PUBLICATIONS

Three-level topologies are widely used in back-to-back converters of wind turbine generation (WTG) systems. In comparison with a

conventional two-level topology, three-level topologies have more advantages, particularly for the high power. Neutral-point clamped

(NPC) and T-type are typical three-level topologies. An open-switch fault of a three-level rectifier that is connected to a permanent-

magnet synchronous generator (PMSG) leads to the current distortion and torque vibration in WTG systems. Furthermore, WTG

systems can break down in the worst case. Therefore, a tolerance control for open-switch faults is required to improve the reliability

of WTG systems. WTG systems by applying the tolerance control can be stopped safely and prevent additional problems. Depending

on the situation, it can keep the operation of WTG systems under open-switch fault. The effects of outer open-switch faults of three-

level rectifiers are analyzed by considering PMSG specifications in this paper. Moreover, a tolerance control for outer open-switch

faults of the NPC and T-type three-level rectifiers are proposed with existing tolerance controls for inner open-switch faults. The

proposed tolerance control is to inject the exact d-axis current value to eliminate current distortion. The simulation and experiment

are conducted to prove the feasibility of the proposed tolerance control and to identify its performance.