A Control Strategy for Power Regulation in a Direct-Drive WECS With Flexible Drive-Train

The ever-increasing penetration of wind power into the electric power systems indicates the need that wind energy conversion systems (WECSs) should be able to regulate their output real power, since their participation in power-flow control is expected to be essential for power systems stability. On the other hand, the tendency to build larger WECSs at competitive costs encourages lighter and, consequently, more flexible drive-trains. However, a softer drive-train may give rise to undamped drive-train oscillations when the WECS exercises output power regulation. This paper proposes an enhanced control strategy that enables a direct-drive WECS based on the permanent magnet synchronous generator (PMSG) to damp its drive-train torsional mode, even if the output real power of the WECS is regulated. A procedure is presented for tuning of the proposed control to ensure the internal stability of the WECS, considering the impacts of the proposed control on the dynamic performance of the host WECS.