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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 51, NO. 1, FEBRUARY 2004 81
A Simple Energy Recovery Circuit for High-Power
Inverters With Complete Turn-On and
Turn-Off Snubbers
Xiangning He, Senior Member, IEEE, Yan Deng, Barry W. Williams, Stephen J. Finney, and
Zhaoming Qian, Senior Member, IEEE
Abstract—This paper presents and analyzes an active energy
recovery circuit for the inductive turn-on snubber and capacitive
turn-off snubber used on high-power gate-turn-off thyristor in-
verters. The circuit performs as a simple switched-mode power
supply and recovers the inductive and capacitive snubbers energy
induced in power inverters back into the dc rail with the aid of an
extra switch. The features and operation of the proposed circuit
are given and supported by PSpice simulations and experimental
results.
Index Terms—Energy recovery, gate-turn-off (GTO) thyristor,
inverter, snubber.
I. INTRODUCTION
P
OWER insulated gate bipolar transistor (IGBT) and gate-
turn-off (GTO) thyristor inverters are widely used in var-
ious industrial equipments such as power supplies and motor
drives. High-power GTO thyristor inverters mandatorily incor-
porate both an inductive turn-on snubber and capacitive turn-off
snubbers. The capacitive turn-off snubber, with
typically
1–4
F, is necessary for safe GTO turn-off. An inductive turn-on
snubber, with
typically 5 to 20 H, not only controls GTO
, hence, turn-on loss, but also controls freewheel diode
reverse recovery. The energy stored in the turn-on snubber in-
ductor is related to the load current magnitude,
, according to
, while the energy stored in the turn-off snubber capac-
itor is related to the supply voltage,
, according to .
The capacitance is usually specified by the GTO thyristor
manufacturer, while the turn-on inductor limits the turn-on di/dt
to about 200–400 A
s, according to . Tradi-
tionally, the stored energies are dissipated as heat in resistors
[1], [2]. In the case of a three-phase inverter the total energy
loss for three legs, including diode recovery current
losses, is
given by
J (1)
The total power loss will be significant because it is propor-
tional to the switching frequency. With high voltages at just a
modest frequency this power loss also becomes unacceptable
Manuscript received September 4, 2001; revised June 11, 2003. Abstract pub-
lished on the Internet November 26, 2003. This work was supported by the Na-
tional Nature Science Foundation of China and the Royal Society of the U.K.
X. He, Y. Deng, and Z. Qian are with the College of Electrical Engineering,
Zhejiang University, Hangzhou 310027, China (e-mail: hxn@cee.zju.edu.cn).
B. W. Williams and S. J. Finney are with the Department of Computing and
Electrical Engineering, Heriot-Watt University, Edinburgh EH14 4AS, U.K.
Digital Object Identifier 10.1109/TIE.2003.822089
because of the loss dependence on
. Numerous snubber con-
figurations have been proposed which attempt to reduce the
losses. Those that dissipate the energy are best represented by
the Undeland snubber [2], [3], were a judicious circuit arrange-
ment minimizes the energy to be dissipated. However, energy
recovery circuits for turn-on and turn-off snubbers of high power
GTO inverters are important in further decreasing losses of in-
dustrial equipments.
Effective passive recovery snubbers for GTO thyristor in-
verters are few in number. Some published possibilities exist
and they all use a high-frequency transformer to transfer recov-
ered energy into the dc voltage rail [4]–[7]. Recovery into the
load seems an unlikely viable possibility since operations would
become undesirably load current magnitude dependant. This is
because the snubber capacitor energy is fixed by the dc supply
and independent of the load current. The major problem for the
passive snubber energy recovery in a inverter is the configura-
tion complexity and more power components would be required
if the improvements for high frequency transformer saturation
or for high secondary diode reverse voltage are made [8], which
limit applications of the circuits.
This paper presents a simple circuit for recovering the
inductive and capacitive snubber energies, which only re-
quire the addition of an extra switch which forms part of a
simple switched-mode power supply (SMPS). The features
and detailed operational processes of the proposed circuit are
given and the PSpice simulations and experimental results are
included.
