will be described with reference to
the accompanying drawings, which show important sample embodiments
of the invention and which are incorporated in the specification
hereof by reference. These drawings illustrate by way of example
and not limitation.
[0037] FIG. 1 shows a sample embodiment as a Full-Bridge Buck-Boost
Converter in a Three Phase AC Full Cycle Topology with
Bi-directional Conducting and Blocking Switches (BCBS). Each BCBS
is shown as appears in FIG. 2 of U.S. Pat. No. 5,977,569, also
shown as switch 201 of FIG. 2. Input filter capacitors 130 are
placed between the input phases and output filter capacitors 131
similarly attached between the output phases in order to closely
approximate voltage sources and to smooth the current pulses
produced by the switches and the inductor 120. Output filter
capacitors are preferably attached in a grounded Y configuration as
shown. An input line reactor 132 may be needed in some applications
to isolate the voltage ripple on the input capacitors 130 from the
utility 122.
[0038] FIGS. 2a-2d show four alternative versions of the basic
Bi-directional Conducting and Blocking Switch (BCBS). FIG. 2a is an
anti-parallel pair of commercially available Reverse-Blocking IGBTs
(IXRH 40N120, 1200 Volt, 55 A). FIG. 2b is the switch cited in U.S.
Pat. No. 5,977,569. FIG. 2c is an anti-parallel pair of
commercially available IGBTs in series with diodes. FIG. 2d is an
anti-parallel pair of commercially available GTOs. Many other BCBS
switch configurations are possible. Each BCBS can block voltage and
conduct current in either direction.
[0039] FIG. 3 shows Prior Art for the "Standard Drive", which is
the most common low voltage motor drive type available, and is a
voltage source pulse width modulated (PWM) topology. Also shown are
various options to allow this drive to achieve more acceptable
operation.
[0040] FIG. 4 shows a conventional hard-switched three phase to
three phase AC buck-boost converter.
[0041] FIG. 5 shows a conventional soft-switched "partial resonant"
three phase to three phase AC buck-boost converter, which has
uni-directional switches, suffers from 1) a long quiescent resonant
"swing back" time when no power is transferred, 2) greatly reduced
frequency of operation as the voltage ratio between input and
output is increased, and 3) inability to sink or source output
current as the output voltage approaches zero.
[0042] FIG. 6 shows the inductor current and voltage waveforms for
the converter, including the "swing back" of inductor voltage in
time period M4.
[0043] FIG. 7 shows a prior art resonant link inverter that bears a
superficial resemblance to this invention, but which in fact is
completely different, as the voltage is sinusoidal and double the
nominal input voltage, and the switches serve only to connect
positive or negative link half-cycles to the input and output.
[0044] FIG. 8 show Prior Art of U.S. Pat. No. 7,057,905 which has
some similarities to this invention in that it is a buck-boost
converter which uses bi-directional switches. It is, however,
basically a conventional, hard-switched, buck-boost converter which
uses bi-directional switches to allow it operate with a DC
component in the inductor in either direction.
[0045] FIG. 9 shows the input line voltages for the current
switching example of FIGS. 11, 12 and 13, with the phase
designations corresponding to those of FIG. 1.
[0046] FIG. 10 shows the output line voltages for the current
switching example of FIGS. 11, 12 and 13, with the phase
designations corresponding to those of FIG. 1.
[0047] FIG. 11 summarizes the line and inductor current waveforms
for a few inductor cycles at and around the inductor cycle of FIGS.
12 and 13.
[0048] FIGS. 12a-12j show voltage and current waveforms on the
inductor during a typical cycle while transferring power at full
load from input to output, as occurs in FIG. 5 while operating the
motor at full power, including full output voltage. FIGS. 12b and
12g are used to summarize inductor/capacitor voltage ramping
current flow between modes, with 12b showing it for positive
inductor current, and 12g for negative inductor current. When
minimum voltage phase pairs are mentioned, that refers to phase
pairs with opposing current, not necessarily the minimum voltage
phase pair, as that is often a phase pair with current going in the
same direction.
[0049] FIG. 13 shows voltage and current waveforms corresponding to
the full power condition of FIG. 12, with the conduction mode
numbers corresponding to the mode, numbers of FIG. 12.
[0050] FIG. 14 is similar to FIG. 13, but shows inductor voltage
and current for an output voltage of about half the full output
voltage.
[0051] FIG. 15 shows an embodiment of the invention with the Full
Bridge Three Phase Cycle Topology, with Controls and I/O Filtering,
including a three phase input line reactor as needed to isolate the
small but high frequency voltage ripple on the input filter
capacitors from the utility.
[0052] FIG. 16 illustrates current and timing relationships for a
DC or single phase AC converter with output voltage equal to the
input voltage.
[0053] FIG. 17 shows the same current and timing relationships as
FIG. 16, but with the output voltage 1/2 of the input voltage.
[0054] FIG. 18 is a spreadsheet, with equations as shown, that
calculates the average output current for a given set of
conditions, as the current discharge time is varied. These
equations may be used in a control system to control switch timing
to give a commanded output current.
[0055] FIG. 19 shows the results of the spreadsheet of FIG. 18 for
the stated conditions with four output voltages as a function of
output discharge time. Also noted on the curves are the inductor
operating frequency.
[0056] FIG. 20 is a version of FIGS. 16 and 17 which shows inductor
current and timing for a regeneration condition where the output
voltage is 1/2 of the input.
[0057] FIG. 21 shows an embodiment of the invention with the DC or
Single Phase portals. If one of the portals is DC, and is always a
higher voltage than the other portal, one-way blocking switches may
be used on that portal.
[0058] FIG. 22 shows an embodiment of the invention with a
Transformer/Inductor, as is common with other Buck-Boost converters
in the Flyback configuration. Any of the embodiments of this
invention may use a transformer/inductor in place of the inductor
if full isolation and/or voltage and current transforming is
desired. Even without the transformer, just using the inductor, a
degree of isolation is provided since the input and output lines
are never directly connected together. If a transformer/inductor is
used, the transformer must have at least some air gap, in order to
produce a magnetizing inductance that does not saturate at the peak
current that is used.
[0059] FIG. 23 shows an embodiment of the invention in a four
portal application mixing single phase AC and multiple DC portals,
as may be used to advantage in a Solar Power application. Other
topologies must use at least two separate converters to handle this
many portals. The switches attached to the solar power source need
only be one way switches, since power the source is DC and power
can only be transferred out of the device. The switches could even
be non-reverse blocking if the DC output only source was always
guaranteed to be higher voltage than all other voltage sources.
[0060] FIG. 24 shows an embodiment of the invention in a three
portal application mixing three phase AC portals and a DC portal,
as may be used to advantage in a Hybrid Electric Vehicle
application.
[0061] FIG. 25 shows an embodiment as a Half-Bridge Buck-Boost
Converter in a Single Phase AC or DC Topology with BCBS. The half
bridge topology requires half as many switches, but also results in
half the power transfer for equivalent switch ratings, and higher
per unit ripple current in the input and output filters
[0062] FIG. 26 show a sample embodiment in a Half-Bridge Buck-Boost
Converter in a Three Phase AC Topology with BCBS. Again, the half
bridge topology requires half as many switches, but also results in
half the power transfer for equivalent switch ratings, and higher
per unit ripple current in the input and output filters
[0063] FIG. 27 shows a sample embodiment in a single phase to three
phase synchronous motor drive.
[0064] FIG. 28 shows a sample embodiment with dual, parallel,
"power modules", each of which consists of 12 bi-directional
switches and a parallel inductor/capacitor. More than two power
modules may of course be used for additional options in multiway
conversion.
[0065] FIG. 29 shows an embodiment of this invention as a three
phase Power Line Conditioner, in which role it may act as an Active
Filter and/or supply or absorb reactive power to control the power
factor on the utility lines.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0066] The numerous innovative teachings of the present application
will be described with particular reference to presently preferred
embodiments (by way of example, and not of limitation).
[0067] Contrast with Other Approaches
[0068] DC-DC Buck-Boost converters employing resonant techniques to
achieve soft switching are also shown in the patent literature
(examples are 4,616,300, issued Oct. 7, 1986; 6,404,654, issued
Jun. 11, 2002). These are not capable of DC-AC or AC-AC operation,
and are also limited in their DC-DC range, in that the output DC
voltage must be larger than some minimum in order to achieve zero
voltage turn-on of the power switch. In contrast to this prior art,
the inventions described below have no restrictions on the relative
voltages between the input and output portals, and power transfer
is bi-directional.
