IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 15, NO. 1, JANUARY 2000
185
A True ZCZVT Commutation Cell for PWM
Converters
Carlos Marcelo de Oliveira Stein, Student Member, IEEE, and Hélio Leaes Hey, Member, IEEE
Abstract—This paper introduces a true zero-current and
zero-voltage transition (ZCZVT) commutation cell for dc–dc
pulsewidth modulation (PWM) converters operating with an
input voltage less than half the output voltage. It provides
zero-current switching (ZCS) and zero-voltage switching (ZVS)
simultaneously, at both turn on and turn off of the main switch
and ZVS for the main diode. The proposed soft-switching
technique is suitable for both minority and majority carrier
semiconductor devices and can be implemented in several dc–dc
PWM converters. The ZCZVT commutation cell is placed out of
the power path, and, therefore, there are no voltage stresses on
power semiconductor devices. The commutation cell consists of a
few auxiliary devices, rated at low power, and it is only activated
during the main switch commutations. The ZCZVT commutation
cell, applied to a boost converter, has been analyzed theoretically
and verified experimentally. A 1-kW boost converter operating at
40 kHz with an efficiency of 97.9% demonstrates the feasibility of
the proposed commutation cell.
Index Terms—High-performance dc–dc power conversion,
IGBT’s, zero-current–zero-voltage switching (ZCZVS).
I. INTRODUCTION
T
HE OVERALL performance of pulsewidth modulation (PWM) converters can be improved by the use of
soft-switching techniques. These techniques allow operation
at higher switching frequencies resulting in higher power
densities without penalizing the efficiency [1]–[13].
There are two main soft-switching approaches, that are the
zero-current switching (ZCS) [1]–[8] and the zero-voltage
switching (ZVS) [9]–[13]. The choice depends on the semiconductor device technology that will be used. For example,
MOSFET’s present better performance under ZVS. This is
because under ZCS the capacitive turn-on losses increase the
switching losses and the electromagnetic interference (EMI).
On the other hand, insulated gate bipolar transistors (IGBT’s)
present better results under ZCS which can avoid the turn-off
losses caused by the tail current [3].
Nevertheless, the ZCS techniques proposed in the literature present some drawbacks such as significant voltage
stress on the main diode, which increases the conduction
losses, and the presence of the resonant inductor in series with the main switch, which increases the magnetic
losses. These drawbacks are not present in the ZCT technique, proposed in [8]. On the other hand, it presents other
Manuscript received February 5, 1998; revised June 29, 1999. Recommended
by Associate Editor, J. Thottuvelil.
The authors are with the Federal University of Santa Maria,
UFSM-CT-DELC, 97105-900 Santa Maria, RS, Brazil (e-mail:
hey@pequim.ctlab.ufsm.br).
Publisher Item Identifier S 0885-8993(00)00382-3.
disadvantages as mentioned in [7] and [22]. Recently, an
improved ZCT technique was presented in [22]. In this proposal, all switches commutates under soft switching. However, the main switch and the main diode have a high peak
current stresses.
The aim of this paper is to introduce a true zero-current and
zero-voltage transition (ZCZVT) commutation cell for dc–dc
PWM converters. The commutation cell provides ZCS and ZVS
simultaneously, at both turn on and turn off of the main switches
and ZVS for the main diodes.
The proposed soft-switching technique is suitable for both
minority and majority carrier semiconductor devices, and can
be implemented in any member of the dc–dc PWM converter
family. The auxiliary shunt resonant network of the ZCZVT
commutation cell is placed out of the power path, and, therefore,
there is no voltage stresses on power semiconductor devices.
The operation of the ZCZVT commutation cell applied to a
boost converter is theoretically analyzed in Section II. A design
guideline and a design example are presented in Section III.
In Section IV, simulation and experimental results on a 1-kW
prototype using IGBT’s as both main and auxiliary switches are
presented. The last section summarizes the conclusions drawn
from this investigation.
II. PRINCIPLE OF OPERATION
A. The ZCZVT PWM Boost Converter
Fig. 1(a) shows the ZCZVT PWM boost converter. It differs
from a hard-switching PWM boost converter by the presence of
an additional shunt resonant network formed by two resonant
and
, a resonant inductor
, a bidirectional
capacitors
and two auxiliary diodes,
and
auxiliary switch
. The main features of this topology are as follows.
• There are no additional voltage stresses on power semiconductor devices.
• Commutation under ZCS and ZVS at both turn on and turn
.
off for the main switch, whenever
• Commutation under ZCS at turn on and under ZCS and
ZVS at turn off for the auxiliary switch.
is commutated under ZVS and
• The output rectifier
its reverse recovery is minimized.
• The ZCZVT PWM commutation cell is placed out of the
main power path, and it is activated during the switching
transitions only.
