WWW.IJITECH.ORG
ISSN 2321-8665
Vol.03,Issue.11,
December-2015,
Pages:2130-2135
Application of Photo Voltaic Array in Single Switch Resonant
Power Converter
B. BALA KRISHNA1, M. SHARANYA2
1
PG Scholar, Vignana Bharathi Institute of Technology, India, Email: balu91.krish@gmail.com.
Assoc Prof, Vignana Bharathi Institute of Technology, India, Email: sharanya2702@gmail.com.
2
Abstract: In this paper we introduce a new topology to
convert the variable output DC voltage of a PVA to a fixed
DC output voltage. A resonant converter is used to fulfill the
application for a desired output voltage. The power capacity
of the converter is 35W and input voltage is considered to be
15V and the desired output voltage is 18V. Resistive load is
placed at the output of the converter and observe the load
characteristics. The complete simulation is carried out in
MATLAB Simulink software with all graphical
representations of the parameters of power electronic
elements.
switching losses. This study represents an expansion on an
earlier conference paper [14], and includes additional
experimental results and estimates of loss breakdown.
Keywords: PV, Zero-Voltage Switching (ZVS), DC Voltage.
Fig.1. Proposed resonant converter topology.
I. INTRODUCTION
Voltage-gain dc/dc converters are found in a variety of
applications [1]–[4]. For example, to connect photovoltaic
panels to the grid, interface circuitry is needed. Some
architectures for this purpose incorporate dc/dc converters to
boost voltage of individual photovoltaic panels to a high dclink voltage, with follow-on electronics for converting dc to
ac (e.g., see, [5] and [6]). The step-up dc/dc converter is a
critical part of this system, and must operate efficiently for a
large voltage step up and for a wide voltage range (e.g., at the
converter input and/or output depending upon the system).
Furthermore, to be compact, it must operate at high switching
frequencies. In conventional hard-switched power converters,
the overlap of current and voltage is large during switching,
resulting in significant power loss, especially at high
frequencies. Soft-switched resonant converter topologies
providing zero-voltage switching (ZVS) or zero-current
switching (ZCS) can greatly reduce loss at the switching
transitions, enabling high efficiency at high frequencies (e.g.,
see, [7] and [8]). Unfortunately, while many soft-switched
resonant designs achieve excellent performance for nominal
operating conditions, performance can degrade quickly with
variation in input and output voltages and power levels [9],
[10]. This paper introduces a new high efficiency resonant
dc/dc converter topology, the resistance compression network
(RCN) converter, which seeks to overcome the
aforementioned challenges. This converter operates with
simultaneous ZVS and near-ZCS across a wide range of input
voltage, output voltage, and power levels, resulting in low
The remainder of this paper is organized as follows:
Section II describes the topology and control of the proposed
RCN dc/dc converter. The converter is analyzed and
methodology for its design is presented in Section III. Section
IV describes the design and implementation of a prototype
RCN dc/dc converter. The experimental results from this
prototype are presented and discussed in Section V. Finally,
Section VI summarizes the conclusion of the paper. The
equations used to estimate the losses in the various
components are given in an Appendix. Resonant converters
are extensively utilized in the application of renewable
energy generation systems. The basic requirements of
resonant converters are their small size and high efficiency. A
high switching frequency is required to achieve small size.
However, the switching loss increases with the switching
frequency, reducing the efficiency of the resonant converters.
To solve this problem, some soft-switching approaches must
be used at high switching frequencies. Zero-voltage switching
(ZVS) and zero-current switching (ZCS) techniques are two
commonly used soft-switching methods [14]–[19]. In these
techniques, either voltage or current is zero during the
switching transition, substantially reducing the switching loss
and increasing the reliability of resonant converters in
renewable energy generation systems. Traditional ZCS
converters operate with constant on-time control. They must
operate with a wide range of switching frequencies when the
ranges of the input source and load are wide, making the filter
circuit design difficult to optimize.
Copyright @ 2015 IJIT. All rights reserved.
