U.S. patent application number 10/643732 was filed with the patent office on 2005-02-24 for pulse width modulation soft-switching control.
Invention is credited to Chen, Keming A., Kajouke, Lateef A., Lazar, James F..
Application Number | 20050041438 10/643732 |
Document ID | / |
Family ID | 34116783 |
Filed Date | 2005-02-24 |
United States Patent
Application |
20050041438 |
Kind Code |
A1 |
Chen, Keming A. ; et
al. |
February 24, 2005 |
PULSE WIDTH MODULATION SOFT-SWITCHING CONTROL
Abstract
A DC/DC converter includes a first leg and a second leg. A
controller employs hard switching in the first leg to reduce the
conduction loss. The controller employs zero voltage in the second
leg to reduce the switching loss.
Inventors: |
Chen, Keming A.; (Torrance,
CA) ; Lazar, James F.; (Moorpark, CA) ;
Kajouke, Lateef A.; (San Pedro, CA) |
Correspondence
Address: |
CHRISTOPHER DEVRIES
General Motors Corporation
Legal Staff, Mail Code 482-C23-B21
P.O. Box 300
Detroit
MI
48265-3000
US
|
Family ID: |
34116783 |
Appl. No.: |
10/643732 |
Filed: |
August 19, 2003 |
Current U.S.
Class: |
363/17 |
Current CPC
Class: |
Y02B 70/10 20130101;
H02M 3/33592 20130101; H02M 7/5387 20130101; Y02B 70/1475
20130101 |
Class at
Publication: |
363/017 |
International
Class: |
H02M 003/335 |
Claims
What is claimed is:
1. A DC/DC converter that converts an input voltage to an output
voltage and includes a transformer having a primary side and a
secondary side, comprising: a primary side bridge rectifier that
communicates with the primary side and includes a first leg that is
connected across said input voltage and includes a first switching
circuit and a second switching circuit, and a second leg that is
connected across said input voltage and that includes a third
switching circuit and a fourth switching circuit; a switch
controller that employs zero voltage switching (ZVS) to control
said third and fourth switching devices and hard switching to
control said first and second switching devices.
2. The DC/DC converter of claim 1 wherein said switch controller
turns off said fourth switching device with ZVS, turns said third
switching circuit on with ZVS and turns said first switching
circuit off with hard switching during a first half cycle.
3. The DC/DC converter of claim 1 wherein said controller turns
said second switching circuit on with hard switching, turns said
third switching circuit off with ZVS, turns said fourth switching
circuit on with ZVS and turns said second switching circuit off
with hard switching during a second half cycle.
4. The DC/DC converter of claim 1 wherein said controller turns off
said fourth switching device with ZVS, turns said third switching
circuit on with ZVS and turns said first switching circuit off with
hard switching during a first half cycle and wherein said
controller turns said second switching circuit on with hard
switching, turns said third switching circuit off with ZVS, turns
said fourth switching circuit on with ZVS and turns second
switching circuit on with hard switching during a second half
cycle.
5. The DC/DC converter of claim 4 wherein said first switching
circuit includes a first transistor having a first gate and a first
diode that is connected antiparallel to said transistor.
6. The DC/DC converter of claim 5 wherein said second switching
circuit includes a second transistor having a second gate and a
second diode that is connected antiparallel to said transistor.
7. The DC/DC converter of claim 6 wherein said third switching
circuit includes a third transistor having a third gate and a third
diode that is connected antiparallel to said transistor and a first
capacitor that is connected in parallel with said third diode.
8. The DC/DC converter of claim 7 wherein said fourth switching
circuit includes a fourth transistor having a fourth gate and a
fourth diode that is connected antiparallel to said transistor and
a second capacitor that is connected in parallel with said
diode.
9. The DC/DC converter of claim 8 wherein when said fourth
switching device turns off during said first half cycle, said
second capacitor is charged and said first capacitor is
discharged.
10. The DC/DC converter of claim 9 wherein said third switching
device is turned on after said first capacitor discharges.
11. The DC/DC converter of claim 10 wherein said first switching
device is turned off when said third switching device is turned
on.
12. The DC/DC converter of claim 8 wherein said third switching
device is turned off after said second switching device is turned
on during said second half cycle.
