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

Abstract

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.