In this paper, a sliding mode control technique is applied to control a variable speed wind energy conversion system (WECS) with a doubly fed induction generator (DFIG) and a cycloconverter. The dynamic behavior of the WECS, including the models of the wind turbine, the DFIG, the cycloconverter and the powers control, is investigated. Stator flux oriented control with sliding mode control and cosine-wave crossing control techniques are applied to achieve the maximum power and the independent control of stator active and reactive powers. The mathematical model of the proposed system is presented and simulated, to demonstrate its performance.