G.Raja Sekhar, Ch.Sai Babu, J.Surya Kumari

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1 Comparison Analysis of P&O and IP&O MPPT Technique for PV System G.Raja Sekhar, Ch.Sai Babu, J.Surya Kumari Abstract: Photo voltaic (PV) generation is becoming increasingly important as a renewable source due to its immense advantages of no fuel cost, pollution free and easily deployed on roof tops. Since the cost of power generation from this source requires a large amount compared to other power generation so normally we use a maximum power point tracking (MPPT) technique to track the maximum possible available power. This paper gives the analytical comparison of two different techniques Perturb and Observe (P&O) and Improved Perturb and Observe (IP&O) methods in maximum power point tracking (MPPT). This paper gives a step by step procedure of modeling photovoltaic array (PVA) Simulation model to be used in Matlab-Simulink GUI environment. The detailed comparision of each MPPT Technique like P&O and IP&O the simulink simulation comparison results of both the techniques show that IP&O gives better MPPT point of tracking than P&O. Keywords: Modeling Of PV Arrays, Maximum Power Point Tracking (MPPT), Perturbation and Observation (P&O), Improved Perturbation and Observation (IP&O), Simulation Results. I. INTRODUCTION Renewable energy sources involve many advantages like no fuel cost, no transporting fuel cost, pollution free and solar energy is the most readily available source of energy, it is free of cost. The solar energy is available in tremendous large amount as one hour of solar energy fulfils one human per year consumption of energy. As many small applications like street lighting, a remote area where conventional power source is not available solar energy is Advantageous. The output power of PV arrays is always changing with weather conditions, which mean solar irradiation and atmospheric temperature. The maximum available power at a particular temperature and solar irradiation varies with respect to temperature and irradiation. So to extract maximum energy at a particular temperature and intensity we operate the solar array at The Maximum power point (MPP) of an array it is usually an essential part of a PV system. Increased radiation with reduced temperature gives a high array output. So the tracker must derive the maximum power always against varying temperature and irradiation, atmospheric conditions. Photo voltaic power generation consist of photo voltaic arrays which has photo voltaic cells the building block of photo voltaic array or photovoltaic module or panels.this PV cells converts sunlight into electricity cells are grouped in parallel or in series to form panels or modules. This paper is organized in the following way section II It discusses with schematic diagram of system which shows the Basic Blocks and there connections and power flow diagram. Section III It shows the Mathematical Modeling of photo voltaic array. Section IV The Boost converter basic operating principle and equations. Section V the two maximum power point tracking techniques P&O and IP&O. Section VI Simulation results and finally conclusions are made. II. PV SYSTEM BLOCK DIAGRAM The Block Diagram shown in Figure.1 clearly shows the sequential flow of the power, the PV array develops the power from the solar energy directly and it will be changes depending up on the Temperature and solar irradiation. The power output from the PV array is fed to the mppt algorithm which generates a sequence of pulses and are send to boost converter which operate depending on the sequence of pulses and makes the PV array to operate at MPP. Fig.1. System Configaration Block Diagram III. Photovoltaic Modeling A. Mathematical modeling of PV - The photo voltaic cell receives energy from sun and converts the sunlight into dc power the equivalent circuit diagram of a photo voltaic cell is shown in figure.2. The PV cell output voltage is a function of the photo current that mainly determined by load current depending on the solar irradiation level during the operation. Fig. 2 PV Cell Circuit Model 230

