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ISSN: 2277-3754 ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 7, January 2013 High Voltage Gain Boost Converter Based On Three State Switching Cell for Solar Energy Harvesting N.Prasad, T.Logeswaran, Dr.A.Senthil Kumar Abstract: - In this paper a three state switching cell boost converter for photovoltaic applications employing MPPT (perturb and observe) algorithm is discussed. A three state switching cell boost converter has advantages such as reduced size of boost inductor and current sharing is performed between two switches leading to the usage of low power rating switches. The maximum power varies with respect to temperature and solar radiation. MPPT algorithm is used to track the maximum power and thereby improving the efficiency of the system. By manipulating the duty cycle the system implements perturb and observe MPPT algorithm. The simulation is performed using MATLAB/SIMULINK under various temperature and solar radiation and waveforms are presented. Index terms: - Three State Switching Cell Boost Converter, Maximum Power Point Tracking (MPPT), Photo Voltaic Power Generation System. I. INTRODUCTION Renewable energy attracts interest for power generation since the non renewable energy like petrol, diesels etc are diminishing and energy crisis is an important issue in most of the nations. Energy production using solar energy could be a solution for the increasing power demands. The photovoltaic generation systems can either be operated as isolated systems or connected to the grid as a part of an integrated system. One of the major advantages of PV technology is that it has no moving parts; it has a long lifetime and low maintenance requirements and most importantly it is one solution that offers eco friendly power. A maximum power point tracking algorithm is absolutely necessary to increase the efficiency of the solar panel as it has been found that only 30-40% of energy incident is converted into electrical energy. Among all the MPPT methods, Perturb & Observe (P&O) is most commonly used because of its simple implementation [7]. Generally the efficiency of the system depends on the boost converter too. To improve the efficiency of the converter soft switching scheme is used [2] .The solar energy is directly converted into the electric energy by the Photovoltaic (PV) module. A PV module consists of a number of solar cells which when connected in series increases the voltage and when connected in parallel increases the module current. Despite mechanically changing the position of the solar panels, MPPT works automatically to keep the output at the maximum power. The concept in Maximum power point tracking is that when the source impedance matches with the load impedance maximum power transfers from the source to load [6], so the source impedance is varied by varying the duty cycle. In this paper three state switching cell boost converter is used even though conventional boost converters can produce high voltage gain, the gain decreases as the duty cycle approaches unity as proved in [1], when connecting boost converters in series losses will increase due to increase of devices [5]. Depending upon the surrounding conditions such as temperature and irradiation, the output power of the solar cell changes and hence its efficiency is low. Thus for the transmission of the power from PV array to the load, high efficiency is needed for the power conditioning systems (PCS). Generally a single stage PV PCS is composed of two conversion stages namely dc/dc conversion stage and dc/ac conversion stage. The maximum power point tracking is applied to the dc/dc converter topology. To solve this disadvantage, three state switching cell boost converter [4] is used because of its reduced ripple currents in both the input and output circuits and hence there is a decrease in the boost inductor magnetic volume. The power is equally divided between two oppositely coupled inductor the stress across the devices are much low so there is no need for any soft switching scheme [10]. II. PV GENERATOR A. Solar Panel The simplest circuit of a solar cell is a current source connected in parallel with a diode. A PV array consists of several photovoltaic cells in series and parallel connections. Series connections are required for increasing the voltage of the module and the parallel connection is required for increasing the current in the array. The PV module is self protected which means even when the ends are short circuited only short circuit current flows and will never make an issue because of the short circuit. 