Micro-inverter based on quasi-Z-source inverter integrating switchless voltage equalizer for photovoltaic panels under partial shading

Abstract

Conventional photovoltaic (PV) systems using a micro-inverter tend to be complex and costly as three separate converters (i.e., a boost converter, inverter, and voltage equalizer to prevent partial shading issues) are necessary. This paper proposes a novel micro-inverter integrating a voltage equalizer to achieve not only system-level but also circuit-level simplifications. The voltage can be boosted by the capacitor-assisted extended-boost quasi-Z-source inverter (CAEB q-ZSI), while the partial shading issues can be precluded by the switchless voltage equalizer based on the voltage multiplier that is driven by a square wave voltage generated in the q-ZSI. The derivation procedure and fundamental operation analysis are explained and discussed. The prototype for a standard 72-cell PV panel consisting of three substrings connected in series was built, and the equalization test was performed emulating a partial shading condition. The extractable maximum power from the PV panel was significantly increased by the prototype, demonstrating the efficacy of the proposed integrated micro-inverter.