Application and Verification of a Leg-Transfer Method for Three-Level Active Neutral-Point-Clamped Inverters for Railway Vehicles

In this paper, a two-leg-transfer switch structure method that can continuously supply three-phase power even when an accident occurs in a power semiconductor of a three-level active neutral-point-clamped (ANPC) inverter for railway vehicles is presented. The proposed method can minimize the ripple effect caused by power semiconductor faults by separating the faulty leg from the main circuit and connecting the load-side circuit to a neutral point. As a result of simulations, the average values of MAE and RMSE can be reduced by 1.53 [A] and 1.77 [A], respectively, when using the proposed leg-transfer switch structure compared to using the conventional structure. In the IGBT failure experiment, when the proposed method was applied to a three-level ANPC inverter, there was only a 0.21 [%] difference from the THD under normal conditions. As a result, the magnitude, phase, and total harmonic distortion of the three-phase current waveforms measured before and after the fault were identical. Thus, normal three-phase power could be effectively supplied to the load when the proposed leg-transfer switch method was applied after a power semiconductor fault occurred in the three-level ANPC inverter. If this leg-transfer switch method is applied in three-level ANPC inverterd for railway vehicles, track schedule errors can be minimized by continuously supplying three-phase power to the electric motor even when an accident occurs in a power semiconductor.