A Fast Open-Circuit Fault Diagnosis Method of Parallel Wind-Turbine Converters via Zero-Sequence Circulating Current Informed Residual Analysis

The parallel operation of converters is increasingly being adopted to meet higher power demands and improve reliability. However, open-circuit faults in semiconductor switches must be located quickly to prevent unnecessary derating and costly offshore interventions. In parallel topologies, zero-sequence circulating current (ZSCC) distorts phase current residuals at fault inception, making conventional residual-based fault diagnosis methods unreliable. This paper proposes a fast fault diagnosis method that integrates phase current residual analysis with real-time ZSCC polarity. The method monitors which residuals exceed a fixed threshold and compares the polarity of the dominant residual with that of the ZSCC. In this way, it can distinguish and locate single-switch, same-converter dual-switch, and cross-converter dual-switch faults. A three-stage timing window mechanism captures residual and ZSCC signatures within only a few sampling periods, enabling precise fault location without additional sensors. Experimental and simulation results verify the accuracy and robustness of the proposed method, demonstrating its potential for practical deployment in offshore wind turbines.