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International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX
Vol. 2 Issue 4, April-2013, pp: (1-4), Available online at: www.erpublications.com
Design and Simulation of a 25/250V DC-DC
boost converter fed by a PV pannel in
SIMSCAPE library of MATLAB
Roshni Singh1, Neeti Dugaya2
12
Department of Electrical and Electronics
Sagar Institute of Research, Technology and Science, Bhopal, India
12
Abstract: The inevitable costs of using fossil fuels to generate electricity have led to attract lots of interest to the
green energy sources recently. Due to high initial investment of solar power plant it is necessary to increase
return of investment’s rate by increasing the efficiency as much as possible. The use of PV panels has become
very attractive as they provide a clean cheap form of energy. Controlling the O/P of a solar PV system is a key
aspect so that the solar panel may be interfaced with boost converter to increase the overall efficiency of the
system. The model presented in this paper is a physical modeling and simulation of solar PV system and DC-DC
boost converter in SIMSCAPE library of MATLAB fed to an ohmic load. The proposed model is able to harvest
solar energy using DC-DC boost converter to 250V which can be directly implemented to numerous loads as
efficiency is improved.
Keywords: Boost Converter, continuous conduction mode, PWM technique, n-channel MOSFET.
Introduction
The DC/DC converters are widely used in regulated switch mode DC power supplies. By a PV array an unregulated DC
voltage is fed to converter and therefore it will be fluctuating due to changes in radiation and temperature. In these converters
the average DC output voltage must be controlled to be equated to the desired value although the input voltage is changing.
From the energy point of view, the amount of energy absorbed from the source and that injected into the load will regulate
the output voltage in the DC/DC converter which is in turn controlled by the relative durations of the absorption and injection
intervals [1]. These two basic processes of energy absorption and injection are controlled by PWM technique.
In this paper a basic circuit of DC-DC boost converter has been proposed which is developed in SIMSCAPE library of
MATLAB. The advantage of SIMSCAPE is that it provides better realistic modeling of physical component so that the
physical modeling can easily be implemented on hardware [2].
Modeling of PV System
The output of PV cell is a function of photon current that can be also determined by load current depending upon the solar
insolation during its operation equation.
𝐼 = 𝐼𝑝ℎ − 𝐼𝑜 [𝑒𝑥𝑝 (
𝑉−𝑅𝑠 𝐼
𝑁𝑉𝑇
) − 1] −𝐼02 [𝑒𝑥𝑝 (
𝑉−𝑅𝑠
𝑁2 𝑉𝑇
) − 1] −
𝑉−𝑅𝑠 𝐼
𝑅𝑠ℎ
……… (1)
Figure 1 Equivalent circuit of a 2 diode PV cell.
Thus PV panel output is dependent on solar insolation and temperature. A two diode model has been provided in SIMSCAPE
library of MATLAB.
DC-DC Converter
In recent years, dc-dc converters are widely used in switched mode power supplies. These converters are generally used either
to step down or step up an unregulated dc input voltage. There are various dc-dc converter topologies such as buck, boost,
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International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX
Vol. 2 Issue 4, April-2013, pp: (1-4), Available online at: www.erpublications.com
buck-boost, Cuk and full bridge converter. Of these five converters, only the buck and boost are basic converter topologies.
The other converters are derived from these two basic converter topologies. Each converter topology has its own principle of
operation, advantages and disadvantages [3].
Design of DC-DC Boost Converter
A boost converter is used in renewable energy systems to step up unregulated dc input voltage to a higher constant output
voltage that is required by loads and batteries. The design and development of boost converter is mainly concerned with its
efficiency, output power and ease of design.
Renewable energy such as solar and wind uses dc-dc boost converter as a medium of power transmission to perform the
process of energy absorption and injection to loads and batteries. This process of energy absorption and injection is performed
by a combination of four components which are diode, inductor, output capacitor and electronic switch. The connection of
boost converter is shown in figure 2 [4]. This process of energy absorption and injection will constitute of switching cycle. In
other words the average output voltage is controlled by switch’s on and off duration. At constant switching frequency,
adjusting the on and off duration of switch is called pulse width modulation switching (PWM). The switching duty cycle, k is
defined as the ratio of the on duration to the switching time period. The energy absorption and injection with the relative length
of switching period will operate the converter in two different modes known as continuous conduction mode (CCM) and
discontinuous conduction mode [3,4].
Figure 2 Electrical equivalent circuit of DC-DC Boost Converter
Continuous mode of Operation
The continuous conduction mode is divided into two modes. Mode 1 begins when switch SW is turned on at t=t on as shown in
figure 3. The input current rises and flows through inductor L and switch SW. IN Mode 1 energy is stored in the inductor.
Mode 2 begins when the switch is turned off at t=toff. That current which was flowing through the switch will now flow
through L, D, C, and load R as shown in figure 4. The inductor current falls until the switch is turned on again in next cycle.
