Maximum power point tracking with capacitor identifier for photovoltaic power system

A perturbation and observation method with a capacitor identifier is presented for maximum power point tracking (MPPT) in a photovoltaic power system. Usually, by increasing or decreasing the duty ratio of on-state of switching device, the maximum power point is tracked. The variation of duty ratio is determined by considering its circuit parameters. However, it is known that actual capacitance of an electrolytic capacitor in parallel with the photovoltaic array has 50% tolerance of its nominal value. If the variation of duty ratio is determined based on its nominal value, the performance of the MPPT is degraded. Thus, we must change the variation of the duty ratio accordingly, based on its actual value. In the system presented, the model reference adaptive system is adapted to identify the capacitor, so the capacitance can be accurately estimated and the variation of the duty ratio can be corrected by the estimated value. As a result, the high performance of the MPPT may be obtained. Experimental results are presented using a proposed power inverter using buck-boost chopper circuits.