Performance Comparison Between Boost-based Closed-loop and Open-loop Maximum Power Point Tracking Techniques of Photovoltaic in Islanded Microgrid Environment

Abstract

In microgrids based on photovoltaic/battery generation, uncertainties during islanded operation can cause voltage and frequency fluctuations, making the control systems involved in the microgrid more difficult to action. From the photovoltaic maximum power point tracking (MPPT) point of view, to reduce the effects of uncertainties it is necessary to use a more robust method that guarantees correct supplying. In this paper, a comparison between two MPPTs based on the conventional Perturb & Observe algorithm is proposed, in the first one MPPT directly returns the duty-cycle for the DC-DC boost converter, being denominated of open- loop, and in the second one, the MPPT output voltage signal passes through internal cascaded proportional-integral loops before being converted in duty-cyle signal, being denominated of closed-loop. The objective is to evaluate the robustness provided by the closed-loop method, especially during the islanded operation. Both algorithms were simulated in MATLAB/Simulink with a 1,725W photovoltaic array (RISEM RMS 72-6-345P). The comparison analysis is based on the power quality delivered to the load through the observation of total harmonic distortion (THD), ripple level, settling time, and steady-state error. Results suggest that the closed-loop method provides a better and more reliable MPPT.