A high efficiency DC MIC for PV energy harvest in FREEDM systems

The future renewable electric energy delivery and management (FREEDM) system provides a DC interface for alternative energy sources. As a result, photovoltaic (PV) energy can be easily delivered through a DC/DC converter to the FREEDM system´s DC bus, without the requirement of an additional DC/AC inverter. For this PV converter, the module integrated converter (MIC) is a good candidate. In this paper, two types of DC MIC structures, parallel connected MICs and series connected MICs, have been compared; the parallel connected MICs have been shown to have more advantages. Then a high efficiency dual mode resonant converter topology is proposed for parallel connected DC MICs. The new resonant converter can change resonant modes adaptively depending on the panel voltage and generated power level. The operation principle of the proposed converter is explained and a DC gain analysis is performed based on the fundamental harmonic analysis (FHA) method. For performance evaluation, a 240W prototype has been built. Compared to LLC converter, the light load to medium load efficiency has been improved greatly and the maximum efficiency reaches 96.5% in the experiment.