WWW.IJITECH.ORG
ISSN 2321-8665
Vol.03,Issue.11,
December-2015,
Pages:2056-2060
Grid Interconnection of High Efficiency Resonant DC/DC Converter in
Photo Voltaic Applications
SRAVANI. K1, D. DEVADARSHANAM2
1
2
PG Scholar, TKR College of Engineering and Technology, Hyderabad, India, E-mail: sravani0247@gmail.com.
Assistant Professor, TKR College of Engineering and Technology, Hyderabad, India, E-mail: devadarshanam9@gmail.com.
Abstract: With the increase in power demand the electrical
power is generated through several renewable sources. These
renewable sources such as PVA (Photo Voltaic Array) which
are utilized have very less operating voltage by which they
cannot be connected to the grid with a higher voltage. This
paper proposes a high efficiency resonant DC-DC converter
with a high switching frequency reducing the losses in the
converter and increasing the efficiency around 95%. The gain
that is generated is about 10 times the input voltage and
operating range is about 200V-400V. And the operating
output power range is between 20-200W. This topology
utilizes a Resistive compensation network (RCN) by which
the efficiency is very high. The complete design and analysis
is carried out in MATLAB Simulink with all the graphical
representations of the elements in the topology.
Keywords: Resistance Compression Network (RCN),
Proportional and Integral (PI), Radio-Frequency (RF),
Module-Integrated Converter (MIC).
I. INTRODUCTION
The photovoltaic (PV) module-integrated converter
(MIC) system is the key technology for the future distributed
production of electricity using solar energy. The PV MIC
system offers “plug and play” concept, greatly optimizing the
energy yield from the PV module. Each PV module has its
own power conversion system, generating the maximum
power from the PV module. To make the PV MIC system
commercially viable, a low-cost and high-efficiency power
conversion scheme should be developed. The PV module
voltage has a low-voltage characteristic. In order to deliver
electric power into the grid, the low PV module voltage
should be converted into a high dc voltage. Thus, a dc–dc
converter with a high-voltage gain is needed. The activebridge dc–dc converter has been used for low-voltage PV
sources. The power switches at low-voltage side are turned
ON at zero voltage. However, the output diode at highvoltage side has high switching power losses due to its
reverse-recovery current. The half-bridge dc–dc converter has
been presented to reduce switching power losses at highvoltage side. The output diodes are turned OFF at zero
current by using the voltage doubler rectifier. However, an
additional half-wave rectifier is needed, which increases
switching power losses. Alternatively, the active-clamped dc–
dc converter has been used for low-voltage PV sources. It
uses the active-clamping circuit and the resonant voltage
doubler rectifier. However, the active-clamping circuit
increases the voltage stress of power switches at low-voltage
side, causing high switching power losses. Additionally,
thermal management problems should be considered for a
practical design of the PV MIC system.
Considering the dynamic response of the converter,
bandwidth limitations of conventional controllers have forced
power electronics engineers to increase switching frequency
or increase output capacitor. Such hardware modification
results in lower efficiency and higher component cost.
However, by improving the controller’s dynamic response,
the transient performance of the converter can be improved.
Therefore, it is not only necessary but also practical to
improve both power efficiency and dynamic response of the
dc–dc converter for low-voltage PV sources.This paper
proposes a high-efficiency dc–dc converter with fast dynamic
response for low-voltage PV sources. An improved activeclamped dc–dc converter is presented by using a dual activeclamping circuit. The voltage stress of power switches can be
reduced at low-voltage side. Also, a modified proportional
and integral (PI) controller is suggested for fast output
voltage control. The transient performance of the proposed
converter is improved. All control functions are implemented
in software with a single-chip microcontroller. The proposed
converter is realized with minimal hardware with a low cost.
The operation of the proposed converter is described. The
control strategy is presented, including the fast output voltage
control and its digital implementation. The performance of
the proposed converter is verified using a 200-W
experimental prototype. The experimental results confirm that
a high efficiency of 97.9% is achieved at 60-V input voltage
for 200-W output power with an improved dynamic
performance.
