Space-Vector Pulse Width Modulation for Four-Leg Voltage Source Inverter Under Line-to-Line Short-Circuit Faults

This paper propose a novel space vector pulse-width modulation (SVPWM) to achieve fault tolerance (FT) under line-to-line (LL) short-circuit (SC) conditions for three-phase four-leg (3P4L) inverter. The primary objective of the proposed method is to maintain normal voltage supply to the all phases while ensuring that zero voltage is applied to the faulted line during an LL fault. To achieve this, a new coordinate transformation method is introduced to accurately extract the magnitude of unbalanced three-phase voltages. The proposed coordinate transformation handles a three-dimensional (3-D) plane under LL fault, enabling conversion to a two-dimensional (2-D) plane via transformation along the $\gamma $ - axis. This transformation remains effective even under LL fault, ensuring reliable voltage magnitude detection and control through the synchronous reference frame (SRF) transformation. Additionally, an SVPWM switching strategy tailored for fault conditions is developed. By analyzing the 3P4L inverter’s switching vector diagram, a specific combination of switching vectors is proposed to apply zero voltage to the faulted line. The effectiveness of the proposed strategy is validated through experimental results from a 30 kW-class 3P4L inverter.