ISSN 2319-8885
Vol.04,Issue.05
February-2015,
Pages:0869-0875
www.ijsetr.com
A ZVS Grid-Connected Three-Phase Inverter Driven Renewable Energy Sources
CHENNAMSETTI PAVANI1, BEELA RAJESH2
1
PG Scholar, Dept of EEE, VITAM College of Engineering, Visakhapatnam, AP, India.
Assistant Professor, Dept of EEE, VITAM College of Engineering, Visakhapatnam, AP, India.
2
Abstract: Renewable Energy Sources are increasingly integrated at the distribution level due to increase in load demand which
utilize power electronic converters. A novel active clamping zero voltage switching SVM controlled three-phase grid connected
inverter is proposed in this paper. The inverter can realize zero voltage switching (ZVS) operation for all switching devices. In
addition, the anti-parallel diode reverse recovery current of all switch devices is suppressed well. Space vector modulation can
be realized with all the switching devices operating at the fixed switching frequency. And the switching voltage stress of all the
power switch devices is equal to the DC link voltage, no additional voltage stresses is added on the power devices. The ZVS
inverter can work both under Grid-connected condition and with independent loads. . In grid-connected application, the inverter
can achieve ZVS in all the switches under the load with unity power factor or less. The different techniques of modelling and
control of grid connected photovoltaics system with objective to help intensive penetration of photovoltaic (PV) production into
the grid have been proposed so far in different papers.
Keywords: Renewable Energy, Grid Connected Soft Switching, Space Vector Modulation (SVM), Zero Voltage Switching
(ZVS), Photovoltaic (PV) System.
I. INTRODUCTION
Renewable energy systems such as PV, solar thermal
electricity such as dish-stirling systems, and WT are
appropriate solar and wind technologies that can be
considered for electric power generation at the distribution
system level. Other renewable energy technologies, such as
the solar central receiver, hydro-electric generation,
geothermal, and large wind farms are normally connected to
the grid at the sub transmission or transmission level
because of the higher power capacities of these types of
systems. Due to increasing air pollution, global warming
concerns, diminishing fossil fuels and their increasing cost
have made it necessary to look towards Renewable Energy
Sources (RES)as a future energy solution. In a high-power
grid-connected inverter application, the six-switch threephase inverter is a preferred topology with several
advantages such as lower current stress and higher
efficiency. To improve the line current quality, the
switching frequency of the grid-connected inverter is
expected to increase. Higher switching frequency is also
helpful for decreasing the size and the cost of the filter.
However, higher switching frequency leads to higher
switching loss [1]. The soft-switching technique is a choice
for a high-power converter to work under higher switching
frequency with lower switching loss and lower EMI noise.
In the past few years, there have been many studies on soft
switching techniques for a three-phase converter. And they
can generally be divided into two configurations according
to the position where the soft-switching function is realized
[2-6] as dc-side and ac-side soft-switching circuits.
The active-clamping ZVS-PWM half-bridge inverter [68] also has lower voltage stress (1.01–1.1 times as high as
the dc-bus voltage). According to [6], in this activeclamping ZVS-PWM half-bridge inverter, to achieve better
soft-switching performance, the slow reverse recovery
switch antiparallel diode is the primary choice because the
diode reverse recovery energy is used to obtain the 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 acside soft-switching techniques suitable for higher power
application. The auxiliary resonant commutated pole
(ARCP) converter achieves zero-voltage turn-on for main
switches and zero-current turn-off for an auxiliary switch
[4]. The ARCP converter has excellent performance, but
two low frequency capacitors are necessary in the resonant
cell and it is difficult to control the capacitors‟ midpoint
voltage without an additional control circuit. A new ZVSPWM single-phase full bridge inverter using a simple ZVSPWM commutation cell is proposed in [5]. No auxiliary
voltage source or low-frequency center-tap capacitor is
needed in the cell.
