U.S. patent number RE41,965 [Application Number 12/205,743] was granted by the patent office on 2010-11-30 for bi-directional multi-port inverter with high frequency link transformer.
This patent grant is currently assigned to Xantrex Technology Inc.. Invention is credited to Richard T. West.
United States Patent |
RE41,965 |
West |
November 30, 2010 |
**Please see images for:
( Certificate of Correction ) ** |
Bi-directional multi-port inverter with high frequency link
transformer
Abstract
This invention is a multi-port power converter where all ports
are coupled through different windings of a high frequency
transformer. Two or more, and typically all, ports have
synchronized switching elements to allow the use of a high
frequency transformer. This concept and type of converter is known.
This invention mitigates a number of limitations in the present art
and adds new capabilities that will allow applications to be served
that would otherwise not have been practical. A novel circuit
topology for a four-quadrant AC port is disclosed. A novel circuit
topology for a unidirectional DC port with voltage boost
capabilities is disclosed. A novel circuit topology for a
unidirectional DC port with voltage buck capabilities is disclosed.
A novel circuit for a high efficiency, high frequency,
bi-directional, AC semiconductor switch is also disclosed.
Inventors: |
West; Richard T. (San Luis
Obispo, CA) |
Assignee: |
Xantrex Technology Inc.
(Livermore, CA)
|
Family
ID: |
34193448 |
Appl.
No.: |
12/205,743 |
Filed: |
September 5, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
10604876 |
Aug 22, 2003 |
07102251 |
Sep 5, 2006 |
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Current U.S.
Class: |
307/64; 363/97;
363/16; 307/66 |
Current CPC
Class: |
H02M
1/10 (20130101); H02J 3/40 (20130101); H02J
7/35 (20130101); H02J 3/381 (20130101); H02M
7/4807 (20130101); H02J 9/067 (20200101); H02J
2300/30 (20200101); H02J 3/387 (20130101); H02M
3/3374 (20130101); Y02B 10/70 (20130101); H02J
2300/24 (20200101); Y02B 90/10 (20130101) |
Current International
Class: |
H02J
1/00 (20060101) |
Field of
Search: |
;307/82,83,72,64,66
;363/37,71,55,16,97 ;323/222 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Paladini; Albert W
Assistant Examiner: Cavallari; Daniel
Attorney, Agent or Firm: Nixon Peabody LLP
Claims
The invention claimed is:
1. A power converter apparatus comprising three or more ports, a
transformer and a control circuit where one end of each port is
connected to a distinct winding on a common transformer core and
where the remaining end of each port is connected to a load or
power source and where each port comprises an arrangement of
capacitive or inductive energy storage elements and semiconductor
switches where individual semiconductor switches are commanded on
and off by said control circuit in a synchronous manner with
semiconductor switches in other ports and where said power
converter apparatus is further defined, as having one port
dedicated to a storage battery, designated for reference herein as
the battery port, having characteristics different from all other
ports, specifically, semiconductor switches in the battery port
operate in a free-running mode and provide frequency and phase
references that are followed by synchronous switches in all
remaining ports and the interface at the battery port transformer
winding is that of a low impedance AC voltage source or sink,
whereas the interface at the transformer windings of all other
ports is that of a high impedance AC current source or sink and
where these two distinct port types, battery and non-battery,
enable energy transfer into or out of all non-battery ports
simultaneously and in an autonomous manner in terms of energy
transfer and where the net energy into or out of all non-battery
ports charges or discharges the storage battery, respectively, via
the battery port.
.Iadd.2. The power conversion system of claim 1, wherein the third
switching circuit is a hybrid switch having first and second switch
poles and comprises: first and second series MOSFET devices
connected in parallel with first and second series IGBT devices
between the first and second switch poles; a gate driver for
driving the first and second series MOSFET devices through a first
node between the first and second series MOSFET devices, and
through a second node between the first and second series IGBT
devices. .Iaddend.
