An algorithm for the estimation of the Maximum Power Voltages in microconverters based PV applications

Abstract

In order to extract the maximum energy from PhotoVoltaic (PV) systems operating under mismatching conditions, the adoption of a Hybrid Maximum Power Point Tracking (HMPPT) technique is necessary. Such a technique is based on the coupled use of two control techniques. The first one is a MPPT technique which is distributed on all the PV modules of the field and which properly regulates the operating voltage of each PV module. It is called Distributed Maximum Power Point Tracking (DMPPT) technique because it is carried out by means of suitable DC/DC converters (microconverters) which are distributed on all the PV modules of the array. The second control technique is called Central Maximum Power Point Tracking (CMPPT) technique because it is carried out by the central inverter which properly regulates the operating voltage of the whole PV array. The adoption of a HMPPT technique is necessary because, in order to extract the maximum available energy from a PV system operating in mismatching conditions, the proper regulation either of the PV modules voltages or of the DC inverter input voltage is necessary. One possible HMPPT technique adopts a Perturb & Observe (P&O) based DMPPT technique and a CMPPT technique which is based on the periodic sweep of the power versus voltage characteristic at the input of the inverter. Such a HMPPT technique is characterised by two major drawbacks: the waste of available energy during the sweep and the relatively low tracking speed. In this paper a new algorithm, called Fast Estimate of the Maximum Power Voltages (FEMPV), which can be profitably used in HMPPT applications in order to overcome the above drawbacks will be discussed. The case of microconverters based on the adoption of the buck, boost and buck-boost topology will be studied in detail.