SiC 99.55%-Efficient Fanless Three-Phase Three-Level Flying Capacitor Converter

The multilevel flying capacitor converter (ML-FCC) has garnered widespread recognition and adoption across various applications over decades. However, achieving an efficiency of ≥99% in the three-level (3L) version of this topology presents a significant challenge. To address this barrier and maximize the converter's efficiency to the greatest extent possible, this article proposes three discontinuous phase-shifted pulse width modulation (DPS-PWM) techniques, which are applied to a 10 kW SiC MOSFET 3L-FCC. These modulation strategies inhibit power device switching when the waveforms reach their peak values, a region referred to as the nonswitching region (NSR) in this article. Even with a substantial load imbalance (>33%), the efficiency of the converter remains largely unaltered. The highest efficiency, achieved at 75% of full load, is approximately 99.55%, while maintaining an efficiency around 99.5% at full load, measured after one hour of fanless operation. Avoiding voltage ripple on flying capacitors (FCs), enhancing the utilization of the input dc voltage/source, and preventing losses associated with FCs and dead-time during the NSR are additional advantages of the proposed modulation approaches.