1
A ZVS Grid-Connected Three-Phase Inverter Driven Renewable
Energy Sources
1
CHENNAMSETTI PAVANI, 2BEELA RAJESH
M.Tech [Scholar], EEE Dept, VITAM College of Engineering, Visakhapatnam, AP-India
2
Assisstant Professor, EEE Dept, VITAM College of Engineering, Visakhapatnam, AP-India
1

few years, there have been many studies on soft switching
Abstract-- A six-switch three-phase inverter is widely used in a
techniques for a three-phase converter. And they can
high-power grid-connected system. However, the anti parallel
generally be divided into two configurations according to
diodes in the topology operate in the hard-switching state
under the traditional control method causing severe switch loss
the position where the soft-switching function is realized [26] as dc-side and ac-side soft-switching circuits.
and high electromagnetic interference problems. In order to
solve the problem, this paper proposes a topology of the
traditional six-switch three-phase inverter but with an
The active-clamping ZVS-PWM half-bridge inverter [6-8]
also has lower voltage stress (1.01–1.1 times as high as the
additional switch and gave a new space vector modulation
dc-bus voltage). According to [6], in this active-clamping
(SVM) scheme. In this way, the inverter can realize zero-
ZVS-PWM half-bridge inverter, to achieve better soft-
voltage switching (ZVS) operation in all switching devices and
switching performance, the slow reverse recovery switch
suppress the reverse recovery current in all anti parallel diodes
antiparallel diode is the primary choice because the diode
very well. And all the switches can operate at a fixed frequency
reverse recovery energy is used to obtain the
with the new SVM scheme and have the same voltage stress as
the dc-link voltage. In grid-connected application, the inverter
can achieve ZVS in all the switches under the load with unity
power factor or less. The aforementioned theory is verified in a
30-kW inverter prototype.
soft
commutation condition. In the ZVS dc-link single-phase
full-bridge inverter [7], the switch voltage is clamped to the
dc-link voltage. The PWM modulation scheme is modified
to achieve ZVS under different power factor loads. Besides
the dc-side soft-switching technique, there are also some ac-
Index Terms-- ZVS; ZCS; hard switching.
side soft-switching techniques suitable for higher power
application. The auxiliary resonant commutated pole
I. INTRODUCTION
(ARCP) converter achieves zero-voltage turn-on for main
IN A high-power grid-connected inverter application, the
switches and zero-current turn-off for an auxiliary switch
six-switch three-phase inverter is a preferred topology with
[4].
several advantages such as lower current stress and higher
The ARCP converter has excellent performance, but two
efficiency. To improve the line current quality, the switching
lowfrequency capacitors are necessary in the resonant cell
frequency of the grid-connected inverter is expected to
and it is difficult to control the capacitors’ midpoint voltage
increase. Higher switching frequency is also helpful for
without an additional control circuit. A new ZVS-PWM
decreasing the size and the cost of the filter. However,
single-phase fullbridge inverter using a simple ZVS-PWM
higher switching frequency leads to higher switching loss
commutation cell is proposed in [5]. No auxiliary voltage
[1]. The soft-switching technique is a choice for a high-
source or low-frequency center-tap capacitor is needed in
power converter to work under higher switching frequency
the cell. The main switches operate at ZVS and the auxiliary
with lower switching loss and lower EMI noise. In the past
switches operate at ZCS. The inductor-coupled ZVT
inverter achieves the zero-voltage turnon condition for main
switches and the near-zero current turn-off condition for
2
auxiliary switches [6]–[8]. This topology offers several
which is similar to the rectifier topology proposed in [8]. All
advantages over the ARCP. The problems associated with
the soft-switching advantages under the rectifier condition
the split dc capacitor bank are avoided, and the ZVT
can be achieved in a grid-connected inverter application, and
operation requires no modification compared to normal
the voltage stress in both main switches and the auxiliary
space vector modulation (SVM) schemes. The peak current
switch is the same as the dc-bus voltage. The operation
stress of the auxiliary switches is half of that of the main
principle of this SVM scheme is described in detail. The
switches.
experimental results of a 30-kW hardware prototype are
The major problem of this topology is to use coupled
presented to verify the theory.
