A SINGLE SWITCH HIGH FREQUENCY RESONANT CONVERTER FOR PV POWER APPLICATIONS
M.Abel1, Dr.D.Kirubakaran2
1- Asst.professor,Dept of EEE, Vi Institute of Technolog,Chennai.
2- Professor& Head, Dept of EEE, St.Joseph’s Institute of Technology,Chennai.
mabel6074@gmail.com1
kirubad@gmail.com2
Abstract
The single switch boost converter can use the zerovoltage switching (ZVS) and/or zero current switching
(ZCS) to reduce the switching losses for highfrequency
switching [4]. However, they are considered for the single
topology.
A novel single switch resonant boost converterwith
zero-voltage switching (ZVS) and zero-current switching (ZCS)
characteristics are proposed in this paper. Single resonant
switch approach decreases the current stress of the main
switching device but also reduces the ripple of the input current
and output voltage. Moreover, by establishing the common softswitching, the singleresonant converter can greatly reduce the
size and cost. The conventional hard switching PWM converter
produces stress on the devices and Electromagnetic interference
noise. The main switchof the proposed converter can achieve
the characteristics of ZVS and ZCS simultaneously to reduce
the switching loss and improve the efficiencywith a wide range
of load. This topology works at less than 50% of the duty
cycle.The operatingprinciple and design method of the
proposed converter are presented. Finally,the simulations
results are analyzedusing Matlab/ Simulink
software
package.The feasibility, output waveforms, efficiency and
exactness of the proposed converter are validated.
Many soft-switching techniques are then introduced
to the boost converters. The boost converters with ZCS or
ZVS are proposed in [5]– [8], [12]. These topologies have
higher efficiency than the conventional boost converters
because the proposed circuits have decreased the switching
losses of the main switches with ZCS or ZVS. Nevertheless,
these circuits can just achieve the junction of ZVS or ZCS
singly or need more auxiliary circuits to reach the soft
switching. In [9],soft-switching circuit for the boost
converter is proposed. However, its main switches are zerocurrent turn-ON and zero-voltage turn-OFF and the
converter works in the discontinuous mode. The maximum
dutycycle of the converter is also limited. Therefore, PWM
power converters can now operate at a much higher
switching frequency, reducing the size of passive
components, reducing the overall cost of the system.
However, the converter switching loss also increases
proportionally to the frequency. The increase in dv/dtand
di/dtcaused by the increased speed, increased stress on the
device and system electromagnetic interference (EMI)
noise.These effects set an upper limit on the frequencies at
which conventional hard-switching PWM converters can
operate.
In the last few decades, various researches have been
performed to improve the switch transition to overcome this
inherent problem of hard-switching PWM converters. By
solving these high voltage and current stress problems,
energy conversions using resonant converters are important
in ensuring both high performance and supporting energy
conservation applications in renewable energy generation
systems.This work proposes a novel single-switch resonant
power converter that has only a single ended structure and is
therefore unlike the traditional ZVS converter, which
musthave an isolated circuit to trigger the active power
switch [13]. The use of a novel single-switch resonant power
converter in the DC/DC energy conversion stage for a
renewable
energy
generation
system
provides
manyadvantages, such as a low number of components, low
cost and high power density. These characteristics, as well as
Keywords: Zero voltage switching (ZVS), Zero-current
switching (ZCS), photovoltaic.
I. INTRODUCTION
The use of power convertersis importantin solar power
generation to have constant power to BESS (Battery Energy
Storage system). Solar power is considered as a main
replacement for energy generation in many countries.Serious
greenhouseeffects, environment pollution and limited fossil
fuels, have forced most engineers to do research on
renewable energy sources [1]. The typical renewable energy
sources include solar power, wind turbine and fuel cells have
the features of cleanliness, abundance and freedom from
maintenance [2]. Currently, solar and wind are most widely
utilized renewable energies. Photovoltaic (PV) arrays and
wind turbine technologies have been undergoing a dramatic
development and now are the world’s fastest growing
energies. Therefore, to develop PV sources as substitute for
fossil fuels has been important [3]. An effective approach is
to adapt a dual-input power supply system by PV renewable
energy sources with a DC/DC converter, which can simplify
power supply and reduce cost. In order to reduce switching
and conducting losses of active switches and improve
efficiency,a DC/DC converter with ZVS,ZCS and
synchronous rectification techniques are usually required.
