On Controlling Wind Power Transmission to the Grid via AC and DC Connections

Abstract

In modern power grids, large renewable energy sources dominated by wind turbine (WT) installations are highly penetrated in a dispersed geographically area. The challenging issue of effectively controlling the power transmission from WTs to the ac grid is considered in this paper. Since long distance lines may be necessary for this connection, the stiffness of the ac grid becomes an essential parameter which is taken into account for the system and control performance. A comprehensive review of the doubly-fed induction generator (DFIG)-based WT system integration via ac or dc transmission is considered and examined in view of a novel, generic, cascaded type control scheme. As expected and shown by extensive simulations, especially for the case of weak ac grids, the controlled de connected WT system response is superior to that of the direct ac connection. Also, in all cases the dc link connection provides an effective and independent power or voltage regulation caused from the fact of relaxing the DFIG operation from other control tasks related to the ac grid characteristics.