U.S. patent application number 15/095841 was filed with the patent office on 2016-08-04 for voltage converter with soft communication networks.
The applicant listed for this patent is Infineon Technologies Austria AG. Invention is credited to Cesar Augusto Braz.
Application Number | 20160226387 15/095841 |
Document ID | / |
Family ID | 52740007 |
Filed Date | 2016-08-04 |
United States Patent
Application |
20160226387 |
Kind Code |
A1 |
Braz; Cesar Augusto |
August 4, 2016 |
Voltage Converter with Soft Communication Networks
Abstract
Embodiments of the present invention describe a voltage
converter and a method for operating the voltage converter. In one
embodiment the voltage converter includes a primary path configured
to generate a pulse modulated voltage or current from an input
direct current (DC) voltage, a transformer arrangement with
m.gtoreq.1 primary windings and n.gtoreq.2 secondary windings
inductively coupled together, the m primary windings being
connected to the primary path, and a secondary path configured to
output a pulsed direct current (DC) voltage or current, wherein the
secondary path includes n capacitors connected in series and n
secondary controllable semiconductor switches, and each of the n
secondary windings is connected via at least one of the secondary
controllable semiconductor switches to at least one of the
capacitors.
Inventors: |
Braz; Cesar Augusto;
(Villach, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies Austria AG |
Villach |
|
AT |
|
|
Family ID: |
52740007 |
Appl. No.: |
15/095841 |
Filed: |
April 11, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14041993 |
Sep 30, 2013 |
9318978 |
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15095841 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 2001/0058 20130101;
Y02B 70/10 20130101; H02M 3/33584 20130101; H02M 7/5387 20130101;
H02M 3/33507 20130101; Y02B 70/1491 20130101 |
International
Class: |
H02M 3/335 20060101
H02M003/335 |
Claims
1. A voltage converter comprising: a primary path configured to
generate a pulse modulated voltage or current from an input direct
current (DC) voltage; a transformer arrangement with m.gtoreq.1
primary windings and n.gtoreq.2 secondary windings inductively
coupled together, the m primary windings being connected to the
primary path; and a secondary path configured to output a pulsed
direct current (DC) voltage or current, wherein the secondary path
comprises n capacitors connected in series and n secondary
controllable semiconductor switches, and wherein each of the n
secondary windings is connected via at least one of the secondary
controllable semiconductor switches to at least one of the
capacitors; and n soft commutation networks, each connected in
parallel to one of the n secondary controllable semiconductor
switches, and each of the n soft commutation networks comprising: a
series connection of a commutation inductance, a first commutation
diode and a commutation capacitor, the series connection being
connected in parallel to the respective secondary controllable
semiconductor switch and the commutation inductance being connected
to a node between the secondary controllable semiconductor switch
and the respective one of the n capacitors; and a second
commutation diode connected between the node between the first
commutation diode and the commutation capacitor, and the node
between the respective secondary winding and the respective one of
the n capacitors.
Description
TECHNICAL FIELD
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/041,993 filed on Sep. 30, 2013, which
application is hereby incorporated herein by reference.
BACKGROUND
[0002] A flyback converter is used in both alternating current (AC)
to direct current (DC) and DC to DC conversion with galvanic
isolation between the input and the output. Galvanic isolation and
voltage conversion is achieved by a transformer whose primary
winding is alternately connected to and disconnected from an input
voltage source and whose secondary winding supplies an output
voltage to an output capacitor via a rectifying diode. There are
two states of a flyback converter in operation. In an on-state, the
energy is transferred from the input voltage source to the
transformer and the output capacitor supplies energy to an output
load. In an off-state, the energy is transferred from the
transformer to the output capacitor load and the output load. A
common flyback converter as outlined above cannot provide reactive
power, i.e., positive voltage with negative current, or negative
voltage with positive current, because of the output diode, which
blocks the current in one direction.
[0003] A bidirectional flyback converter can provide reactive power
because the (high-voltage) diode is replaced by a (high-voltage)
switch that allows for current flow in both directions. In
bidirectional flyback converters, metal oxide semiconductor
field-effect transistors (MOSFET) are commonly employed as
high-voltage switches. However, high-voltage MOSFETs have higher
on-state resistances than those of low voltage MOSFETs and the
maximum voltage for high-voltage MOSFETS is 1,000 Volts (V).
Therefore, there is a need for an improved high-voltage
bidirectional flyback converter with MOSFETs.