1
the fact that the novel ZVS resonant power converter has
only asingle active power switch, cause the novel power
converter to have a very simple structure, low switching
losses, a small volume and a low weight.Additionally, since
the commutations in the active power switch of the resonant
power converter are performed at zero voltage, the
switchinglosses are very low, resulting in very high
efficiency.
This work develops a novel current-fed resonant
converter with ZVS and ZCS operations of both the active
power switch and the energy blocking diode for energy
conversion. Figure 2 shows a basic circuit diagram of the
proposed novel single-switch resonant converter for
renewable energygeneration applications. It comprises a
source side inductor Lm, a Metal Oxide Semiconductor Field
Effect Transistor (MOSFET) that operates as a power switch
S, a shunt capacitorCr, a resonant Ls, an energy-blocking
diode D and a filter capacitor Co. The capacitor Coand the
load resistance R together forms a first-order low-pass output
filter, which reduces the ripple voltage below a specified
level. The MOSFET is favored device because its body
diode can be used as an anti-parallel diode DEfor
bidirectional power switch.
II. PV MODEL
PV array consists of solar cells, where each cell is
basically a p-n junction. The equivalent circuit of a solar cell
is shown in Fig. 1.
PV array modeling can be implemented from the
mathematical model in (1), which is derived from a cell’s
equivalent circuit where all cells are identical
Io = Np ∗ Iph − Np ∗ Irs ∗ (exp (q⁄(kTA)
Vo
Ns
) − 1)(1)
WhereV0 and I0 represent the PV array output voltage
andcurrent respectively. Rsand Rshare the solar cell series
andshunt resistances. q is the electron charge (1.6 × 10−19
C); Ais dimensionless junction material factor, kis
Boltzmann constant ,T the temperature (in Kelvin),
NpandNsare the number of cells connected in parallel
andseries respectively.
Fig.2proposed novel single-switch resonant power converter
Fig.3 plots the key current and voltage waveforms that
explain the operation of the converter. The steady-state
operations of the novel single-switch resonant power
converter can be divided into six modes in accordancewith
the conducting active power switch in one high frequency
cycle.
Mode I: (betweenωt0 and ωt1)
Fig.4 shows the equivalent circuit of mode I.The active
power switch S is remains OFF, before ωt0 and the resonant
tank current ILs is positive and greater than DC input current
iLm.So the inductor current Ls makes the energy blocking D
forward bias. The switch has to be turned ON only at zero
voltage. If this condition is not satisfied the energy stored in
the capacitor C will be dissipated in the active power switch
S. The diodeDEis connected in antiparallel to switch S which
is made to conduct in this mode and its conduction is due to
difference between currents iLm –iLs which is negative to
prevent the dissipation of energy. The negative current is
made to flow through the antiparallel diode D. The turn on
signal is applied to the gate of the active power switch S
when the capacitor voltage decreases to Zero. Thus active
power switch turns on under ZCS and ZVS condition. Since
iLs is positive the energy blocking diode D is forward biased
and turns on. The antiparallel diode DE is reversed biased by
a positive current iLm-iLsat the end of this mode ends.
Fig. 1 Equivalent circuit of a PV cell
Therefore, either direct or indirect coupling can be used to
operate the PV array at its optimum power point. In direct
coupling,the PV array is directly connected to the load and
periodic finetuning is required [10]. In the other method,
indirect coupling,automatically tracking of the optimum
operating point is facilitated by connecting a power
converter between the PV array generator and the load.
III. ANALYSIS OF THE PROPOSED CONVERTER
Fig.2 shows the proposed circuit. It applies the common softswitching technique. Fig. 2 is explained with six operating
modes,depending on the duty cycle of the main switch.One
topology is less than 50% duty cycle and another one more
than 50% duty cycle. Here less than 50% duty cycle
topology operating principle is described in this section.
