Differential-Mode and Common-Mode Coupled Inductors for Parallel Three-Phase AC–DC Converters

In this paper, an integrated structure of coupled inductors is proposed for three-phase ac–dc power conversion. According to the differential-mode and common-mode, three coupled inductors are integrated into two inductors; one for suppressing only differential-mode circulating current, the other only for common-mode circulating current. With a series connection, two proposed inductors can be designed to replace the three coupled inductors with an identical impedance and smaller size. The proposed inductors can easily be built with standard shape cores which gives a large advantage on design for manufacturability. Analytic solutions of the maximum magnetic flux for the proposed inductors are derived for space vector PWM (SVPWM) and discontinuous PWM (DPWM)60° to estimate possible size-reduction in flux-limited designs. The solutions show that maximum volt-seconds is reduced by 33% for whole modulation index range in the DPWM60° case and a high modulation index range for the SVPWM case. A simple design guideline to replace the conventional coupled inductors is provided. The validity of the proposed integration is verified by circuit simulation and finite element analysis. A prototype design shows that the total weight and volume of the coupled inductors could be reduced by 20%. The proposed integration has been verified by an experiment with 1 kW paralleled three-phase converters.