SUMMARY OF THE INVENTION
[0004] A voltage converter according to an embodiment of the
invention comprises a primary path configured to generate a pulse
modulated voltage from an input DC voltage; a transformer
arrangement with m.gtoreq.1 primary windings and n.gtoreq.2
secondary windings inductively coupled together, the m primary
windings being connected to the primary path; and a secondary path
configured to output a pulsed DC voltage; wherein the secondary
path comprises n capacitors connected in series and n secondary
controllable semiconductor switches; and each of the n secondary
windings is connected via at least one of the secondary
controllable semiconductor switches to at least one of the
capacitors.
[0005] Other systems, methods, features and advantages will be, or
will become, apparent to one with skill in the art upon examination
of the following figures and detailed description. It is intended
that all such additional systems, methods, features and advantages
be included within this description, be within the scope of the
invention, and be protected by the following claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The system may be better understood with reference to the
following drawings and description. The components in the figures
are not necessarily to scale, emphasis instead being placed upon
illustrating the principles of the invention. Moreover, in the
figures, like referenced numerals designate corresponding parts
throughout the different views.
[0007] FIG. 1 is a circuit diagram of a bidirectional flyback
switched mode converter with reactive power capability using lower
voltage semiconductor switches;
[0008] FIG. 2 is a circuit diagram of a bidirectional flyback
switched mode converter according to FIG. 1 with additional soft
commutation networks;
[0009] FIG. 3 is a diagram illustrating a primary current, a
secondary current and a soft commutation current over time;
[0010] FIG. 4 is an alternative transformer structure with two
transformers whose primary windings are connected in series;
and
[0011] FIG. 5 is an alternative transformer structure with two
transformers whose primary windings are connected in parallel.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0012] A bidirectional flyback switched mode converter with
reactive power capability according to an embodiment of the
invention is schematically illustrated in FIG. 1. The converter of
FIG. 1 includes a transformer 1 with a primary side which forms
part of a primary path 2 and a secondary side which forms part of a
secondary path 3. The primary side has a primary winding 4 and the
secondary side has two secondary windings 5 and 6. Furthermore, the
primary path 2 includes a controllable switch 7, in the present
example a MOSFET, such as an N-type depletion mode MOSFET
(NMOSFET), a capacitor 8 and a control circuit 9 for controlling
the switch 7. Switch 7 and primary winding 4 are connected in
series and the series connection is connected in parallel to
capacitor 8. In the present example, capacitor 8 transforms a
current supplied by a DC current source 10, such as a photovoltaic
element, into a DC voltage so that DC current source 10 and
capacitor form a DC voltage source. This DC voltage is chopped by
switch 7 and supplied to primary winding 4.
[0013] Primary path 2 further includes a switch 11, e.g., an
NMOSFET controlled by control circuit 9 and a capacitor 12 which
are connected in series and as series connection in parallel to the
primary winding 4 of transformer 1. When switch 7 is turned off,
switch 11 is turned on. The leakage energy is transferred to the
capacitor 12 through switch 11, and the voltage across capacitor 12
is used to reset transformer 1. As a result, the voltage across
switch 7 is clamped.
[0014] Secondary path 3 includes beside the two secondary windings
5 and 6 two switches 13 and 14, e.g., NMOSFETs controlled by
control circuit 9, each of which is connected in series to one of
the secondary windings 5 and 6. Secondary path 3 further includes
two capacitors 15 and 16, connected in series. Capacitor 15 is
connected in parallel to the series connection of switch 13 and
secondary winding 5 and capacitor 16 is connected in parallel to
the series connection of switch 14 and secondary winding 6. Switch
7 is controlled to provide sine pulse width modulation in order to
generate 50 Hz (or 60 Hz) rectified sinusoidal currents in the
secondary windings 5 and 6 and the corresponding switches 13 and
14. FIG. 1 shows above winding 5, a voltage-time diagram of the
rectified sinusoidal current on the secondary side. Whenever switch
7 is on, switches 13 and 14 are off, and vice versa. Switches 13
and 14 work as active diodes with reduced conduction losses. The
capacitors 15 and 16 have sufficiently small capacity so that the
shape of the currents is not distorted. The objective is to divert
the high-frequency carrier current pulses and smooth the current to
its intended frequency: 50 Hz or 60 Hz. Switch 11, along with
capacitor 12 and the leakage inductance of transformer 1, form a
soft-switching network to promote soft switching (zero-voltage
switching) of switch 7 (loss less turn on).
