Doubly-Fed Induction Generators (DFIG) are widely used nowadays in grid-connected Wind Turbine Systems (WTS). The typical control strategy for WTS is the maximum power coefficient tracking method. However, this method limits desirable ancillary services from WTS, such as power quality improvement in the network. Therefore this paper derives the optimal reference power coefficient of the WTS that can enhance the participation of the DFIG in the load balancing and reactive power support to the grid. The unbalanced power compensation is performed only by the Grid Side Converter (GSC), while a proper reactive power share between the GSC and the rotor side converter is used to achieve optimal active power injection. The performance of the proposed optimization approach, based on the capability curve of the DFIG-GSC in steady state, is compared with the typical maximum power point tracking method. The results were obtained by simulating a 2-MW DFIG-WTS in MATLAB/Simulink.