Optimum matching parameters of an MPPT unit used for a PVG-powered water pumping system for maximum power transfer

Abstract

Photovoltaic generator (PVG)-powered water pumping has the potential to bring potable water to millions of people in developing countries. However, due to the high initial cost of PVG units, sophisticated load matching is required between the water pumping system and PVG, in order to be able to extract maximum available power from an available PVG unit at all solar radiation levels. This requires an intermediate circuitry between the PVG unit and the motor driving the water pump, which is usually termed as maximum power point trackers (MPPT). This present paper therefore investigates the optimum matching parameters of a power conditioning circuit, which is composed of a double step-up dc–dc converter (DSUC). This MPTT circuit is used for interfacing a permanent magnet (PM) motor-driven water pumping system to a PVG for extracting maximum available power from PVG, hence maximizing the energy utilization efficiency and price–performance ratio of the whole system. It is shown that two key parameters of the DSUC, which are the duty cycle and chopping frequency, are dominating the performance of the whole system, and they are interrelated and load dependent. Therefore, optimum values of these parameters need to be determined. An example system is provided in which a complete modelling is presented in time domain and through numerical experiments it is demonstrated how the optimum values of these two key matching parameters can be determined for a given system. The MPPT circuit used in this investigation is suitable for optimum matching of all types of loads to PVG units, provided that an optimum frequency–duty cycle pair is determined for the choppers in DSUC for every 5% bands of solar radiation between 20 and 100%. Copyright © 2005 John Wiley & Sons, Ltd.