Chinese Journal of Electronics
Vol.21, No.4, Oct. 2012
A Novel Soft Switching Converter with Active
Auxiliary Resonant Commutation∗
CHU Enhui, HOU Xutong and ZHANG Huaguang
(College of Information Science and Engineering, Northeastern University, Shenyang 110819, China)
Abstract — In order to realize a simple topology, high
efficiency, high frequency, low voltage stress, easily controlled soft switching converter, a novel soft switching converter with active auxiliary resonant commutation is presented in this paper. Soft switching of main power switch
and auxiliary power switch can be achieved by using active auxiliary resonant network. It is very attractive for
high power application where IGBT (Insulated gate bipolar transistor) is predominantly used as the power switch.
Its operation principle is analyzed through its application
to the boost converter. The novel soft switching cell can be
also used in other basic DC-DC converter. A 3kW, 16kHz
prototype which uses IGBT was made. The effectiveness
of the proposed converter is confirmed by the experimental
results.
ever it need extra three auxiliary power switches and a transformer, so the topology is quite complex and hard to control,
and disadvantage to improve conversion efficiency and realize
miniaturization.
This paper puts forward a novel active soft switching converter which uses a sample active auxiliary resonant network
to achieve soft switching of the main power switch and the auxiliary power switch with low voltage and current stress. This
novel converter has a sample topology and control strategy,
because the novel resonant network only adds one auxiliary
active switch. This paper has made a detailed analysis of the
novel soft switching topology and its feasibility is verified by
experiment.
Key words — Active auxiliary resonant commutation,
Active DC-DC converter, Soft-switching.
II. Circuit Description and Operation
Principle
I. Introduction
The hard-switching PWM (Pulse-width moderation) converter is widely used in lots of fields such as communication
and network servers due to its simple topology, easy to control, constant switching frequency and good output regulating
characteristics. In high voltage or high power situations, power
devices suffer from a large voltage or current stress with large
switching losses, and the EMI (Electro-magnetic interference)
caused by voltage peaks and surge current may influence the
normal operation of the converter. In order to solve these problems effectively, many soft-switching technologies[1−8] have
been presented in recent years, such as resonant switching
technology, zero switching technology, zero transfer technology, auxiliary resonant network technology and so on. Among
these technologies, zero transfer technology adopts active auxiliary resonant network[9−14] , can control resonant process of
resonant component through auxiliary power switch, so that
it can keep the advantage of PWM chopper-fed circuits while
realizing soft switching, reduces switching loss, and it has become the focus of power electronics. At present, many novel
chopper-fed circuit topologies have been proposed, but there
still exists some shortages, such as complex topology, high voltage and current stress of active power switch, irrealizable softswitching of auxiliary power switch, large circulating current
and so on. Above problem can be solved in Ref.[15], how∗ Manuscript
1. Circuit description
Fig.1 shows the presented novel active auxiliary resonant
converter topology in which S1 , D1 , Lm and Co represent the
main power switch, the output rectifier diode, the input filter
inductor and the output filter capacitor, respectively, DS1 is
the anti-parallel diode of the main power switch S1 . The active
auxiliary resonant network is composed of a resonant inductor
Lr , a resonant capacitor Cr , a lossless snubber capacitor CS ,
an auxiliary power switch S2 , and an auxiliary diode D2 .
Fig. 1. Novel active auxiliary resonant converter
2. Circuit operation
The mode transition and the working waveforms of novel
active auxiliary soft switching converter are depicted in Fig.2
and Fig.3, respectively. The gate voltage pulse sequences of
the main power switch S1 and the auxiliary power switch S2
are shown in Fig.3, too.
Received Apr. 2010; Accepted June 2012. This work is supported by the Fundamental Research Funds for the Central
Universities (No.N100404015).
Chinese Journal of Electronics
752
In order to simplify the analysis, we assume that: (1) All devices of the circuit
are in ideal condition, the input filter inductance Lm is large enough to be instead
of constant current source ILm . (2) The
output filter capacitor Co is large enough
to be instead of constant voltage source Vo .
The operating principle in mode transitions of this converter treated here is explained as follows:
• Mode 0 [0, t0 ]: Before time t0 , the
stored energy of the inductor Lm is transferred to the load side. When the auxiliary power switch S2 is turned on, Mode 0
changes to Mode 1.
