Improvements on the incremental conductance MPPT method applied to a PV string with single-phase to three-phase converter for rural grid applications

Abstract

A power electronic interface that integrates a photovoltaic string with a single-phase grid to feed a threephase induction motor, while driving a fan-type load, is presented. The interface is composed of a single-phase active rectifier and a three-phase inverter with output transformer, wherein the Photovoltaic (PV) string is straightly connected to the DC-link, avoiding the use of additional converter for maximum power point tracking, commonly seen in previous works. However, in this system configuration, disturbances at the DC-link may occur due to increments and decrements of load active power, with consequent low-frequency oscillations at the AC grid side of the active rectifier. Therefore, a modified Incremental Conductance based algorithm is proposed, with which low-frequency oscillations around the maximum power point are minimized even under disturbances at the DC-link. Moreover, the overall system energy management, composed of control algorithms, that integrates maximum power point identification, DC-link voltage regulation, motor speed controller and power quality at the input AC mains, is also proposed. Simulation results are provided to evaluate the system effectiveness under AC mains with voltage sag occurrence, load transient and steady-state conditions at different solar irradiance levels.