inductors, which are normally bulky in high-power
applications. An improved ZVS inverter used two coupled
magnetic components in one resonant pole to ensure the
II. SWITCHING TECHNIQUES
A. HARD AND SOFT SWITCHING
main switches operating under the ZVS condition and the
In the 1970’s, conventional PWM power converters were
auxiliary switches operating under the ZCS condition when
operated in a switched mode operation. Power switches have
the load varies from zero to full. Since an independent
to cut off the load current within the turn-on and turn-off
coupled magnetic component structure avoids the unwanted
times under the hard switching conditions. Hard switching
magnetizing current antiparallel loop, the size of the coupled
refers to the stressful switching behavior of the power
inductors can be minimized with lower magnetizing
electronic devices. The switching trajectory of a hard-
inductance, and its saturation can be eliminated. The ZVS
switched power device is shown in Fig.1.
timing requirement is also satisfied over the full load range
I
Safe Operating Area
by using the variable timing control with simple and reliable
ZV detection. The zero-current transition (ZCT) inverter
On
Hard-switching
achieves ZCS in all of the main and auxiliary switches and
their antiparallel diodes. This topology needs six auxiliary
snubbered
switches and three LC resonant tanks. The simplified threeswitch ZCT inverter [23] needs only three auxiliary switches
to achieve zero-current turn-off in all of the main switches
and auxiliary switches. Compared with the six-switch ZCT
Soft-switching
Off
V
inverter, the resonant tank current stress of the three-switch
ZCT inverter is higher.
Fig.1 Typical switching trajectories of power switches.
The structure of the ZVS-SVM controlled three-phase PWM
rectifier is similar to the ACRDCL converter. With the
special SVM scheme proposed by the authors, both the main
switches and the auxiliary switch have the same and fixed
switching frequency. The reverse recovery current of the
switch be turned ON under the zero-voltage condition.
Moreover, the voltage stress in both main switches and the
auxiliary switch is only 1.01–1.1 times of the dc-bus voltage.
In this paper, a ZVS three-phase grid-connected inverter is
proposed. The topology of the inverter is shown in Fig. 2,
During the turn-on and turn-off processes, the power device
has to withstand high voltage and current simultaneously,
resulting in high switching losses and stress. Dissipative
passive snubbers are usually added to the power circuits so
that the dv/dt and di/dt of the power devices could be
reduced, and the switching loss and stress be diverted to the
passive snubber circuits. However, the switching loss is
proportional to the switching frequency, thus limiting the
maximum switching frequency of the power converters.
3
Typical converter switching frequency was limited to a few
frequency modulation (FM) for output regulation. Variable
tens of kilo-Hertz (typically 20kHz to 50kHz) in early
switching frequency operation makes the filter design and
1980’s. The stray inductive and capacitive components in
control more complicated.
the power circuits and power devices still cause considerable
In late 1980’s and throughout 1990’s, further improvements
transient effects, which in turn give rise to electromagnetic
have been made in converter technology. New generations
interference (EMI) problems. Fig.2 shows ideal switching
of soft-switched converters that combine the advantages of
waveforms and typical practical waveforms of the switch
conventional PWM converters and resonant converters have
voltage. The transient ringing effects are major causes of
been developed. These soft-switched converters have
EMI.
switching waveforms similar to those of conventional PWM
converters except that the rising and falling edges of the
waveforms are ‘smoothed’ with no transient spikes. Unlike
the resonant converters, new soft-switched converters
usually utilize the resonance in a controlled manner.
Resonance is allowed to occur just before and during the
turn-on and turn-off processes so as to create ZVS and ZCS
conditions. Other than that, they behave just like
conventional PWM converters. With simple modifications,
Fig.2. Typical switching waveforms of (a) hard-switched
many customized control integrated control (IC) circuits
and (b) soft-switched devices
designed for conventional converters can be employed for
soft-switched converters. Because the switching loss and
In the 1980’s, lots of research efforts were diverted towards
stress have been reduced, soft-switched converter can be
the use of resonant converters. The concept was to
operated at the very high frequency (typically 500kHz to a
incorporate resonant tanks in the converters to create
few Mega-Hertz). Soft-switching converters also provide an
oscillatory (usually sinusoidal) voltage and/or current
effective solution to suppress EMI and have been applied to
waveforms so that zero voltage switching (ZVS) or zero
DC-DC, AC-DC and DC-AC converters. This chapter
current switching (ZCS) conditions can be created for the
covers the basic technology of resonant and soft-switching
power switches. The reduction of switching loss and the
converters. Various forms of soft-switching techniques such
continual improvement of power switches allow the
as ZVS, ZCS, voltage clamping, zero transition methods etc.
