Partial shading conditions decreases the output power from photovoltaic systems and causes multiple ‎maximum power points on output characteristics because of the mismatching power losses among the PV ‎modules. The shading pattern, the shaded area and the PV array topology are the main factors which affects the ‎mismatching power losses. The main aim of this paper is to study and enhance the ‎performance of a PV system under different array topologies and partial shading conditions and reach to the ‎most convenient topology. PV array topologies including series, parallel, series-parallel and total-cross-tied are ‎studied. Row, column, narrow, wide, middle and random partial shading patterns are considered at the ‎different PV array topologies. The performance is measured according to the maximum output power, ‎mismatching power losses, fill factor, efficiency, open circuit voltage and short circuit current. The parameters and data specification ‎of Suntech Power STD250-20/Wd‎ PV module are used for the simulation based on MATLAB/Simulink ‎software.‎