Variable Switching Frequency Phase Shift Modulation for Zero-Voltage-Switching in Two-Parallel SiC Converters

Zero-voltage-switching (ZVS) schemes are effective approaches for parallel converters to increase switching frequency, efficiency, and power density. However, existing ZVS methods based on variable switching frequency control face either a wide switching frequency range or excessive current ripples, resulting in high current stress and suboptimal efficiency. To address this issue, this article proposes a variable switching frequency phase shift pulse width modulation (VSF-PSPWM) for parallel converters. All switches operate in critical ZVS regions, thereby eliminating unnecessary current ripple. In the proposed VSF-PSPWM, the switching frequencies of three pairs of interleaved triangular carriers with 180° phase difference are first synchronized and varied to shape the half-bridge (HB) currents into quadrilateral waveforms, creating sufficient ZVS conditions for all switches. Then, in over-ZVS regions, the 180° is switched to a derived optimal phase shift angle to reduce the unnecessary current ripples. Meanwhile, the initial values of the carriers within each carrier cycle are modified to achieve positive and negative peak symmetry of the quadrilateral circulating current. Finally, experiments are conducted on a two-parallel SiC converter prototype to verify the effectiveness of the proposed method.