.Iadd.3. A power conversion system comprising: a transformer
comprising a first winding, a second winding, and a third winding;
a first switching circuit coupled to the first winding and to first
terminals for connection to a DC power source; a buck regulator
coupled to the first winding and having a diode, inductor and a
switch; a second switching circuit coupled to the second winding
and to second terminals for connection to an electrical power
storage device; and a third switching circuit coupled to the third
winding and to third terminals for connection to an AC power source
or load, a boost circuit coupled to the third winding and having an
inductor and a switch; and a control circuit for controlling the
first, second and third switching circuits such that at least some
of the time, the first, second, and third switching circuits are
all active, with switching of the first, second and third switching
circuits being synchronized with respect to each other.
.Iaddend.
.Iadd.4. The power conversion system of claim 3, wherein the
control circuit is configured to switch the third switching circuit
so as to produce a line-frequency power waveform. .Iaddend.
.Iadd.5. The power conversion system of claim 3, wherein the first
switching circuit is configured to perform boost regulation.
.Iaddend.
.Iadd.6. The power conversion system of claim 3, wherein the first
switching circuit comprises: a first semiconductor switch coupled
to one of the first terminals and to one end of the first winding;
a second semiconductor switch coupled to the one of the first
terminals and to another end of the first winding; and a third
semiconductor switch coupled to the one of the first terminals, and
coupled through a diode to a center tap of the first winding.
.Iaddend.
.Iadd.7. The power conversion system of claim 6, wherein the first
switching circuit comprises an inductor coupled to another one of
the first terminals and to the diode so as to conduct current from
the first terminal through the diode. .Iaddend.
.Iadd.8. The power conversion system of claim 6, wherein the first,
second and third semiconductor switches are unidirectional
semiconductor switches. .Iaddend.
.Iadd.9. The power conversion system of claim 3, wherein the second
switching circuit comprises first, second, third and fourth
semiconductor switches arranged in an H-bridge configuration.
.Iaddend.
.Iadd.10. The power conversion system of claim 9, wherein the
first, second, third and fourth semiconductor switches are
unidirectional semiconductor switches. .Iaddend.
.Iadd.11. The power conversion system of claim 3, wherein the third
switching circuit is configured to perform boost regulation.
.Iaddend.
.Iadd.12. The power conversion system of claim 3, wherein the third
switching circuit comprises: a first semiconductor switch coupled
to one of the third terminals and to one end of the third winding;
a second semiconductor switch coupled to the one of the third
terminals and to another end of the third winding; and a third
semiconductor switch coupled on one side thereof to another one of
the third terminals and to a center tap of the third winding, and
coupled on another side thereof to the one of the third terminals
through an inductor. .Iaddend.
.Iadd.13. The power conversion system of claim 12, wherein the
first, second and third semiconductor switches are bidirectional.
.Iaddend.
.Iadd.14. The power conversion system of claim 3, comprising one of
a photovoltaic array, a DC generator and a fuel cell coupled to the
first terminals. .Iaddend.
.Iadd.15. The power conversion system of claim 3, comprising a
battery coupled to the second terminals. .Iaddend.
.Iadd.16. The power conversion system of claim 3, wherein the third
terminals are coupled to a utility grid. .Iaddend.
.Iadd.17. A power conversion system comprising: a transformer
comprising a first winding, a second winding, and a third winding;
a first switching circuit coupled to the first winding and to first
terminals for connection to a DC power source; a second switching
circuit coupled to the second winding and to second terminals for
connection to an electrical power storage device; and a third
switching circuit coupled to the third winding and to third
terminals for connection to an AC power source or load; a boost
circuit having an inductor and a switch; and a control circuit for
controlling the first, second and third switching circuits such
that at least some of the time, the first, second, and third
switching circuits are all active, with switching of the first,
second and third switching circuits being synchronized with respect
to each other, wherein the first switching circuit comprises: a
first semiconductor switch coupled to one of the first terminals
and to one end of the first winding; a second semiconductor switch
coupled to the one of the first terminals and to another end of the
first winding; and a third semiconductor switch coupled to another
one of the first terminals, and coupled through an inductor to a
center tap of the first winding. .Iaddend.
.Iadd.18. The power conversion system of claim 17, wherein the
first switching circuit comprises a diode coupled to the one of the
first terminals and to the inductor so as to conduct current
flowing through the inductor and through one of said first and
second semiconductor switches. .Iaddend.