The main switches operate at ZVS and the auxiliary
switches operate at ZCS. The inductor-coupled ZVT
inverter achieves the zero-voltage turn on condition for
main switches and the near-zero current turn-off condition
for auxiliary switches [6]–[8]. This topology offers several
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CHENNAMSETTI PAVANI, BEELA RAJESH
advantages over the ARCP. The problems associated with
in high switching losses and stress. Dissipative passive
the split dc capacitor bank are avoided, and the ZVT
snubbers are usually added to the power circuits so that the
operation requires no modification compared to normal
dv/dt and di/dt of the power devices could be reduced, and
space vector modulation (SVM) schemes. The peak current
the switching loss and stress be diverted to the passive
stress of the auxiliary switches is half of that of the main
snubber circuits. However, the switching loss is
switches. The major problem of this topology is to use
proportional to the switching frequency, thus limiting the
coupled inductors, which are normally bulky in high-power
maximum switching frequency of the power converters.
applications. An improved ZVS inverter used two coupled
Typical converter switching frequency was limited to a few
magnetic components in one resonant pole to ensure the
tens of kilo-Hertz (typically 20kHz to 50kHz) in early
main switches operating under the ZVS condition and the
1980‟s. The stray inductive and capacitive components in
auxiliary switches operating under the ZCS condition when
the power circuits and power devices still cause
the load varies from zero to full. Since an independent
considerable transient effects, which in turn give rise to
coupled magnetic component structure avoids the unwanted
electromagnetic interference (EMI) problems. Fig.2 shows
magnetizing current anti-parallel loop, the size of the
ideal switching waveforms and typical practical waveforms
coupled inductors can be minimized with lower magnetizing
of the switch voltage. The transient ringing effects are major
inductance, and its saturation can be eliminated. The ZVS
causes of EMI.
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-s witching
achieves ZCS in all of the main and auxiliary switches and
their anti-parallel diodes. This topology needs six auxiliary
switches and three LC resonant tanks. The simplified threeswitch ZCT inverter [3] needs only three auxiliary switches
snubbered
to achieve zero-current turn-off in all of the main switches
and auxiliary switches. Compared with the six-switch ZCT
inverter, the resonant tank current stress of the three-switch
ZCT inverter is higher.
Soft-s witching
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, which is similar to the rectifier topology proposed
in [8]. All the soft-switching advantages under the rectifier
condition can be achieved in a grid-connected inverter
application, and the voltage stress in both main switches and
the auxiliary switch is the same as the dc-bus voltage. The
operation principle of this SVM scheme is described in
detail. The experimental results of a 30-kW hardware
prototype are presented to verify the theory.
II. SWITCHING TECHNIQUES
A. Hard and Soft Switching
In the 1970‟s, conventional PWM power converters were
operated in a switched mode operation. Power switches
have to cut off the load current within the turn-on and turnoff times under the hard switching conditions. Hard
switching refers to the stressful switching behavior of the
power electronic devices. The switching trajectory of a
hard-switched power device is shown in Fig.1. During the
turn-on and turn-off processes, the power device has to
withstand high voltage and current simultaneously, resulting
Off
V
Fig.1. Typical switching trajectories of power switches.
Fig.2. Typical switching waveforms of (a) hard-switched
and (b) soft-switched devices.
In the 1980‟s, lots of research efforts were diverted
towards the use of resonant converters. The concept was to
incorporate resonant tanks in the converters to create
oscillatory (usually sinusoidal) voltage and/or current
waveforms so that zero voltage switching (ZVS) or zero
current switching (ZCS) conditions can be created for the
power switches. The reduction of switching loss and the
continual improvement of power switches allow the
switching frequency of the resonant converters to reach
hundreds of kilo-Hertz (typically 100kHz to 500kHz).
Consequently, magnetic sizes can be reduced and the power
density of the converters increased. Various forms of
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.05, February-2015, Pages: 0869-0875
A ZVS Grid-Connected Three-Phase Inverter Driven Renewable Energy Sources
resonant converters have been proposed and developed.
comprising a semiconductor switch S and resonant
However, most of the resonant converters suffer several
elements, Lr and Cr. The switch S can be implemented by a
problems. When compared with the conventional PWM
unidirectional or bidirectional switch, which determines the
converters, the resonant current and voltage of resonant
operation mode of the resonant switch. Two types of
converters have high peak values, leading to higher
resonant switches, including zero-current (ZC) resonant
conduction loss and higher V and I ratings requirements for
switch and zero-voltage (ZV) resonant switches, are shown
the power devices. Also, many resonant converters require
in Fig.3 and Fig.4, respectively.
frequency modulation (FM) for output regulation. Variable
switching frequency operation makes the filter design and
control more complicated. In late 1980‟s and throughout
Lr
Lr
1990‟s, further improvements have been made in converter
technology. New generations of soft-switched converters
that combine the advantages of conventional PWM
Cr
converters and resonant converters have been developed.