13. The DC/DC converter of claim 8 wherein said first capacitor
charges and said second capacitor discharges when said third
switching device is turned off.
14. The DC/DC converter of claim 13 wherein said fourth switching
device is turned on when said second capacitor is discharged.
15. A method for operating a DC/DC converter including a primary
side bridge rectifier with a first leg that is connected across
said input voltage and includes a first switching circuit and a
second switching circuit, and a second leg that is connected across
said input voltage and that includes a third switching circuit and
a fourth switching circuit, comprising: during an first half cycle:
turning on said first switching circuit on with hard switching;
turning off said fourth switching device with zero voltage
switching (ZVS); turning said third switching circuit on with said
ZVS; and turning said first switching circuit off with hard
switching.
16. The method of claim 15 further comprising: during a second half
cycle: turning said second switching circuit on with hard
switching; turning said third switching circuit off with said ZVS;
turning said fourth switching circuit on with said ZVS; and turning
said second switching circuit off with hard switching.
17. A DC/DC converter comprising: a first leg; a second leg; and a
controller that employs hard switching in the first leg to reduce
conduction loss and zero voltage in the second leg to reduce
switching loss.
18. The DC/DC converter of claim 17 further comprising a
transformer that communicates with said first and second legs and
that includes a primary side and a secondary side.
19. The DC/DC converter of claim 17 further comprising an input
voltage source, wherein said first leg is connected across said
input voltage source and includes a first switching circuit and a
second switching circuit.
20. The DC/DC converter of claim 19 wherein said second leg is
connected across said input voltage and includes a third switching
circuit and a fourth switching circuit, wherein said controller
employs zero voltage switching (ZVS) to control said third and
fourth switching devices and hard switching to control said first
and second switching devices.
Description
FIELD OF INVENTION
[0001] The invention relates generally to DC/DC converters, and
more specifically relates to reducing conduction and switching
losses in DC/DC converters.
BACKGROUND OF THE INVENTION
[0002] DC/DC converters produce an output voltage at a different
voltage level than an input voltage to the DC/DC converter. For
example, DC/DC converters are commonly used to increase a DC input
voltage to a higher output voltage or to decrease a DC input
voltage to a lower output voltage. In addition, DC/DC converters
provide electrical isolation and power bus regulation. DC/DC
converters are employed in a variety of applications, including
power supplies for personal computers, office equipment, spacecraft
power systems, laptop computers, telecommunications equipment, and
DC motor drives.
[0003] The input to a DC/DC converter is typically an unregulated
DC voltage. The DC/DC converter produces a regulated output voltage
that has a magnitude and/or a polarity that differs from the input
voltage. Typical DC/DC converters employ switching devices, such as
MOSFETs, IGBTs, BJTs and thyristors, to regulate and convert the
input voltage. A controller controls the switching frequency and
sequence of the switching devices to produce a desired output
voltage. For example, the controller may implement a pulse width
modulation (PWM) approach to vary the duty cycle of switching
devices. With PWM, the switching frequency is constant and the duty
cycle varies with load and voltage requirements.
[0004] DC/DC converters typically include a transformer that
isolates the converter input and output. The transformer reduces
the stress on the switching devices and improves the efficiency of
the switching devices. Conventional PWM converters turn off the
switching devices when current is flowing through them, which is
commonly referred to as hard switching. When hard switching is used
at high frequencies, relatively high switching losses occur.
Switching losses are especially pronounced in high power, high
voltage applications where hard switching is utilized.
[0005] To reduce switching losses, DC/DC converters implement
either zero-current switching (ZCS) or zero-voltage switching
(ZVS), which are commonly referred to as soft switching. In devices
using ZCS, the switching devices are turned off when there is zero
current flowing through the switching devices. In devices using
ZVS, the switching devices are turned on when there is no voltage
across the switching devices. Neither of these two distinct
approaches strike an optimum balance between switching and
conduction losses.