2
Fig. 4 Equivalent circuit for Mode I
Mode II: (between ωt1 and ωt2)
Fig.5 shows the equivalent circuit of mode II.The switch S
turned ON in this mode. In the choke inductor LM,the current
iLm increases continuously with the applied line voltage. A
natural commutation occurs by the antiparallel diode DE to
the active power switch S due to current iL-ILs. As a result
the capacitor voltage VC is clamped at zero. Hence the
switch is turned on at zero voltage. The resonant current iLs
passes through the energy blocking diode D and it is
conducting.When the inductor current ILsdecreases to zero
and diode D is reverse biased, mode III begins.
Fig. 3 Steady-state operating waveforms
Fig. 5 Equivalent circuit for Mode II
Mode III: (between ωt2and ωt3)
Fig.6 shows the equivalent circuit of mode I.The
active power switch S remains in ON state and choke
inductor current ILmincreases continuously and flows through
the switch S.The inductor current ILsdecreases till it reaches
zero and going into negative state is prevented by energy
blocking diode D and it is reverse biased.The diode D is still
reverse biased since ILs is negative. An important fact is that
the DC source is never connected directly to the load in this
novel single switch converter. The energy stored in choke
inductor Lm during the turn on process of active power
switch is transferred to the output load when it is turned off.
At the time when the power switch is turned off this mode
becomes end.
Fig.6 Equivalent circuit for Mode III
Mode IV: (between ωt3and ωt4)
Fig.7 shows the equivalent circuit of mode I.At the instant of
ωt3active power switch S is turned OFF. Capacitor current ic
becomes iLm and capacitor voltage vc which is proportional
to iLm rises linearly from zero to finite positive value. This is
required for ZVS operation. Capacitor C is charged by ic and
the energy is transferred from the dc input source to
capacitor. In this mode output capacitor Co supplies power to
load resistor R.When the energy blocking diode D becomes
forward biased (Vc> Vo) and this mode ends.
3
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 are 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. Typical converter switching frequency
was limited to a few tens of kilo-Hertz (typically 20 kHz
to50 kHz). The stray inductive and capacitive components
inthe power circuits and power devices still cause
considerable transient effects, which in turn give rise to
electromagnetic interference (EMI) problems. The transient
ringing effects are major causes of EMI.
Fig. 7 Equivalent circuit for Mode IV
Mode V: (betweenωt4 and ωt5)
Fig.8 shows the equivalent circuit of mode I.In this mode the
active power switch S remains in OFF state. The energy
blocking diode D is turned ON and at the same time inductor
current iLsis positive, which results in a resonant stage
between inductance Ls and capacitor C.During this interval
capacitor voltage Vc continuously increases up to its peak
value and capacitor current Ic is maintained positive. At ωt5
capacitor current icresonates to zero and this mode ends.
In resonant converters using resonant tank to create
oscillatory 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 100 kHz to 500 kHz). Consequently, magnetic
sizes can be reduced, the power density of theconverters
increased the resonant current and voltage resonant
converters have high peak values leading tohigher
conduction loss and higher V and I ratingsrequirements for
the power devices. Also, many resonantconverters require
frequency modulation (FM) for outputregulation. Variable
switching frequency operation makesthe filter design and
control more complicated. The operating characteristics of
this novel single-switch resonant power converter, it is
generally assumed that when the low-pass filter or load
circuit is a voltage sink type, the output capacitance in
parallel with the load resistor is assumed to be very large so
its voltage is approximately constant. Therefore, the output
circuit viewed from the output terminals of the rectifier can
be replaced by a constant voltage sink. As a result, the link
voltage has constant positive and negative amplitudes,
depending on whether theinductor current enters or leaves
the energy-block diode, respectively.
In idealized steady-state voltage and current waveforms of
the proposed novel single-switch resonant power converter
for a switching frequency fs and a resonant frequency fo.
Notably, operating below resonance is preferred because the
active power switch turns on at zero current and zero
voltage; thus, the freewheeling diode does not need to have
very fast reverse-recovery characteristics.
