Modified Discontinuous PWM for Size Reduction of the Circulating Current Filter in Parallel Interleaved Converters

Parallel voltage-source converters (VSCs) require an inductive filter to suppress the circulating current. The size of this filter can be minimized by reducing either the maximum value of the flux linkage or the core losses. This paper presents a modified discontinuous pulsewidth modulation (DPWM) scheme to reduce the maximum value of the flux linkage and the core losses in the circulating current filter. In the proposed PWM scheme, the dwell time of an active vector is divided within a half-carrier cycle to ensure simultaneous occurrence of the same zero vectors in both VSCs. A function to decide the ratio of the dwell time of the divided active vector is also presented. The effect of the proposed PWM scheme on the maximum value of the flux linkage and the core losses is analyzed and compared with that of the space vector modulation and 60$^\circ$ clamped DPWM schemes. The analytical expressions for the maximum value of the flux linkage are derived for each of these PWM schemes. In addition, the effect of the proposed PWM scheme on the line current ripple and the switching losses is also analyzed and compared. To verify the analysis, experimental results are presented, which prove the effectiveness of the proposed PWM scheme.