2 N S AKT N P ph pv N P O Vpv PV RS q ln O (1) Current output of a PV cell: q V pv pvrs I N N exp 1 (2) pv p ph P o N s AKT I K T 298 (3) ph scr t 100 The variables terms in above equation are described as shown I : output current of a PV cell, pv Io : PV cell saturation current, I : light generated current in a PV cell, ph N s : Number of modules connected in series N : Number of modules connected in parallel p R s : The series resistance of cell (0.001 ohm) A: An ideality factor = 1.6 K : Boltzmann constant=1.3805e-23nm/k T :cell temperature in Kelvin=298K Q: electron charge=1.6e-19 Coulombs PV cell short-circuit current at 25 c and100mw/cm 2 The reference temperature=301.18k The short-circuit current temperature coefficient =0.0017A/ C. λ=is the PV cell illumination (MW/cm2) =100Mw/cm2 Saturation current at E go = is the band gap for silicon=1.1ev. Both k and t have the same temperature unit, either Kelvin or Celsius,the ideality factor A is used to fit the curve to actual characteristic.the voltage obtained from the cell is given by equation (1) it is multiplied by the number of the cells connected in series to calculate the full array voltage.since the array current is the sum of the current I c is obtained by dividing the array current by the number of cells connected in parallel before being used which is only valid for a certain operating temperature T c with its corresponding solar irradiation level change, the voltage and current outputs of the PV array will follow this change.an increase in solar irradiation causes the output current to increase and the horizontal part of the curve moves upwards increase in cell temperature causes the voltage to move leftward, while decreasing the temperature causes the opposite effect. The V-I curves figure 8a, 8b show how a photovoltaic module responds to all possible different solar irradiation and cell temperature conditions. Characteristic I V curve of a practical PV device and the three limiting points: short circuit (0, Isc), MPP (Vmp, Imp), and open circuit (Voc, 0). The V-I characteristics shown in figure 3 has only one mpp point (Vmp, Imp) where the load operating point must coincide with this so that the load can be delivered maximum power only one load value produces a maximum power.to operate the module at MPP, a dc-dc power electronic converter is accompanied with PV system this converter is nothing but a booster converter which boosts the voltage of PV array available at low voltage to the voltage of load which requires higher voltage. B. Conventional P&O with Fixed Perturb- Perturbation and Observation (P&O) can track the Maximum Power Point (MPP) all the time, irrespective of the atmospheric conditions, like temperature and irradiation P&O algorithms are widely used in MPPT because of their simple structure. In this method, a fixed perturb value is utilized to generate a reference signal for the outer control loop this perturb value dependent on the system designer. The algorithm compares periodically perturbation in the operating voltage of the PV array. It can be seen that incrementing (decrementing) the voltage increases (decreases) the power when operating on the left of the MPP.As Shown in figure.3 and decreases (increases) the power when on the right of the MPP. Therefore, if there is an increase in power, the subsequent perturbation should be kept the same to reach the MPP and if there is a decrease in power, the perturbation should be reversed. The flow chart algorithm and implementation block diagram of P&O are show in figure.5 and figure.6 respectively. As a result of previous experience the designer decides the fixed perturb value which is designer dependent. Therefore, the solution provided by this method is not generic and system dependent. For small perturb steps, the tracking is slow but the power/voltage oscillations are minimal. In the case of large perturb step, faster tracking is achieved with increased oscillations. Hence, P&O techniques with fixed perturb suffer an inherent tracking oscillations trade off problem. A PI controller following the MPPT is utilized to control the power converter. Fig. 3. Maximum Power Point (V mp, I mp ) Fig.4 Conventional With Fixed Perturbation and Observation Flow Chart 231

3 Table1 Perturbation Table The perturbation table 1 helps how the perturb value changes with previous perturb to change in power sign.the power obtained from the PV array changes continuously with this perturb table the action of perturb to be done is followed in MPPT algorithm. Table2 Comparison of MPPT Methods Fig.5. Conventional with fixed Perturbation and Observation C. Improved P&O with Fixed Perturb- In this technique, converter duty ratio is used instead of utilizing the array voltage or current as the perturbed signal. This eases the control process as it eliminates the PI/hysteresis controller after the MPPT block as shown in figure7, enabling direct control of the converter s duty cycle. The perturb step is fixed and designer dependent. Hence, the previously mentioned trade off problem still persists. In order to improve the performance of P&O techniques, the modified calculation of the perturb value is utilized instead of the fixed values. All though this technique is better and efficient from the previous technique of P&O but suffer from certain disadvantages which can be eliminated in other technique which is the future scope of the project. The Improved P&O techniques review and simulation results for the both the techniques P&O and Improved P&O are discussed in the following sections. IV. SIMULATION RESULT The PV array characteristics are obtained by keeping the array at fixed temperature and varying solar irradiation in steps of 10 Wcm-2from 20Wcm-2 to 100 cm-2 the characteristics are shown in the figure.8a that for a constant solar intensity the current remains constant with increasing voltage up to 100Volts after which it decreases. It is further observed that the current increase with increasing intensity. Fig 6. Improved with fixed Perturbation and Observation Fig 7 a. V-I Curve with different irradiation The effect of temperature variations on the V-I characteristics of the PV cell is shown in figure. 8b. A marginal variation in current is observed for a temperature variation from 25 C to 65 C for a voltage up to 100Volts. Above this value the current decreases in a sharp manner for small variation in voltage. It is further seen that the voltage of which the cell current becomes zero increases with decreasing temperature. 232

4 Fig 7 b. V-I Curve for Different Temperature Fig 12. Boost Converter Output Power Fig13. Boost Converter Input Voltage or PV Array Output voltage Fig 8. P-V Curve for Different Temperatures Variation Fig 14. Boost Converter Input Current or PV Array outptut Current Fig 9. P-V Curve for Different Irradiations Variation Fig 15. Boost converter Input Power or PV Array Output Power Fig 10. Boost Converter Output Voltage Fig 16. P&O MPPT Technique Input Voltage Fig 11. Boost Converter Output Current Fig 17. P&O MPPT Technique Input Current 233

5 Fig 18. P&O MPPT Technique Input Power Fig 23. Temperature Constant and Irradiation vs. Efficiency Fig 19. IP&O MPPT Technique Input Voltage Fig 24. Temperature constant and Irradiation vs. power Fig 20. IP&O MPPT Technique Input Current Fig 21. IP&O MPPT Technique Input Power Fig 25. Irradiation constant and Temperature vs. efficiency Fig 22. Comparison of P&O and Improved P&O MPPT Technique power Fig 26. Irradiation constant and Temperature vs. power 234