Fig. 8 Equivalent circuit for Mode V
Mode VI: (between ωt5andωt5)
Fig.9 shows the equivalent circuit of mode I.This cycle
begins at ωt5 when capacitor voltage Vcresonates from
negative values to zero. The inductor LS and energy blocking
diode DE is still conducting. So the output power continues
to flow through C and R. The active power switch S is turned
ONto eliminate switching losses and mode I begins.
Fig. 9 Equivalent circuit for Mode VI
IV.OPERATING CHARACTERISTICS
To realize ZVS operation of the active power switch, the
turn-on signal of the active power switch S should be applied
while its body diode is conducting. In discontinuous interval
operating cycle of theswitching frequencyexceeds one
complete cycle of the resonant frequency, and so in this
mode of operationfs<fo. During the in which the source
inductor current is positive, the power is fed to the load
through the energy-blocking diode D. When the energy-
The single switch resonant boost converter specially
designed to ensure ZCS and ZVS operation under wide load
range. In the conventional switched mode operation of PWM
power converters, power switches have to cut off the load
current within the turn-on and turn-off times under the hard
switching conditions. During the turn-on and turn-off
processes, the power device has to withstand high voltage
and current simultaneously, resulting in high switching
4
blocking diode D is turned on, theresonant circuitresonate at
under-damped frequency.
Figure 12 displays the voltage and currentwaveforms of the
source side choke inductance Lm at the input terminal. This
inductance value set large value to maintain constant current
for continuous operation.
V.DESIGN AND SIMULATION RESULTS
The renewable energy generation system as primary
source to the proposed single-switch resonant power
converter. The solar panel output designed as a small scale
range.Here proposed single-switch resonant power
converterwas connected to solar energy generation system
that consisted of a DC source with an output voltage of15V.
The conduction losses of the novel single-switch resonant
power converter are proportional to the forward voltage of
the energy-blocking diode. . To realize ZVS operation of the
active power switch and ZCS operation of the energyblocking diode of this novel converter, the switching
frequency must be less value of resonant frequency.The
developed novel single switch resonant power converter is
applied to a 12 ohm load resistor.
Fig. 12Voltage and current waveforms of
inductor
source side
Fig.13 shows the voltagewaveform VC and the current
waveform IC of the resonantcapacitor, respectively. Fig.14
plots the voltage waveformsof the resonant inductor VLsand
the current waveform of theresonant inductor ILs.
The following
simulation results were analyzed under
specificdesign parameter of resonant boost converter at
constant pulse width modulation scheme. Fig.10, shows the
waveforms of the active power switch current and voltage
across the switch .The figure11shows the waveforms of the
active power switch S, where VGSrepresents the trigger signal
on active power switch S, and VDSrepresents the voltage
across the active power switch S.
Fig.13 Voltage and current waveforms of resonant capacitor
Fig.10 current and voltage waveforms of MOSFET
Fig. 14Voltage and current waveforms of inductor Ls
Fig.11 Gate signal and voltage waveforms of MOSFET
5
Fig.15 plots the voltage waveforms of the antiparallel
diodevoltage and current respectively. Fig. 16 shows the
input voltage and input current waveforms of energy
blocking diode.
switchreduced. The efficiency of 97.8% with output power
of 32W andinput voltage of 15V are obtained.
REFERENCES
[1].F. Katiraei,R.Iravani, N. Hatziargyriou, and A.Dimeas,
“Power andenergy magazine,” IEEE, vol. 6, no.3, pp. 54–65,
May/Jun. 2008.
[2].A.Seon-Ju,P.Jin-Woo, C. Il-Yop, M. Seung-li, K. SangHee, and N.Soon- Ryul, “Power-sharing method of multiple
distributed generators considering control modes and
configurations of a microgrid,” Power Del., IEEE Trans.,
vol. 25, no. 3, pp. 2007–2016, Jul. 2010.
