Soft-Switching Analysis of Beat Frequency Modulated Microinverters

A novel beat frequency modulation strategy has recently been proposed for microinverter applications. As converters controlled using such modulation schemes involve switching at two different frequencies, the soft-switching performance of the converters varies with time and is worthwhile investigating. This paper introduces a systematic way to examine the soft-switching performance in beat frequency modulated resonant power converters. Firstly, soft-switching in beat frequency modulated series resonant converter (SRC)-based microinverter is analyzed at various frequencies of operation and different loaded quality factors. Furthermore, a comparative analysis is carried out between beat frequency modulated LLC and SRC-based microinverters in terms of soft-switching range, converter gain and rms currents. LLC converter showed significant improvement in soft-switching range compared to SRC while achieving the required converter gains. To validate the theoretical predictions made, 250-W beat frequency modulated series resonant and LLC converters are built and tested at various operating frequencies and loaded quality factors. Experimental results are in good agreement with the theoretical predictions.