II. E
NERGY RECOVERY SNUBBER
CIRCUIT
The complete energy recovery turn-on and turn-off snubber
for a full-bridge GTO thyristor inverter to be considered, is
shown in Fig. 1, which is based on the Undeland snubber. In the
Undeland circuit the snubber energy is dissipated in the resis-
tive element
, which may be inductive and located remotely
although it is possible that only one turn-on inductor be used for
three bridge legs. Until now no full passive recovery solutions
for the Undeland snubber have been proposed, most probably
due to the fact that the temporary stored energy voltage is out-
side the supply voltage rail limits. Fig. 2 is a bridge leg configu-
ration with a simplified circuit for the proposed snubber, which
will be used in analysis. One switch, two diodes, and one in-
ductor form a SMPS in Fig. 2 and snubber energy is transferred
into the dc rail. The capacitor
acts as an intermediate store
0278-0046/04$20.00 © 2004 IEEE
82 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 51, NO. 1, FEBRUARY 2004
Fig. 1. Full bridge with the proposed energy recovery circuit for turn-on and turn-off snubbers.
Fig. 2. Bridge leg snubber with the simplified energy recovery circuit.
for snubber energy. In the case of the active recovery circuit,
the magnitude of the capacitance determines which of two pos-
sible modes, recovery occurs in. For small
the capacitor is
discharged to the rail voltage on a cycle by cycle basis, while
for
large the SMPS is operated so as to maintain a con-
stant voltage greater than
on [9]. The constant capacitor
voltage mode affords faster snubber reset for a given maximum
switch voltage, but at the expense of high semiconductor volt-
ages, hence, losses, at all load current levels. The circuit also
requires that
be precharged and that the voltage be mon-
itored and maintained to be near constant at all load current
levels. The one SMPS step-up inverting chopper can be used for
three inverter bridge legs and the switch for this chopper too can
have its own snubber energy recovery circuit [9]. The voltage re-
quirement of
can be reduced by reconnection to the dc rail.
However, in order to fulfil the primary snubber function, with
low loop inductance,
could be split between the 0 V and dc
supply rails.
By adding the diode
, smaller capacitance can be
used, without the need of monitoring or feedback control for
the SMPS switch. The operational processes at turn-on and
turn-off for the top and bottom devices in the bridge leg can be
analyzed in detail by using the method as in [4] and the main
equations are given below.
A. GTO G1 Turns On (see Fig. 3)
The current in
with an initial value of zero increases lin-
early until
, then discharges from an initial value
of
and charges. The current path is shown in Fig. 3(a).
The energy on
transfers to , causing an overshoot voltage,
,on and G2, which if , is given by
(2)
The time for energy to transfer from
to is
(3)
Then, the SMPS switch for energy recovery turns on, shown in
Fig. 3(b),
resonates with with a peak switch current, ,
given by
(4)
The switch is turned on for a time of at least
which is given
by
(5)
The diode
prevents from resonating to a voltage below
the dc rail. The current
given by (4) freewheels through
HE et al.: ENERGY RECOVERY CIRCUIT FOR HIGH-POWER INVERTERS WITH COMPLETE TURN-ON AND TURN-OFF SNUBBERS 83
(a) (b)
(c) (d)
Fig. 3. Current paths at G1 turn-on process.
, and the switch as maintains the energy ,
shown in Fig. 3(c). When the switch is turned off this energy is
released into the dc rail via diode
. The current falls from that
given by (4) to zero, linearly in a time
, given by
(6)
which is independent of the load current. The current path is
given in Fig. 3(d).
When the inductor
current falls to zero, controlled
reverse-recovery current flows through diode
. The subse-
quent voltage snap is clamp by
to via diode , which
facilitates recovery onto
of diode reverse-recovery energy
.
B. GTO G1 Turns Off (see Fig. 4)
The initial values of the current in
and voltage on at G1
turn-off are
and zero, respectively. Turn-off no longer occurs
at a fixed voltage and bridge switch losses are lower at all load
current levels and equal at maximum load current, for a given
maximum overshoot voltage
on at turn-off. The switch
is turned on a fixed time after a leg switch is commutated, and
remains on for a fixed on-period. That is, the SMPS is turned on
at time
after a GTO thyristor is commutated
(7)
for a time longer than
which is different from that in (5) and
given by
(8)
Note that both
and are load current magnitude indepen-
dent. During time
all the inductor snubber energy is trans-
ferred to
and , charging them to a voltage
(9)
that is, the overshoot
is
(10)
Fig. 4 shows the current path at G1 turn-off.