B. BALA KRISHNA, M. SHARANYA
However, the traditional ZVS scheme eliminates capacitive
Tc= reference cell operating temperature
turn-on losses and decreases the turnoff switching losses by
Vc= cell voltage, V.
reducing the rate of increase in voltage, reducing the overlap
The Boltzmann constant and the reference temperature have
between the switch voltage and the switch current. This work
to be in same units ie., either 0C or 0K. The mathematical
develops a novel single-switch highly efficient converter with
modeling of the above equation can be constructed using
ZVS topology based on the traditional ZVS concept for
simulink blocks is as below.
renewable energy generation applications. Its important
features include a simple circuit structure, ease of control,
soft switching for active power devices, low switching losses,
and high energy conversion efficiency. This novel singleswitch high-efficiency converter with ZVS topology can be
considered to be an extension of the traditional ZVS power
converter. It utilizes a capacitor across the active power
switch in the novel single-switch power converter to generate
a freewheeling stage with a traditional ZVS power converter,
enabling the novel converter to operate with a constant
frequency and a markedly much reduced circulating
energy.This paper proposes a novel single-switch resonant
power converter that has only a single ended structure and is
therefore unlike the traditional ZVS converter, which must
have an isolated circuit to trigger the active power switch
[20]–[22]. The use of a novel single-switch resonant power
converter in the dc/dc energy conversion stage in a renewable
energy generation system provides many advantages, such as
a low number of components, low cost, and high power
density. These characteristics, as well as the fact that the
novel ZVS resonant power converter has only a single active
Fig.2. Simulink model of Vc.
power switch, cause the novel power converter to have a very
simple structure, low switching losses, a small volume, and a
The above design is for a single cell voltage, in order to
low weight. In addition, since the commutations in the active
increase
the voltage of the PVA the cell voltage has to be
power switch of the resonant power converter are performed
multiplied
to a desired values considering each cell voltage as
at zero voltage, the switching losses are very low, resulting in
0.4V.
So,
the
number of series connected cells (Ns) can be
very high efficiency.
calculated as
Ns = Vo/0.4
(2)
II. PVA MODELING
For efficient renewable power generation PVA is used to
generate power from solar irradiation. As the load demand is
increasing day by day the power generation also has to be
increased, but due to the traditional way of power generation
is causing global warming. Due to this the efficiency of the
PVA has to be increased by adding silicon surface on the
panel. And also employ MPPT techniques to track maximum
power during any irradiation and atmospheric conditions. The
design of PVA is done in MATLAB with Simulink block,
with mathematical representation.Voltage of PVA completely
depends on solar irradiation (Sx) and ambient temperature
(Tx). PVA (Photo voltaic array) is a combination of series
and parallel solar cells arranged in an array to generated the
required voltage and current. Each series combination of cells
can be considered as photo voltaic module. Increase in series
cells increases the voltage and increase in parallel cells
increases the current capacity. Formulation for voltage of
each cell is given below
To get each cell current, the total current output from the
dependable source has to be divided by number of parallel
connected cells (Np). Therefore, parallel connected cells are
considered as
Np = Io/Icell
The representation in simulink is taken as
(1)
Where, k = Boltzmann constant (1.38 × 10-23 J/oK).
Ic = cell output current, Amp.
Iph = photocurrent
I0 = reverse saturation current of diode
Rs= series resistance of cell
Fig.3. Simulink modeling of Ns & Np.
International Journal of Innovative Technologies
Volume.03, Issue No.11, December-2015, Pages: 2130-2135
(3)
Application of Photo Voltaic Array in Single Switch Resonant Power Converter
For the calculation of Vcx (cell voltage) and Iphx
(Photocurrent) we need correction factors CTV CTI CSV CSI.