[3].Y.Zhilei, X. Lan, and Y. Yangguang, “Seamless transfer
of single-phase grid-interactive inverters between gridconnected and stand-alone modes,Power Electron., IEEE
Trans., vol. 25, no. 6, pp. 1597–1603, Jun. 2010.
[4]. A. M. Rahimi, and A. Emadi, “DiscontinuousConduction Mode DC/DCConverters Feeding ConstantPower Loads,” IEEE Transactions onIndustrial Electronics,
Vol. 57, No. 4, pp. 1318-1329, April 2010.
[5]. F. Liu, J. Yan, and X. Rua, “Zero-Voltage and ZeroCurrent-SwitchingPWM Combined Three-Level DC/DC
Converter,” IEEE Transactionson Industrial Electronics,
Vol. 57, No. 5, pp. 1644-1654, May 2010.
[6]. W. Li, J. Xiao, Y.i Zhao, and X. He, “PWM Plus Phase
Angle Shift(PPAS) Control Scheme for Combined Multiport
DC/DC Converters,”IEEE Transactions on Power
Electronics, Vol. 27, No. 3, pp. 1479-1489,March 2012.
[7]. C. M. Wang, “A Novel ZCS-PWM Flyback Converter
with a SimpleZCS-PWM Commutation Cell,” IEEE
Transactions on IndustrialElectronics, Vol. 55, No. 2, pp.
749-757, February 2008.
[8]. Y. M. Chen, Y. C. Liu, and S. H. Lin, “Double-Input
PWM DC/DCConverter for High-/Low-Voltage Sources,”
IEEE Transactions onIndustry Electronics, Vol. 53, No. 5,
pp. 1538-1545, October 2006.
[9] .C. Liu, A. Johnson, and J. S. Lai, “DC/DC Converter for
Low-VoltageFuel Cell Applications,” IEEE Transactions on
Industry Applications,Vol. 41, No. 6, pp. 1691-1697,
November/Decrmber 2005.
[10].W.Rong-Jongand
W.Wen-Hung,
“Grid-connected
photovoltaic generation system,” Circuits Syst. I: Regul.
Papers, IEEE Trans., vol. 55, no. 3,pp. 953–964, Apr. 2008.
[11]. R. M. Cuzner, D. J. Nowak, A. Bendre, G. Oriti, and A.
L. Julian,“Mitigating Circulating Common-Mode Currents
Between Parallel Soft-Switched Drive Systems,” IEEE
Transactions on Industry Applications,Vol. 43, No. 5, pp.
1284-1294, September/October 2007.
[12]. M. L. da S. Martins, J. L. Russi, and H. L. Hey,“Novel
DesignMethodology and Comparative Analysis for ZVT
PWM ConvertersWith Resonant Auxiliary Circuit,” IEEE
Transactions on IndustryApplications, Vol. 42, No. 3, pp.
779-796, May/June 2006.
Fig.15 Voltge and Current waveforms of antiparallel diode
Fig. 16 Input voltage and input current waveforms of
energyblockingdiode
Simulation was performed under the following conditions.
Constant switching frequency fs=72kHz, resonant frequency
fo=95kHz, duty cycle k=0.337, output voltage Vo= 17.5V,
and output power Po= 30.4W. To reduce input current ripple
andmaintain stability of the output voltage, the low-pass
filters at the input and output terminals, which use a choke
inductor and an electrolytic capacitor, are set to Lm= 10µH
and Co= 200µFrespectively. The low-pass filter is designed
to be small, light, and low-cost. Under the aforementioned
operating conditions,the two parameters of the novel singleswitch resonant powerconverter are calculated as follows.
C=0.16µFLs=17µH .The simulation results were measured
atinput voltage Vin=15 V and input current Iin=2.12 A.
VI. CONCLUSION
A novel boost converter designed with both zero
voltageSwitching and zero-current-switching functions. The
simulation results thusobtained using MATLAB/Simulink is
proposed in this paper. Theduty cycle of this topology can be
more or less than 50%. The resonant inductor Lr, resonant
capacitor Cr
to become resonateat under resonance
frequency way to reach ZVS and ZCS of the main switches
.Here
voltage stress and current stress
across the
6