Power decoupling capability with PR controller for Micro-Inverter applications

Abstract

Micro-inverters have been known as promising structures for small-scale PV systems. However, these structures need energy storage elements to balance the instantaneous output and input power. Demanding a large size capacitor forces using an electrolytic type at the dc-link that affects the micro-inverter lifetime. This paper presents a new Active Power Decoupling (APD) circuit for the micro-inverters to reduce the capacitor size at the dc-link and utilize film capacitors instead of electrolytic types. The proposed APD circuit is based on a single-phase flyback converter. This structure is controlled based on the PQ theory and a Proportional Resonant (PR) controller for delivering the PV panel energy to the grid and eliminating the pulsation power through the switching pattern control. Simulations and experimental results of a 180 W single-phase micro-inverter prototype were performed to evaluate the performance of the proposed structure and the control scheme. It was found that this controller can accurately regulate the switching pattern to remove the ripples of input current and voltage. Furthermore, the robustness and fast dynamic performance of the proposed configuration have been confirmed during input power variation. In conclusion, this single-phase micro-inverter structure has an efficiency of ∼ 91%, THDi of 3.6%, and a long lifetime.