[0015] In order to provide a DC-AC conversion, the pulsed DC
voltage over the series connection of capacitors 15 and 16 is
unfolded by a switching H-bridge that alternately outputs the
pulses inverted and non-inverted. The H-bridge comprises four
switches 17-20, e.g., NMOSFETs, controlled by control circuit 9, in
bridge configuration with one of the switches 17-20 in each leg of
the H-structure. A bridge structure is a type of electrical circuit
in which two circuit branches in parallel with each other are
"bridged" by a third branch, e.g., a load connected between the
first two branches at some intermediate point along them, the
intermediate point separates two legs per branch from each other.
Switches 17-20, which unfold the rectified current to an AC current
without DC level, are controlled to enable a voltage or current to
be applied across a load in either direction, wherein the switches
in one branch are never closed at the same time.
[0016] The bidirectional flyback converter illustrated in FIG. 1
may form the basis for a solar micro-inverter with reactive power
capability. For example, the flyback converter's secondary path has
been modified in order to be able to absorb the negative current by
replacing the rectifying diode with high-voltage MOSFETs 13 and 14.
The secondary winding has been split in two windings, which divide
the output voltage by two allowing, for example, 650V voltage-class
MOSFETs to be used as synchronous rectifiers in a 1,200V secondary
path. Auxiliary switch 11 and clamping capacitor 12, with the
leakage inductance of the transformer 1, form an active-clamp
network which provides zero-voltage switching (ZVS) turn-on to
switch 7.
[0017] In the present example, ZVS works as follows. Every time
switch 7 opens, the energy in the transformer leakage inductance is
stored into capacitor 12, storing a voltage higher than that in
winding 4. Before every time the switch 7 is turned on, the switch
11 is turned on first, for a small period of time, and the voltage
in capacitor 11 plus the input voltage is applied to winding 4. The
difference between this applied voltage and the reflected voltage
in winding 4 is then applied onto the leakage inductance. Then a
current flows through the leakage inductance with direction into
winding 4. The switch 11 is then turned off and the current flowing
in the leakage inductance discharges the output charge (Qoss) of
switch 7, forcing the voltage between switch 7 and primary winding
4 to swing to zero. Once the drain voltage is zero, the switch 7 is
turned on with zero-voltage switching.
[0018] In reactive power, switches 13 and 14 operate as controlling
switches and switch 7 operates as an active diode. Energy flows
from the output to the input. The modulation scheme applied to the
switches 13 and 14 may also be sine pulse width modulation.
[0019] Referring now to the converter shown in FIG. 2, in which
circuitry (indicated by a darkened area) that controls commutation
has been added to the flyback converter shown in FIG. 1. The
circuitry includes an inductor 21 connected in series to the
primary winding (e.g., the already present inductance of the
primary winding) and two soft commutation networks coupled with the
secondary windings. Each soft commutation network may include a
series connection of a commutation inductance 22a or 22b, a first
commutation diode 23a or 23b, and a commutation capacitor 24a or
24b, the series connection being connected in parallel to the
respective secondary controllable semiconductor switch 13 or 14 and
the commutation inductance commutation being connected to the node
between the secondary controllable semiconductor switch 13 or 14
and the respective one of the n capacitors 15 and 16. A second
commutation diode 25a or 25b may be connected between the node
between the first commutation diode 23a or 23b and the commutation
capacitor 24a or 24b, and the node between the respective secondary
winding 5 or 6 and the respective one of the n capacitors 15 and
16.
[0020] A high-voltage MOSFET has a higher reverse recovery charge
(Qrr) and a higher output charge (Qoss) than, for example, a
Silicon Carbide junction field effect transistor (JFET). When the
converter is operated in continuous current mode (CCM), Qoss and
Qrr may increase the turn-on losses of switch 7. Moreover,
secondary side high-voltage MOSFETs may be subject to hard
commutation of their body diodes every time switch 7 is turned on,
which, at high frequencies, may cause the destruction of these
devices.
