Transformerless Wind Energy System Based on a Series Double NPC Multilevel Rectifier and a Six-Phase Asymmetrical PMSG

This paper introduces a transformerless configuration of generator and power converter that is suitable for offshore wind energy systems. The proposed configuration is based on a series connection of two neutral point clamped (NPC) multilevel rectifiers, powered by a six-phase asymmetrical permanent magnet synchronous generator (PMSG). Additionally, this work proposes a control strategy that opens the door to a fault-tolerance mode, by the use of independent controllers for each NPC converter, directly operating in a large-signal nonlinear space. This closed-loop system permits to prevent disruptions due to faults at either the generator winding or one of the NPC converter, by allowing a modular modification of set-points over the whole system operating region. Simulation results show the feasibility of the proposed configuration, rendering a promising solution for future wind energy generation systems.