switching frequency of the resonant converters to reach
are addressed. The emphasis is placed on the basic operating
hundreds of kilo-Hertz (typically 100kHz to 500kHz).
principle and practicality of the converters without using
Consequently, magnetic sizes can be reduced and the power
much mathematical analysis.
density of the converters increased. Various forms of
resonant converters have been proposed and developed.
B. Resonant Switch
However, most of the resonant converters suffer several
Prior to the availability of fully controllable power
problems. When compared with the conventional PWM
switches, thyristors were the major power devices used in
converters, the resonant current and voltage of resonant
power electronic circuits. Each thyristor requires a
converters have high peak values, leading to higher
commutation circuit, which usually consists of a LC resonant
conduction loss and higher V and I ratings requirements for
circuit, for forcing the current to zero in the turn-off process.
the power devices. Also, many resonant converters require
This mechanism is in fact a type of zero-current turn-off
4
process. With the recent advancement in semiconductor
Resonant-type DC-DC
Converters
technology, the voltage and current handling capability, and
the switching speed of fully controllable switches have
significantly
been
improved.
In
many
high
Conventional Resonant
Converters
power
Quasi-Resonant Converters
Multi-Resonant Converters
applications, controllable switches such as GTOs and IGBTs
Constant Frequency
Operation
Phase Shift-modulated
have replaced thyristors. However, the use of resonant
Variable Frequency
Operation
Load-Resonant Converters
circuit for achieving zero-current-switching (ZCS) and/or
zero-voltage-switching (ZVS) has also emerged as a new
Series Resonant
Converters
technology for power converters. The concept of resonant
Parallel Resonant
Converters
Constant Frequency
Operation
Variable Frequency
Operation
Series-Parallel
Resonant Converters
Fig.5: Classification
switch that replaces conventional power switch is introduced
in this section.
A
resonant
switch
is
a
sub-circuit
comprising
III. ZVS-QRC
a
semiconductor switch S and resonant elements, Lr and Cr.
In these converters, the resonant capacitor provides a
The switch S can be implemented by a unidirectional or
zero-voltage condition for the switch to turn on and off. A
bidirectional switch, which determines the operation mode
quasi-resonant buck converter designed for half-wave
of the resonant switch. Two types of resonant switches,
operation is shown in Fig.6 - using a ZV resonant switch.
including zero-current (ZC) resonant switch and zero-
Basic relations of ZVS-QRCs are given in Equations (1a-
voltage (ZV) resonant switches, are shown in Fig.3 and
1e).
Fig.4, respectively.
ILr
Lr
Dr
Lr
Lr
Lf
+
v oi
-
Cr
Df
Cf
+ vc -
Cr
S
Vi
Io
S
Cr
(a)
Fig.6: Schematic diagram.
(b)
Fig.3 Zero-current (ZC) resonant switch.
M 
Lr
Lr
S
(a)
Lr
Cr
Zr 
Cr
S
Vo
Vi
Cr
(b)
fr 
Fig.4 Zero-voltage (ZV) resonant switch.
C. CLASSIFICATION
1
2  Lr Cr
r
The classification of the switching techniques are presented
here in this fig.5.

(1a)
(1b)
(1c)
RL
Zr
(1d)
fs
fr
(1e)
+
Vo
-
5
IV. RESULTS
The results pertaining to the schematic discussed in the
previous section are presented here in this section. When the
switch S is turned on, it carries the output current Io. The
supply voltage Vi reverse-biases the diode Df. When the
switch is zero-voltage (ZV) turned off, the output current
starts to flow through the resonant capacitor Cr. When the
resonant capacitor voltage VCr is equal to Vi, Df turns on.
