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
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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
Roshni Singh1, Neeti Dugaya2
12Department of Electrical and Electronics
12Sagar Institute of Research, Technology and Science, Bhopal, India
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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
Page | 6
International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX
Vol. 2 Issue 4, April-2013, pp: (1-4), Available online at: www.erpublications.com
Page | 6
International Journal of Enhanced Research Publications, ISSN: XXXX-XXXX
Vol. 2 Issue 4, April-2013, pp: (1-4), Available online at: www.erpublications.com
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-IoexpV-RsINVT-1-I02expV-RsN2VT-1-V-RsIRsh ……… (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, 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=ton 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=11-kVin………….. (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
Lmin=(1-k)2kR2f ……………. (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=kRfVr …………. (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=∆VoutVout …………… (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.
Figure 6 MATLAB Simulation Model of Boost Converter fed from solar cell developed in SIMSCAPE library.
TABLE 1
Specifications of Boost Converter
Parameters / Value / UnitInput 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
Simulation Results using SIMSCAPE
Figure 7 Simulated response of output voltage of boost converter at radiation of 1000W/m2.
Figure 8 Simulated response of inductor current.
Figure 9 Simulated response of MOSFET current.
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.
References
[1]. B.M Hasaneen and Abel A. Elbaset Mohammed, “Design and stimulation of DC/DC boost converter,” Power System Conf. Middle-East, pp. 335-34. 2008.
[2]. Nikhil Kumar and Suresh Gawre, “Physical design and modeling of 24V/48V DC-DC boost converter for solar PV application by using SIMSCAPE library in MATLAB.” IJACEEE Vol 2, no. 2, May 2014.
[3]. Ned Mohan, Tore M. Undeland and Williams P. Robbins, Power Electronics: Converters, Applications and Design, 3rd ed., John Wiley &Sons: USA, 2003, pp. 161-197.
[4]. S Masri, P. W. Chan, “Design and development of a DC-DC boost converter with constant output voltage.” University Saint Malaysia, 14300.
[5]. Mohammed H. Rashid, “Power Electronics: Circuits, Devices and Applications”. Prentice-Hall. Inc. Englewood Cliffs, Book, Second Edition, 1993.
[6]. ‘Matlab-Simulink User’s Guide’. Theamathworks. Version 6.0.0.8 R12
[7]. ‘Power System Blockset User’s Guide’, The Mathworks, Version 6.0.0.88 R12
[8]. U. Ribes-Mallada, R.Levva and P. Garces, “Sensitivity analysis in boost converter optimal design.” IEEE Trans. Power Electron., vol. 2011.
[9]. Sajib Chakraborty and Saila Ishrat Annie, “Design of single-stage buck and boost converters for photovoltaic inverter applications,” IEEE Trans. Power Electron., vol. 2014.
[10]. S.Zahra Mirbagheri and Saad Mekhilef, “MPPT with Inc.Cond method using conventional interleaved boost converter”, Energy Procedia 42 (2013) 24-32
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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
Page | 6