It's necessary to track the maximum power point (MPP) of the photovoltaic (PV) array rapidly and accurately and it can increase the output power of PV array. This paper summarizes the methods of maximum power point tracking (MPPT). Such as hill climbing and perturb & observe. Under solar irradiance changing rapidly conditions, however, these methods cannot meet the requirements of the system. Many new MPPT methods are proposed in recent years. It concentrates on four novel methods applied to partial-shading conditions. A systematic discussion is also provided at the end of the paper that focuses on the major advantages and disadvantages of each MPPT strategies.