Operation of a Bidirectional Series-Resonant Converter With Minimized Tank Current and Wide ZVS Range

Due to wide soft-switching operation range, high-frequency isolated resonant converters are featured with low switching losses. Therefore, it is meaningful to minimize the resonant tank current in an isolated resonant converter in order to enhance the overall system efficiency. In this work, a bidirectional series-resonant converter under phase-shifted modulation combined with a modified pulsewidth modulation gating scheme is addressed. The modified pulsewidth modulation gating scheme is helpful to keep more switches operating in zero-voltage switching (ZVS) at light load. According to the steady-state analysis with the fundamental harmonic approximation approach, a specified control strategy with minimum rms tank current based on three control dimensions is proposed in closed form. The validity of the proposed control strategy is verified through experimental tests. The pulsewidth of modulated voltage using the modified gating scheme is larger than that of the conventional pulsewidth modulation voltage, which compensates for the effects of more high-order harmonics on rms current. Therefore, compared with existing control strategies for minimum current operation, the proposed control strategy demonstrates comparable performance in depressing conduction loss and wider soft-switching range in high load range. And it is able to achieve higher efficiency at light load, thanks to more switches working in ZVS.