[0069] A "partial-resonant" 3 phase AC-AC Buck-Boost converter is
described in Kim et al., "New Bilateral Zero Voltage Switching
AC/AC Converter Using High Frequency Partial-resonant Link", Korea
Advanced Institute of Science and Technology, (IEEE 1990), and
shown in FIG. 5, which uses uni-directional switches. This
converter has many desirable attributes, including soft-switching,
but has important differences from the inventive circuits and
methods described below: [0070] 1) has significantly reduced
utilization of the inductor/capacitor, [0071] 2) has higher per
unit RMS current loading on the input/output capacitors, [0072] 3)
has a lower operating frequency for a given turn-off condition
which leads to larger, costlier, and less efficient I/C) filtering,
[0073] 4) cannot deliver or receive current to/from the output for
sufficiently low output voltages and/or power factors, [0074] 5)
and has no lower limit on the operating frequency as output power
factor and/or output voltage approaches zero. The lowered operating
frequency can lead to destructive resonances with the required
input filters. Input filters were not shown in this reference, but
are normally required. As shown in FIG. 6 (also from the Kim et al.
paper), time period M4, reduced inductor/capacitor utilization
results from the resonant "swing back" time as the voltage on the
inductor/capacitor resonantly swings from the output voltage back
to the input voltage, and at full power typically requires 33% of
the total power cycle, such that no power transfer occurs for 33%
of the time. Thus, that: converter achieves only one power transfer
cycle for each cycle of the inductor, whereas the converter of FIG.
1 preferably has two power transfers per inductor cycle, as enabled
by the use of bi-directional switches.
[0075] FIG. 7 shows another prior art converter, from Rajashekara
et al., "Power Electronics", Chapter 30 in The Electrical
Engineering Handbook (ed. R. Dorf 2000). That converter bears a
superficial resemblance to the converter of FIG. 1, in that it has
12 bi-directional switches and a parallel Inductor/capacitor; but
the topology is different, and the mode of operation is totally
different. The converter of FIG. 7 does not have I/O filter
capacitors, and indeed cannot operate with such capacitors. The
converter of FIG. 7 is actually a resonant link converter, such
that the inductor/capacitor voltage and current is sinusoidal and
resonant as shown in the figure. That converter must be isolated
from voltage sources and sinks by inductance (e.g. line reactors,
transformers, or motor inductance), since the voltages between its
switches and said inductance rapidly swing over a range almost
twice as high as the peak line-to-line voltages. (Various such high
voltages are imposed on the input and output inductances by
selectively enabling/disabling appropriate switch pairs for each
half cycle of the inductor/capacitor, as indicated.) By contrast,
the converter of FIG. 1 is not resonant, and the peak inductor
voltage is just the peak line-to-line voltage. The converter of
FIG. 1 could not be operated as the converter of FIG. 7, and the
converter of FIG. 7 could not be operated as the invention of FIG.
1
[0076] U.S. Pat. No. 7,057,905 shows a buck-boost power converter
with bi-directional switches and a method of operating same. This
is a conventional hard-switched buck-boost converter, in that it
has no capacitance in parallel with the inductor and has only one
power cycle per inductor cycle, except that the additional input
switch capability allows it to operate with an inductor DC offset
current in either direction. It may also apply both polarities to
the inductor during a single power cycle to better control the
operating frequency.
[0077] As compared with this invention, U.S. Pat. No. 7,057,905,
operates with a DC bias current in the inductor, such that it
cannot do two power cycles per inductor cycle as this invention
can, and cannot therefore do soft switching. It is prohibited from
doing so since, as shown in FIG. 8, it only has the two output
switches 80 and 81, such that, in order to transfer current to the
output in one direction, the inductor current must also be in that
same direction. Thus, in order to produce current flow into the
output capacitor 24, current must flow "upwards" through inductor
82. To replenish inductor energy transferred to the output, the
inductor must be reconnected to the input with opposite polarity,
which is a hard switched operation, necessitating the hard reverse
turn-off of output switches 80 and 81 by turning on two appropriate
input switches. This invention, in contrast, simply turns off the
two output switches, which then causes the inductor voltage to
increase to the input level, but with opposite polarity from the
previous input connection, and excess inductor energy (if any) is
returned back to the input, and then inductor current is reversed,
after which inductor energy is again transferred to the output, but
with opposite current flow, facilitated by additional
hi-directional switches that connect the inductor to the output
with opposite polarity, said switches not being present in U.S.
Pat. No. 7,057,905. Additionally, since in this invention the
inductor voltage is never forced from its "natural" direction,
capacitance in parallel with the inductor is allowed to facilitate
soft turn-off. Said soft switching of this invention allows this
invention to operate with much higher switching frequencies with
consequent large reductions in the reactive component sizes and
losses.
[0078] The prior art of Buck-Boost resonant converters are not
capable of operating, as this invention does, in the "Full Cycle"
mode (described below), in which the inductor (or transformer) is
operated with full alternating current, with no DC component in any
windings. This mode of operation requires bi-directional (AC)
switches, and produces two power transfers for each cycle of the
inductor/capacitor, resulting in superior utilization of the
inductor/capacitor and I/O filters, while also allowing current
transfer at low output voltages or low power factors.
[0079] The shortcomings described above are not intended to be
exhaustive, but rather among the many that tend to impair the
effectiveness of previously known techniques for power conversion.
Other noteworthy problems may also exist; however, those mentioned
here are sufficient to demonstrate that methodologies appearing in
the art have not been altogether satisfactory.
[0080] Highlights and Overview
[0081] The shortcomings listed above are reduced or eliminated by
the disclosed techniques. These techniques are applicable to a vast
number of applications, including but not limited to all DC-DC,
DC-AC, and AC-AC power conversions.
[0082] The present application discloses power converters which are
generally of the Buck-Boost family, but which use capacitance,
either parasitic alone or with added discrete device(s), in
parallel with the Buck-Boost inductor to achieve low turn-off
switching stresses (i.e. "soft switching") on the semiconductor
switches, allowing relatively slow and inexpensive switches to be
used. In alternative disclosed embodiments, as discussed below,
operation without such added capacitance is possible, at the
expense of higher forward turn-off switching losses. The converter
of FIG. 5 cannot operate without the parallel capacitor, as it
would then become the classic hard-switched buck-boost converter of
Ngo.
[0083] In FIG. 1, and various other disclosed embodiments, even
with little or no parallel capacitance is used, switch turn on
always occurs as the switch transitions from reverse to forward
bias, allowing for low turn-on losses. Reverse recovery of the
switches is accomplished with low rates of current decrease, and
with low reverse recovery voltage, leading to near zero loss
reverse recovery switching.
[0084] The embodiments described below are believed to be the first
application of the Buck-Boost inductor in full Alternating Current
(AC) mode, which is referred to herein as the "Full Cycle" mode and
which results in two power transfers per inductor cycle. Buck-Boost
converters, including those of the Ngo and Kim references cited
above, have a DC bias in the inductor current, and only one power
transfer per inductor cycle.
[0085] The disclosed inventions can also be used for DC-AC, AC-DC,
AC-AC, or DC-DC conversion, with no limitation on the relative
magnitudes of the voltages involved as long as the voltage rating
of the switches is not exceeded. However, if the implementation is
such that one portal is always a higher voltage than the other
portal, then the switches connected to said higher portal need only
be able to block voltage in one direction.
[0086] Full electrical isolation and/or greater voltage and current
conversion may be achieved by using an inductor/transformer instead
of the simple inductor. Note that the inductor/transformer will
typically not have current in both sides at the same time, so its
operation is more like a split inductor (as in a flyback converter)
than like a simple transformer (as in a push-pull converter.
Another significant difference between buck-boost and push-pull is
that the push-pull output voltage is fixed as a multiple or
fraction of the input voltage, as given by the turns ratio, while
the buck-boost has no such limitation. Push-pull topologies are
described at http://en.wikipedia.org/wiki/Push-Pull_Converter,
which (in its state as of the filing date) is hereby incorporated
by reference. A push-pull is quite unlike a buck-boost or flyback
converter, in that the transformer is not operated as an
energy-transfer inductor. In a buck-boost or flyback, input current
pumps energy into a magnetic field, which is then drained to drive
output current; thus the input and output currents flow at
different times.
[0087] Inductor/transformer leakage inductance is typically a
significant concern of buck-boost designs. This is typically dealt
with by minimizing the leakage, and sometimes by adding circuit
elements to deal with it. By contrast, the inventions described
below can tolerate large parasitic capacitance, and thus inductors
or transformers with very close windings can be specified, to
minimize the leakage inductance. The standard hard switched
buck-boost cannot tolerate parasitic capacitance, which makes it
very difficult to minimize the leakage inductance for those
configurations.
[0088] The innovative converter circuits, in various embodiments
are constructed of semiconductor switches, an inductor,
advantageously a capacitor in parallel with the inductor, and input
and output filter capacitances. A control means, controlling the
input switches, first connects the inductor, initially at zero
current, to the input voltage, which may be DC or the highest
line-to-line voltage AC pair in a three phase input, except at
startup, in which case a near zero-voltage line pair is used. The
control then turns off those switches when the current reaches a
point, determined by the control to result in the desired rate of
power transfer. The current then circulates between the inductor
and capacitor, which results in a relatively low rate of voltage
increase, such that the switches are substantially off before the
voltage across them has risen significantly, resulting in low
turn-off losses.
[0089] With DC or single phase AC input, no further current is
drawn from the input. With 3 phase AC input, the control will again
connect the inductor to the input lines, but this time to the
line-to-line pair which has a lower voltage then the first pair.
