To address stringent reliability demands of offshore renewable energy systems, particularly wind power, this paper proposes an NPC three-level rectifier based on relay-driven topology and control scheme, featuring excellent fault-tolerant capability. The proposed strategy enables real-time identification of fault locations and types, followed by relay-actuated topological reconfiguration for effective isolation of faulty phases. By redefining modulation sectors and vector sequences, and generating pulse-width modulation (PWM) signals through duty-cycle calculation combined with triangular carrier comparison, the system realizes two-level modulation control and maintains stable operation even in case of IGBT failures. This approach not only enables rapid post-fault recovery while ensuring balanced three-phase currents, but also stabilizes neutral-point voltage, significantly improving system robustness under harsh offshore conditions. Relay-centric topology eliminates need for additional power switches, further enhancing cost-effectiveness and structural simplicity of offshore wind power conversion systems.
Zheng et al. (2026) studied this question.