B. Operation Principles
To simplify the analysis, the input filter inductance and the
are assumed large enough, and, thereoutput filter capacitor
0885–8993/00$10.00 © 2000 IEEE
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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 15, NO. 1, JANUARY 2000
Fig. 1. ZCZVT PWM boost converter.
Fig. 2. Operation stages.
fore, the input current and the output voltage of the converter
are considered constant over one switching cycle. The simplified circuit diagram is presented in Fig. 1(b). As shown in Fig. 2,
14 operating stages exist during one switching cycle, which are
described as follows.
: The active switches are off, and the input
Stage 1—
flows through the output rectifier
. During this
current
and
are
stage, the resonant capacitors voltages
(
for
) and , respectively.
clamped at
: At , the auxiliary switch
is turned
Stage 2—
increases due to the resonance
on under ZCS. The current
and
. The voltage
evolves in a resonant
between
way until it reaches . At this time, the diode
turns on.
and the resonant capacitor
The resonant inductor current
can be expressed as follows:
voltage
(1)
(2)
where
and
DE OLIVEIRA STEIN AND HEY: TRUE ZCZVT COMMUTATION CELL FOR PWM CONVERTERS
187
Fig. 3. Theoretical waveforms.
where
The duration of this resonant stage is equal to
and
(3)
: During this stage, the current
inStage 3—
, when the output rectifier
is
creases linearly up to
turned off under ZCS and ZVS. The resonant inductor current
is given by
(4)
is
where
is given by
when
. The time interval of this stage
The duration of this resonant stage is defined by
(8)
: The current
decreases linearly
Stage 5—
, when
is turned off. To achieve soft
until it reaches
commutation for the main switch , its turn-on signal should
is conducting. The inductor
be applied while the diode
can be expressed as
current
(9)
(5)
: The current
continues to increase
Stage 4—
and
. When the voltage
due to the resonance between
reaches zero, the diode
turns on. The resonant inand the resonant capacitor voltage
ductor current
can be expressed as follows:
(6)
(7)
is
where
is equal to
when
. The time interval of this stage
(10)
: At , the main switch is turned on
Stage 6—
continues
under ZCS and ZVS condition. The current
to ramp down until it reaches zero and the current through main
. The resonant inductor current
is
switch reaches
given by
(11)
188
Fig. 4. Relationship between k
IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 15, NO. 1, JANUARY 2000
and k
with k as parameter.
The time interval of this stage is equal to
The time interval of this stage is equal to
(12)
(18)
: The capacitor
and the inductor
Stage 7—
form a half-cycle resonance through the main switch and the
, which reverses the polarity of the voltage
.
diode
can be turned off
During this stage, the auxiliary switch
under ZCS and ZVS conditions. The resonant inductor current
and the resonant capacitor voltage
can be expressed as follows:
: During this stage, the diode
is on
Stage 10—
and the main switch can be turned off under ZCS and ZVS.
reaches the input current again, the diode
turns
When
and the resonant caoff. The resonant inductor current
can be expressed as follows:
pacitor voltage
(19)
(13)
(20)
(14)
is
where
stage is equal to
The time interval of this stage is equal to
when
. The time interval of this
(15)
(21)
: The operation of the circuit at this stage
Stage 8—
is similar to that of the hard-switching PWM boost converter.
The input current flows through the main switch .
: At ,
is turned on again under ZCS.
Stage 9—
increases due to the resonance between
As the current
and
, the current through the main switch decreases
at the same rate since the sum of the two is equal to input current
. This stage ends when the current through the main switch
reaches zero. At this time, the diode
turns on again. The resand the resonant capacitor voltage
onant inductor current
can be expressed as follows:
: At , the resonant capacitor voltage
Stage 11—
begins to increase due to the resonance between
,
and
. When the resonant capacitor voltage
reaches the diode
turns on. The resonant inductor curand the resonant capacitors voltages
and
rent
can be expressed as follows:
(22)
(16)
(17)
(23)
DE OLIVEIRA STEIN AND HEY: TRUE ZCZVT COMMUTATION CELL FOR PWM CONVERTERS
189
(30)
(24)
where
is
(31)
when
is
when
.
where
The time interval of this stage is equal to
(32)
and
is
when
.
where
: During this stage, the capacitor
is
Stage 14—
by the input current. At this moment
linearly charged up to
turns on, beginning another switching
the output rectifier
is given by
cycle. The resonant capacitor voltage
The time interval of this stage is equal to
(33)
(25)
is
when
.
where
: The voltage
continues to inStage 12—
and
. When
crease due to the resonance between
reaches zero, the diode
turns on again and
turns off.
and the resonant capacitor
The resonant inductor current
can be expressed as follows:
voltage
The time interval of this stage is equal to
(34)
Fig. 3 shows the theoretical waveforms of the ZCZVT PWM
boost converter.
