Photovoltaic (PV) systems are becoming increasingly popular due to its advantages such as abundant availability, eco-friendly nature and low maintenance requirement. In large PV arrays occurrence of partial shading is very high. Under partially shaded conditions the P-V curve of the array exhibits multiple peaks and the conventional maximum power point tracking (MPPT) algorithms fail to detect the global peak. Recently particle swarm optimisation (PSO) technique has gained significant attention due to its ability to locate the maximum power point for any type of P-V curve. Many variations of PSO algorithm to improve its effectiveness are also available. One variation is the accelerated PSO (APSO) where the algorithm is modified to simplify the search process. This study proposes a simple and efficient MPPT for a PV system using a modified APSO algorithm. The proposed algorithm has been validated through simulation and experimental setup for different shading patterns.