State space based modeling and sensitivity analysis of DFIG in an unbalanced network

This paper presents a state space based control methodology and sensitivity analysis of doubly-fed induction generator (DFIG) systems using the (dq)⁺ and (dq)^- synchronous reference frames. The electromagnetic torque, active and reactive power values of stator, rotor and dc voltage of the back-to-back converters are defined in terms of voltages and currents in both reference frames. The proposed control model helps to maintain constant total active power output and constant electromagnetic torque in both balanced and unbalanced conditions. Specific sensitivity analysis of the DFIG system is provided for different unbalanced voltage levels. A case study using the proposed modeling and control strategy is presented by simulating a 1.5 MW DFIG wind turbine connected to an unbalanced network. The results indicate the effectiveness of the proposed method.