C. Soft Commutation Conditions
(26)
1) Main Switch: In order to achieve commutation under
ZVS and ZCS at turn on for the main switch (stage 5) and
(stage 7), the following
at turn off for the auxiliary switch
inequality should be satisfied:
(35)
(27)
is
when
. The time interval of this
where
stage is equal to (28), given at the bottom of the page.
: At
, the voltage
begins to
Stage 13—
,
and
, until
decrease due to the resonance between
reaches zero, when
turns off. During this stage, the
can be turned off under ZCS and ZVS. The
auxiliary switch
and the voltages
and
can be excurrent
pressed as follows:
This constrain may be undesirable in some applications such
as in power-factor-correction circuits. However, it could be relaxed by the use of an auxiliary voltage source which would
ensure the required energy for the proper operation of the auxiliary circuit.
In order to achieve commutation under ZVS and ZCS at turn
off for the main switch (stage 9), the following inequality
should be satisfied:
(36)
(29)
or
(37)
where
(28)
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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 15, NO. 1, JANUARY 2000
maximum value of the input inductor filter current;
minimum value of the input voltage source;
a factor that guarantees the inequality (36).
2) Auxiliary Switch: The auxiliary switch is activated twice
per period, as described in the beginning of this section. The
auxiliary switch turn on under ZCS is ensured since the resonant
is connected in series with it. On the other hand,
inductor
must
to achieve turn off under ZCS and ZVS the diode
conduct during this commutation. During the first turn off this
conducts
condition is always satisfied, because the diode
the resonant current during the stage 7. The conduction of the
during the second turn off depends on the existence
diode
of the stage 13. Unfortunately, there is no close-form solution
for the duration of the stage 13. However, it is possible to find
and
numerically the ratio between the resonant capacitors
, named
, for a given
and
(dc voltage conversion
ratio), which ensures the existence of stage 13. Fig. 4 gives the
as a function of
for different values of .
values of
Fig. 5. Power stage circuit.
TABLE I
UTILIZED COMPONENTS AND PARAMETERS
IN SIMULATION AND IN THE BREADBOARDED CONVERTER
III. DESIGN GUIDELINES AND EXAMPLE
In this section, a design procedure and an example of how to
determine the component values of the proposed ZCZVT PWM
boost converter are given.
The input data are defined as follows:
W;
• output power:
V;
• output voltage:
V (±10%);
• input voltage:
%;
• approximate efficiency:
.
• ripple of the input filter inductance:
1) From the input data it is possible to achieve the dc voltage
conversion ratio, which is given by
The dc voltage conversion ratio was defined to satisfy
(35).
is calculated to control its di/dt
2) The resonant inductor
rate and, therefore, to minimize the reverse recovery of
the output diode. In this design example, this value was
chosen equal to 40 A/µs
3) With the values of the output power, the minimum input
voltage and the approximate efficiency, it is possible to
define the input power and the maximum dc input current
W
A.
nF
must be chosen greater than one.
where the parameter
It is worth mentioning that the selection of a large value
would increase the current stresses in the circuit.
of
was initially defined equal to
In this design example,
1.3 to compensate for the intrinsic losses of the practical
of 33 nF,
setup. By taking a commercial value for
.
results in
5) The next step is to define the value of the resonant capac. From Fig. 4, with the values of the parameters
itor
and is obtained the value of parameter
, which is
. The procedure to obtain the Fig. 4
the ratio of
is explained in detail in [21].
and
, the parameter
is
With
is defined as
equal to 1.05. Therefore, the capacitor
follows:
nF
Commercial value utilized:
nF. Therefore,
.
6) From (18) is defined the maximum value to fall time of
the main switch , which is given by
4) From (37) is calculated the value of the resonant capacitor
, which is given by
ns
DE OLIVEIRA STEIN AND HEY: TRUE ZCZVT COMMUTATION CELL FOR PWM CONVERTERS
Fig. 6.
191
Waveforms for the ZCZVT PWM boost converter.
In this example design, the fall time of the main switch
must be smaller than 400 nF to assure its turn off under
ZVS and ZCS.
7) From (3), (5), (8), (10), (12), (18), (21), (25), (28), (32),
and (34) is defined the sum of the resonant time intervals,
which must be to involve a small fraction of the switching
period. In this example design, this sum has been chosen
equal to 20% of the switching period. Therefore, the maximum switching frequency is given by
kHz
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IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 15, NO. 1, JANUARY 2000
The switching frequency was assumed equal to 40 kHz.
