International Journal of Computer Applications (0975 – 8887) Volume 56– No.12, October 2012 5 Improvement of the “Perturb and Observe” MPPT Algorithm in a Photovoltaic System under Rapidly Changing Climatic Conditions Ali Chermitti URMER Research unit, Tlemcen University, B.P. 119, Tlemcen,Algeria Omar Boukli-Hacene Tlemcen University, FT/GEE/Laboratory of automatic B.P. 230, Chetouane, Algeria Bencherif Mohamed URMER Research unit, Tlemcen University, B.P. 119, Tlemcen, Algeria ABSTRACT The power delivered by a photovoltaic power system depends strongly on the level of sunlight, the cell temperature and the nature of the load supplied, Itis therefore highly unpredictable. This paper presents the improvement of the MPPT algorithm Perturb and Observe (P & O) under rapidly changing climatic conditions. The results of the simulation in Simulink confirm the efficiency of the proposed method. General Terms Photovoltaic systems,Maximum Power Point Tracking,Optimization system, Rapidly changing climatic conditions. Keywords Photovoltaic system, Perturb and Observe MPPT algorithm, Modeling, Improvement, Simulation, Rapidly changing climatic conditions. 1. INTRODUCTION The renewable energy sources like wind, solar, geothermal and biomass represent an alternative to traditional methods of producing electrical energy. The latters reject harmful combustion wastes and seriously affect the quality of life on earth. Solar energy can be converted directly into electricity using photovoltaic panels (PV) through the photovoltaic effect. However, the conversion efficiency is low and the cost of power generated is relatively high. The power characteristic of the PV generator (PVG) is nonlinear and has a particular point for which the power generated by the PVG is maximal. This is usually noted MPP (Maximum Power Point). The MPPT (Maximum Power Point Tracker) is an electronic device inserted between the PVG and its load. It aims to maintain the operating point of the system as close to the MPP. There are several MPPT algorithms in the literature, the most widely used algorithm is the “Perturb and Observe” (P&O). The purpose of this paper is the study, analysis and improvement of P&O MPPT algorithm under a rapid change in the radiation level. This paper is organized as follows: the PV generator is described in Part II. The matching stage between PVG and a load is presented in Part III. The MPPT converter and the P&O MPPT algorithm are described in Part IV. The improvement of P&O algorithm in the case of a rapid change of the lighting level is detailed in Part V. The simulation results are illustrated in Section VI, followed by a conclusion in the last part. 2. THE PHOTOVOLTAIC GENERATOR The PV cell is the basic element of a PV system. A set of cells electrically connected together form a PV module, several modules form a panel and several panels form a PV array. We will use the term PV generator (PVG) to designate a module or a PV panel. 2.1 Modeling of the PVG Fig 1: PV module (PVG) One realizes a PV panel by connecting several PV cells properly between them. The mathematical model of the PVG is given by[1,2,3,4,5,6,7,20]:                    C th s P s P P oc P P sc P V N R I V V I I exp 1 =  where the subscript "P" indicates the parameters of the panel and the index "C", the parameters of the PV cell [1,5,6,12]. 2.2 Current/Voltage (I/V) Characteristic of the PVG Figure 2 illustrates theI/V characteristics of a PVG and a resistive load R. The resistance characteristic is a line of slope 1/R. The operating point (OP) is located at the intersection of the two curves. In the AB region of the curve the PVG behaves as a current generator and in the CD region it behaves like a voltage source. In the intermediate zone BC, the characteristic of the PVG is nonlinear, it is in this area that we find the MPP (Maximum Power Point) for which the PVG