A General Low-Frequency Zero-Sequence Circulating Current Suppression Approach for Coordinated PWM Schemes in Two-Parallel Three-Phase Two-Level Power Converters

This paper addresses the challenge of mitigating low-frequency circulating currents caused by imbalanced inductance while preserving the inherent benefits of coordinated PWM schemes. The analysis reveals that traditional common-mode injection is incompatible with the coordinated PWM schemes. To resolve this, this paper proposes a general approach to suppress the low-frequency circulating current for the coordinated PWM schemes. Unlike the traditional common-mode signal injection, the proposed method features the different-mode signal injection into different phases at specific vector angles. The proposed method preserves the intricate vector sequences of coordinated PWM schemes, maintaining their original benefits. Moreover, a comprehensive control model and structure are developed to support differential-mode signal injection. Finally, two typical coordinated PWM schemes were chosen as case studies, covering both clamping and non-clamping methods. The proposed method was applied to these schemes to suppress low-frequency circulating currents, and the effectiveness was validated through testing on a prototype. Experimental results confirm that the proposed method effectively suppresses low-frequency circulating currents while retaining the performance characteristics of the original PWM schemes. This work is a progressive extension of the existing coordinated PWM schemes to enhance their practical applicability.