IJSTE - International Journal of Science Technology & Engineering Volume 2 Issue 08 February 2016 ISSN (online): 2349-784X Performance Evaluation of Maximum Power Point Tracking Algorithm with Buck-Boost Dc- Dc Converter for Solar PV System Ahteshamul Haque Department of Electrical Engineering Jamia Millia Islamia University, New Delhi-25 Abstract Maximum power point tracking is used in solar PV energy conversion system to extract maximum power from solar PV (Photovoltaic). MPPT algorithm is implemented in the control circuit of Power electronics DC-DC converters. The behavior of MPPT depends upon the type of the type of DC DC converter used. The objective of this paper is to analyze the working of MPPT with buck-boost DC DC converter. The simulation is study is done by using PSIM simulation software. Keywords: MPPT, Solar PV, Power Electronics, Buck-Boost Converter, PSIM I. INTRODUCTION Global Energy Crisis and climate change threats leads the researchers to look for alternate sources of energy [1-2]. Solar Energy is considered as the most reliable source among all renewable energy sources (RES) [3-8]. Solar PV is used to convert solar energy into electrical energy. Solar PV exhibits nonlinear characteristics and its efficiency is also low. It becomes essential to extract maximum power from solar PV under all ambient conditions. MPPT (Maximum Power Point Tracking) algorithm is used to extract maximum power from solar PV [9-10]. The MPPT is implemented in the control circuit of Power electronics converters. A converter without MPPT system only regulates the output voltage of PV module, but it does not ensure that PV system is operating at the maximum power point MPP [11]. The operation of MPPT depends on the type of converter used [12-14]. In this paper a buck-boost dc-dc converter is used and the performance of MPPT is evaluated. II. SOLAR PV CHARACTERISTIC Fig. 1: Equivalent model of PV Cell Fig. 2: Solar PV Power Characteristics with different Solar Irradiation level All rights reserved by www.ijste.org 255
The basic element of solar PV system is PV cells. These cells are connected to form modules. It is further expanded in the form of arrays as per the power requirements. These PV cells exhibit nonlinear characteristics. The output of the PV cell varies with solar irradiation and with ambient temperature. The equivalent circuit model of PV cell given in Fig (1). The characteristic equation of PV cell based on this model is given by equation 1, 2 and 3 [3]. I = Iph Ios {exp [(q/akt) (V + I Rs)] 1} - (V +I*Rs)/Rp (1) Ios = Ior exp [q EGO/ Bk ((1/Tr) (1/T))] [T/Tr] 3 (2) Iph = S [Isc + KI (T- 25)]/100 (3) Where I am the PV module output current, V is the PV cell output voltage, R p is the parallel resistor, R s is the series resistor. I os is the PV module reversal saturation current, A, B are ideality factors, T is temperature ( o C), k is boltzmann s constant, I ph is the light-generated current, q is electronic charge, K I is short-circuiting current temperature coefficient at I SC. S is solar irradiation (W/m 2 ), I SC is short-circuit current at 25 o C and 1000 W/m 2, E GO is bandgap energy for silicon, T r is reference temperature and I or is saturation current at temperature T r. The plot of solar PV output power is shown in Fig (2). It can be seen that the power and current varies non-linearly with the variation in solar irradiation and with ambient temperature. III. P&O MPPT TECHNIQUE Perturb and observe (P&O) method is a MPPT scheme proposed by researchers. In perturb and observe method the perturbation is applied either in the reference voltage or in the reference current signal of the solar PV. The flow chart of the P&O method is shown in Fig 3. In this chart Y is shown as the reference signal. It could be either solar PV voltage or current. The main aim is to reach to the MPP. To achieve it the system operating point is changed by applying a small perturbation ( Y) in solar PV reference signal. After each perturbation the power output is measured. If the value of power measured is more than the previous value then the perturbation in reference signal is continued in the same direction. At any point if the new value of solar PV power is measured less than the previous one then perturbation is to apply in the opposite direction. This process is continued till MPP is reached. In [8] the P&O method uses the solar PV panel current as a reference signal. The issue with this method is it becomes oscillatory around MPP. Table 1 gives the summary of P&O MPPT method. Table - 1 Summary of the Perturb & Observe MPPT Method Perturbation Change in Power Next Perturbation Positive Positive Positive Positive Negative Negative Negative Positive Negative Negative Negative Negative Fig. 3: Flowchart Diagram of the conventional Perturb & Observe MPPT method All rights reserved by www.ijste.org 256
