Abstract:

It is necessary to develop an efficient maximum power point tracking （MPPT） method to improve the output efficiency of a photovohaic （PV） system. In this paper, some theoretical analyses and simulations are performed. It is found that the output photocurrent of the same piece of solar cell remains constant when the tempera- ture and irradiation are the same and when the diode quality factors and reverse saturation currents are different. Based on this conclusion, a variable-voltage MPPT algorithm that tracks the maximum power point in different weather conditions is proposed. In the proposed algorithm, the combined perturb and observe （PO） method is used to acquire the actual diode quality factor and reverse saturation current, and a comprehensive compensation without the PO method is employed to track the actual maximum power point. The correctness and effectiveness of the pro- posed algorithm are finally verified in different weather conditions.

Key words: photovoltaic system, renewable energy, maximum power point tracking, photocurrent, Diode factor, reverse saturation current