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Modulation Method and Control Strategy for Full-Bridge-Based Swiss Rectifier to Achieve ZVS Operation and Suppress Low-Order Harmonics of Injected Current

The Swiss-type rectifier (SR) uses a three-phase unfolder circuit to convert the ac voltage into two time-varying positive voltages. The power factor correction of ac sides and the stable dc voltage output can be realized by using two dc–dc topologies without any bulky decoupling capacitors. By applying the phase-shifted full-bridge topology into the dc structure, both the soft-switching and the high-frequency electrical isolation can be achieved. However, the power coupling between two full bridges using the traditional modulation method will affect the zero-voltage switching (ZVS) condition of lagging legs. Then, the duty cycle loss caused by the transformer leakage inductance will affect the input and output performance. Therefore, a new method using the up-counting mode modulation is proposed to implement the ZVS for both the lagging switches. Then, the relationship between the duty cycle loss and the extra 6N ± 1 harmonics added into the input current is theoretically analyzed. Hence, to suppress the low-order harmonics, a novel compensation strategy is proposed. The proposed modulation method and control strategy have been successfully verified by the experiments. 95% efficiency under half-rated power and 3% input current total harmonic distortion (THD) under rated power have been achieved under a 10-kW 380 Vac input/400 Vdc output prototype with 90-kHz switching frequency.