• Mode 1 [t0 , t1 ]: At the instant t0 , then
the switch S2 is turned on under a principle
of ZCS with the aid of the resonant inductor Lr , the current through the diode D1 ,
begins to flow to the active auxiliary resonant network. The current flowing through
the resonant inductor Lr , and the resonant
capacitor Cr , and the switch S2 increases
sinusoidally. The current iLr across Lr , the
Fig. 2. Mode transitions and equivalent circuits. (a) Mode 0; (b) Mode 1; (c) Mode
2; (d) Mode 3; (e) Mode 4; (f ) Mode 5; (g) Mode 6; (h) Mode 7
current iD1 across D1 and the voltage vCr across Cr is
where Z1 =
Vo
sin ω1 (t − t0 )
Z1
Vo
= ILm −
sin ω1 (t − t0 )
Z1
= [1 − cos ω1 (t − t0 )]Vo
vCr (t1 ) = 1 −
iLr =
(1)
iD1
(2)
vCr
2012
(3)
√
Lr /Cr , ω1 = 1/ Lr Cr .
1−
Z1
IL
Vo m
2 Vo
The on-period t01 in Mode 1 is
1
Z1
sin−1
ILm
t01 =
ω1
Vo
(5)
(6)
• Mode 2 [t1 , t2 ]: At the instant t1 , when the diode D1 is
ZCS turned off, the current flowing through D1 commutates
through the active auxiliary resonant network. The lossless
snubber capacitor Cs , connected in parallel with the main
power switch S1 is produced the edge-resonant mode with
a resonant inductor Lr and resonant capacitor Cr . Therefore, the lossless snubber capacitor Cs becomes the discharging
mode, and the voltages across Cs drops gradually. The current
iLr across Lr , the voltage vCr across Cr and the voltage vCs
across Cs is
iLr =
V1
sin ω2 (t − t1 ) + I1 cos ω2 (t − t1 ) − I1 + iLr (t1 )
Z2
C
[V1 − V1 cos ω2 (t − t1 ) + I1 Z2 sin ω2 (t − t1 )]
Cr
ILm
+
(t − t1 ) + vCr (t1 )
Cr + Cs
C
= [V1 cos ω2 (t − t1 ) − I1 Z2 sin ω2 (t − t1 ) − V1 ]
Cs
ILm
(t − t1 ) + Vo
+
Cr + Cs
(7)
vCr =
vCs
Fig. 3. Key waveforms of converter
The current iLr and the voltage vCr at instant t1 can be
given by
iLr (t1 ) = iCr (t1 ) = ILm
(4)
(8)
(9)
C
Cr Cs
where I1 = iLr (t1 )−
IL , V1 = Vo −vCr (t1 ), C =
,
Cs m Cr + Cs
Lr (Cr + Cs )
Cr + Cs
, ω2 =
.
Z2 =
Cr Cs
Lr Cr Cs
A Novel Soft Switching Converter with Active Auxiliary Resonant Commutation
The current iLr and the voltage vCr at instant t2 can be
given by
Lr i2Lrpeak − Cr V22
(10)
iLr (t2 ) =
Lr
V12 + (I1 Z2 )2
C
iLrpeak =
+
IL
(11)
Z2
Cs m
ILm
Cs
(t2 − t1 ) +
Vo + vCr (t1 ).
Cr
Cr
• Mode 3 [t2 , t3 ]: When the voltage across the snubber
capacitor Cs becomes zero, the anti-parallel diode Ds1 of the
main power switch S1 is naturally turned on. As a result, the
main power switch S1 can achieve ZVS (Zero-voltage switching) and ZCS (Zero-current switching) hybrid soft commutation in a turn-on transition state when the current flow through
the anti-parallel diode Ds1 decreases and naturally shifts to
the main power switch S1 by giving the gate voltage signal of
the main power switch S1 while Ds1 is turned on.
The current iLr across Lr and the voltage vCr across Cr
is
where V2 = vCr (t2 ) =
V2
sin ω1 (t − t2 )
Z1
= I2 Z1 sin ω1 (t − t2 ) + V2 cos ω1 (t − t2 )
iLr = I2 cos ω1 (t − t2 ) −
(12)
vCr
(13)
where I2 = iLr (t2 ), V2 = vCr (t2 ).
The voltage vCr at instant t3 can be given by
Z12 I22 + V22
The on-period t23 in Mode 3 is
Z1 I2
1
tan−1
t23 =
ω1
V2
Cr (t3 )
=
Z12 I22 + V22
(15)
The on-period t34 in Mode 4 is
t34 =
π
ω1
(16)
• Mode 5 [t4 , t5 ]: When the auxiliary power switch S2 is
turned off, the resonant current flowing through the inductor
Lr and the capacitor Cr becomes zero, all the circuit operations are identical to the conduction state of the conventional
Boost converter.