During the time
, resonates with with a peak switch
current,
given by
(11)
The diode
prevents from resonating to a voltage below
the dc rail. The current
given by (11) freewheels through
, and the switch as maintains the energy .
When the switch is turned off this energy is released into the dc
rail via diode
. The SMPS switch must be able to commutate
the current
, which is usually less than the maximum load
84 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 51, NO. 1, FEBRUARY 2004
(a) (b)
(c) (d)
Fig. 4. Current paths at G1 turn-off process.
current, . The current falls from that given by (11) to zero,
linearly in a time
, given by
(12)
Although the reset time
, unlike , is load current mag-
nitude dependent, if necessary the SMPS switch can be turned
on before this current reaches zero.
When the inductor
current falls to zero, controlled
reverse-recovery current flows through diode
. The subse-
quent voltage snap is clamp by
to via diode , which
facilitates recovery onto
of diode reverse-recovery energy
, which is the same as when G1 turns on.
The relationship between the control pulses for the SMPS
switch and GTO G1 (V(IGBT) and V(GTO), respectively) and
the voltage on
and current in ( and , respec-
tively) is shown in Fig. 5. Similar results can be obtained from
analysis of the operational processes of the bottom GTO, G2, at
turn-on and turn-off.
III. D
ISCUSSION
In order to allow energy transfer to , when G1 turns on (or
off), turn-on of the SMPS switch is delayed for a period
, such
that
(13)
In fact, considering the time
at turn-on and
at turn-off which are the times for snubber
inductor current from 0 to
and snubber capacitor voltage
from 0 to
, respectively, would be slightly larger than that
based on (13). The on period for the SMPS switch is fixed as
where
(14)
The maximum energy recovery time
for , peak current
in and GTO maximum over shoot voltage, respectively,
can be expressed by
(15)
Let
(16)
In practice,
and can be assumed. If
, and are the bases for time, current and voltage,
so the normalized maximum times, peak current and overshoot
HE et al.: ENERGY RECOVERY CIRCUIT FOR HIGH-POWER INVERTERS WITH COMPLETE TURN-ON AND TURN-OFF SNUBBERS 85
Fig. 5. Control pulses for main and auxiliary switches (GTO and IGBT), and voltage on , and current in .
Fig. 6. Relationship between normalized
, , , and
capacitor ratio
.
voltage for , , , and of the circuit are represented
by
, , , and , and simply given in (17)
(17)
Figs. 6 and 7 show the normalized time, peak current, and
overshoot voltage functions against the inductor ratio and ca-
pacitor ratio, which could be the reference for the proposed cir-
cuit design. Similar curves can be drawn if
be
assumed.
In the simple case shown in this paper, the SMPS switch turns
on with
as the snubber inductor and turns off with as the
soft-clamped capacitor. The turn-off loss for this active switch,
although exists, is very small because of the low switch current
decreased by value, according to (17). It is usually ab-
sorbed by the switch and could be recovered by additional cir-
Fig. 7. Relationship between normalized , , , and inductor
ratio
.
cuits if necessary [9]. However, more components are needed
and the circuit would be complicated.
IV. S
IMULATIONS AND EXPERIMENTATIONS
Fig. 8 shows PSpice simulation results for the proposed
energy recovery circuit at G1 turn-on {Fig. 8(a)] and turn-off
[Fig. 8(b)], where for illustrative purposes IGBTs instead
of GTOs are used as main power switching devices to
confirm that the proposed circuit functions correctly. With
V rail voltage and A load current , the
main circuit parameters are
H F F H
from which
, , , , and can be derived. Fig. 9
shows simulation results at G2 turn-on [Fig. 9(a)] and turn-off
[Fig. 9(b)], and both Figs. 8 and 9 are identical, which confirms
the above analysis is correct. The recovered energies in one
phase leg at the loads of 10 and 22 A are given in Table I, and
it shows that the presented snubber recovery circuit is effective
at different load conditions.
Fig. 10 shows the experimental waveforms for the circuit.