Turn on is accomplished as the relevant switches transition from
reverse to forward bias. After drawing the appropriate amount of
charge (which may be zero if the control determines that no current
is to be drawn from the pair, as for example that the pair is at
zero volts and input unity power factor is desired), the relevant
switches are again turned off. Under most conditions, the voltage
on the inductor will then reverse (with relatively low rates of
voltage change due to the parallel capacitance). With 3 phase AC
output, the control will turn on switches to allow current to flow
from the inductor to the lowest voltage pair of lines which need
current, after the relevant switches become forward biased, with
the control turning off the switches after the appropriate amount
of charge has been transferred. The inductor voltage then ramps up
to the highest output line-to-line pair for 3 phase AC, or to the
output voltage for single phase AC or DC. Again, switches are
turned on to transfer energy (charge) to the output, transitioning
from reverse to forward bias as the voltage ramps up. If the output
voltage is larger then the highest input voltage, the current is
allowed to drop to zero, which turns off the switch with a low rate
of current reduction, which allows for the use of relatively slow
reverse recovery characteristics. If the output voltage is less
then the highest input voltage, the switches are turned off before
current stops, so that the inductor voltage ramps up to the input
voltage, such that zero-voltage turn on is maintained.
Alternatively, the switches may be turned off before the point
cited in the previous sentence, so as to limit the amount of
current into the output. In this case, the excess energy due to
current in the inductor is directed back into the input by turning
on switches to direct current flow from the inductor into either
the highest voltage pair in three phase, or the single phase AC or
DC input.
[0090] In a three phase AC converter, the relative charge per cycle
allocated to each input and output line pair is controlled to match
the relative current levels on each line (phase). After the above
scenario, when zero current is reached the inductor is reconnected
to the input, but with a polarity reversed from the first
connection, using switches that are complimentary to the switches
used in the first half of the cycle. This connection can occur
immediately after zero current (or shortly after zero current if
the input voltage is less than the output voltage, to allow the
capacitor voltage time to ramp back down), giving full utilization
of the power transfer capability of the inductor. No resonant
reversal is required as in the time period M4 of the Kim converter
shown in FIGS. 5 and 6.
[0091] The disclosed embodiments are inherently capable of
regeneration at any condition of output voltage, power factor, or
frequency so in motor drive or wind power applications, the motor
may act as a generator, returning power to the utility lines.
[0092] In an AC motor drive implementation, input and output
filtering may be as little as line-to-neutral connected capacitors.
Since switching losses are very low due to soft switching, the
Buck-Boost inductor can be operated at a high inductor frequency
(typically 5 to 20 kHz for low voltage drives), allowing for a
single, relatively small, and low loss, magnetic device. The
current pulse frequency is twice the inductor frequency. This high
frequency also allows the input and output filter capacitors to be
relatively small with low, high frequency ripple voltage, which in
turns allows for small, low loss line reactors.
[0093] Input voltage "sags", as are common when other motors are
connected across the line, are accommodated by temporarily drawing
more current from the input to maintain a constant power draw and
output voltage, utilizing the boost capability of this invention,
avoiding expensive shutdowns or even loss of toque to the
application.
[0094] The full filter between the converter and an attached
voltage source (utility) or sink (motor, another utility, or load)
includes the line capacitance (line-to-line or line-to-neutral, as
in Y or Delta), and a series line inductance (or hue reactor as
it's generally called). When driving a motor, the line reactance is
just the inductance of the motor. I show this L-C filter in my
preferred embodiments, and also mentioned it in my earlier claims.
So it is a power filter, AND it does important conditioning for the
converter.
[0095] The preferred converter benefits from having very low
impedence voltage sources and sinks at the inputs and outputs.
(This is a significant difference from the converter of FIG. 7,
which has line reactance (inductors) at the I/O, not capacitance.)
The link inductor current must be able to be very rapidly switched
between the link capacitor and the I/O capacitors, and line
reactance would prevent that from incurring, and in fact would
likely destroy the switches. The physical construction of the
converter should preferably be carefully done to minimize all such
inductance which may impair link reactance switching.
[0096] The line capacitance itself does not have to be really any
particular value, but for proper operation the change in voltage on
the line capacitance while charging or discharging the link
inductance should only be a small fraction of the initial voltage,
let's say less than 10%. There are other restraints as well For a
20 hp, 460 VAC prototype, 80 microF of line-to-neutral capacitance
results in only a 1 to 2% ripple voltage. (This large capacitance
was chosen in order to get the ripple current within the
capacitor's current rating.) Capacitors could be made with lower uF
for the same current rating, resulting in smaller, cheaper
capacitors, and higher voltage ripple, but this is all that is
available right now.
[0097] Another important consider is the resonant frequency formed
by the L-C of the line reactance and the line capacitance (the I/O
power filter). This frequency must be lower than the link power
cycle frequency in order to not have that filter resonant with the
voltage ripple on the line capacitance. For my 20 hp 460 VAC
prototype, the link frequency is 10 kHz, so the link power cycle
frequency is 20 kHz (2 power cycles per link voltage cycle), and
the resonant frequency of the L-C I/O is lower than 2 kHz, so that
works well.
[0098] So, to summarize, the capacitance needs to be large enough
to reasonably stabilize the I/O voltage to allow the link inductor
charge/discharge to occur properly, and the L-C resonant frequency
needs to be less than twice the link voltage frequency, and
generally at least 4 to 10 times lower.
[0099] It should also be noted that too much capacitance on line
filter can lead to excess reactive power on the utility
connection,
Further Detail
[0100] Referring initially to FIG. 1, illustrated is a schematic of
a three phase converter 100 that embodies the present invention.
The converter 100 is connected to a first and second power portals
122 and 123 each of which may source or sink power, and each with a
port for each phase of the portal. It is the function of said
converter 100 to transfer electric power between said portals while
accommodating a wide range of voltages, current levels, power
factors, and frequencies between the portals. Said first portal may
be for example, a 460 VAC three phase utility connection, while
said second portal may be a three phase induction motor which is to
be operated al variable frequency and voltage so as to achieve
variable speed operation of said motor. This invention may also
accommodate additional portals on the same inductor, as may be
desired to accommodate power transfer to and from other power
sources ardor sinks, as shown in FIGS. 23 and 24.
[0101] Referring to FIG. 1, the converter 100 is comprised of a
first set of electronic switches S.sub.1u, S.sub.2u, S.sub.3u,
S.sub.4u, S.sub.5u, and S.sub.6u that are connected between a first
port 113 of a link inductor 120 and each phase, 124 through 129, of
the input portal, and a second set of electronic switches S.sub.1I,
S.sub.2I, S.sub.3I, S.sub.3I, S.sub.4I, S.sub.5I and S.sub.6I that
are similarly connected between a second port 114 of link inductor
120 and each phase of the output portal. A link capacitor 121 is
connected in parallel with the link inductor, forming the link
reactance. Each of these switches is capable of conducting current
and blocking current in both directions, and may be composed of the
bi-directional IGBT 201 of FIG. 2, as shown in U.S. Pat. No.
5,977,569, Many other such bi-directional switch combinations are
possible, such as anti-parallel reverse blocking IGBTs 200 of FIG.
2.
[0102] Most of these switch combinations contain two independently
controlled gates, as shown with all the switches for FIG. 2, with
each gate controlling current flow in one direction. In the
following description, it is assumed that two gate switches are
used in each switch, and that the only gate enabled in a switch is
the gate which controls current in the direction which is desired
in the subsequent operation of the switch. Thus, when each switch
mentioned below is said to be enabled, said enabling occurs before
conduction occurs, since that portion of the switch is reversed
biased at the instant of being enabled, and does not conduct until
it becomes forward biased as a result of the changing voltage on
the parallel pair of inductor and capacitor. Any switch embodiment
which has only one gate, such as a one way switch embedded within a
full wave bridge rectifier, must be enabled only when the voltage
across it is very small, which requires precise and accurate timing
that may be difficult to achieve in practice.
[0103] The converter 100 also has input and output capacitor
filters 130 and 131, respectively, which smooth the current pulses
produced by switching current into and out of inductor 120.
Optionally, a line reactor 132 may be added to the input to isolate
the voltage ripple on input capacitor filter 131 from the utility
and other equipment that may be attached to the utility lines.
Similarly, another line reactor, not shown, may be used on the
output if required by the application.
[0104] For illustration purposes, assume that power is to be
transferred in a full cycle of the inductor/capacitor from the
first to the second portal, as is illustrated in FIG. 13. Also
assume that, at the instant the power cycle begins as shown in FIG.
9, phases A.sub.i and B.sub.i have the highest line to line voltage
of the first (input) portal, link inductor 120 has no current, and
link capacitor 121 is charged to the same voltage as exists between
phase A.sub.i and B.sub.i. The controller FPGA 1500, shown in FIG.
