Cost-effective 97%-efficiency charge-pump voltage balancer for multi-level PWM photovoltaic micro-inverter

Abstract

In this paper, cost-effective high-efficiency photovoltaic (PV) power conditioning system (PCS) applicable for small-scale grid tied micro inverters usually under 400 W is proposed. The two-stage PCS consists of a modified H-bridge topology producing 5-level output and a boost converter magnetically-coupled with a secondary charge-pump circuit to provide charge balancing with isolation. Compared to the previous multi-level micro-inverter systems, the inverter circuit has reduced the part count, the DC-DC stage enables Maximum Power Point Tracking (MPPT) without power-conversion efficiency compromise during the voltage balancing operation at the neutral point of the DC-link capacitor for a low-cost 5-level photovoltaic inverter. Also, the voltage ratios are automatically maintained by the coupled-inductor turns ratio, thereby eliminating the additional control circuit for maintaining voltage balancing. Proposed micro-inverter topology is proved by the simulation and hardware prototype experiments.