Both G2 turn-on [Fig. 10(a)] and turn-off [Fig. 10(b)] wave-
86 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 51, NO. 1, FEBRUARY 2004
(a) (b)
Fig. 8. Simulation waveforms for the proposed circuit at G1 (a) turn-on and (b) turn-off. V(3,2):
; V(5): ; I(Lt): .
(a) (b)
Fig. 9. Simulation waveforms for the proposed circuit at G2 (a) turn-on and (b) turn-off. V(2):
; V(5): ; I(Lt): .
TABLE I
S
IMULATIONS FOR SNUBBER ENERGY RECOVERY AT DIFFERENT CONDITIONS
forms are shown and correspond with simulations. The com-
parison between simulated and experimental recovery energies
is given in Table II, which confirms the theoretical and analysis
results very well.
V. C
ONCLUSION
A new active snubber energy recovery circuit for high-power
inverters has been presented. The circuit uses one additional
switch to form part of a SMPS and to recover the inductive and
capacitive snubber energy into the dc rail. The proposed circuit
configuration is simple and suitable for use in GTO thyristor
full-bridge inverters, even in three-phase inverters, where the
HE et al.: ENERGY RECOVERY CIRCUIT FOR HIGH-POWER INVERTERS WITH COMPLETE TURN-ON AND TURN-OFF SNUBBERS 87
(a) (b)
Fig. 10. Experimental results for the proposed circuit at G2 (a) turn-on and (b) turn-off. Top to bottom:
140 V/div; 140 V/div; 2 A/div.
TABLE II
C
OMPARISON BETWEEN SIMULATIONS AND
EXPERIMENTS
complete turn-on and turn-off snubbers are essential. The anal-
ysis and operational processes of the circuit given in the paper
show that it works effectively and has been confirmed by simu-
lations and experimental results.
R
EFERENCES
[1] P. H. Swanepoel and J. D. van Wyk, “Analysis and optimization of re-
generative linear snubbers applied to switches with voltage and current
tails,” IEEE Trans. Power Electron., vol. 9, pp. 433–442, July 1994.
[2] T. Undeland, F. Jenset, A. Steinbakk, T. Rogne, and M. Hernes,
“A snubber configuration for both power transistor and GTO PWM
inverters,” in Proc. IEEE PESC’84, June 1984, pp. 42–53.
[3] F. Blaabjerg, “Snubbers in PWM-VSI inverter,” in Proc. IEEE PESC’91,
June 1991, pp. 104–110.
[4] X. He, B. W. Williams, S. J. Finney, Z. Qian, and T. C. Green, “Anew
snubber circuit with passive energy recovery for power inverters,” Proc.
IEE—Elect. Power Applicat., vol. 143, no. 5, pp. 403–408, 1996.
[5] W. McMurray, “Efficient snubbers for voltage-source GTO inverters,”
IEEE Trans. Power Electron., vol. 2, pp. 264–272, May 1987.
[6] J. Holtz, S. Salama, and K. H. Werner, “A nondissipative snubber circuit
for high-power GTO inverters,” IEEE Trans. Ind. Applicat., vol. 25, pp.
620–626, July/Aug. 1989.
[7] M. Jung, “Improved snubber for GTO inverters with energy recovery by
simple passive network,” in Proc. EPE’87, 1987, pp. 15–20.
[8] X. He, S. J. Finney, B. W. Williams, and Z. Qian, “Bridge leg snubbers
for GTO thyristor inverters,” in Conf. Rec. IEEE-IAS Annu. Meeting,
vol. 2, 1995, pp. 1038–1045.
[9] J. A. Taufiq and Y. Shakweh, “New snubber energy recovery scheme for
high power traction drive,” in Proc. IEEJ Int. Power Electronics Conf.,
Japan, Apr. 1995, pp. 825–830.
Xiangning He (M’95–SM’96) received the B.Sc.
and M.Sc. degrees from Nanjing University of
Aeronautics and Astronautics, Nanjing, China, in
1982 and 1985, respectively, and the Ph.D. degree
from Zhejiang University, Hangzhou, China, in
1989.