15, now turns on switches S.sub.1u and S.sub.2I, whereupon current
begins to flow from phases A.sub.i and B.sub.i into link inductor
120, shown as Mode 1 of FIG. 12a. FIG. 13 shows the inductor
current and voltage during the power cycle of FIG. 12, with the
Conduction Mode sequence 1300 corresponding to the Conduction Modes
of FIG. 12. The voltage on the link reactance remains almost
constant during each mode interval, varying only by the small
amount the phase voltage changes during that interval. After an
appropriate current level has been reached, as determined by
controller 1500 to achieve the desired level of power transfer and
current distribution among the input phases, switch S.sub.2I is
turned off. Current now circulates, as shown in FIG. 12b, between
link inductor 120 and link capacitor 121, which is included in the
circuit to slow the rate of voltage change, which in turn greatly
reduces the energy dissipated in each switch as it turns off. In
very high frequency embodiments of this invention, the capacitor
121 may consist solely of the parasitic capacitance of the inductor
and/or other circuit elements.
[0105] To continue with the cycle, as shown as Mode 2 FIG. 6c and
FIG. 13, switch S.sub.3I is next enabled, along with the previously
enabled switch S.sub.1u. As soon as the link reactance voltage
drops to just less than the voltage across phases A.sub.i and
C.sub.i, which are assumed for this example to be at a lower
line-to-line voltage than phases A.sub.i and B.sub.i, as shown in
FIG. 9, witches S.sub.1u and S.sub.3I become forward biased and
start to further increase the current flow into the link inductor,
and the current into link capacitor temporarily stops. The two "on"
switches, S.sub.1u, and S.sub.3I, are turned off when the desired
peak link inductor current is reached, said peak link inductor
current determining the maximum energy per cycle that may be
transferred to the output. The link inductor and link, capacitor
then again exchange current, as shown if FIG. 12b, with the result
that the voltage on the link reactance changes sign, as shown in
graph 1301, between modes 2 and 3 of FIG. 13. Now as shown in FIG.
12d, output switches S.sub.5u and S.sub.6I are enabled, and start
conducting inductor current into the motor phases A.sub.o and
B.sub.o, which are assumed in this example to have the lowest
line-to-line voltages at the present instance on the motor, as
shown in FIG. 10. After a portion of the inductor's energy has been
transferred to the load, as determined by the controller, switch
S.sub.5u is turned off, and S.sub.4u is enabled, causing current to
flow again into the link capacitor, which increases the link
inductor voltage until it becomes slightly greater than the
line-to-line voltage of phases A.sub.o and C.sub.o, which are
assumed in this example to have the highest line-to-line voltages
on the motor, as shown in FIG. 10. As shown in FIG. 12e, most of
the remaining link inductor energy is then transferred to this
phase pair (into the motor), bringing the link inductor current
down to a low level. Switches S.sub.4u and S.sub.6I are then turned
off, causing the link inductor current again to be shunted into the
link capacitor, raising the link reactance voltage to the slightly
higher input line-to-line voltage on phases A.sub.i and B.sub.i.
Any excess link inductor energy is returned to the input. The link
inductor current then reverses, and the above described link
reactance current/voltage half-cycle repeats, but with switches
that are complimentary to the first half-cycle, as is shown in
FIGS. 6f to 6j, and in Conduction Mode sequence 1300, and graphs
1301 and 1302, FIG. 12g shows the link reactance current exchange
during the inductor's negative current half-cycle, between
conduction modes.
[0106] FIG. 11 summarizes the line and inductor current waveforms
for a few fink reactance cycles at and around the cycle of FIGS. 12
and 13.
[0107] Note that TWO power cycles occur during each link reactance
cycle: with reference to FIGS. 12a-12i, power is pumped. IN during
modes 1 and 2, extracted OUT during modes 3 and 4, IN again during
modes 5 and 6, and OUT again during modes 7 and 8. The use of
multi-leg drive produces eight modes rather than four, but even if
polyphase input and/or output is not used, the presence of TWO
successive in and out cycles during one cycle of the inductor
current is notable.
[0108] As shown in FIG. 12 and FIG. 13, Conduction Mode sequence
1300, and in graphs 1301 and 1302, the link reactance continues to
alternate between being connected to appropriate phase pairs and
not connected at all, with current and power transfer occurring
while connected, and voltage ramping between phases while
disconnected (as occurs between the closely spaced dashed vertical
lines of which 1303 in FIG. 13 is one example.
[0109] In general, when the controller 1500 deems it necessary,
each switch is enabled, as is known in the art, by raising the
voltage of the gate 204 (FIG. 2) on switch 200 above the
corresponding terminal 205, as an example. Furthermore, each switch
is enabled (in the preferred two gate version of the switch) while
the portion of the switch that is being enabled is zero or reverse
biased, such that the switch does not start conduction until the
changing link reactance voltage causes the switch to become forward
biased. Single gate AC switches may be used, as with a one-way
switch embedded in a four diode bridge rectifier, but achieving
zero-voltage turn on is difficult, and conduction losses are
higher.
[0110] In FIG. 15, current through the inductor is sensed by sensor
1510, and the FPGA 1500 integrates current flows to determine the
current flowing in each phase (port) of the input and output
portals. Phase voltage sensing circuits 1511 and 1512 allow the
FPGA 1500 to control which switches to enable next, and when.
[0111] By contrast, note that the prior art structure of FIG. 8 has
four bi-directional switches on the input, and two on the output,
with a link inductor (no parallel capacitor) in between. That
patent is a hard switched buck-boost, and, like all prior
buck-boost converters, it has only 1 power transfer per link
inductor cycle. Moreover, the link inductor has a DC current
component, unlike the converter of FIG. 1 (which has NO average DC
current, only AC).
[0112] FIG. 14 illustrates inductor current and voltage waveforms
when the converter of FIG. 1 and FIG. 12 is operating with reduced
output voltage. Link inductor 120 current from the input increases
during modes 1 and 2 to a maximum level as for the full output
voltage case of FIG. 13, but since the output voltage is half as
high as for the full output voltage case, link inductor current
decreases only half as quickly while discharging to the output
phases in modes 3 and 4. This will generally supply the required
output current before the link inductor current has fallen to zero
or even near zero, such that there is a significant amount of
energy left in the link inductor at the end of mode 4 in FIG. 14.
This excess energy is returned to the input in mode 5 and 1. Mode 1
in FIG. 14 begins prior to the vertical axis. It can be seen that
with zero output voltage, the current during modes 3 and 4 (and 7
and 8) will not decrease at all, so that all link inductor energy
is returned to the input, allowing for the delivery of output
current but with no power transfer, as is required for current
delivered at zero volts.
[0113] The Kim converter cannot return this excessive inductor
energy back to the input, as this requires bidirectional switches.
Thus the Kim converter must wait until the inductor energy drops to
a sufficiently low value, with the result that the link reactance
frequency drops to a very low value as the output voltage
approaches zero. This in turn can cause resonances with input
and/or output filters. With zero voltage output, the Kim converter
cannot function at: all.
[0114] Note that the modes cited in Kim et al. differ somewhat from
the modes cited here. This is due to two reasons. The first is
that, for brevity, the "capacitor ramping", or "partial resonant"
periods in this invention are not all numbered, as there are 8 of
those periods. As indicated in FIGS. 12b and 12g, voltage ramping
periods preferably occur between each successive pair of conduction
triodes. The second reason is that Kim et al. operate their
converter such that it draws current from one input phase pair per
power cycle, and likewise delivers current to one phase pair per
power cycle. This results in only two conduction modes per link
reactance cycle, since their converter only has one power cycle per
link reactance cycle. By contrast, FIG. 12 shows current being
drawn and delivered to both pairs of input and output phases,
resulting in 4 modes for each direction of link inductor current
during a power cycle, for a total of 8 conduction modes since there
are two power cycles per link reactance cycle in the preferred
embodiment. This distinction is not dependent on the topology, as
either three phase converter may be operated in either 2 modes or 4
conduction modes per power cycle, but the preferred method of
operation is with 4 conduction modes per power cycle, as that
minimizes input and output harmonics. For single phase AC or DC, it
is preferred to have only two conduction modes per power cycle, or
four modes per link reactance cycle, as there is only one input and
output pair in that case. For mixed situations, as in the
embodiment of FIG. 24 which converts between DC or single phase AC
and three phase AC, there may be 1 conduction mode for the DC
interface, and 2 for the three phase AC, for 3 conduction modes per
power cycle, or 6 modes per link reactance cycle. In any case,
however, the two conduction modes per power half-cycle for three
phase operation together give a similar power transfer effect as
the singe conduction mode for single phase AC or DC.
[0115] Control algorithms may use this ability of recycling
inductor energy to advantage in order to control current transfers,
as is required by many converter control algorithms for vector or
volts/Hz control. One such possible algorithm is explained in FIGS.
16 through 20. FIGS. 16, 17, and 20 show possible current profiles
for the fink inductor during a power cycle of positive current.
