Modeling and control of DC/AC converters for photovoltaic grid-tie micro-inverter application

Abstract

Abstract This paper is devoted to the modelling and control for a low cost, high-power quality single-phase voltage source inverter (VSI) for a grid-tied PV-based micro-inverter system. The first stage includes a high-efficiency isolated boost dual half-bridge dc-dc converter topology which interfaces to the PV panel and produces a dc-link voltage. The second stage is comprised of a single-phase VSI circuit. A state-space average model for a 1-Φ VSI with low-pass LCL filter topology has been developed. The steady-state and dynamic performance of the system can be improved by using three cascaded control loops. The fast inner current controller is adopted to regulate the inductor current of the inverter thereby improved dynamic response of the system. The small-signal analysis is conducted to assess the robustness of the proposed controller. An outer dc bus voltage control loop is employed to keep the constant voltage across the dc-bus capacitor. Next, the grid-side current loop is employed to regulate the grid current with a low total harmonic distortion level. The Bode-diagrams are plotted to assess the stability of each control loops. Finally, a 500 Watts, 110\u202fV, 50\u202fHz micro-inverter prototype is fabricated and tested. The simulation and experimental results are given to show the effectiveness of the proposed control scheme.