A Fault-Tolerant Permanent-Magnet Traction Module for Subway Applications

A fault-tolerant permanent-magnet traction module is proposed for subway application, which has three different operation modes: normal, isolation, and fault-tolerant mode. In normal mode, 2 three-phase permanent-magnet synchronous machines (PMSMs) are controlled by 2 three-leg voltage-source inverters (VSIs), respectively. The proposed module can output maximum torque and reach the maximum velocity. When one leg fails, the corresponding PMSM is isolated from the fault VSI and the fault subway train operates in isolation mode, in which the traction effort is reduced but the maximum velocity can be maintained under light load. However, the fault subway train will stop if the load is heavy. To avoid the stop, the fault subway train is switched into fault-tolerant mode, in which the healthy VSI and fault VSI are reconfigured to 1 five-leg VSI by a fault-tolerant bridge. Due to lower phase-phase voltage apportionment ratio, the fault-tolerant mode is not used until the velocity is decreased to half of the maximum velocity. In fault-tolerant mode, the nonadjacent selection principle is proposed to prevent the common leg from overcurrent damage. The subway train equipped with the proposed module can maintain basic operation performances if any leg fails. The performances are analyzed and the effectiveness is verified by experimental results.