The voltage vCr at instant t5 can be given by
vCr (t5 ) = vCr (t4 ) = −
Z12 I22 + V22
• Mode 6 [t5 , t6 ]: When the main power switch S1 is turned
off with ZVS, the current flowing through the boost inductor
Lm flows to the snubber capacitor Cs . Therefore, the lossless
snubber capacitor Cs becomes charging mode and the voltages across the lossless capacitor Cs increases gradually. the
voltage vCs across Cs is
vCs =
ILm
(t − t5 )
Cs
(18)
The voltage vCr at instant t6 can be given by
vCr (t6 ) = vCr (t5 ) = −
Z12 I22 + V22
(19)
The on-period t56 in Mode 6 is
t56 =
Cs
(Vo + vCr (t5 ))
ILm
(20)
• Mode 7 [t6 , t7 ]: When the voltage across the lossless
snubber capacitor Cs becomes larger than the sum of the voltage across the resonant capacitor Cr and the output voltage
V0 , the auxiliary diode D2 is naturally turned on. When the
voltage across the lossless snubber capacitor Cs is equal to the
output average voltage Vo and the voltage across the auxiliary
resonant capacitor Cr becomes zero, the diode D2 is naturally
turned off. At the same time, the diode D1 is turned on and
Mode 7 shifts to Mode 0. The voltage vCr across Cr and the
voltage vCs across Cs is
ILm
(t − t6 ) + vCr (t6 )
Cr + Cs
ILm
=
(t − t6 ) + Vo + VCr (t6 )
Cr + Cs
vCr =
(21)
vCs
(22)
The on-period t34 in Mode 7 is
(14)
• Mode 4 [t3 , t4 ]: When the current of the main power
switch S1 becomes bigger than the current flowing through a
boost inductor Lm , the diode Ds2 in anti-parallel with the auxiliary power switch S2 is naturally turned on, and the current
flowing through S2 begins to commutate to the anti-parallel
diode Ds2 . By cutting the gate voltage pulse signal delivered
to the auxiliary power switch S2 , during this period, an auxiliary power switch S2 can achieve complete ZVS and ZCS hybrid soft commutation in a turn-off transition when the current
flowing through the auxiliary power switch S2 shifts exactly.
The voltage vCr at instant t4 can be given by
vCr (t4 ) = −vCr (t4 ) = −
753
(17)
t67 = −
vCr (t6 )
(Cr + Cs )
ILm
(23)
This active auxiliary resonant converter repeats cyclically
the steady-state operation described above.
III. Experimental Results and
Performance Evaluations
1. Design specifications and operating waveforms
Based on the circuit topology and analyses above, a 3kW,
16kHz prototype based on IGBT has been built. Input voltage VS = 200V, output voltage Vo = 380V, output power
range Po = 1kW-3kW, main power switch S1 and auxiliary
power switch S2 adopts Mistubishi CM75DU-24H; the output rectifier diode D1 adopts high efficiency and high speed
Toshiba 30JL2C41; D2 adopts high dielectric strength and
high speed soft recovery Hitachi DFM30F12. Input filter inductor Lm = 1.024mH, resonance inductor Lr = 7.6μH, resonant capacitor Cr = 121 nF, resonance snubber capacitor
CS = 33 nF, smoothing output capacitor Co = 8200μF.
Fig.4 illustrates the voltage and current switching waveforms and its v − i trajectory of the main power switch S1 . It
can be seen that there is no voltage and current peak in the
main switch S1 and low dv/dt and di/dt reduce voltage and
current stress of the switch. In addition, from v − i traces of
S1 , ZVS and ZCS turn-on and ZVS turn-off in S1 is achieved.
Fig.5 illustrates the voltage and current switching waveforms
and its v − i trajectory of the auxiliary power switch S2 . It
754
Chinese Journal of Electronics
2012
can be seen that ZVS and ZCS turn-off and ZCS turn on in
S2 is achieved. These experimental results verify the previous
theoretical analysis.
Fig. 7. Voltage and current waveforms and v − i trajectory of
auxiliary switch S2 with clamping diode. (a) Waveforms; (b) v − i trajectory
Fig. 4. Voltage and current waveforms and v − i trajectory of
main switch S1 . (a) Turn-on waveforms; (b) Turn-on
v − i trajectory; (c) Turn-off waveforms; (d) Turn-off
v − i trajectory
ping diode, without clamping diode and hard switching (with
RC snubber circuit) are shown in Fig.8, respectively. It can
be seen that the actual efficiency of the proposed novel softswitching converter, especially the converter with clamping
diode Dc , is higher than that of hard switching for the required output power range. Especially, for 3kW breadboard
setup, the actual power conversion efficiency of soft-switching
PWM scheme can achieve 97.8%. And moreover, for high
frequency switching, this power circuit can, achieve higher efficiency characteristics.