.Iadd.19. The power conversion system of claim 17, wherein the
first, second and third semiconductor switches are unidirectional
semiconductor switches. .Iaddend.
Description
BACKGROUND OF INVENTION
The field of this invention is power electronics and electrical
power conversion. Electronic power inverters are devices for
converting direct current (DC) power, usually from a storage
battery, into alternating current (AC) power for household
appliances. Some inverters also convert power from an AC source to
charge the storage battery used by the inverter. Devices capable of
power transfer in either direction, DC-to-AC or AC-to-DC are
commonly referred to as inverter/chargers or bi-directional
inverters. Inverters are also used in renewable and distributed
energy systems to convert DC power from photovoltaic panels, fuel
cells or wind turbines into power that can be delivered into the
utility grid. There is a growing demand for an inverter product
with this capability that can also charge storage batteries and
support AC loads when the utility grid is not available.
Residential systems with both renewable energy sources and energy
storage components typically use a battery-centric topology. This
is because the battery provides a stable voltage and high peak
power capabilities. In these systems, the renewable energy source
interfaces to the battery through a DC-to-DC converter or charge
controller to provide the required matching and regulation
functions. The battery is in turn connected to a DC-to-AC inverter,
to support the system loads, and to a battery charger. Additional
energy sources as well as DC loads would also logically tie in at
the storage battery connection point. With the present state of
technology, this arrangement typically provides the most cost
effective and highest performance system solution. There are a
number of inherent limitations with this approach. (i) The storage
battery voltages are relatively low compared to the AC voltages
that the inverter produces. A common power conversion method is to
convert the low DC battery voltage into a low AC voltage and then
use a transformer to convert to a higher AC voltage. This approach
requires a heavy, expensive, and typically inefficient, low
frequency transformer. (ii) The conversion efficiency from the
renewable energy source to the battery to the utility grid is low
because of the additive losses from each successive power
conversion stage. (iii) Higher voltage, higher efficiency, lower
cost photovoltaic series "string" arrays are not practical because
of the photovoltaic/battery voltage disparity. (iv) Individual
power converters in battery-centric systems are usually autonomous.
It is advantageous for all power converters to act in concert in
order to achieve optimum battery life and to better support the
system loads.
SUMMARY OF INVENTION
The invention is a multi-port power electronics topology, with a
high frequency transformer as the common power "conduit" and
interface point for all ports. This invention would allow for
energy systems that are high-frequency-transformer-core-centric as
opposed to battery-centric. This invention mitigates essentially
all of the limitations of battery-centric energy systems. The
underlying power converter concept used for this invention was
originally invented by William McMurry and disclosed in U.S. Pat.
No. 3,517,300 in 1970. Since then, others have expanded the
potential capabilities of these power converters but with
less-than-novel or with technically obvious variations on the
original McMurry invention. The invention disclosed herein involves
a number of novel power circuit topologies that allow much greater
port flexibility and provide enhanced performance. The invention
allows a port to perform as a boost or buck converter when sourcing
power into the high frequency transformer, a capability that has
not been previously established. These added capabilities allow
applications to be served that would otherwise not have been
practical. Also, the invention allows each non-battery port to
"see" only the reflected battery characteristics at the transformer
interface so that the operation of all non-battery ports are
independent and non-interactive. The preferred embodiment of the
invention is intended for residential electrical energy systems.
There are three ports; a bi-directional battery port that allows a
storage battery to source energy to the transformer or sink energy
from the transformer to charge the battery, a bi-directional AC
port that allows the transformer to source energy to loads and also
to sink or source energy from a utility grid at unity power factor,
and a renewable energy port that sources energy into the
transformer and is capable of controlling the operating point of
the renewable energy source and the amount of power delivered into
the transformer. Products developed using this invention will be
(i) lighter because transformers operating at ultrasonic
frequencies are much smaller than line frequency transformers (ii)
lower cost because of the smaller transformer and the
system-integrated power conversion approach and (iii) more
efficient because of fewer power conversion stages and the lower
core and copper losses associated with high frequency transformers.
These advantages are had without sacrificing the isolation
properties of a transformer.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 illustrates the preferred embodiment of the invention, a
power converter for residential energy systems having a
photovoltaic (PV) array, a storage battery and a multipurpose
utility/load/generator interface.