6 V. CONCLUSION This Paper proposes generalized design of Photo voltaic array, and the simulation results are shown. It Compares perturbation and observation (P&O), Improved perturbation and observation (IP&O) techniques of maximum power point tracking (MPPT) methods.the P&O technique is a simple and lucid MPPT Method which has a disadvantages of using of PI controller for Error reduction and has indirect control on the boost converter. The IP&O MPPT technique is an advanced technique compared to conventional P&O method.in this method also fixed perturb is used and duty ratio is considered which improves the efficiency of the algorithm.advantages of both the techniques are discussed and the later technique IP&O is the best and better accurate MPPT tracker technique than P&O is shown through simulation results and graphs. [9] D.Y. Lee, H.J. Noh, D.S. Hyun and I. Choy, An improved MPPT converter using current compensation methods for small scaled pv applications. Proceedings of APEC, 2003, pp [10] A.K. Mukerjee, Nivedita Dasgupta, DC power supply used as photovoltaic simulator for testing MPPT algorithms., Renewable Energy, vol. 32, no. 4, pp , [11] Katshuhiko ogata, MODERN CONTROL ENGINEERING - Printice Hall of India Private Limited. AUTHOR BIOGRAPHY G.Raja Sekhar was born in Kakinada, India. He received the B.Tech (Electrical and Electronic Engineering) degree from JNTUK in 2009 and pursing M.Tech (ADVANCED POWER SYSTEMS) from JNTUK His area of interesting Power Systems, Non Conventional Sources, Photo voltaic energy system for maximum power point tracking. rajasekhareee232@gmail.com. REFERENCES [1] J Surya Kumari, Ch Sai Babu et.al, An Enhancement of Static Performance of Multilevel Inverter for Single Phase Grid Connected Photovoltaic modules, International journal of Recent Trends in Engineering, Academy Publishers, Finland, Vol. 3, No. 3, May 2010, pp [2] Balakrishna S, Thansoe, Nabil A, Rajamohan G, Kenneth A.S., Ling C. J., The Study And Evaluation Of Maximum Power Point Tracking Systems, Proceedings Of International Conference On Energy And Environment 2006 (ICEE 2006), Organized by University Tenaga Nasional, Bangi, Selangor, Malaysia; August 2006, pp [3] Jawad Ahmad, A Fractional Open Circuit Voltage Based Maximum Power Point Tracker for Photovoltaic Arrays, Proceedings of 2 nd IEEE International Conference on Software Technology and Engineering, ICSTE 2010, pp [4] R. Faranda, S. Leva, V. Maugeri, MPPT techniques for PV systems: energetic and cost comparison. Proceedings of IEEE Power and Energy Society General Meeting- Conversion and Delivery of Electrical Energy in the 21st Century, 2008, pp [5] I.H. Altas; A.M. Sharaf, A Photovoltaic Array Simulation Model for Matlab-Simulink GUI Environment. Proceedings of IEEE, IEEE [6] Abu Tariq, M.S. Jamil, Development of analog maximum power point tracker for photovoltaic panel. Proceedings of IEEE International Conference on Power Electronic Drive Systems, 2005, PEDS 2005, pp [7] M.A.S. Masoum, H. Dehbonei, Theoretical and experimental analysis of photovoltaic systems with voltage and current based maximum power point trackers, IEEE Transactions on Energy Conversion, vol. 17, No. 4, pp , Dec [8] J.H.R. Enslin, M.S. Wolf, D.B. Snyman and W. Swiegers, Integrated photovoltaic maximum power point tracking converter, IEEE Transactions on Industrial Electronics, Vol. 44, pp , December Ch. Sai Babu received the B.E from Andhra University (Electrical & Electronics Engineering), M.Tech in Electrical Machines and Industrial Drives from REC, Warangal and Ph.D in Reliability Studies of HVDC Converters from JNTU, Hyderabad. Currently he is working as a Professor in Dept. of EEE in JNTU, Kakinada. He has published several National and International Journals and Conferences. His area of interest is Power Electronics and Drives, Power System Reliability, HVDC Converter Reliability, Optimization of Electrical Systems and Real Time Energy Management. chs_eee@yahoo.co.in J.Surya kumari was born in Kurnool, India in She received the B.Tech (Electrical and Electronics Engineering) degree from S.K University, India in 2002 and the M.Tech (High voltage Engineering) from J.N.T University, Kakinada in In 2005 she joined the Dept. Electrical and Electronics Engineering, R.G.M. College of Engineering and Technology, Nandyal, as a Assistant Professor. She has published several National and International Conferences. Her field of interest includes Power electronics, Photovoltaic system, Power systems and High voltage engineering