[0021] The soft commutation network described above in connection
with FIG. 2 overcomes the above-mentioned issues. Inductor 21
serves two purposes here. It provides ZVS to switch 7, just as in
the active-clamp topology with switch 11 and capacitor 12, and
promotes soft commutation of the body diodes of the high-voltage
MOSFETs. During the soft commutation of the body diodes, the
additional current required to recover their Qrr and charge the
high-voltage MOSFETs Qoss is trapped in inductance 21. Diodes 23a
and 23c, along with capacitors 24a and 24b, provide a path and
storage, respectively, through transformer 1, to the trapped energy
in inductance 21. As switch 7 opens, the energy associated to Qrr
and Qoss, now stored in capacitors 24a and 24b, is then sent back
to the output through diodes 25a and 25b, prior to the high-voltage
MOSFETs conduction. During the reactive-power processing mode
inductors 22a and 22b provide zero-current turn-on to switches 13
and 14.
[0022] As described above, the micro-inverter illustrated in FIG. 2
includes a bidirectional flyback converter with a voltage-clamp
network (switch 11, clamping capacitor 12 and inductor 21, to
provide ZVS to switch 7. The converter secondary side may use two
(or more) identical secondary winding circuits (soft commutation
networks) connectable in series by switches 13 and 14, which work
as either synchronous rectifier switches, when processing active
power, or as control switches, when processing reactive power, when
switch 7 works as a synchronous rectifier. The secondary winding
circuits are series connected in order to match, for example, the
mains high voltage and yet utilize lower voltage MOSFETs (650V)
than what would otherwise be required of a single output stage,
e.g., a 1,200V switch. The soft commutation networks soften the
commutation of the high-voltage MOSFETs body diodes, avoiding their
destruction. The energy related to this soft commutation
(associated with Qrr and Qoss of the high-voltage MOSFETs),
initially trapped in inductance 21, is recovered and stored in
capacitors 24a and 24b, and then sent to the output once switch 7
opens.
[0023] FIG. 3 shows simulation results as current I over time t for
the transformer primary current Ip and secondary current Is,
highlighting the current related to Qrr and Qoss of the
high-voltage MOSFETs, i.e., soft commutation current Scc.
[0024] FIGS. 4 and 5 illustrate transforming circuits that may
substitute the transformer 1. In the circuit shown in FIG. 4 two
transformers 26 and 27 are employed which have each one primary
winding and one secondary winding, wherein the primary windings of
transformers 26 and 27 are connected in series. In the circuit
shown in FIG. 5 the primary windings of two transformers 26 and 27
are connected in parallel. However, any other constellations with
different numbers of transformers, different numbers of primary
windings, different numbers of secondary windings and different
connection structure are applicable as well.
[0025] The converters described above could be used both for AC-DC
and DC-DC power conversion. It is suitable for applications in the
low power as well as the high power range. Any switch, inductor,
diode or capacitor device can be substituted by a number of
respective devices, which may be connected in parallel or in
series. Primary and secondary control may be independently of one
another, or depended from each other, e.g., performed by a
multiplicity of controllers or only a single controller (as shown).
In the examples described above, control circuit 9 provides control
signals for all switches. Switches 7, 13 and 14 may be controlled
as in common bidirectional flyback converters and switches 17-20
may be controlled as in common H-bridge circuits.
[0026] Instead of MOSFETs based on silicon material, transistors
using wide-band gap material such as gallium nitride, silicon
carbide, zinc oxide, any other suitable material may be
employed.
[0027] Referring again to FIG. 1, the converter shown can simply be
operated as a DC/DC converter by omitting the unfolding bridge
(switches 17-20) and using the respective terminals of capacitors
15 and 16 for connecting a DC load (or a high voltage battery). For
step-up DC/DC converters, the input source 10 could be a DC current
source, such as a photovoltaic panel, or voltage sources, such as a
battery or battery banks, or fuel cells.
[0028] In DC/DC converter applications the output capacitors 15 and
16 are bigger than that of the micro-inverter outlined above to
have a constant voltage source at the output, with little ripple,
whereas in the micro-inverter application the purpose of such
capacitors is to divert the high-frequency current from the output,
that would just receive the 50 Hz or 60 Hz current.
[0029] Furthermore, other variations and alternatives are possible
as well. For example, as will be obvious to those of ordinary skill
in the art, other circuit elements can be added to, or be used as
substitutes in, the specific circuit embodiments discussed above,
such as other types of switching means, other types of control
units, etc. Furthermore, the invention may be used in a large range
of different applications.
[0030] While various embodiments of the invention have been
described, it will be apparent to those of ordinary skill in the
art that many more embodiments and implementations are possible
within the scope of the invention. Accordingly, the invention is
not to be restricted except in light of the attached claims and
their equivalents.
* * * * *