The formulation is given as
(4)
The correction factors are given as
Fig. 5. Combined diagram of CV CI & Vc mathematical
models
Where, βT = 0.004 and T = 0.06
Ta = reference temperature
Tx = ambient temperature
Sc = reference solar irradiation
Sx = ambient solar irradiation
The values of Tx and Sx changes depending upon the Sun
rays which change continuously and unpredictably. The
effect of change in solar irradiation varies the cell
photocurrent and also the cell voltage (Vc). Let us consider
the initial solar irradiation is Isx1 & the increase of the
irradiation is Isx2 which in turn increases the temperature from
Tx1 to Tx2, photocurrent from Iphx1 to Iphx2. The mathematical
modeling of the correction factors in simulink is given below
The total system diagram of the PVA with all the
mathematical formulation are put into a subsystem to make it
clear and understandable. The output of the Vc multiplied
with the Ns constant block defining the total voltage of the
combined cells of the PVA is fed to the voltage controlled
voltage source block so as to generate the required voltage. A
diode is connected in series at the positive terminal of the
PVA to avoid reverse currents passing into the PVA. To
reduce the ripples a capacitor can be added later after the
diode in parallel as the capacitor doesn’t allow sudden change
of voltages dV/dt. The complete PVA module with internal
block construction is shown in the fig. below
Fig.6. Complete diagram of PVA.
Fig.4. CI & CV modeling.
Depending upon the solar irradiation and temperature the
values of CV & CI are calculated which is fed to Vc block to
get the cell voltage value as shown below
III. OPERATING MODES OF CONVERTER
Mode I—Between ωt0 and ωt1: Prior to Mode I, the active
power switch S is off. The resonant tank current iLs is
positive and exceeds the dc input current iLm. The power
switch must be turned on only at zero voltage. Otherwise, the
energy stored in the capacitor C will be dissipated in the
active power switch S. To prevent this situation, the
antiparallel diode DE must conduct before the power switch
is turned on. Since the capacitor current iC is negative, it
flows through capacitor C. When the capacitor voltage vC
falls to zero, a turn-on signal is applied to the gate of the
active power switch S. Therefore, the active power switch S
turns on under ZCS and ZVS conditions[23]. At the
beginning of this mode, the antiparallel diode DE conducts
because the difference between currents iLm − iLs is
negative. In this mode, the energy-blocking diode D is turned
on because the resonant tank current iLs is positive. Fig. 3
presents the equivalent circuit of this mode. The initial
condition of the inductor current iLs is I+Ls0. Then, the
International Journal of Innovative Technologies
Volume.03, Issue No.11, December-2015, Pages: 2130-2135
B. BALA KRISHNA, M. SHARANYA
instantaneous inductor current and the voltage across
capacitor C can be evaluated using
Fig.7. Mode I circuit operation.
Fig.9. Mode III circuit operation.
This mode ends as soon as the antiparallel diode DE is
reverse biased by a positive current iLm − iLs.
This mode is exited at the time when the power switch S is
turned off.
Mode II—Between ωt1 and ωt2: In this period, the switch S
remains in the ON state. Fig. 4 shows the equivalent
circuit.The line voltage is applied to the choke inductor Lm,
andiLm increases continuously. In this mode, the current iL −
iLs naturally commutates from the antiparallel diode DE to
the active power switch S. Accordingly, the voltage across
the capacitor C is clamped at zero. The resonant current iLs
passes through the energy-blocking diode D. During this
interval, the inductor current iLs is expressed as follows,
where I+Ls1 is the initial current in the inductor iLs:
Mode IV—Between ωt3 and ωt4: At the beginning of Mode
IV, the active power switch S is switched off. The capacitor
current iC becomes iLm. Then, the capacitor voltage vc rises
from zero to a finite positive value. For ZVS operation,S is
switched off at zero voltage, and the capacitor voltage vc
increases linearly from zero at a rate that is proportional to
iLm.The capacitor current ic flows through capacitor C to
charge C, transferring the energy from the dc input source to
capacitor C. During this mode, the output power of load
resistor R is supplied by the output capacitor Co. Fig. 2
reveals that the active power switch S is turned off under the
ZVS condition. Fig. 6 presents the equivalent circuit.