This is for the case of only two conduction modes per power cycle,
as this invention uses for single phase AC or DC. The power cycle
for negative inductor current is the mirror image of the cycles
shown, as there are two power cycles per inductor cycle. Timing
intervals T1, T2, T3, Tr1, and Tr2 are shown. T1 is the time for
the first conduction mode, when current is increasing from the
input. T2 is the second conduction mode, in which the inductor is
connected to the output, either decreasing in current for power
transfer to the output (positive power) as in FIGS. 16 and 17, or
increasing in current for power transfer from the output negative
power) as in FIG. 20. T3 is the actually the first part of
conduction mode 1 in which excess link inductor energy is either
returned to the input during, positive power or delivered from
output to input during negative power. Tr1 and Tr2 are the "partial
resonant", or "capacitor ramping" times during which all switches
are off and the voltage on the link reactance is ramping. For three
phase operation, intervals T1 and T2 are sub-divided, with T1
consisting of two conduction modes for the two input phase pairs
from which current is drawn, and likewise for T2 for deliver of
current to the output phases. The relative times and inductor
current levels determine the charge and therefore the relative
current levels among the phases. For three phase operation with
zero or near-zero power factor, T2 may subdivided into negative and
positive energy transfer periods. Note that similar durations are
used for ramping the converter in BOTH directions. However, the
ramping durations can be different between input and output phases,
as load draw varies due to extrinsic circumstances. The charge time
from the input can be held constant, with the discharge time to the
output varied to vary average output current (see FIG. 19). Excess
link inductor energy (current) is returned to the input in T3. But
all charge times and transitions on the link reactance are
perfectly symmetric about the zero points of voltage and current
(see FIG. 13).
[0116] For the single phase AC and DC operation of FIGS. 16 through
20, the average output current is given by the equation at the
bottom of FIGS. 16, 17, and 20, with the "Charge over T2" given by
the integral of the link inductor current over the time interval of
T2. For positive power, the peak link inductor current I1 may be
held constant, while T2 is varied, to control average output
current (Iavg-out). An algorithm to calculate Iavg-out is shown in
FIG. 18. For a given set of circuit parameters and input and output
voltages, T2 (first column in FIG. 18) may be varied to control
Iavg-out (6.sup.th column). Resulting other time intervals and
power levels are also calculated. An input voltage of 650 volts and
an output voltage of 600 volts is used for FIG. 19. FIG. 19 shows
the results of the algorithm for other output voltages, with the
650 volt input, as a function of T2, in micro-seconds (uS). An
average (filtered) output current level of 26 amps is shown for the
650 volt output curve with a T2 of 27 uS, for a power output of
16.8 kW. Note that the link reactance frequency remains constant at
10 kHz for the 650 volt output curve, regardless of T2 and
Iavg-out. For the other curves, with lower output voltage,
frequency drops for lower output voltage, but never drops below 5
kHz even for zero output volts. Also note that Iavg-out for 0 volts
goes to 55 amps for T2 of 50 uS, which is more than double Iavg-out
at maximum power, even though maximum inductor current remains
constant at 11.0 amps. For lower converter losses when lower output
currents are commanded, the controller 1500 may be programmed to
reduce T1, thereby reducing the peak inductor current.
[0117] FIG. 19 also shows some specific drive parameters for the
example 460 VAC, 20 hp drive. The link inductor is 140 pH, and may
be constructed as an air core copper wound inductor, with thin,
flat, ribbon wire so as to have a low ratio of AC to DC resistance
from the skin effect, and wound like a roll of tape. This
configuration optimizes the inductance to resistance ratio of the
inductor, and results in relatively high parasitic capacitance.
Such a design cannot be used by hard switched converters, as this
high parasitic capacitance causes high losses, but with this
invention the high parasitic capacitance is a benefit. The ramp, or
parallel, link capacitance is comprised of two parallel AVX
(FSV26B0104K-) 0.1 .mu.F film capacitors capable of handling the
RMS current load of about 25 amps. Peak inductor current is 110
amps. Commercially available reverse-blocking IGBT switches, IXYS
part 40N120 55 A, 1200 V, arranged in anti-parallel pairs as shown
in FIG. 2, 1200, may be used. In a standard hard switched
application, such as a current source drive, this switch has
relatively high turn-on and reverse recovery losses caused by the
slow reverse recovery time of the device, but when used in this
invention, both turn-on and reverse recovery losses are negligible
even at a per device maximum switching frequency of 10 kHz and 110
amps peak current. High RMS current capacitors from AVX
(FFV34I0406K) totaling, 80 .mu.F line-to-neutral, may be used for
the input and output capacitors. The Altera Cyclone III FPGA may be
used for the controller, implementing the algorithms described
above to control current flow, and using either vector or Volts/Hz
to control a 20 hp motor. Isolated power supplies, gate drivers,
and digital isolators allow the FPGA to control the on-off states
of the IGBTs. Voltage and current sensing circuits, with
analog-digital interfaces to the FPGA, allow for precise switch
timing to control current flow.
[0118] As may be surmised by those skilled in the art, the current
resulting from the above described operation of the converter is in
many applications, controlled by controller 1500 to result in a
sinusoidal varying current from the input, normally in phase with
the input voltage so as to produce a unity power factor on the
input, and sinusoidally varying voltage and current on the motor,
so as to operate the motor at the highest possible efficiency
and/or performance.
[0119] In those cases where the motor is acting as a generator, as
may occur when the frequency applied to the motor via the converter
is rapidly decreased, the above described operating cycle is
reversed, with current being drawn from the motor phases and
injected into the input phases.
[0120] In general, the input and output frequencies are
substantially less than the frequency at which the link reactance
is operated. For 60 Hz input, a typical operating frequency of the
link reactance may be 10 kHz for low voltage (230 to 690 VAC)
drives and converters, and 1.5 kHz for medium voltage (2300 on up)
drives and converters, with current pulse frequencies twice those
frequencies, or higher if multiple, synchronized power in are used,
as shown in FIG. 28, input and Output frequencies may vary from
zero (DC) to over well over 60 Hz, and may even be up to 20 kHz in
audio amplifier applications.
[0121] The motor drive of FIG. 1 has the following
characteristics-- [0122] Low harmonic, unity power factor current
draw from the utility, regardless of output voltage. Current is
drawn from each phase in high frequency pulses, similar to a
current source converter, with input capacitors and optionally,
line inductors, converting the pulsed current flow to sinusoidal
current flow. [0123] Ability to step up or step down voltage from
input to output, allows full output voltage even in the presence of
input voltage sags, as commonly occurs in industrial power systems.
[0124] Sinusoidal output voltage with small voltage ripple allows
standard induction motors, as well as low reactance synchronous
motors, to be used. Output capacitors filter the pulsed current.
Ripple frequency is always high so as to avoid any resonance
problems with input and/or output filters or reactances. [0125]
Ability to supply 200% or higher of nominal output current at low
output voltages, indefinitely, as may be advantageous for starting
large inertial loads. With near zero output voltages, the converter
is operated at about half of maximum frequency, with the inductor
first fully charged by the input, then discharging at that full
level into the output for twice the full voltage discharge period,
then discharging to zero current back into the input, repealing
that cycle but with reverse current. Peak currents remain the same,
but output current is doubled. [0126] input-Output isolation,
resulting in zero common mode voltages on the output. Since there
is never a moment when the input and output lines are connected
together, as happens continuously in voltage and current source
drives, as well as matrix converters, the average output voltage
remains at ground potential. This eliminates the need for isolation
transformers. [0127] Slow reverse recovery devices are usable. Rate
of change of current during commutation is relatively slow, and
applied reverse voltage after reverse recovery is also low, so the
switches used may have rectifier diode like recovery
characteristics. Reverse blocking IGBTs and GTOs are inherently
slow to reverse recover, and so this invention is well suited for
these devices. [0128] Slower forward turn-off devices are usable.
Turn-off dv/dt is relatively low due to the capacitance in parallel
with the inductor. [0129] Compact, lightweight, and efficient.
Voltage source drives with input/output quality similar to this
invention require multiple heavy and bulky power inductors, one on
each of the input and output lines. Current source drives require a
very large and heavy DC inductor in order to generate Inn output
voltage. This invention only needs a single small, compact AC
inductor and the relatively small and lightweight input and output
filter capacitors and input line reactor, Total weight for a
suitably filtered, commercially available voltage source drive for
40 hp is over 300 pounds, while the drive of this invention will
weigh less than 30 lbs for 40 hp. Lack of large input/output filter
inductors significantly improves the efficiency of this invention
over conventional drives. No transformers are needed since input
current harmonics are low and there is no common node output
voltage. [0130] Moderate parts count. Using bi-directional
switches, only 12 power switches are needed for this invention.
Using commercially available unidirectional switches with reverse
blocking (reverse blocking IGBT or GTO) requires 24 switches. A 12
pulse input voltage source drive requires 24 switches (18 diodes
and 6 active switches). [0131] High bandwidth. Since the current
amplitude is determined twice each cycle of the inductor, the
current control bandwidth of this invention is inherently very
high, making the invention suitable for high bandwidth servo
applications and even high power audio amplifiers.
[0132] Another embodiment of this invention is shown in FIG. 21,
which shows a single phase AC or DC to single phase AC or DC
converter. Either or both input and output may be AC or DC, with no
restrictions on the relative voltages. If a portal is DC and may
only have power flow either into or out of said, portal, the
switches applied to said portal may be uni-directional. An example
of this is shown with the photovoltaic array of FIG. 23, which can
only source power.