102 Fig.1 Equivalent Circuit of the PV Cell ISSN: 2277-3754 ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 7, January 2013 The equation that gives the voltage current characteristics of When the voltage and the current characteristics are a solar cell is given by multiplied, the P-V characteristics is obtained as shown in Figure.4 Where IPH=light saturated current or photo current Is=cell saturation of dark current Q=charge of an electron (1.602×10-19) K= Boltzmann‟s constant (1.38×10-23) A=Ideal factor (2.15) Tc=cell‟s working temperature RSH=Shunt resistance RS=Series resistance The photocurrent mainly depend on temperature and solar radiation given by the equation Fig. 4 P-V Characteristics Curve of Solar Panel Where Isc=Cell‟s short circuit current Ki=Cell‟s short circuit temperature coefficient Tref=Cell‟s reference temperature H=Solar radiation. Based on the above shown equations a MATLAB /SIMULINK model was designed as shown below The simulation is carried out for a cell surface temperature of 50° C, 20 solar cells in series and 2rows of solar cells in parallel. The irradiation varies from 250 Watt per sq. cm. to 1000 Watt per sq. cm,. The simulation is run for a total of 1 second, with the irradiation taking up a new value every 0.25 seconds. Fig. 5 Plot of Output Voltage, Current and Power of PV Panel Fig 2. MATLAB/SIMULINK model of a solar PV array Fig. 3 I-V Characteristics of a Solar Panel B. MPPT algorithm Numerous techniques have been proposed so far to realize MPP. These MPPT methods vary in complexity, sensors required, convergence speed, cost, range of effectiveness, implementation hardware, popularity, and in other respects. Among them the Perturb-and Observe (P&O) method, is the most common. The P&O algorithm is mostly used, due to its ease of implementation. Module Voltage, current and power measured at kth instant .Module Voltage, current and power calculated at k+1th instant. ∆P is calculated by ∆P=P (k+1)-P(k) and ∆Vis calculated by ∆V=V(k+1)-V(k). Based on the values of ∆V and ∆P the duty cycle is varied. If ∆P>0 and ∆V>0 then D=D- ∆D. If ∆P>0 and ∆V<0 then D=D+ ∆D. If ∆P<0 and ∆V <0 then D=D+ ∆D. If ∆P<0 and ∆ V>0 then D=D- ∆D. Where D= duty cycle and ∆D is perturbation 103 ISSN: 2277-3754 ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 7, January 2013 A .Operation Fig. 8 First and Third Operating Stage Fig. 6 P&O Algorithm Fig. 9 Second Operating Stage Fig.10 Fourth Operating Stage Fig. 7 MATLAB/SIMULINK Model Of Perturb and Observe Algorithm III. THREE STATE SWITCHING CELL BOOST CONVERTER A three state switching cell boost converter is an efficient dc –dc boost converter providing high voltage gain by means of voltage multiplier stages. It reduces the input ripple by means of oppositely coupled inductor and reduces output ripple by means of output capacitor. A three state switching cell boost converter has a high voltage gain and high efficiency. In three state switching cell boost converter the duty cycle has to be more than 0.5 for nominal operation of the converter circuit. There are two low power rating switches in the converter. The first and third stage as shown in Figure.8 is that the switches S1, S2 are turned on so that the supply charges the input inductor. The second operating stage as shown in Figure.9 is that S1 is still turned ON and S2 is turned OFF so that the diode Dm2 and D1 are forward biased. The current through the winding Np2 divides into two paths so that in one path the current discharges the capacitor C2 and supplies the load through diode D1 and thereby charging the capacitor Co. The second path through diode Dm2 and charges the capacitor C1 and the circuit close through the switch S1.The first path adds the input voltage with the energy stored in the boost inductor along with the charge in the capacitor C2 thereby boosting the input voltage. The fourth stage as shown in Figure.10 is that the switch S2 is turned ON and the switch S1 is OFF so that the current through the transformer winding Np1divides into two paths so that in first path the current discharges through the capacitor and flows through the diode D2 and the load. 104 ISSN: 2277-3754 ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 7, January 2013 By substituting the values in the above said formulas the values obtained is as follows Parameters Symbol Value Boost inductor Lb 66.5 µH Duty cycle D 0.58 C1 4.6 µH C2 2.3 µH C3 1.2 µH Output Capacitor Cout 680uF Resistance of Load R 20 Ω Multiplier capacitor Fig.11 Switching Pulses for Switch S1, S2 IV. PROPOSED MODEL The three state switching cell boost converter obtained by substituting the above values is as follows Fig.12 Proposed Model of the Project A three state switching cell boost converter with high voltage gain to about 9.5 can be obtained as the input voltage is 42V and the obtained output voltage is nearly 400V and the parameters for designing this converter is as