FIG. 2 illustrates an alternate power converter circuit topology
for residential energy systems having a renewable energy source, a
storage battery and a multipurpose utility/load/generator
interface.
FIG. 3 illustrates the sequence of high frequency switch closures
in a two-port power converter using the invention. The condition
shown is a battery at the two-quadrant DC port delivering power to
a load at the four-quadrant AC port.
FIG. 4 illustrates the sequence of high frequency switch closures
in a two-port power converter using the invention. The condition
shown is an AC voltage source at the four-quadrant AC port
delivering power to (charging) the battery at the two-quadrant DC
port.
FIG. 5 illustrates an alternate power converter topology for
residential energy systems having a renewable energy source, a
storage battery and a split-phase, multipurpose,
utility/load/generator interface.
FIG. 6 illustrates a typical, known bi-directional semiconductor
switch capable of bipolar voltage blocking, bi-directional current
control and bi-directional current conduction.
FIG. 7 illustrates an alternate, bi-directional semiconductor
switch capable of bipolar voltage blocking, bi-directional current
control and bi-directional current conduction using IGBT instead of
MOSFET devices.
FIG. 8 illustrates a novel, composite, bi-directional semiconductor
switch capable of bipolar voltage blocking, bi-directional current
control and bi-directional current conduction.
DETAILED DESCRIPTION
FIG. 1 illustrates the preferred embodiment of the invention, a
three-port power converter topology with one bi-directional battery
port, at terminals 12 and 13, one four-quadrant AC port, at
terminals 61 and 62, and one unidirectional renewable energy port
at terminals 84 and 85. Two types of semiconductor switch elements
are shown. Switches 21-24 and 91-93 have unipolar voltage blocking,
unidirectional current control and bi-directional current
conduction capabilities and are referred to as unidirectional
semiconductor switches on all diagrams. Switches 41-43 have bipolar
voltage blocking, bi-directional current control and bi-directional
current conduction capabilities and are referred to as
bi-directional switches in all diagrams. The battery port, at
terminals 12 and 13, contains a typical, full-bridge arrangement of
power switches 21-24 and is connected to winding 31 of high
frequency transformer 30. Switch pairs 21, 23 and 22, 24 are
alternately closed and opened at a high rate, typically greater
than 20 kHz, providing the transformer with square wave excitation
from a relatively low impedance source. The switching is free
running and the duty cycle remains fixed at 50%. The AC port, at
terminals 61 and 62, contains a typical center-tapped, half-bridge
switch topology using bi-directional semiconductor switches 41 and
42. Switches 41 and 42 are always operated synchronously with
switch pairs 21, 23 and 22, 24 to basically unfold the high
frequency AC square wave on windings 33 and 34. The flux in
transformer 30 is always reversed at the switching frequency of
bridge 20. Unlike switch pairs 21, 23 and 22, 24, switches 41 and
42 will operate at duty cycles from zero to 50%, as commanded by a
control circuit, to provide the desired current or voltage
regulation for the AC port. The inclusion of switch 43 allows the
AC port to act as a boost circuit in, conjunction with inductor 51,
when delivering energy from utility grid 66 to high-frequency
transformer 30. Switch 43 also allows an efficient path for
freewheeling inductor current when power is being delivered from
transformer 30 to AC loads 64 or utility grid 66. Without switch
43, a limited boost function can be had by simultaneously closing
switches 41 and 42, causing transformer windings 33 and 34 to be
short-circuited, and opening all bridge 20 switches. This works
well for two-port converters but limits the transformer
availability for converters with three or more ports because the
transformer is unable to sink or source power at any port when
windings 33 and 34 are shorted. Also, anytime bridge 20 is not in
conduction, the operation of one port becomes dependent on the
operation of other ports and the value of this power conversion
approach is severely compromised. The inclusion and function of
switch 43 in the AC port is novel and part of this invention. It
should be noted that if power is flowing into the AC port, inductor
51 acts as a boost inductor, if power is flowing out of the AC
port, inductor 51 acts as a filter component in conjunction with
capacitor 52. The renewable energy port, at terminals 84 and 85,
provides the ability for the converter to track the maximum power
point of photovoltaic (PV) array 83 under various ambient
conditions. The basic function of the port is that of a buck
regulator. Energy from PV array 83 is stored in capacitor 55.