[0133] FIG. 22 shows an embodiment of the invention as a Flyback
Converter. The circuit of FIG. 21 has been modified, in that the
link inductor is replaced with a transformer 2200 that has a
magnetizing inductance that functions as the link inductor. Any
embodiment of this invention may use such a transformer, which may
be useful to provide full electrical isolation between portals,
and/or to provide voltage and current translation between portals,
as is advantageous, for example, when a first portal is a low
voltage DC battery bank, and a second portal is 120 volts AC, or
when the converter is used as an active transformer.
[0134] In the embodiments of this invention shown in FIGS. 23 and
24, the number of portals attached to the link reactance is more
than two, simply by using more switches to connect in additional
portals to the inductor. As applied in the solar power system of
FIG. 23, this allows a single converter to direct power flow as
needed between the portals, regardless of their polarity or
magnitude. Thus, the solar photovoltaic array may be at full power,
400 volts output, and delivering 50% of its power to the battery
bank at 320 volts, and the 50% to the house AC at 230 VAC. Prior
art requires at least two converters to handle this situation, such
as a DC-DC converter to transfer power from the solar PV array to
the batteries, and a separate DC-AC converter (inverter) to
transfer power from the battery bank to the house, with
consequential higher cost and electrical losses. The switches shown
attached to the photovoltaic power source need be only one-way
since the source is DC and power can only flow out of the source,
not in and out as with the battery.
[0135] In the power converter of FIG. 24, as could be used for a
hybrid electric vehicle, a first portal is the vehicle's battery
bank, a second portal is a variable voltage, variable speed
generator run by the vehicle's engine, and a third portal is a
motor for driving the wheels of the vehicle. A fourth portal, not
shown, could be external single phase 230 VAC to charge the
battery. Using this single converter, power may be exchanged in any
direction among the various portals. For example, the
motor/generator may be at full output power, with 50% of its power
going to the battery, and 50% going to the wheel motor. Then the
driver may depress the accelerator, at which time all of the
generator power may be instantly applied to the wheel motor.
Conversely, if the vehicle is braking, the full wheel motor power
may be injected into the battery bank, with all of these modes
using a single converter.
[0136] FIGS. 25 and 26 show half-bridge converter embodiments of
this invention for single phase/DC and three phase AC applications,
respectively. The half-bridge embodiment requires only 50% as many
switches, but results in 50% of the power transfer capability, and
gives a ripple current in the input and output filters which is
about double that of the full bridge implementation for a given
power level.
[0137] FIG. 27 shows a sample embodiment as a single phase to three
phase synchronous motor drive, as may be used for driving a
household air-conditioner compressor at variable speed, with unity
power factor and low harmonics input. Delivered power is pulsating
at twice the input power frequency.
[0138] FIG. 28 shows a sample embodiment with dual, parallel power
modules, with each module constructed as per the converter of FIG.
1, excluding the I/O filtering. This arrangement may be
advantageously used whenever the converter drive requirements
exceed that obtainable from a singe power module and/or when
redundancy is desired for reliability reasons and/or to reduce I/O
filter size, so as to reduce costs, losses, and to increase
available bandwidth. The power modules are best operated in a
manner similar to multi-phase DC power supplies such that the link
reactance frequencies are identical and the current pulses drawn
and supplied to the input/output filters from each module are
uniformly spaced in time. This provides for a more uniform current
draw and supply, which may greatly reduce the per unit filtering
requirement for the converter. For example, going from one to two
power modules, operated with a phase difference of 90 degrees
referenced to each of the modules inductor/capacitor, produces a
similar RMS current in the I/O filter capacitors, while doubling
the ripple frequency on those capacitors. This allows the same I/O
filter capacitors to be used, but for twice the total power, so the
per unit I/O filter capacitance is reduced by a factor of 2. More
importantly, since the ripple voltage is reduced by a factor of 2,
and the frequency doubled, the input line reactance requirement is
reduced by 4, allowing the total line reactor mass to drop by 2,
thereby reducing per unit line reactance requirement by a factor of
4.
[0139] FIG. 29 shows an embodiment as a three phase Power Line
Conditioner, in which role it may act as an Active Filter and/or
supply or absorb reactive power to control the power factor on the
utility lines. If a battery, with series inductor to smooth current
flow, is placed in parallel with the output capacitor 2901, the
converter may then operate as an Uninterruptible Power Supply
(UPS).
[0140] According to various disclosed embodiments, there is
provided: A Buck-Boost Converter, comprising: an energy-transfer
reactance; a first bridge switch array comprising at least two
bidirectional switching devices which are jointly connected to
operatively connect at least one terminal of said reactance to a
power input, with reversible polarity of connection; a second
bridge switch array comprising at least two bidirectional switching
devices which are jointly connected to operatively connect at least
one terminal of said reactance to a power output, with reversible
polarity of connection; wherein said first switch array drives said
reactance with a nonsinusoidal voltage waveform.
[0141] According to various disclosed embodiments, there is
provided: A Buck-Boost Converter, comprising: an energy-transfer
reactance; first and second power portals, each with two or more
ports by which electrical power is input from or output to said
portals; first and second half-bridge switch arrays interposed
between said reactance acid a respective one of said portals, and
each comprising one bidirectional switching device for each said
port of each said power portal; wherein said switch arrays are each
operatively connected to respective ones of said portals.
[0142] According to various disclosed embodiments, there is
provided: A Full-Bridge Buck-Boost Converter, comprising: first and
second full bridge switch arrays, each comprising at least four
bidirectional switching devices; a substantially parallel
inductor-capacitor combination symmetrically connected to be driven
separately by either said switch array; one of said switch arrays
being operatively connected to a power input, and the other thereof
being operatively connected to supply a power output.
[0143] According to various disclosed embodiments, there is
provided: A Buck-Boost Converter, comprising: first and second
switch arrays, each comprising at least two bidirectional switching
devices; a substantially parallel inductor-capacitor combination
connected to each said switch array; wherein a first one of said
switch arrays is operatively connected to a power input, and is
operated to drive power into said inductor-capacitor combination
with a non-sinusoidal waveform; and wherein a second one of said
switch arrays is operated to extract power from said
inductor-capacitor combination to an output.
[0144] According to various disclosed embodiments, there is
provided: A Buck-Boost Converter, comprising: first and second
switch arrays, each comprising at least two bidirectional switching
devices; an energy-transfer reactance connected to each said switch
array; wherein a first one of said switch arrays is connected
through respective capacitive reactances to a polyphase power
input, and operated to drive power into said reactance from
multiple different legs of said power input in succession with a
non-sinusoidal waveform; and wherein a second one of said switch
arrays is operated to extract power from said reactance to an
output.
[0145] According to various disclosed embodiments, there is
provided: A power converter, comprising: an energy-transfer
reactance comprising at least one inductor; an input switch array
configured to drive AC current through said reactance; and an
output network connected to extract energy from said reactance;
wherein said input switch array performs at least two drive
operations, in the same direction but from different sources,
during a single half-cycle of said reactance.
[0146] According to various disclosed embodiments, there is
provided: A power converter, comprising: an energy-transfer
reactance comprising at least one inductor, and operating at a
primary AC magnetic field frequency which is less than half of the
reactance's resonant frequency; an input switch array configured to
drive AC current through said reactance; and an output network
switch array connected to extract energy from said reactance;
wherein said input switch array performs at least two drive
operations, in the same direction but from different sources,
during a single half-cycle of said reactance.
[0147] According to various disclosed embodiments, there is
provided: A power converter, comprising: an energy-transfer
reactance comprising at least one inductor, and operating at a
primary AC magnetic field frequency which is less than half of the
reactance's resonant frequency; an input switch array configured to
drive current through said reactance; and an output switch array to
extract energy from said reactance; wherein said input switch array
performs at least two different drive operations at different times
during a single cycle of said reactance, and wherein said output
switch array performs at least two different drive operations at
different times during a single cycle of said reactance.
[0148] According to various disclosed embodiments, there is
provided: A Buck-Boost Converter, comprising: an energy-transfer
reactance comprising at least one inductor; an input switch array
configured to drive AC current, with no average DC current, through
said reactance; and an output network connected to extract energy
from said reactance.
[0149] According to various disclosed embodiments, there is
provided: A Buck-Boost Converter, comprising: an energy-transfer
reactance comprising at least one inductor; a plurality of input
switch arrays, each said array configured to drive AC current, with
no average DC current, through said reactance; and a plurality of
output switch arrays, each connected to extract energy from said
reactance; said arrays having no more than two switches driving or
extracting energy from said reactance at any given time; wherein
said input switch arrays individually drive said reactance with a
nonsinusoidal voltage waveform.
[0150] According to various disclosed embodiments, there is
provided: A power conversion circuit, comprising an input stage
which repeatedly, at various times, drives current into the
parallel combination of an inductor and a capacitor, and
immediately thereafter temporarily disconnects said parallel
combination from external connections, to thereby transfer some
energy from said inductor to said capacitor; wherein said action of
driving current is performed in opposite senses and various times,
and wherein said disconnecting operation is performed substantially
identically for both directions of said step of driving current;
and an output stage which extracts energy from said parallel
combination, to thereby perform power conversion.