follows Duty cycle Fig.13 Three State Switching Cell Boost Converter Boost inductor Multiplier capacitor The maximum power is transferred when the source impedance matches with the load impedance. For matching the matching the impedances the duty cycle is varied in the converter. The switches are synchronized by the following method. Output capacitor Where Vo = Output voltage Vi = Input voltage Gv = voltage gain D = duty cycle Mc = number of multiplier stages Fs = switching frequency Fig. 14 PWM Generation for Switches S1, S2 105 ISSN: 2277-3754 ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 7, January 2013 Photovoltaic Systems”, IEEE Applied Power Electronics Here V2 is 1800 phase shifted from V1 and both are carrier Colloquium (APEC), pp. 22-27, 2011. frequency which is compared by the common voltage Vc. The output power waveform obtained through the maximum [7] N. Femia, G. Petrone, G. Spagnuolo, and M. Vitelli, power point tracking algorithm is shown below. “Optimization of perturb and observe maximum power point tracking method,” IEEE Trans. Power Electron., vol. 20, no. 4, pp. 963–973, Jul. 2005. [8] O. Abutbul, A. Gherlitz, Y. Berkovich and A. Ioinovici, “Boost converter with high voltage gain using a switched capacitor circuit”, Proceedings of the 2003 International Symposium on Circuits and Systems (ISCAS 2003), vol. 3, pp. 296-299, May2003. [9] R. J. Wai, W. H. Wang, and C. Y. Lin, “High-performance stand-alone photovoltaic generation system,” IEEE Trans. Ind. Electron., vol. 55,no. 1, pp. 240–250, Jan. 2008. [10] R. P. T Bascopé, et al., “A generalized high voltage gain boost converter based on three-state switching cell,” Proceedings of the 32nd IECON, pp. 1927-1932, Sept. 2006. [11] Samuel Vasconcelos Araújo,, Rene P Torrico- Bascope and Grover V Torrico- Bascope “High efficient high step up converter for fuel cell processing based on three state commutation cell” IEEE transactions on industrial electronics,vol 57,no 6,2010. Fig.15 Output Power of PV Panel V. CONCLUSION The simulation results of solar panel, three state switching cell boost converter are presented. The maximum power point tracking algorithms namely perturb and observe algorithm used. All simulations are performed in matlab/simulink modeling and simulation platform. The output voltage and output power of the PV panel are obtained. The source impedance is matched with the load impedance for maximum power transfer from source to load and high voltage gain is obtained through this three state switching cell boost converter. REFERENCES [1] N. Mohan, T. M. Undeland and W. P. Robbins, Power Electronics: Converters, Applications and Design, 2nd ed., New York: John Wiley & Sons, Inc., 1995, pp. 177-178. [2] Doo-Yong Jung, Young-Hyok Ji, Sang-Hoon Park, Yong-Chae Jung, and Chung-Yuen Won (2011) „Interleaved Soft-Switching Boost Converter for Photovoltaic Power-Generation System‟, IEEE Transactions on Power Electronics, Vol. 26, No. 4, pp: 1137-1145. [12] W. Xiao and W. G. Dunford, “A modified adaptive hill climbing MPPT method for photovoltaic power systems,” in Proc. IEEE PESC, 2004, pp. 1957–1963. AUTHOR’S PROFILE N.Prasad received his BE degree in Electrical and Electronics Engineering in 2009 and he is currently doing ME (Applied electronics) in Kongu Engineering College. His area of interest includes applications of power electronics in renewable energy. T.Logeswaran is with the Kongu Engineering College, Perundurai, Tamilnadu in the Department of Electrical and Electronics Engineering as Assistant Professor. He received his BE degree in Electrical and Electronics Engineering in 2002 and ME degree in 2007.He is pursuing his research work in area of Electrical Engineering. Dr.A.Senthil kumar is with Dr.Mahalingam College of Engineering and Technology as Professor and Head in the Department of Electrical and Electronics Engineering, Pollachi. He received his BE degree in 1995 and ME degree in 2001 and Ph.D in VLSI in 2009. He has published 5 Papers in International Journals in the area of Low power VLSI design. He has received Academic Excellence award from Bharathidasan University for the outstanding performance in ME [3] G. V. T. Bascopé and I. Barbi, “Comparison of the high current boost converters generated with three-stage switching cell,” Proceeding of the 9th Brazilian Power Electronics Conference, 2003. [4] Grover victor torrico - bascope, Ivo Barbi “A single phase PFC based on three state switching cells” 35th IEEE power electronics specialists conference, Germany, 2008. [5] J. W. Baek, M. Ryoo, T. Kim, D. Yoo and J. Kim, “High boost converter using voltage multiplier”, Proceedings of the 31st IECON, Nov. 2005. [6] Mei Shan Ngan and Chee Wei Tan, “A Study of Maximum Power Point Tracking Algorithms for Stand-Alone 106