Unidirectional switch 93 is turned on and off at a rate typically
greater than 20 kHz and with a duty cycle established by a control
circuit to regulate the PV voltage and/or power. When switch 93 is
closed, diode 71 is back-biased and current flows through boost
inductor 56 and returns through either transformer winding 37 and
unidirectional switch 91 or through transformer winding 38 and
unidirectional switch 92. When PV energy is available, switches 91
and 92 always operate at 50% duty cycle and in tandem with switch
pairs 22, 24 and 21, 23 respectively. When switch 93 is opened, the
freewheeling inductor current is conducted through diode 71 and
either transformer winding 37 and unidirectional switch 91 or
transformer winding 38 and unidirectional switch 92, whichever path
is active at the time. The three-switch buck port topology
described here is novel and is part of this invention. FIG. 2
illustrates an alternate topology for the renewable energy port, at
terminals 84 and 85. The basic function of the port is that of a
boost regulator. In the preferred embodiment, the renewable energy
source is either fuel cell 81 or DC generator 82. Energy from the
renewable source is stored in capacitor 55. Unidirectional switch
93 is turned on and off at a rate typically greater than 20 kHz and
with a duty cycle established by a control circuit to regulate the
port voltage and/or power. When switch 93 is closed, current flows
from capacitor 55 to charge inductor 56. When switch 93 is opened,
the current flowing in inductor 56 is conducted through diode 71
and either transformer winding 37 and unidirectional switch 91 or
transformer winding 38 and unidirectional switch 92, whichever path
is active at the time. Switches 91 and 92 operate at 50% duty cycle
and in tandem with switch pairs 22, 24 and 21, 23 respectively, but
may also be switched off when switch 93 is on. The three-switch
boost port topology described is novel and is part of this
invention. FIG. 3 illustrates one method of synchronizing the
battery port and AC port switching elements to convert power from a
storage battery to supply household AC loads. In this mode, AC
voltage is regulated across the load. Regulation methodologies are
known and typically use voltage and current feedback, reference
values and error amplifiers to implement a fast inner current
control loop and a slower outer AC voltage regulation loop. FIG. 3
illustrates the sequence of a complete high frequency switching
cycle at point in time where a small portion of the positive
voltage half-sine across the load is being created. In FIG. 3A,
switch 41 is closed simultaneously with bridge pair 21, 23 causing
current to flow out of the battery and into the load in the
direction shown. In FIG. 3B, switch 41 is opened, interrupting the
current flow from the battery, and at the same time switch 43 is
closed. Switch 43 acts as a freewheeling diode to provide a path
for the inductor current. In FIG. 3C, bridge pair 21, 23 are opened
and bridge pair 22, 24 is closed, at the same time switch 43 is
opened and switch 42 is closed. Current still flows through the
load in the same intended direction even though the flux in the
transformer has reversed. In FIG. 3D, switch 42 is opened,
interrupting the current flow from the battery and at the same time
switch 43 is closed, again providing a path for the inductor
current. The sequence is then repeated 3A, 3B, 3C, 3D, 3A, etc. The
ratio of switch 41 and 42 "on" times to the switching period
controls the amount of energy transferred and is effectively the
PWM duty cycle controlled by the regulator. The selection of switch
41 verses 42 controls the polarity of the voltage delivered to the
load. The alternation of switch pairs 21, 23 and 22, 24 at high
frequencies enable the use of a high frequency transformer. FIG. 4
illustrates one method of synchronizing the battery port and AC
port switching elements to convert power from the AC utility grid
to charge the storage battery. In this mode, AC current is sourced
from the utility grid at unity power factor. The amplitude of the
sine wave current out of the utility is proportional to the
instantaneous battery charge current commanded by the system
controller's charge algorithm. Regulation methodologies are known
and typically use voltage and current feedback, reference values
and error amplifiers to implement a current control loop with a
sinusoidal current reference that is synchronous with the AC line
voltage. FIG. 4 illustrates the sequence of a complete high
