CHIA SEET CHIN et al: EFFECT OF PARTIALLY SHADED CONDITIONS ON PHOTOVOLTAIC . . . IJSSST, Vol. 12, No.3 ISSN: 1473-804x online, 1473-8031 print 52 Effect of Partially Shaded Conditions on Photovoltaic Array’s Maximum Power Point Tracking Chia Seet Chin, Prabhakaran Neelakantan, Soo Siang Yang, Bih Lii Chua, Kenneth Tze Kin Teo Modelling, Simulation and Computing Laboratory School of Engineering and Information Technology Universiti Malaysia Sabah, Kota Kinabalu, Malaysia. msclab@ums.edu.my, ktkteo@ieee.org Abstract: Maximum power point tracking algorithm is widely implemented in photovoltaic system to maximize the PV array output power. In general, Perturb and Observe (P&O) is simple thus being selected to continuously track the array maximum power point (MPP). Under uniform solar irradiance, PV array characteristic is non-linear and consisting only one MPP along the functional operating voltage. However, when the PV array is partially shaded, the P-V characteristic becomes more complex with multiple MPPs. The occurrence of multiple MPP might cause the PV array to be trapped at the local MPP. At this operating condition of local MPP, PV array will generate lesser output power. In this study, the performance of PV array is explored especially when each PV module is at 30% and 70% shaded conditions. Simulation results show that PV array at absolute MPP can generate greater output power with the largest increased by 74.6% hence achieving higher power efficiency. Keywords: PV array; partially shaded conditions; maximum power point; perturb and observe I. INTRDUCTION The world primary energy demand is expected to increase 1.7% per year from the year 2002 and expending more than 50% at 2030 [1]. It is projected the main global energy consumption will be continuously dominated by fossil fuel. Due to the awareness of global warming and climate change, nations are concerned of the planet's carbon emissions and fossil fuel used. Therefore, renewable energy resources such as solar energy will play a significant role in the world energy in the upcoming future [2]. Solar energy is the sun’s radiant energy where the radiate amount is enormous. Solar energy can be converted directly into electrical energy via solar cell and the phenomenon is commonly described as photovoltaic (PV) effect [3]. Solar energy has gained the world’s interest as it is a promising option of renewable energy. The conversion of solar energy to electrical energy is static, quite, free of moving object and does not have any negative impact to the environment. Therefore, the annual growth of the world PV industry has reached an average of 30% during the past decade [4]. Commercial PV module is configured from series, parallel or combination of series and parallel connection of PV cells. Solar irradiance, cell temperature, tilt angle shaded condition and the operating condition are among the factors that will influence the output current and power characteristics of the PV module. However, the electricity generation is mainly affected by the level of solar irradiance. The amount of incident light to the PV module will determine the total generation charge carrier hence the generated current in the PV module [5, 6]. In general, PV array is formed by a couple of PV modules to obtain larger output power. II. LITERATURE REVIEW In [2], [3] and [4], the authors presented the non-linearity of the I-V and P-V characteristics when the PV system is under uniform illumination of sunlight. Generally, PV system has a unique operating point named as maximum power point (MPP) which will produce maximum power at the optimum voltage and current. The authors in [4] proved that the MPP is varied according to the amount of solar irradiance as the PV characteristics diverse as the changing of the atmospheric conditions. Cell temperature is one of the factors discussed in [3] which will influence the position of MPP. However, [3] and [4] did not discuss the effect of partially shaded condition on the PV system. In [3] and [7], the authors proposed maximum power point tracking (MPPT) algorithm to identify the MPP in the uniform illuminated PV system. According to [7], Perturb and Observe (P&O) method is commonly used for its simplicity and low cost implementation. P&O is able to maximize the power generation of the PV system by continuously tracking the MPP regardless of the changing of the atmospheric conditions. However, the research is only limited to the uniform illuminated conditions. The studies in [8], [9] and [10] show that when the PV array is under partially shaded conditions (PSC), the array characteristics become more complex with multiple MPPs. PSC is defined as the circumstance where one or more of the PV modules in the array received less amount of solar irradiance. The existence of multiple MPPs reduces the effectiveness of MPPT algorithm since the power losses of