S
S
Cr
These soft-switched converters have switching waveforms
similar to those of conventional PWM converters except
(a)
(b)
that the rising and falling edges of the waveforms are
„smoothed‟ with no transient spikes. Unlike the resonant
Fig.3. Zero-current (ZC) resonant switch.
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
Lr
Lr
processes so as to create ZVS and ZCS conditions. Other
than that, they behave just like conventional PWM
converters. With simple modifications, many customized
Cr
control integrated control (IC) circuits designed for
conventional converters can be employed for soft-switched
S
S
converters. Because the switching loss and stress have been
Cr
reduced, soft-switched converter can be operated at the very
high frequency (typically 500kHz to a few Mega-Hertz).
(a)
(b)
Soft-switching converters also provide an effective solution
to suppress EMI and have been applied to DC-DC, AC-DC
Fig.4. Zero-voltage (ZV) resonant switch.
and DC-AC converters. This chapter covers the basic
technology of resonant and soft-switching converters.
III. INVERTER TOPOLOGY AND MODULATION
Various forms of soft-switching techniques such as ZVS,
SCHEME
ZCS, voltage clamping, zero transition methods etc. are
The topology in Fig.5 is composed of a standard PWM
addressed. The emphasis is placed on the basic operating
inverter and a clamping branch. The clamping branch
principle and practicality of the converters without using
consists of active switch S7, resonant inductor Lr , and
much mathematical analysis.
clamping capacitor Cc .
B. Resonant Switch
Prior to the availability of fully controllable power
switches, thyristor were the major power devices used in
power electronic circuits. Each thyristor requires a
commutation circuit, which usually consists of a LC
resonant circuit, for forcing the current to zero in the turnoff process. This mechanism is in fact a type of zero-current
turn-off process. With the recent advancement in
semiconductor technology, the voltage and current handling
capability, and the switching speed of fully controllable
switches have significantly been improved. In many high
power applications, controllable switches such as GTOs and
IGBTs have replaced thyristors. However, the use of
resonant circuit for achieving zero-current-switching (ZCS)
and/or zero-voltage-switching (ZVS) has also emerged as a
new technology for power converters. The concept of
resonant switch that replaces conventional power switch is
introduced in this section. A resonant switch is a sub-circuit
Fig.5. Grid line voltage and inverter output current
waveform.
During most time of operation, the active switch S7 is in
conduction, and energy circulates in the clamping branch.
When the auxiliary switch S7 is turned OFF, the current in
the resonant inductor iLr will discharge the parallel
capacitors of the main switch and then the main switch can
be turned ON under the zero-voltage condition. When the
main switch is turned ON, Lr suppresses the reverse
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.05, February-2015, Pages: 0869-0875
CHENNAMSETTI PAVANI, BEELA RAJESH
recovery current of an anti parallel diode of the other main
with unity power factor, ia > 0 and ic <ib <0 in SECT1-1.
switch on the same bridge. Since there are three legs in the
The phase voltage and phase current in phase A obtains the
main bridge, normally the auxiliary switch must be activated
maximum value; there exist four switching states as shown
three times per PWM cycle if the switch in the three legs is
in Fig. 8: 111, 100, 110, and 000. The equivalent circuits of
modulated asynchronously. To make the auxiliary switch
these four switching states are shown in Fig. 8.
having the same switching frequency as the main switch, a
special SVM scheme is proposed to control the inverter.
Suppose that the grid-connected inverter works with unity
power factor; the grid line voltage and the inverter output
current waveform are shown in Fig. 6.
Fig.6. Grid line voltage and inverter output current
waveform.
The corresponding voltage sector definition is shown in
Fig. 7.
Fig.8. Four switching states in the SECT1-1: (a) state
111, (b) state 100, (c) state 110, and (d) state 000.
