V/sup 2/-based power tracking for nonlinear PV sources

The photovoltaic generator exhibits a nonlinear i/v characteristic and its maximumpower point varies with solar insolation. A V2 based MPP tracking scheme is developed using a SEPIC topology. Mathematical models are formulated and a tracking algorithm then is evolved. A combined photovoltaic-system simulation model is developed in the SIMULINK. For a given solar insolation, the tracking algorithm changes the duty ratio of the convertor such that the solarcell- array voltage equals the voltage corresponding to the maximum-power point. This is done by the tracking algorithm, which mainly computes the power, proportional to the square of the terminal voltage, and changes the duty ratio of the convertor so that this power is a maximum. The proposed algorithm is implemented in real time with the help of an analogue device DSP module. Results are obtained for different types of loads, including battery and other nonlinear loads. Experimental investigations are carried out for different numbers of samples and an optimum number of samples is found which results in the minimum magnitude of steady-state oscillations. It is shown, experimentally, that tracking of the maximum-power point can be achieved within 200 ms. The proposed peak-power-tracking effectiveness is compared with that of the conventional ‘VI’-based tracking scheme.