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
Copyright @ 2015 IJIT. All rights reserved.
SRAVANI. K, D. DEVADARSHANAM
switching losses. This study represents an expansion on an
earlier conference paper, and includes additional
experimental results and estimates of loss breakdown. 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.
II. PVA MODEL
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
(4)
(5)
Fig. 1. Simulink model of Vc.
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
Tc= reference cell operating temperature
Vc= cell voltage, V.
The Boltzmann constant and the reference temperature
have to be in same units ie., either 0C or 0K. The
mathematical modeling of the above equation can be
constructed using simulink blocks is as below.
The above
design is for a single cell voltage, in order to increase the
voltage of the PVA the cell voltage has to be multiplied to a
desired values considering each cell voltage as 0.4V. So, the
number of series connected cells (Ns) can be calculated as
(2)
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
Fig. 2. Simulink model of Ns & Np.
The correction factors are given as
(6)
(7)
(8)
Where, βT = 0.004 and T = 0.06
Ta = reference temperature
Tx = ambient temperature
Sc = reference solar irradiation
Sx = ambient solar irradiation
(9)
(3)
The values of Tx and Sx changes depending upon the Sun
For the calculation of Vcx (cell voltage) and Iphx
rays which change continuously and unpredictably. The
(Photocurrent) we need correction factors CTV CTI CSV CSI.
effect of change in solar irradiation varies the cell
The formulation is given as
International Journal of Innovative Technologies
Volume.03, Issue No.11, December-2015, Pages: 2056-2060
Grid Interconnection of High Efficiency Resonant DC/DC Converter in Photo Voltaic Applications
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
Fig.3.
Fig. 5. Complete diagram of PVA.
Fig. 3. CI & CV model.
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 Fig.4.
Fig. 4. Combined diagram of CV CI &Vc mathematical
models.
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.5 below.
III. RCN CONVERTER TOPOLOGY AND CONTROL
The dc/dc converter proposed here consists of an inversion
stage, a transformation stage, and a rectification stage, as
shown in Fig. 1. The inversion and rectification stages use
standard designs. However, the transformation stage and the
control of the converter are new. The topology of the
proposed RCN converter is shown in Fig. 2. The converter as
shown is designed to step-up voltage. The transformation
stage consists of a matching network, a transformer, and an
RCN. The matching network composed of Lrp and Crp acts as
a filter and provides a voltage gain, hence reducing the
transformer turns ratio requirement. One issue with highturns-ratio step-up transformers that exists in many topologies
is that the parasitic leakage inductance of the transformer can
undesirably ring with its secondary side winding capacitance
at the switching transitions. This creates large ringing in the
current and voltage waveforms, and high-frequency losses.
The matching network also eliminates this ringing by
absorbing the transformer parasitics. The 1:N transformer
provides additional voltage gain and isolation. The RCN
(composed of Ls and Cs) is a special single input, multioutput
matching network that provides desirable impedance control
characteristics. The RCN technique was originally proposed
and applied for radio-frequency (RF) applications, such as
very-high-frequency dc/dc converter systems and RF power
amplifiers; here, we exploit if for high efficiency power
conversion.
The function of the RCN is to automatically regulate the
converter operating power and waveforms in a desirable
manner as the input and output voltages vary. As applied
here, the RCN also includes a series resonant tank (composed
of Lr and Cr). Its purpose is to provide additional filtering.
The inverter stage is simply a full-bridge inverter (composed
of switches S1 − S4). A full bridge is used instead of a half
bridge to reduce the voltage gain requirement from the
matching network and the transformer. The rectification stage
is composed of two half-bridge rectifiers. A prototype of the
RCN dc/dc converter of Fig.6 has been designed and built.
The designed dc/dc converter is meant for large-step-up
applications such as the two-stage photovoltaic-to-grid
conversion system shown in Fig.2. The RCN dc/dc converter
can be used to convert the low (widely varying) output
voltage of a photovoltaic panel into a high dc-link voltage, for
International Journal of Innovative Technologies
Volume.03, Issue No.11, December-2015, Pages: 2056-2060
SRAVANI. K, D. DEVADARSHANAM
example. The design specifications for this prototype are
IV. SIMULINK MODEL AND RESULTS
given in Table I. The converter is required to operate over an
Simulation results of this paper is shown in bellow Figs.7 to
input voltage range of 25–40V, an output voltage range of
9.
