Current-fed dual-half-bridge converter directly connected with half-bridge inverter for residential photovoltaic system

A current-fed dual-half-bridge (CF-DHB) converter directly connected with a half-bridge (HB) inverter unit is proposed for residential photovoltaic power conversion systems. The proposed inverter requires only half as many switching devices as the full-bridge two-stage inverters and does not have to use a large dc-link capacitor. However, the converter unit suffers from 120-Hz dc-link voltage fluctuation and 60-Hz capacitor voltage unbalance, which degrade the control performance of the half-bridge inverter. To suppress both dc-link voltage fluctuation and capacitor voltage unbalance, we propose to use appropriate repetitive controllers, that are used to determine the nominal duty-ratio and the phase-shift. To make the proposed CF-DHB operate at the maximum power point (MPP), we use the incremental conductance method that offers smooth transition to MPP. Experimental results show that the proposed inverter system achieved high MPP tracking efficiency, low total harmonic distortion, high power conversion efficiency, and medium power capacity.