IV. BOOST DC DC CONVERTER Fig. 4: Schemtaic of Boost DC DC converter Table II Parameters of DC-DC BOOST Converter S.No. Name of the Parameter Values 1 Vin VMPP : when MPP is working 2 MOSFET 20A, 600V 3 DIODE 12A, 1000V 4 L 1mH, 15A Saturation 5 C 1000 uf 6 Vo Based on duty cycle expression 7 RLOAD Variable 8 Frequency 20 khz 9 Power Output W The schematic of boost converter is shown in Fig. 4. The specifications of components are shown in Table I. The boost converter is designed to work in continuous conduction mode. The relationship between boost converter input and output is given by: Vo = D Vin/ (1-D) (4) V. MPPT WITH BOOST DC-DC CONVERTER Fig. 5: Block Diagram of Buck -Boost DC DC converter Fig. 6: MPP Zone on I-V Curve All rights reserved by www.ijste.org 257
Fig. 7: Rin Vs Duty Cycle The block diagram of buck - boost dc-dc converter with MPPT is shown in Fig. 5. The MPP zone for buck -boost converter is shown in Fig. 6. The variation of input impedance with duty cycle is shown in Fig. 7. Equation 5 is the relationship between input and out impedances with duty cycle. The MPPT will be working with buck -boost converter between B and C in Fig. 6, where Rload >> R MPP. The MPPT will be working between A and B. The MPPT will be working for the entire range on solar PV characteristic. VI. RESULT AND DISCUSSION Pmax (W) 39.5 39.48 39.46 39.44 39.42 39.4 Po (W) 30 20 10 0 0.05 0.1 0.15 0.2 Time (s) Fig. 8: MPP Working for Buck -BOOST Converter when RLOAD > RMPP. Pmax (W) 44 42 38 36 34 Po (W) 30 20 10 0 0.05 0.1 0.15 0.2 Time (s) Fig. 9: MPP Failed for Buck -BOOST Converter when RLOAD < RMPP. All rights reserved by www.ijste.org 258
Fig. 8 and 9 are simulation results. Fig. 8 shows that MPPT is working R LOAD > R MPP. The maximum PV power and Load power is almost same. Fig. 9 shows that MPPT is working when R LOAD < R MPP. The power is same as MPP power of solar PV. These results shows that entire PV characteristic is MPPT working zone with buck - boost DC DC converter. VII. CONCLUSION The main objective of the paper is to evaluate the performance of MPPT with buck- boost DC DC converter in terms of MPPT working zone. The MPPT with buck -boost dc-dc converter is analysed and simulation results are presented. It is evident that MPPT is functional in the entire zone of PV characteristic curve. ACKNOWLEDGEMENT The research work of this paper is done by using the instruments purchased under MNRE R&D project sanctioned. REFERENCES [1] Godfrey Boyle, Renewable energy power for a sustainable future, Oxford University Press, 2014. [2] Sathish Kumar Kollimalla and Mahesh Kumar Mishra, Variable perturbation size adaptive P&O MPPT algorithm for sudden Changes in Irradiance, IEEE Trans. Sustainable Energy, vol. 5, no. 3, pp.1949-3029, Jul. 2014. [3] Dezso Sera Laszlo Mathe, Tamas Kerekes, Sergiu Viorel Spataru, and Remus Teodorescu, On the perturb-and-observe and incremental conductance MPPT Methods for PV Systems, IEEE Journal. Photovoltaics, vol. 3, no. 3, pp. 2156-3381, Jul. 2013. [4] Andrea Montecucco and Andrew R. Knox, Maximum power point tracking converter based on the open-circuit voltage method for thermoelectric generators, IEEE Trans. Power Electronics, vol. 30, no. 2, Feb.2015. [5] Ian Laird and Dylan Dah-Chuan Lu, High step-up DC/DC topology and MPPT algorithm for use with a thermoelectric Generator, IEEE Trans. Power Electronics, vol. 28, no. 7, pp.0885-8993, Jul. 2013. [6] Kashif Ishaque, Zainal Salam,Muhammad Amjad, and Saad Mekhilef, An improved particle Swarm optimization (PSO) based MPPT for PV with reduced steady-state oscillation, IEEE Trans. Power Electronics, vol. 27, no. 8, pp. 0885-8993,Aug. 2012. [7] Moacyr Aureliano Gomes de Brito, Luigi Galotto Jr., Leonardo Poltronieri Sampaio, Guilherme de Azevedo e Melo, and Carlos Alberto Canesin, Evaluation of the main MPPT techniques for photovoltaic applications, IEEE Trans. Industrial Electronics, vol. 60, no. 3,pp.0278-0046,Mar.2013. [8] Tey Kok Soon and Saad Mekhilef, A fast-converging MPPT technique for photovoltaic system under fast-varying solar irradiation and load Resistance, IEEE Trans. Industrial Informatics, vol. 11, no. 1,pp. 1551-3203, Feb. 2015. [9] Carl Ngai-Man Ho, Hannes Breuninger, SamiPettersson, Gerardo Escobar, Leonardo Augusto Serpa, and Antonio Coccia, Practical design and implementation procedure of an interleaved boost converter using SiC diodes for PV applications, IEEE Trans. Power Electronics, vol.27, no. 6,pp.0885-8993, Jun. 2012. [10] Zaheeruddin, SK Mishra, Ahteshamul Haque, Performance evaluation of modified perturb & observe maximum power point tracker for Solar PV system, Springer Internat. Journal, System assutance engg. & manag., pp. 1-10, Jun. 2015. [11] R. Seyezhai and B.L. Mathur, Design and implementation of interleaved boost converter for fuel cell systems, internat. Journal, hydrogen energy 37(2012) 3897-3903. [12] Po-Wa Lee, Yim-Shu Lee, David K. W. Cheng, and Xiu-Cheng Liu, Steady-state Analysis of an interleaved boost converter with coupled inductors, IEEE Trans.Indust. Electronics, vol. 47, no. 4, pp. 0278-0046, Aug. 2000. [13] G.J. Kish, J.J. Lee, and P.W. Lehn, Modelling and control of photovoltaic panels utilising the incremental conductance method for maximum power point tracking, IET Renew. Power Gener., 2012, Vol. 6, Iss. 4, pp. 259 266. [14] A. Haque, Maximum power point tracking (MPPT) scheme for solar photovoltaic system, Taylor & Francis Group, Energy Technology & Policy (2014) 1, pp. 115 122. All rights reserved by www.ijste.org 259