250–400V and over a wide output power range of 20–200W.
The value of Xs was calculated using (3) with the output
power set to a value of 200 W and input voltage set to its
minimum value of 25 V and output voltage set to 400 V. This
ensures output power of 200 W across the entire input voltage
range. To ensure output power of 200 W across the entire
output voltage range the maximum value of Xs needs to be
selected with an input voltage set at 25 V, output power at
200 W and varying the output voltage from 250 to 400 V.
[A]
Discrete,
Ts = 1e-06 s.
k
m
Goto
D1
Goto1
CM
Ro
Cin
+
1+
+2
Lrp
Crp
m
k
Vin
+
Cdc
+
+
+
Co
+
D2
a
m
Scope1
i +
-
Ls
S
S
m
S2
+
Cdc1
P2
m
k
g
+
D
g
D
S1
+
R
[B]
From1
a
[B]
P1
[A]
From
D3
2
a
1
T1
g
+
Lr
Crs
a
m
D4
S
S
S4
m
S3
+
m
k
From3
D
From2
g
[A]
D
[B]
12
Wind system wm
wind speed
A
b
B
c
C
+
+
a
C
-
+
- v
VM1
Scope2
AC-DC
m
+
+
-
-
+
-
PVA
+`
-`
DC-DC2
Fuel Cell Stack
+
+`
-
-`
DC-DC1
Fig. 7. Proposed DC-DC converter.
Fig.6. RCN network.
The two values are very similar in this case as the RCN
greatly reduces the variation in output resistance with change
in output voltage. From this, the value of Ls and Cs were
obtained using Ls = Xs/ω and Cs =1/ωXs. The values of Lrp
and Crp were calculated using(4) and (6), which makes the
input impedance of the matching network resistive. However,
the value of Lrp was increased slightly to provide slightly
inductive loading of the inverter to achieve ZVS switching of
the inverter switches. For the design of the magnetic
structure, a tradeoff was made between loss and size. For the
transformer and inductors, different core sizes (RM10,
RM12, and RM14) and types of windings (litz wire and foil)
were considered. For the transformer, RM12 provided a good
balance between loss and size. Copper foil was chosen for the
primary winding due to the high current (With a maximum
peak current of 9.42 A) and litzwire was chosen for the
secondary winding to reduce the proximity effect given the
large number of turns (with a maximum peak current of 1.57
A). For the inductors (Ls,Lr, and Lrp), RM12 core and litz
wire were chosen. The design value for Cs was 1300 pF and
for Cr was 1000 pF. A single mica capacitor Crs of 560 pF
was used to provide the correct net capacitance, as shown in
Fig. 6. This capacitor had a maximum peak voltage of 795 V
with a dc voltage of 200 V. Six 10 nF ceramic capacitors with
very low equivalent series resistance (ESR) were used for Crp.
These capacitors saw a maximum peak voltage of 65.6 V.
Further design details of this converter are given in [22]. A
photograph of the top side of the prototype converter is
shown in Fig. 9 and the bottom side is shown in Fig. 9.
Fig. 8. Pulse generation for converter.
Fig. 9. Output voltage and current of DC-DC converter.
V. CONCLUSION
With the above results of the DC-DC converter the output
voltage of the converter has a very high gain value of 10
times that of the input voltage. The high voltage of 250V is
connected to a DC bus with all renewable source connected
sharing the power of the proposed DC-DC converter to the
load. The output power of the converter is 20W with high
efficiency of 95%.
International Journal of Innovative Technologies
Volume.03, Issue No.11, December-2015, Pages: 2056-2060
Grid Interconnection of High Efficiency Resonant DC/DC Converter in Photo Voltaic Applications
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International Journal of Innovative Technologies
Volume.03, Issue No.11, December-2015, Pages: 2056-2060