frequency switching cycle at point in time where a small portion of
a positive current half-sine is being sourced from the utility
grid. In FIG. 4A, switch 43 is closed and the inductor charges from
the instantaneous utility line voltage. Bridge pair 21, 23 is
closed but the states of the bridge pairs are irrelevant because
switches 41 and 42 are both open. In FIG. 4B, switch 43 is opened
and switch 41 is simultaneously closed. The inductor current flows
into the transformer. In FIG. 4C, bridge pair 21, 23 are opened and
bridge pair 22, 24 is closed, at the same time switch 41 is opened
and switch 43 is closed, charging the inductor. In FIG. 4D, switch
43 is opened and switch 42 is simultaneously closed and current is
again delivered to the transformer. The sequence is then repeated
4A, 4B, 4C, 4D, 4A, etc. The ratio of switch 43 "on" time to switch
41 and 42 "on" times controls the energy transferred. The
transformer turns ratio is such that the battery cannot be charged
from the utility grid under normal conditions without the boost
circuit. The selection of switch 41 verses 42 is selected based on
the instantaneous AC line polarity. In this battery charging mode,
switch 43 provides a boost regulator function and switch pairs 21,
23 and 22, 24 operate as synchronous rectifiers. FIG. 5 illustrates
two AC ports configured for interface to a split-phase utility or
to deliver power to split-phase loads. FIG. 6 illustrates one
method for configuring a switch element with the required
characteristics for use as switches 41, 42 and 43 as referenced in
FIG. 1. Terminals 11 and 12 are the switch poles. The two terminals
are interchangeable with respect to any polarity reference. MOSFETs
7 and 8 are connected in a common source configuration so that
voltage can be blocked in either direction and current flow can be
controlled in either direction. Gate driver 4 drives MOSFETS 7 and
8 through resistors 5 and 6 respectively. MOSFETs 7 and 8 are
switched simultaneously. The Vcc 2 to Vss 3 power supply and the
logic drive signal 1 are electrically isolated from the other
switch elements in a typical power converter. A number of MOSFET
devices may be paralleled so that the conduction voltage drop of
the MOSFET is always lower than the conduction voltage of the
MOSFET parasitic diode. As such, current never flows through the
MOSFET parasitic diodes. The configuration shown in FIG. 6 is
known. FIG. 7 illustrates a second method for configuring a switch
element with the required characteristics for use as switches 41,
42 and 43 in FIG. 1. The method is essentially the same as shown in
FIG. 6 except that Insulated Gate Bipolar Transistors (IGBTs) are
used in place of FETs. This logical extension is obvious and
therefore considered known by default. FIG. 8 illustrates a hybrid
switch that incorporates the best features of both the MOSFET and
IGBT bi-directional switches and is the preferred method for
configuring a switch element with the required characteristics for
use as switches 41, 42 and 43 in FIG. 1. Terminals 13 and 14 are
the switch poles. The two terminals are interchangeable with
respect to any polarity reference. IGBTs 9 and 10 are connected in
a common emitter configuration and each are connected in parallel
with MOSFETs 11 and 12 respectively. Voltage can be blocked in
either direction and current flow can be controlled in either
direction. Gate driver 4 drives all semiconductor devices through
gate resistors 5-8. The Vcc 2 to Vss 3 power supply and the logic
drive signal 1 are electrically isolated. In higher voltage
applications, the hybrid switch illustrated in FIG. 8 operates with
lower losses over a wider range of currents than either the MOSFET
only or the IGBT only bi-directional switch. MOSFET devices exhibit
a resistive "on" characteristic while IGBT devices exhibit a
semiconductor junction "on" characteristic. In the AC port
application discussed, the IGBT devices handle the high peak
currents more cost effectively than the MOSFET devices. High peak
currents are shunted from the MOSFETS by the IGBTs. At lower
currents, the current is shunted from the IGBTs and parasitic
MOSFET diodes by a MOSFET "on" resistance that represents a lower
voltage drop than the semiconductor "on" voltage. Additionally, if
separate drivers are used for the IGBTs and the MOSFETs, the MOSFET
turnoff can be delayed with respect to the IGBT turnoff to take
advantage of the faster MOSFET switching speeds. This
bi-directional hybrid switch is novel and is part of this
invention.
* * * * *