Fig. 5. Voltage and current waveforms and v − i trajectory of
auxiliary switch S2 . (a) Waveforms; (b) V − i trajectory
From the voltage and current waveforms in Fig.5, it can
be also seen that the voltage across the auxiliary power switch
S2 has a parasitic oscillation phenomenon at S2 ZCS turn off.
In order to suppress the parasitic oscillation phenomenon, an
extra clamping diode Dc is needed in the original circuit in
Fig.1, and the new active auxiliary resonant converter topology with clamping diode Dc is shown in Fig.6. The clamping
diode Dc is naturally turned on as soon as the voltage of the
auxiliary power switch S2 exceed output voltage 380V, then
the parasitic peak voltage can be suppressed effectively. The
voltage and current waveforms and its v − i trajectory of the
auxiliary power switch S2 in case of adding a clamping diode
are represented in Fig.7. As shown in Fig.7, a large oscillation in Fig.5 disappears, and the peak voltage is effectively
suppressed. Therefore, the over voltage across the auxiliary
power switch S2 can be reduced positively.
2. Efficiency evaluation
The actual output power Po of the prototype with clam-
Fig. 6. Novel active auxiliary resonant converter with clamping diode DC
Fig. 8. Curves of efficiency
3. EMI characteristic
Fig.9(a) and Fig.9(b) illustrate the measured EMI characteristic graphs of the soft-switching converter and the hardswitching converter (RC snubber in the drain of S1 ) under the
horizontal antenna condition and the vertical antenna condition, respectively. It can be seen that the EMI interference of
the soft-switching converter is much smaller than that of the
hard-switching converter during the whole frequency range of
30MHz–1GHz. Additionally, the EMI interference can reduce
42.7dBμV/m (at 34.05MHz) and 37.1 dBμV/m (at 230MHz)
as much as possible, respectively, under the horizontal antenna
condition and the vertical antenna condition. It is more effective to use a active soft-switching converter to suppress the
radiated emission.
Fig. 9. Noise measurement of radiated EMI. (a) Under the
horizontal antenna condition; (b) Under the vertical
antenna condition
A Novel Soft Switching Converter with Active Auxiliary Resonant Commutation
IV. Conclusions
In this paper, a novel soft-switching converter with active auxiliary resonant network in the load side is presented.
The operation principle of the converter has been analyzed in
detail, and parameters of the resonant network have been presented. By the theory analysis and experiments using 3kW,
16kHz prototype, some conclusions have been reached as below:
(1) The soft-switching of power switches can be realized
by using the simple active auxiliary resonant network, which
can eliminate the overlapping phenomenon of voltage and current and reduce the switching loss. (2) Low di/dt and dv/dt
can lower voltage and current stress of switches, reduce EMI
problems aroused by hard-switching PWM converter and solve
the reverse-recovery problem of the output rectifier diode. (3)
ZCS and ZVS can be ensured under the wide load condition.
(4) An actual high efficiency of 97.8% can be achieved based
on the 5kW prototype.
The circuit proposed in this paper is suitable for large and
medium power soft-switching converters.
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CHU Enhui was born in 1965. He
received the M.S. degree in automation
from Northeastern University, Shenyang,
China, in 1993, and the Ph.D. degree from
Yamaguchi University, Yamaguchi, Japan,
in 2003. He is currently an assistant professor and supervisor for M.S. student in the
College of Information Science and Engineering, Northeastern University. His main
research interests include power electronics
and its application, high-frequency soft switching power conversion
system and its control. (Email: chuenhui@mail.neu.edu.cn)
HOU Xutong
was born in 1988.
He received the B.S. degree in electronic
information science and technology from
Shenyang University of Chemical Technology, Shenyang, China, in 2011. He is currently a M.S. graduate student in the College of Information Science and Engineering, North-eastern University. His research
interests focus on three level soft switching
converter.
ZHANG Huaguang
was born in
1959. He is currently a professor in the
College of Information Science and Engineering, Northeastern University. His current research interests include fuzzy control, chaos control, neural networks-based
control, nonlinear control, signal processing, and their industrial applications.