[0151] According to various disclosed embodiments, there is
provided: A power conversion circuit, comprising: an input stage
which repeatedly drives current into the parallel combination of an
inductor and a capacitor, and immediately thereafter temporarily
disconnects said parallel combination from external connections, to
thereby transfer some energy from said inductor to said capacitor;
wherein said input stage drives current in different senses at
different times; and an output stage which repeatedly couples power
out of said parallel combination, and immediately thereafter
temporarily disconnects said parallel combination from external
connections, to thereby transfer some energy from said inductor to
said capacitor; wherein said output stage couples power out of said
combination during two opposite directions of current therein;
wherein said input and output stages both disconnect said parallel
combination substantially identically for both directions of
current in said combination.
[0152] According to various disclosed embodiments, there is
provided: A Soft Switched Universal Full-Bridge Buck-Boost
Converter, comprising: an inductor with a first and second port; a
capacitor attached in parallel with said inductor; connections to a
plurality of voltage sources or sinks (portals) of electric power
each with a plurality of ports; a first set of electronic
bi-directional switches that comprise said connections between said
first port of the inductor and each said port of each said portal,
with one said switch between the first port of the inductor and
each port of each portal; a second set of electronic bi-directional
switches that comprise said connections between said second port of
the inductor and each port of each portal, with one switch between
the second port of the inductor and each port of each portal;
capacitive filtering means connected between each said port within
each said portal; control means to coordinate said switches to
connect said inductor to port pairs on each portal, with no more
than two switches enabled at any given time; said control means
further coordinating said switches to first store electrical energy
in the inductor by enabling two switches on a given input portal to
connect the inductor to said input portal, then disabling the
switches after the proper amount of energy has been stored in the
inductor; and said control means may enable further pairs of
switches on the same or other input portals so as to further
energize the inductor, and disable said switches after the
appropriate inductor energizing is complete; said control means
further enables another pair of switches on another, output, portal
to transfer some or all, of the inductor energy into said output
portal, and then disables said switches after the desired amount of
charge has been transferred to said portal; said control means may
enable further pairs of switches on the same or other output
portals so as to further send charge into said output portals, and
disable said switches after the desired amount of charge has been
transferred to said portal; and if the inductor has excess energy
after discharging into the last output portal, said control means
then enables an appropriate switch pair to direct said excess
energy back into the input portal; wherein said control means may
modify the above sequence so as to achieve any required energy
transfer among the ports and portals; said inductor magnetically
storing electrical energy in the form of electric current, using
said switches; energy transfer from one or more input portals to
said inductor occurring, via current flow through two or more said
ports of one or more said portals, with only one pair of ports; and
cyclically repeating said energy and charge transfers.
[0153] According to various disclosed embodiments, there is
provided: A Soft-switched Half-Bridge Buck-Boost Converter,
comprising: first and second power portals, each with two or more
ports by which electrical power is input from or output to said
portals, first and second half-bridge switch arrays, each
comprising one bidirectional switching device for each said port of
each said power portal, an energy-transfer link reactance with one
port connected to both said switch arrays, and with the other port
connected to an actual or virtual ground, such that said actual or
virtual ground maintains at a relatively constant voltage, each of
said switch arrays being connected to a power portal with said
portal possessing capacitive reactance between the legs of said
portals configured so as to approximate a voltage source, with
power transfer occurring between said portals via said
energy-transfer reactance, said link energy-transfer reactance
consisting of an link inductor and capacitance in parallel, said
power transfer being accomplished in a first power cycle as one or
more pairs of input portal legs are singularly or sequentially
connected to said energy-transfer reactance to store energy via
increased current flow and inductance into said link inductor,
followed by one or more pairs of output portal legs singularly or
sequentially connected to said energy-transfer reactance to remove
energy via decreased current flow and inductance from said link
inductor, with any excess energy in said link inductor subsequently
returned back to one or more said input portal leg pairs, followed
by a reversal of current within said link inductor and a repeat of
the heretofore described energy transfer, to constitute a second
power cycle, from input to output portal leg pairs, but with
opposite but equal current flow in said link inductor and utilizing
switches of said switch arrays which are complimentary to said
switches used for said first cycle of said power transfer; said
first and second power cycles comprising a single voltage cycle of
the energy-transfer link reactance; said capacitance, in
conjunction with said current reversal, producing soft-switching of
said switches with low-voltage turn-off, zero voltage turn-on, and
low reverse recovery losses; said bidirectional switching devices
being capable of blocking voltage in either direction and
conducting current in either direction; wherein said power transfer
cycles are continuously repeated by said control means to produce
said power transfer on a continuing basis; and wherein control
means coordinate said switching actions to produce current and
power transfer via said power cycles as required to produce desired
output voltage and current, as may be used to drive single or
polyphase motors at variable speed and voltage, or to drive any
other electrical DC, single phase AC, polyphase AC, and/or multiple
DC loads; said capacitance, in conjunction with said current
reversal, producing soft-off-switching of said switches with
low-voltage turn-off, as current is shunted from each turning-off
switch into said substantially parallel capacitance, said switches
having soft turn-on as diodes as the link reactance voltage causes
control means enabled switches to transition from reverse to
forward bias, said switches having soft reverse blocking turn-off
as the link inductor current linearly decreases to zero after
discharging into an output port.
[0154] According to various disclosed embodiments, there is
provided: A Soft-switched Full-Bridge Buck-Boost Converter,
comprising: first and second power portals, each with two or more
ports by which electrical power is input from or output to said
portals, first and second full-bridge switch arrays, each
comprising two bidirectional switching devices for each said port
of each said power portal, a energy-transfer link reactance
symmetrically connected to both said switch arrays, each of said
switch arrays being connected to a power portal with said portal
possessing capacitive reactance between the legs of said portals
configured so as to approximate a voltage source, with power
transfer between said portals via said energy-transfer reactance,
Said link energy-transfer reactance consisting of an link inductor
and capacitance in parallel, said power transfer being accomplished
in a first power cycle as one or more pairs of input portal legs
are singularly or sequentially connected to said energy-transfer
reactance to store energy via increased current flow and inductance
into said link inductor, followed by one or more pairs of output
portal legs singularly or sequentially connected to said
energy-transfer reactance to remove energy via decreased current
flow and inductance from said link inductor, with any excess energy
in said link inductor subsequently returned back to one or more
said input portal leg pairs, followed by a reversal of current
within said link inductor and a repeat of the heretofore described
energy transfer, to constitute a second power cycle, from input to
output portal leg pairs, but with opposite but equal current flow
in said link inductor and utilizing switches of said switch arrays
which are complimentary to said switches used for said first cycle
of said power transfer; Said first and second power cycles comprise
a single voltage cycle of the energy-transfer link reactance; Said
bidirectional switching devices being capable of blocking voltage
in either direction and conducting current in either direction;
Said power transfer cycles being continuously repeated by said
control means to produce said power transfer on a continuing basis;
Said control means coordinating said switching actions to produce
current and power transfer via said power cycles as required to
produce desired output voltage and current, as may be used to drive
single or polyphase motors at variable speed and voltage, or to
drive any other electrical DC, single phase AC, polyphase AC,
and/or multiple DC loads; Said capacitance, in conjunction with
said current reversal, producing soft-off-switching of said
switches with low-voltage turn-off, as current is shunted from each
turning-off switch into said substantially parallel capacitance;
Said switches having soft turn-on as diodes as the link reactance
voltage causes control means enabled switches to transition from
reverse to forward bias; Said switches having soft reverse blocking
turn-off as the link inductor current linearly decreases to zero
after discharging into an output port.
[0155] According to various disclosed embodiments, there is
provided: An electric, vehicle, comprising at least one motor, at
least one electrical energy storage device, and a power converter
as above.
[0156] According to various disclosed embodiments, there is
provided: A solar energy system comprising at least one
photovoltaic array, at least one electrical energy storage device,
and a power converter as above.
[0157] According to various disclosed embodiments, there is
provided: A motor system comprising a polyphase power line
connection, a polyphase motor, and a power converter as above
connected therebetween as a variable-frequency drive.
[0158] According to various disclosed embodiments, there is
provided: A multiple power module soft-switched converter,
comprising multiple converters as above connected in parallel
between an input portal and an output portal, and commonly
controlled to minimize harmonics in the current drawn from and
delivered to said input and output portals.
[0159] According to various disclosed embodiments, there is
provided: According to various disclosed embodiments, there is
provided: A composite of n converters as above, connected at least
partially in parallel, and operating at inductor phase angles
separated by 180/n degrees; whereby the amount of input output
filtering can be reduced.
[0160] According to various disclosed embodiments, there is
provided: A method for operating a Buck-Boost Converter, comprising
the actions of: (a) operating a first bridge switch array,
comprising bidirectional switching devices, to operatively connect
at least one terminal of a reactance to a power input, with
polarity which reverses at different times; (b) operating a second
bridge switch array, comprising bidirectional switching devices, to
operatively connect at least one terminal of said reactance to a
power output, with polarity which reverses at different times;
wherein said actions (a) and (b) are never performed
simultaneously.