The energy transferred to the load will be that energy which was stored in the inductor. Hence, the output voltage obtained will
be more as compared to the input voltage and is expressed as:
𝑉𝑜𝑢𝑡 =
1
1−𝑘
𝑉𝑖𝑛 ………….. (2)
Here Vout denotes output voltage, k is duty cycle and Vin is input voltage [3] [4].
Figure 3 Mode 1- Equivalent circuit of boost converter during ton
Figure 4 Mode 2- Equivalent circuit of boost converter during toff
In order to operate the converter in continuous conduction mode, the value of inductance is calculated such that the inductor
current IL flows continuously and never falls to zero as shown in figure 5. Thus, L is given by
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International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX
Vol. 2 Issue 4, April-2013, pp: (1-4), Available online at: www.erpublications.com
𝐿𝑚𝑖𝑛 =
(1−𝑘)2 𝑘𝑅
2𝑓
……………. (3)
Here Lmin denotes minimum inductance, k is duty cycle, R is output resistance and f is switching frequency of switch SW [5].
Figure 5 Boost converter waveforms at continuous conduction mode.
For the desired output voltage ripple the required output capacitance is given by
𝐶𝑚𝑖𝑛 =
𝑘
𝑅𝑓𝑉𝑟
…………. (4)
Where Cmin denotes the minimum capacitance, k is duty cycle, R represents output resistance, f the switching frequency of
switch SW and Vr is output voltage ripple factor [3]. Vr can be expressed as
𝑉𝑟 =
∆𝑉𝑜𝑢𝑡
𝑉𝑜𝑢𝑡
…………… (5)
Proposed System
In this paper, a boost converter operated in continuous conduction mode is designed to step up an input voltage of 25V to a
higher output voltage of 250V. The selection of specification of components in the proposed model is as follows:
1) Selection of Electronic Switch
The electronic switch SW in figure 2 has been chosen on the basis of its voltage and current rating which should be higher
than the maximum input voltage and current. From the proposed system, the rating of the converter is 100W with an input
voltage ranging from 6V to 23V. Therefore, electronic switch such as n-channel MOSFET and thyristor handling capacity
should meet the specification of the proposed design.
2) Selection of Inductor
Equation (3) is the minimum inductance for boost converter to operate in continuous conduction mode, therefore the
selection of the inductor should be higher than the calculated value. Inductors with ferrite code or equivalent are
recommended.
3) Selection of Diode
Diode reverse voltage rating is the main consideration for selecting the diode. The other important consideration is its
ability to block the required off-state voltage stress and have sufficient peak and low forward voltage drop, average current
handling capability, low reverse recovery and fast switching characteristics,.
4) Selection of Output Capacitor
Equation (4) provides the minimum capacitance for calculating ripple voltage. The selection of capacitor should be higher
than the calculated value. Equivalent series resistance (ESR) is important consideration for the selection of output capacitor
because capacitor’s ESR affects efficiency. Low ESR capacitors are used for best performance. ESR can be reduced by
connecting few capacitors in parallel.
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International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX
Vol. 2 Issue 4, April-2013, pp: (1-4), Available online at: www.erpublications.com
Figure 6 MATLAB Simulation Model of Boost Converter fed from solar cell developed in SIMSCAPE library.
TABLE 1
Specifications of Boost Converter
Parameters
Value
Unit
Input Voltage
25
Volts
Output Voltage
250
Volts
Switching
frequency
10000
Hz
Duty Cycle
90
%
Inductor value
0.75
mH
Capacitor value
72
𝜇F
Ripple
0.01
Load resistance
250
ohms
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International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX
Vol. 2 Issue 4, April-2013, pp: (1-4), Available online at: www.erpublications.com
Simulation Results using SIMSCAPE
300
250
Voltage (Volt)
200
150
100
50
0
0
0.005
0.01
0.015
0.02
Time (Sec.)
0.025
0.03
0.035
0.04
Figure 7 Simulated response of output voltage of boost converter at radiation of 1000W/m2.
12
10
Inductor current (Amp)
8
6
4
2
0
0
0.005
0.01
0.015
0.02
Time (Sec)
0.025
0.03
0.035
0.04
Figure 8 Simulated response of inductor current.
15
Switch Current (Amp.)
10
5
0
0
0.5
1
1.5
2
Time (Sec)
2.5
3
3.5
4
-3
x 10
Figure 9 Simulated response of MOSFET current.
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International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX
Vol. 2 Issue 4, April-2013, pp: (1-4), Available online at: www.erpublications.com
Conclusion
This paper concerns with design and simulation of DC-DC boost converter to operate in PV system in SIMSCAPE library of
MATLAB. The output voltage is boosted up to 250V when fed by a 25V solar cell. With the help of PWM technique duty
cycle is kept as 90% at 10 KHz switching frequency. The main advantage of dealing with physical signal is the ease of
implementation with hardware.
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