Modulation of Two Parallel-Connected Converter with Reduced Circulating Current

Two parallel-connected converters are preferred to improve ac-side current ripple, thermal management, power capability, maintainability of the system. The two-parallel connected converters may be modulated considering the system as a single three-level (3L) converter. Therefore, the 3L space vector PWM may be used to reduce the ac-side current ripple. This is done by applying the three nearest vectors in an equivalent 3L space vector diagram. However, a high frequency circulating current is present in the ac side which depends on the difference between the common-mode (CM) voltages generated by the individual converters. The CM voltage difference is analyzed in this paper. Using this analysis, a modulation strategy is proposed to reduce the circulating current while applying the three nearest vectors in the equivalent 3L space vector diagram. The paper presents the carrier based implementation of the proposed method which is verified by simulation results.