A Multiple Open-Circuit Fault Diagnosis Method for Two-Level Three-Phase Voltage Source Converters Based on Average-Phase Voltage Model

This article presents a fault diagnosis method in the two-level three-phase voltage source converter (VSC) systems based on the average-phase voltage (APV) model without additional sensors or hardware circuits, which can diagnose and locate multiple open-circuit (OC) faults correctly and quickly. First, based on the idea of APV within one switching period and the changing rules of basic voltage vector after OC faults, the APV model consisting of grid-side APV (GAPV) model, prefault converter-side APV (CAPV) model, and postfault CAPV model is proposed. The APV model can be used to estimate the phase voltage under different OC faults. And then, the residual feature between GAPV and CAPV is analyzed under different single or multiple OC faults. With the help of the proposed APV model, both single and multiple OC faults can be diagnosed by deviation polarity, which avoids the complex deviation polarity sequences judgment. Meanwhile, the fault diagnosis method has the ability of correctness verification, which can strengthen the robustness and prevent false alarms. Finally, the effectiveness of the proposed model and method is validated with experiments; the multiple OC faults can be located within 2.5 ms.