This starts the resonant stage. When VCr equals zero, the
anti-parallel diode turns on. The resonant capacitor is
shorted and the source voltage is applied to the resonant
(b) Relationship between M and .
inductor Lr. The resonant inductor current ILr increases
linearly until it reaches Io. Then Df turns off. In order to
Fig.7 Half-wave, quasi-resonant buck converter with ZVS.
achieve ZVS, S should be triggered during the time when the
anti-parallel diode conducts. It can be seen from the
waveforms that the peak amplitude of the resonant capacitor
voltage should be greater or equal to the input voltage (i.e.,
Io Zr > Vin). From Fig.7(a), it can be seen that the voltage
conversion ratio is load-sensitive. In order to regulate the
output voltage for different loads r, the switching frequency
ZVS converters can be operated in full-wave mode. The
circuit schematic is shown in Fig.8(a). The circuit
waveforms in steady state are shown in Fig.8(b). The
operation is similar to half-wave mode of operation, except
that VCr can swing between positive and negative voltages.
The relationships between M and  at different r are shown
in Fig.8(c).
should also be changed accordingly.
ILr
1 cycle
ILr
IO
t0
t1
t1 '
t1 "
Lr
t
t2 '
t3
Lf
+
v oi
-
+ vc -
t2
0
Dr
Cr
Io
Df
+
Vo
-
Cf
t4
(a) Schematic diagram.
vc
1 cycle
ZrIO
ILr
IO
t2
0
t0
t1
t1'
t1"
vi
0
t
t0
t1
t1 '
t1 "
t2
t2 '
t3
t
t2 '
t3
t4
t3
t4
vc
t4
(a) Circuit waveforms.
ZrIO
vi
0
t
t0
t1
t1 '
t1"
t2
t2 '
(b) Circuit waveforms.
6
[3] D. M. Divan, “Static power conversion method and
apparatus having essentially zero switching losses and
clamped voltage levels,” U.S. Patent 48 64 483, Sep. 5,
1989.
[4] M. Nakaok, H. Yonemori, and K. Yurugi, “Zero-voltage
soft-switched
PDMthreephaseAC–DC
active
power
converter operating at unity power factor and sinewave line
current,” in Proc. IEEE Power Electronics Spec. Conf.,
1993, pp. 787–794.
[5] H. Yonemori, H. Fukuda, and M. Nakaoka, “Advanced
(c) Relationship between M and .
three-phase ZVS- PWM active power rectifier with new
Fig.8 Full-wave, quasi-resonant buck converter with ZVS.
resonant DC link and its digital control scheme,” in Proc.
Comparing Fig.7(b) with Fig.8(c), it can be seen that M is
IEE Power Electron. Variable Speed Drives, 1994, pp. 608–
load-insensitive in full-wave mode. This is a desirable
613.
feature. However, as the series diode limits the direction of
[6] G. Venkataramanan, D. M. Divan, and T. Jahns,
the switch current, energy will be stored in the output
“Discrete pulse modulation strategies for high frequency
capacitance of the switch and will dissipate in the switch
inverter system,” IEEE Trans. Power Electron., vol. 8, no. 3,
during turn-on. Hence, the full-wave mode has the problem
pp. 279–287, Jul. 1993.
of capacitive turn-on loss, and is less practical in high
[7] G. Venkataramanan and D. M. Divan, “Pulse width
frequency operation.
modulation
VII. CONCLUSION
with
resonant
dc
link
converters,”
inProc.Conf.RecordIEEEInd.Appl.Soc.Annu.
Meeting,
1990, pp. 984–990.
Through study and analysis, of the ZVS schematic and its
[8] Y. Chen, “A new quasi-parallel resonant dc link for soft-
results are made with a motive to understand its
switching PWM inverters,” IEEE Trans. Power Electron.,
characteristics. In practice, ZVS-QRCs are usually operated
vol.13,no.3,pp.427–435,May 1998.
in half-wave mode rather than full-wave mode. By replacing
the ZV resonant switch in the conventional converters,
various ZVS-QRCs can be derived. A comparative analysis
in the previous section paved a path towards vital
conclusions in its applications.
V. REFERENCES
[1] N. Mohan, T. Undeland, and W. Robbins, Power
Electronics: Converters, Applications and Design. New
York: Wiley, 2003, pp. 524–545.
[2] M. D. Bellar, T. S. Wu, A. Tchamdjou, J. Mahdavi, and
M. Ehsani, “A review of soft-switched DC–AC converters,”
IEEE Trans. Ind. Appl., vol. 34, no. 4, pp. 847–860,
Jul./Aug. 1998.