Maximum Power Point Tracking with Estimating Capacitance of Capacitor Connected to Photovoltaic Array

Abstract

This paper presents a perturbation and observation method with a capacitance estimation for the maximum power point tracking (MPPT) in a photovoltaic power system. Usually, by increasing or decreasing the duty ratio of power switching devices, the maximum power point is tracked. The variation of duty ratio is determined by considering the circuit parameters. However, it is well known that actual capacitance of an electrolytic capacitor in parallel with the photovoltaic array has 50% tolerance of its nominal value and also the capacitor degrades its value as time passes. If the variation of duty ratio is determined by its nominal value, the performance of MPPT may be degraded. Therefore, we must use the actual capacitance in order to improve the MPPT performance. In our system, we adapt the model reference adaptive system to estimate the capacitance, then we can obtain the accurate capacitance and correct the variation of duty ratio by the estimated value. As a result, we may obtain the high performance of MPPT. Experimental results show that the proposed method can track the maximum power point stably instead of the variation of capacitance using a newly developed inverter using Buck-boost chopper circuits.