Determining the output voltage of a PV panel corresponding to the maximum power point (MPP) under variable temperature and irradiation conditions is essential for tracking the maximum power point. The P&O method is widely used due to its simplicity and ease of implementation. A disadvantage of the P&O algorithm is that the PV panel operation points oscillate around the MPP which causes energy loss. In general, the conventional fixed step-size method can exhibit a fast dynamic response when a large step-size is used. On the contrary, if a small step-size is used, the steady-state operation can be improved, but the dynamic response is deteriorated. In this paper, a novel auto-scaling variable step-size maximum-power -point-tracking (MPPT) method is proposed. The proposed method can automatically adjust the step-size of the tracking algorithm to achieve the fast dynamic response that can adapt to weather changes and thereby achieve stable steady-state output power. In this modified P&O method, a large perturbation step is adopted when the present operating point is far from the MPP whereas a small step-size is adopted in the close vicinity of MPP.
A theoretical analysis and the design principle proposed algorithm are provided and its feasibility is also verified by simulation results.