A Secondary-Side Modulation Method for Suppressing Transient Voltage Spikes in Cycloconverter-Based DC-AC Converters

To suppress transient voltage spikes across the ac-side MOSFET in cycloconverter-based dc-ac converters, this article proposes a secondary-side modulation (SSM) method that synchronizes MOSFET turn-off with the channel current zero-crossing. This synchronization minimizes body-diode conduction time, thereby suppressing the transient voltage spikes. The method enhances design flexibility by enabling the use of Si MOSFETs with lower breakdown voltage and lower on-resistance, while relaxing constraints on transformer leakage inductance - all without additional clamping circuits. Experimental results on a 300 W prototype demonstrate a 110 V reduction in peak transient voltage with a 950 V Si MOSFET. The suppressed voltage stress further allows for the adoption of a 650 V Si MOSFET, achieving a peak efficiency of 94.18% at 110 V/50 Hz output. Thus, the proposed SSM offers an efficient and cost-effective solution for cycloconverter-based dc-ac converters in photovoltaic and other industrial applications.