If the switching sequence in SECT1-1 is 111- 100-110111, as shown in Fig. 4, then the zero vectors will always be
111 and switch S1 will always be in conduction. When the
switching state changes from 111 to 100, switches S6 and
S2 will be turned ON simultaneously.
Fig.7. Grid voltage and inverter current space vector
diagram.
In voltage SVM, the whole utility cycle can be divided
into six voltage sectors, and every grid voltage sector can
still be divided into two different smaller sectors according
to the maximum value of the phase current in the inverter.
For example, the grid voltage sector SECT1 can be divided
into SECT1-1 and SECT1-2. In SECT1-1, the absolute
value of the phase-A current obtains the maximum value,
and in SECT1-2, the absolute value of the phase-C current
does the same. Since the operation of the converter is
symmetrical in every 30◦, assume that the inverter is
operating in SECT1-1. If the grid-connected inverter works
Fig.9. Switching sequence in SECT1-1: 111-100-110-111.
IV. MATLAB DESIGN AND SIMULATION RESULTS
A ZVS grid connected three phase inverter is modeled
and simulated using the MATLAB. The MATLAB model
of A ZVS three phase inverter is shown in the Fig 7.1. The
three phase source is connected to the auxiliary switch it is
shown in fig 7.2. The fig 7.3 shows that the controlling
method in the simulation of ZVS three phase inverter.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.05, February-2015, Pages: 0869-0875
A ZVS Grid-Connected Three-Phase Inverter Driven Renewable Energy Sources
A. ZVS Three phase inverter
The fig 12 shows that the grid line voltage and inverter
output current of proposed three phase waveforms at voltage
vector lags with 300 phase shift of current vector at
inductance load.
Fig.10. Simulation diagram of ZVS three phase inverter
Fig.13. Inverter output current and grid voltage at
capacitance load.
The fig.13 shows that the grid line voltage and inverter
output current of proposed three phase ZVS waveforms at
voltage vector leads with 300 phase shift of current vector at
capacitance load. In this grid is working at leading power
factor.
The fig.11 shows that the grid line voltage and inverter
output current waveforms at voltage vector are equal to
current vector at resistive load.
B. Simulation of ZVS Three Phase Inverter with PV Cell
The below figure shows that the zero voltage switching
three phase inverter with PV array. In this the input supply
is given as PV array which we taken as dc supply and it is
connected to auxiliary switch. The three legs which are
connected to three phase voltage and current source
measurement and the controlling method is done in the
circuit. Finally we conclude the outputs by grid line voltage
and inverter current outputs by power RMS values at
different power factors.
Fig.12. Output Voltage & Current of Proposed Three
Phase ZVS based Grid Connected Inverter at
inductance load.
Fig.14. Simulation diagram of a ZVS using PV cell.
Fig.11. Output Voltage & Current of Proposed Three
Phase ZVS based Grid Connected Inverter.
International Journal of Scientific Engineering and Technology Research
Volume.04, IssueNo.05, February-2015, Pages: 0869-0875
CHENNAMSETTI PAVANI, BEELA RAJESH
inverter and also applied to PV system, it can realize ZVS
operation for all switching devices, and the reverse recovery
current in the antiparallel diodes of all switching devices is
suppressed well. SVM can be realized at the fixed switching
frequency. And the switching voltage stress across all the
power switch devices is the same as the dc link voltage. The
ZVS can be achieved in the grid connected ZVS inverters
under the load with unity power factor or less. The reduced
switching loss increases its efficiency. Finally Matlab based
model is developed and simulation results are presented.
Fig.15. Output waveforms of the proposed ZVS three
phase inverter.
Fig.16. RMS value.
VII. CONCLUSION
The recent trends in small scale power generation using
the with the increased concerns on environment and cost of
energy, the power industry is experiencing fundamental
changes with more renewable energy sources (RESs) or
micro sources such as photovoltaic cells, small wind
turbines, and micro turbines being integrated into the power
grid in the form of distributed generation . These RES-based
distribution generation systems are normally interfaced to
the grid through power electronics and energy storage
systems. The analysis are presented verified through that the
SVM controlled three-phase soft-switching grid connected
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Volume.04, IssueNo.05, February-2015, Pages: 0869-0875