[0161] According to various disclosed embodiments, there is
provided: A method for operating a Buck-Boost Converter, comprising
the actions of: operating a first bridge switch array, comprising
bidirectional switching devices, to operatively connect at least
one terminal of a substantially parallel inductor-capacitor
combination to a power input, with polarity which reverses at
different times; wherein said first switch array is operatively
connected to a power input, and is operated to drive power into
said inductor-capacitor combination with a non-sinusoidal waveform;
and operating a second one of said switch arrays to extract power
from said inductor-capacitor combination to an output.
[0162] According to various disclosed embodiments, there is
provided: A method for operating a power converter, comprising the
actions of: driving an energy-transfer reactance with a full AC
waveform, at a base frequency which is less than half the resonant
frequency of said reactance; coupling power into said reactance, on
each cycle thereof, with two different drive phases, respectively
supplied from two different legs of a polyphase power source; and
coupling power out of said reactance, on each cycle thereof, with
two different: connection phases, respectively driving two
different: legs of a polyphase power output.
[0163] According to various disclosed embodiments, there is
provided: A method for power conversion, comprising the actions of:
driving, an energy-transfer reactance with a full AC waveform, at a
base frequency which is less than half the resonant frequency of
said reactance; coupling power into said reactance, on each cycle
thereof, with two different drive phases, respectively supplied
from two different legs of a polyphase power source; and extracting
power from said reactance to an output.
[0164] According to various disclosed embodiments, there is
provided: A Buck-Boost power conversion method, comprising:
operating an input switch array configured to drive AC current
through an energy-transfer reactance, at an average current
magnitude which is more than 100 times as great as the average DC
current within said reactance; said energy-transfer reactance
comprising at least one inductor; and operating an output network
to extract energy from said reactance.
[0165] According to various disclosed embodiments, there is
provided: A method for operating a power conversion circuit,
comprising the steps of repeatedly, at various times: driving
current into the parallel combination of an inductor and a
capacitor, and immediately thereafter temporarily disconnecting
said parallel combination from external connections, to thereby
transfer some energy from said inductor to said capacitor; wherein
said action of driving current is performed in opposite senses and
various times, and wherein said disconnecting operation is
performed substantially identically for both directions of said
step of driving current; and extracting energy from said parallel
combination, to thereby perform power conversion.
[0166] According to various disclosed embodiments, there is
provided: A method for operating a power conversion circuit,
comprising the steps of repeatedly, at various times: a) driving
current into the parallel combination of an inductor and a
capacitor, and immediately thereafter temporarily disconnecting
said parallel combination from external connections, to thereby
transfer some energy from said inductor to said capacitor; b)
coupling power out of said parallel combination, and immediately
thereafter temporarily disconnecting said parallel combination from
external connections, to thereby transfer some energy from said
inductor to said capacitor; wherein said disconnecting operation,
in said step a, is performed substantially identically for both
directions of said step of driving current; and wherein said
disconnecting operation, in said step b, is performed substantially
identically for both directions of said step of driving
current.
[0167] According to various disclosed embodiments, there is
provided: Methods and systems for transforming electric power
between two or more portals. Any or all portals can be DC, single
phase AC, or multi-phase AC. Conversion is accomplished by a
plurality of bi-directional conducting and blocking semiconductor
switches which alternately connect an inductor and parallel
capacitor between said portals, such that energy is transferred
into the inductor from one or more input portals and/or phases,
then the energy is transferred out of the inductor to one or more
output portals and/or phases, with said parallel capacitor
facilitating "soft" turn-off, and with any excess inductor energy
being returned back to the input. Soft turn-on and reverse recovery
is also facilitated. Said bi-directional switches allow for two
power transfers per inductor/capacitor cycle, thereby maximizing
inductor/capacitor utilization as well as providing for optimum
converter operation with high input/output voltage ratios. Control
means coordinate the switches to accomplish the desired power
transfers.
Modifications and Variations
[0168] As will be recognized by those skilled in the art, the
innovative concepts described in the present application can be
modified and varied over a tremendous range of applications, and
accordingly the scope of patented subject matter is not limited by
any of the specific exemplary teachings given. It is intended to
embrace all such alternatives, modifications and variations that
fall within the spirit and broad scope of the appended claims.
[0169] While the proceeding Figures illustrate exemplary
embodiments of a converter. Buck-Boost converter and methods of
operation therefore, other circuits (including variations of the
foregoing circuits) and methods of operation therefore are well
within the broad scope of the present invention. For a better
understanding of power electronics including Buck-Boost converter
technologies, see Principles of Power Electronics, by Kassakian, M.
Schlecht, Addison-Wesley Publishing Company (1991). The
aforementioned reference is herein incorporated by reference.
[0170] The disclosed converter circuits are advantageously
applicable to a wide variety of systems, including for example:
[0171] Electric vehicles, in which electrical interconversion is
required among, some or all of a traction motor, a battery, an
energy source (engine or fuel cell), and an external charging
connection. The source impedances and load impedances of all these
elements can be very different from each other, and can vary widely
over time with different load conditions or hysteretic history.
Moreover, the traction motor itself can be operated, using the
disclosed converter technology, as a variable-frequency AC drive.
[0172] Photovoltaic systems, as discussed above, are another
attractive application. Here too electrical interconversion is
required among some or all of a photovoltaic array, a battery
array, a utility input, an energy source (engine or fuel cell),
unknown line loads (applicances), and possibly an external power
filter with significant stored energy. In this application reactive
power compensation may also be desired. [0173] Variable-frequency
motor drive is an attractive and extremely broad class of
applications. Note that online systems according to the present
application can also be used for reactive power compensation,
and/or to implement soft shutdown using a stored energy source.
Online systems according to the present application can also be
easily reconfigured for a very wide variety of source or power line
voltages and frequencies, possibly with a change of inductor and/or
a change of switches. Motor-generator traction applications can
particularly benefit from less stringent requirements on generator
power quality. [0174] HVDC transmission is another attractive class
of applications. In this case the reduced requirements for switch
ratings are particularly attractive. [0175] Large arc and plasma
drive applications are also very attractive. In such cases the load
often has a negative marginal impedance, and active current control
is very useful. In many applications, such as arc furnaces, the
impedance of the load may change substantially as a process
progresses, and the agile control capabilities of the disclosed
system configurations can be very advantageous here. [0176] In
general, the very high bandwidth active control ability of the
disclosed inventions are useful in a wide range of systems. The
disclosed converter architectures are much better, in this respect,
than current source converters, and even than voltage-source
converters.
[0177] Additional general background, which helps to show
variations and implementations, may be found in the following
publications, all of which are hereby incorporated by reference:
[0178] U.S. Pat. Nos. 5,903,448, 4,616,300, 6,404,654, 5,977,569,
and 7,057,905; [0179] Ngo, "Topology and Analysis in PWM Inversion,
Rectification, and Cycloconversion" Dissertation (1984); [0180] Kim
and Cho, "New Bilateral Zero Voltage Switching AC/AC Converter
Using High Frequency Partial-resonant Link", IEEE (1990); [0181] K.
Rajashekara et al., "Power Electronics", Chapter 30 of The
Electrical Engineering Handbook (ed. R. Dorf 2000); M. Kassakian,
Principles of Power Electronics, (1991). [0182] M. Brown, Practical
Switching Power Supply Design (1990); [0183] Cheron: Soft
Commutation (1992); [0184] Facts Worth Knowing about Frequency
Converters 2ed. (Danfoss) (1992); [0185] Gottlieb, Irving: Power
Supplies, Switching Regulators, Inverters, and Converters (2.ed.
0.1994); [0186] Hughes: Electric Motors and Drives 2ed. (1993)`
[0187] Kenjo: Power Electronics for the Microprocessor Age 2ed.
(1994); [0188] Kislovski et al.: Dynamic Analysis of Switching-Mode
DC/DC Converters (1991); [0189] Lenk: Simplified Design of
Switching Power Supplies (1995); [0190] McLyman C. W. T.: Designing
Magnetic. Components for High Frequency DC-DC Converters (1993);
[0191] Mohan: Power Electronics: Converters, Applications, and,
Design 2ed. (1995); [0192] Nave, Mark: Power Line Filter Design for
Switched-Mode Power Supplies (1991); [0193] Schwarz: Design of
industrial Electric Motor Drives (1991); [0194] Shah, Rajesh J.:
Simplifying Power Supply Tech (1995); [0195] Tihanyi, Laszlo:
Electromagnetic Compatibility in Power Electronics (1995); [0196]
Wu, Keng. C.: Pulse Width Modulated DC-DC Converters 1997).
[0197] None of the description in the present application should be
read as implying that any particular element, step, or function is
an essential element which must be included in the claim scope: THE
SCOPE OF PATENTED SUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED
CLAIMS. Moreover, none of these claims are intended to invoke
paragraph six of 35 USC section 112 unless the exact words "means
for" are followed by a participle.
[0198] The claims as filed are intended to be as comprehensive as
possible, and NO subject matter is intentionally relinquished,
dedicated, or abandoned.
* * * * *
References