IV. SIMULATION AND EXPERIMENTAL RESULTS
Following the design example shown in the preceding section, a 40-kHz 1-kW ZCZVT PWM boost converter has been
simulated with Microsim PSpice using ideal components, and
a prototype has been implemented to verify the operation and
the performance of the proposed ZCZVT commutation cell. The
power circuit is shown in Fig. 5. Its main parameters are summarized in Table I. The active switches were implemented with
a UFS (ultrafast switches) series IGBT’s from Harris Semiconductor, which present built-in antiparallel hyperfast diodes. The
main switch was a HGTP7N60C3D (600 V, 7 A), and the auxiliary switch was a HGTP3N60C3D (600 V, 3 A). The output
rectifier and the auxiliary diode used were a hyperfast diodes
RHRP870 (700 V, 8 A) from Harris Semiconductor.
Fig. 6 shows the simulation and the experimental waveforms.
They confirm the previously mentioned analysis. As can be seen
in Fig. 6(a), the commutations of the main switch occurs truly
without losses, i.e., under ZCS and ZVS simultaneously. This is
a very interesting feature of the proposed ZCZVT commutation
cell. The maximum voltage across the main switch is equal to
the output voltage.
is turned on
Fig. 6(b) shows that the auxiliary switch
under ZCS and turned off under ZCS and ZVS. Since the resocontrol the
rate of the output rectifier, it
nant inductor
helps to minimize the reverse recovery losses of this diode.
From Fig. 6(c), it can be seen that the maximum voltage
across the output rectifier is equal to output voltage and it is
commutated under ZVS at turn on and ZCS and ZVS at turn
off.
The experimental results show that the converter operates
and
, reducing
with very low ringing and with low
its EMI emission. Owing to this, in the breadboarded converter
it was not necessary to use any clamp circuit.
Fig. 7 shows the measured efficiency of the boost converter
with the proposed ZCZVT commutation cell as function of the
output power, whose value was equal to 97.9% at full load (1
kW). Fig. 7 also includes the efficiency curve of the same circuit without the proposed commutation cell for comparison proposes. Without the proposed commutation cell the converter efficiency at full load was 91.5%.
V. CONCLUSIONS
A true ZCZVT commutation cell was proposed in this paper,
and to verify its feasibility it was applied to a PWM boost converter. Operating principles and commutation process were described and verified by experimental results obtained from a
prototype operating at 40 kHz, with an input voltage rated at
155-V and 1-kW output power. The measured efficiency at full
load was 97.9%.
As shown by theoretical analysis and experimental results,
the main features obtained are as follows.
• The ZCZVT PWM commutation cell is placed out of the
main power path, and, therefore, there are no additional
voltage stresses on power semiconductor devices. Moreover, it is activated during the switching transitions only.
Fig. 7.
Efficiency of the boost converter.
• Soft switching for all power semiconductor devices is
achieved. The main switch commutates under ZCS and
ZVS simultaneously at turn on and turn off. Thus, it is
suitable for both minority and majority carriers semiconductor device applications such as MOSFET’s, IGBT’s,
MCT’s, etc. The auxiliary switch commutates under ZCS
at turn on and under ZCS and ZVS at turn off. The output
rectifier commutates under ZVS and its reverse recovery
is minimized.
• Taking into account the experimental results, the converter
operates practically without ringing and with low
and
on the power devices, which can reduce the
EMI emission.
• The converters are regulated by the conventional PWM
technique at constant frequency.
• Among several soft-switching techniques presented in
the literature, mainly the ZCS techniques, the proposed
ZCZVS commutation cell is a candidate and can be
implemented in any member of the PWM family.
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Carlos Marcelo de Oliveira Stein (S’95) was born
in Santiago, RS, Brazil, in 1970. He received the B.E.
and M.S. degrees in electrical engineering in 1996
and 1997, respectively, from the Federal University
of Santa Maria, Rio Grande do Sul, Brazil. He is currently working toward the Ph.D. degree in electrical
engineering at the Federal University of Santa Maria.
His research interests include power switching
converters, power-factor-correction techniques, and
soft-switching techniques.
Mr. Stein is currently a member of the Brazilian
Society of Power Electronics (SOBRAEP).
Hélio Leaes Hey (M’88) was born in Santa Maria,
RS, Brazil, in 1961. He received the B.S. degree from
the Catholic University of Pelotas, Brazil, in 1985
and the M.S. and Ph.D. degrees from the Federal University of Santa Catarina, Santa Catarina, Brazil, in
1987 and 1991, respectively.
From 1989 to 1993, he was with the Federal
University of Uberlândia, Brazil. Since 1994, he has
been with the Federal University of Santa Maria,
Rio Grande do Sul, Brazil, where he is currently
a Professor. He is also an Editor of the Brazilian
Power Electronics Journal. His research interests include power switching
converters, power-factor-correction techniques, and soft-switching techniques.