BRIEF SUMMARY OF THE INVENTION
[0006] A DC/DC converter converts an input voltage to an output
voltage and includes a transformer having a primary side and a
secondary side. A primary side bridge rectifier communicates with
the primary side and includes a first leg that is connected across
the input voltage. The first leg includes a first switching circuit
and a second switching circuit. A second leg is connected across
the input voltage and includes a third switching circuit and a
fourth switching circuit. A controller employs zero voltage
switching (ZVS) to control the third and fourth switching devices
and hard switching to control the first and second switching
devices.
[0007] In other features, the controller turns off the fourth
switching device with the ZVS, turns the third switching circuit on
with the ZVS and turns the first switching circuit off with hard
switching during a first half cycle.
[0008] In yet other features, the controller turns the second
switching circuit on with hard switching, turns the third switching
circuit off with the ZVS, turns the fourth switching circuit on
with the ZVS and turns the second switching circuit off with hard
switching during a second half cycle.
[0009] In still other features, the first switching circuit
includes a first transistor having a first gate and a first diode
that is connected antiparallel to the transistor. The second
switching circuit includes a second transistor having a second gate
and a second diode that is connected antiparallel to the
transistor. The third switching circuit includes a third transistor
having a third gate and a third diode that is connected
antiparallel to the transistor and a first capacitor that is
connected in parallel with the third diode. The fourth switching
circuit includes a fourth transistor having a fourth gate and a
fourth diode that is connected antiparallel to the transistor and a
second capacitor that is connected in parallel with the diode.
[0010] In still other features, when the fourth switching device
turns off during the first half cycle, the second capacitor is
charged and the first capacitor is discharged. The third switching
device is turned on after the first capacitor discharges. The first
switching device is turned off when the third switching device is
turned on. The third switching device is turned off after the
second switching device is turned on during the second half cycle.
The first capacitor charges and the second capacitor discharges
when the third switching device is turned off. The fourth switching
device is turned on when the second capacitor is discharged.
[0011] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present invention will become more fully understood from
the detailed description and accompanying drawings, wherein;
[0013] FIG. 1 is a simplified schematic of a DC/DC converter
including a controller that employs a combination of ZVS and hard
switching to reduce the combined switching and conduction losses
according to the present invention; and
[0014] FIG. 2 illustrates control signals used by a controller to
control switching devices according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The following description of the preferred embodiment(s) is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses. For purposes of clarity, the
same reference numbers will be used in the drawings to identify
similar elements.
[0016] The DC/DC converter according to the present invention
selectively employs both hard switching and ZVS to selectively
reduce conduction and switching losses. FIG. 1 is a simplified
schematic of a DC/DC converter 10 that operates with significantly
reduced switching and conduction losses. The converter 10 includes
a primary side bridge 14 with a first leg 18 and a second leg 22
that are connected between a first bus line 26 and a second bus
line 30. The first leg 18 includes a first switching circuit 34
connected in series with a second switching circuit 38. The second
leg 22 includes a third switching circuit 42 connected in series
with a fourth switching circuit 46.
[0017] The first switching circuit 34 includes a first switching
device Q1 connected in parallel with a first diode D1. The second
switching circuit 38 includes a second switching device Q2
connected in parallel with a second diode D2. The third switching
circuit 42 includes a third switching device Q3 connected in
parallel with a third diode D3 and a first capacitor C3. The fourth
switching circuit 46 includes a fourth switching device Q4
connected in parallel with a fourth diode D4 and a second capacitor
C4.
[0018] The switching devices Q1, Q2, Q3 and Q4 can be any switching
device suitable for high frequency, high power electrical
switching. For example, the switching devices Q1, Q2, Q3 and Q4 can
be a metal oxide semiconductor field effect transistor (MOSFET), an
insulated gate bipolar transistor (IGBT), a bipolar junction
transistor (BJT), or other suitable transistors. For convenience,
switching devices Q1, Q2, Q3 and Q4 will be referred to herein
merely as switches.
[0019] The converter 10 further includes a transformer 50 having a
primary coil 54, a secondary coil 58, and a leakage inductor
L.sub.lkg. The opposite end of the primary coil 54 is connected to
the second leg 22 between the third switching circuit 42 and the
fourth switching circuit 46. The primary side bridge 14 also
includes a first filter capacitor Cin connected between the first
and second bus lines 26 and 30. The primary side bridge is
connected to a DC power source, such as a battery, that provides a
DC input voltage Vin.
