Optimal preview stator voltage-oriented control of DFIG WECS

In this study, a new optimal preview control (OPC) is proposed for stator active and reactive power controls of a doubly fed induction generator (DFIG) wind energy conversion system (WECS). These powers are controlled by rotor currents to avoid the stator active and reactive power pulsations. This OP controller is designed based on linear quadratic regulator (LQR) approach. In view of efficient superior tracking and disturbance rejection ability, OPC is chosen to control active and reactive powers of WECS. The proposed OPC is designed in order to minimise the error due to cross-coupling-induced electromotive force (emf) and emf-induced due to stator flux using feedforward compensation loops. This controller is developed for both sub-synchronous and super-synchronous modes of DFIG with stator voltage-oriented control (SVOC). An augmented error system is derived for tracking the desired response (active and reactive power controls) of DFIG WECS. Then, the constraints in error state equation are minimised by selecting quadratic performance index in which weighing factors are used for achieving faster rotor current control dynamics. Finally, pulse width modulation switching scheme for voltage-source converters has been designed with outputs of rotor current control loop dynamics. Extensive simulations are conducted using MATLAB/Simulink and then experiments are carried out using OPAL-RT and hardware set-up developed in the laboratory for DFIG WECS for validating the efficacy of the proposed control algorithm. The performances of the proposed LQR-OPC are compared with that of sliding mode field-oriented control (SM-FOC) and direct torque control (SM-DTC). From the comparison, it is observed that the LQR-OPC algorithm with SVOC technique applied to DFIG WECS provides excellent steady-state stability and zero steady-state error in face of transient disturbances both on rotor side and grid side compared with traditional FOC and DTC methods.