From 1985 to 1986, he was an Assistant Engineer
at the 608 Institute of the Aeronautical Industrial
General Company of China. From 1989 to 1991,
he was a Lecturer at Zhejiang University. In 1991,
he obtained a Fellowship from the Royal Society of
the U.K., London, and conducted research in the Department of Computing
and Electrical Engineering, Heriot-Watt University, Edinburgh, U.K., as a
Post-Doctoral Research Fellow for two years. In 1994, he joined Zhejiang
University as an Associate Professor. Since 1996, he has been a Full Professor
in the Department of Electrical Engineering (now the College of Electrical
Engineering) at Zhejiang University. He is also presently the Head of the
Department of Applied Electronics and the Director of the Power Electronics
Research Institute at Zhejiang University. His research interests are power
electronics and their industrial applications. He is the holder of eight Chinese
patents.
Dr. He received the 1989 Excellent Ph.D. Graduate Award, the 1995 Elite
Prize Excellence Award, the 1996 Outstanding Young Staff Award, and the 1998
First Prize Excellent Teaching Award from Zhejiang University for his teaching
and research contributions. He received two 1998 and one 2002 Scientific and
Technological Progress Awards from the Zhejiang Provincial Government and
the State Education Ministry of China, respectively, and four Excellent Paper
Awards. He is a Fellow of the Institution of Electrical Engineers, U.K.
Yan Deng was born in Sichuan, China, in 1973.
He received the B.E.E. degree from the Department
of Electrical Engineering, Zhejiang University,
Hangzhou, China, in 1994, and the Ph.D. degree in
power electronics and electric drives from the Col-
lege of Electrical Engineering, Zhejiang University,
in 2000.
Since 2000, he has been a faculty member at Zhe-
jiang University, teaching and conducting research on
power electronics. He is currently an Associate Pro-
fessor. He has authored more than 20 papers pub-
lished in international and national conferences/transactions. His research in-
terests are topologies and control for switch-mode power conversion.
88 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 51, NO. 1, FEBRUARY 2004
Barry W. Williams received the M.Eng.Sc. degree from the University of Ade-
laide, Adelaide, Australia, in 1978, and the Ph.D. degree from Cambridge Uni-
versity, Cambridge, U.K., in 1980.
After seven years as a Lecturer at Imperial College, University of London,
U.K., he was appointed to a chair of electrical engineering at Heriot-Watt Uni-
versity, Edinburgh, U.K., in 1986. His teaching covers power electronics (in
which he has a text published) and drive systems. His research activity includes
power semiconductor modeling and protection, converter topologies and soft-
switching techniques, and application of ASICs and microprocessors to indus-
trial electronics.
Stephen J. Finney received the M.Eng. degree from Loughborough Univer-
sity of Technology, Loughborough, U.K., in 1988, and the Ph.D. degree from
Heriot-Watt University, Edinburgh, U.K., in 1995.
For two years, he was with the Electricity Council Research Centre laborato-
ries near Chester, U.K. He is currently a Lecturer at Heriot-Watt University. His
areas of interest are soft-switching techniques, power semiconductor protection,
energy recovery snubber circuits, and low-distortion rectifier topologies.
Zhaoming Qian (SM’92) graduated in radio
engineering from the Department of Electrical
Engineering, Zhejiang University, Hangzhou, China,
in 1961, and received the Ph.D. degree in applied
science from the Catholic University of Leuven and
the Interuniversity Microelectronics Center (IMEC),
Leuven, Belgium, in 1989.
Since 1961, he has been teaching and conducting
research on electronics and power electronics at Zhe-
jiang University, where he became a Professor in the
Department of Electrical Engineering in 1992. He is
currently the Deputy Director of the National Engineering Research Center for
Applied Power Electronics and the Deputy Director of the Scientific Committee
of the National Key Laboratory of Power Electronics at Zhejiang University.
His main professional interests include power electronics and industrial appli-
cations, EMC in power electronic systems, and system integration in power elec-
tronics. He has authored one book on EMC design and more than 250 papers.
Dr.Qian received Excellent Education Awards from the China Education
Commission and from Zhejiang University in 1993, 1997, and 1999, Science
and Technology Progress Awards from the China Education Commission in
1999 and 2003, and Excellent Paper Awards. He has served as a Vice-Chairman
of the IEEE PELS Beijing Chapter since 1995.
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