[0020] The converter 10 further includes a secondary side bridge
rectifier 62 that includes a third leg 66 and a fourth leg 70
connected between a third bus line 74 and a fourth bus line 78. The
third leg 66 includes the secondary coil 58 of the transformer 50
connected in series with a fifth switching circuit 82 which
includes a fifth switching device S1 connected in parallel with a
fifth diode D5. The fourth leg 70 includes a sixth switching
circuit 86 that includes a sixth switching device S2 connected in
parallel with a sixth diode D6. The rectifier 62 further includes a
second filter capacitor Co connected between the third and fourth
bus lines 74 and 78. The third bus line 74 includes a first
inductor L1 connected between the fourth leg 70 and the second
filter capacitor Co. A second inductor L2 is connected in parallel
with the first inductor L1 and the secondary coil 58 of the
transformer 50.
[0021] A controller 90 is connected to the switches Q1, Q2, Q3, Q4,
S1 and S2 and controls the operation of the switches Q1, Q2, Q3,
Q4, S1 and S2. The controller 90 can be any control device suitable
for controlling the operation of the switches Q1, Q2, Q3, Q4, S1
and S2. For example a microprocessor, a programmable logic
controller (PLC) an Application Specific Integrated Circuit (ASIC),
a circuit, or any other device may be used. The controller 90
utilizes pulse width modulation (PWM) to sequentially transition
the switches Q1, Q2, Q3, Q4, S1 and S2 between an On position and
an Off position.
[0022] More specifically, the controller 90 implements a desired
duty cycle to control the transitioning of the switches Q1-Q4 to
chop a current signal created by Vin. The chopped current flows
through the primary coil 54 in accordance with the duty cycle,
thereby creating an electro-magnetic field in the transformer 50.
The electro-magnetic field generates current through the secondary
coil 58. The current is rectified by an appropriate switching
sequence of the switches S1 and S2. The switching sequence is
controlled by the controller 90.
[0023] The rectified current provides the voltage Vo, having a
desired voltage level, to a load (not shown) connected across the
third and fourth bus lines 74 and 78. The duty cycle implemented by
the controller 90 transitions the switches Q1-Q4 between the On and
Off positions in a sequence that operates the converter 10 with
significantly reduced switching and conduction losses with respect
to the switching and conduction losses of known DC/DC
converters.
[0024] FIG. 2 is a state diagram 100 illustrating the control
signals used by the controller 90 to control the switches Q1, Q2,
Q3 and Q4 during one duty cycle Ts. The state diagram 100 also
illustrates current patterns of a current i.sub.L1 flowing through
the first inductor L1, a current i.sub.d1 flowing through the
switch S2, and a current i.sub.Ts flowing through the secondary
coil 58 of the transformer 50 during the duty cycle Ts.
[0025] During a first half cycle, the switching sequence proceeds
as follows: Switch Q.sub.4 turns off at t.sub.1 (soft switching).
Capacitor C.sub.4 is charged to V.sub.in and capacitor C.sub.3
discharges to 0. Switch Q.sub.3 can turn on with zero voltage
switching. Switch Q.sub.1 is turned off immediately, which is a
hard switching of switch Q.sub.1. While there is some switching
loss, there is a substantial savings overall due to reduced
conduction loss.
[0026] The next half cycle proceeds as follows: At t.sub.3, switch
Q.sub.2 is turned on, which is a hard turn on. Switch Q.sub.3 is
still on from the previous half cycle. Switch Q.sub.3 can be turned
off with zero voltage soft switching. Capacitor C.sub.3 charges and
capacitor C.sub.4 discharges. When capacitor C.sub.4 reaches 0
volts, switch Q.sub.4 is turned on with zero voltage switching.
Switch Q.sub.2 is then turned off, which is a hard switching
transition.
[0027] Those skilled in the art can now appreciate from the
foregoing description that the broad teachings of the present
invention can be implemented in a variety of forms. Therefore,
while this invention has been described in connection with
particular examples thereof, the true scope of the invention should
not be so limited since other modifications will become apparent to
the skilled practitioner upon a study of the drawings, the
specification and the following claims.
* * * * *