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Soft-Switched Modulation Techniques for an Isolated Bidirectional DC–AC

Two carrier-based unipolar-sinusoidal pulse width modulation (SPWM)-oriented modulation techniques for an isolated bidirectional dc–ac converter are proposed, compared, and validated in this paper. The dc–ac converter is composed of a full-bridge (FB) inverter cascaded with a cycloconverter through a high-frequency transformer. Both modulation techniques proposed in this paper can realize zero-voltage switching (ZVS) for the FB inverter and zero-current switching or ZVS for the cycloconverter in all load range, and are able to suppress the voltage spikes introduced by the transformer leakage inductance as well. In order to increase the converter efficiency and power density, we propose to utilize SiC MOSFETs for the converter. The first modulation technique enables the utilization of Si-SiC hybrid switches with no synchronous rectification (SR), for the purpose of lowering the converter cost. The second modulation technique requires all switches to be SiC MOSFETs, but with SR, which increases the converter efficiency. A 400-V dc to 240-V ac 1.2-kW prototype has been developed to validate the effectiveness and performance of the proposed carrier-based unipolar-SPWM-oriented modulation techniques.