The following equation gives the inductor current iLs(t) of
the single-switch power converter circuit:
iLs(t)=0.
Fig.8. Mode II circuit operation.
The circuit operation enters Mode III when the inductor
current iLs falls to zero.
Mode III—Between ωt2 and ωt3: In Mode III, the active
power switch S remains in the ON state, and the input dc
current iLm continuously increases. The choke inductor
current iLm flows through the active power switch S. The
inductor currentiLs falls until it reaches zero and is prevented
from going negative by the energy-blocking diode D.
Notably, the dc input source is never connected directly to the
output load in the novel single-switch converter. Energy is
stored in the choke inductor Lm when the active power
switch is turned on and is transferred to the output load when
the active power switch is turned off.Fig. 5 displays the
equivalent circuit of this mode. Accordingly, the inductor
current iLs(t) and the capacitor voltage vc(t) of the converter
circuit are as given in iLs(t)=0.
Fig.10. Mode IV circuit operation.
Mode V—Between ωt4 and ωt5: In Mode V, the active
power switch S remains in the OFF state. The inductor
current iLs is positive, and the energy-blocking diode D is
turned on, yielding a resonant stage between inductor Ls and
capacitor C. In this interval, the capacitor current iC is still
positive. Hence, the capacitor voltage vc continues to
increase to its peak value. Applying Kirchhoff’s law to Fig. 7
yields the inductor current iLs(t) that is shown in
iLs(t)= ILm [1 − cos ωo(t − t4)]
International Journal of Innovative Technologies
Volume.03, Issue No.11, December-2015, Pages: 2130-2135
Application of Photo Voltaic Array in Single Switch Resonant Power Converter
IV. SIMULINK RESULTS AND OUTPUTS
Fig.11. Mode V circuit operation.
+V +C5 cos ωo(t − t4)+ IoR [1 − cos ωo(t − t4)] .
Mode V ends when capacitor current iC resonates to zero at
ωt5, and operating Mode VI then begins.
Mode VI—Between ωt5 and 2π: This cycle begins at ωt5
when capacitor voltage vc resonates from negative values to
zero [24]. The active power switch S is turned on when ωt =
2π to eliminate switching losses. Fig. 8 illustrates the
equivalent circuit. In this interval, the inductor current iLs is
expressed as follows:
Fig.13. Simulink model of proposed topology.
iLs(t)= ILm [1 − cos ωo(t − t5)]
The following equation yields the capacitor voltage vc(t) of
the resonant capacitor:
vc(t)= ZoILm sin ωo(t − t5)+ V +C6 cos ωo(t − t5)
+ IoR [1 − cos ωo(t − t5)] + I+C6 · Zo sin ωo(t − t5).(16)
Before the cycle of the resonant inductor current iLs
oscillation ends, the active power switch S is kept off
condition, constraining the positive current to flow
continuously through the energy-blocking diode D. In
addition to the active power switch, the energy-blocking
diode in the novel converter is also commutated under soft
switching. This feature makes the novel single-switch
resonant power converter topology particularly attractive for
high-efficiency energy conversion applications.When the
driving signal Vgs again excites the active power switch S,
this mode ends, and the operation returns to Mode I in the
following cycle.
Fig.12. Mode VI circuit operation.
Fig.14. Output Voltage of the converter.
Fig.15. Output power of the converter.
International Journal of Innovative Technologies
Volume.03, Issue No.11, December-2015, Pages: 2130-2135
B. BALA KRISHNA, M. SHARANYA
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V. CONCLUSION
With the above circuit analysis and description of the
operating modes the output voltage of 18V has been achieved
with a power output of 34W with a R load of 10ohms. The
input voltage of 15V has been successfully converted to 18V
from the PVA and dynamic characteristics of the converter
can be seen in the last section with all output waveforms.
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International Journal of Innovative Technologies
Volume.03, Issue No.11, December-2015, Pages: 2130-2135