Control of a full-converter Permanent Magnet Synchronous Wind Generator with Neutral Point Clamped converters during a network fault

This paper analyses the behaviour of a full-converter wind generation system with a back-to-back conversion structure using Neutral Point Clamped (NPC) converters during network faults. A Permanent Magnet Synchronous Generator (PMSG) is used as the generator. The main problems of this structure during voltage sags are firstly, the accumulation of power in the DC-link due to the reduction of power delivered to grid, and secondly, the control of the neutral point voltage. Three control strategies are proposed with the purpose of optimizing operation under network fault conditions. The characteristics of those strategies with regard to DC-link voltage control, torque variations required of PMSG and neutral point voltage control are also discussed.