Relay-driven topology reconfiguration enabling robust NPC rectifiers for offshore wind power systems

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.