LQR with integral action applied to a wind energy conversion system based on doubly fed induction generator

This paper presents the design of a Linear Quadratic Regulator (LQR) with Integral action (LQRI) applied to a wind energy conversion system (WECS) based on doubly fed induction generator (DFIG). The controller is used to achieve speed regulation for maximum power extraction from the wind turbine, DC bus voltage regulation, to make the machine draw its magnetizing current only from the stator and to keep the power factor at unity for the grid-side converter. The model of this latter is set in the d-q rotating reference frame synchronized with phase a of grid voltages while stator flux oriented vector control is used for the rotor-side converter. Knowing that the standard LQR provide essentially proportional gains, the DFIG dynamic is augmented with the integral of the q component of the grid-side converter currents, the d component of the machine-side converter currents, DC bus voltage and machine´s speed in order to cancel steady-state errors. The DFIG is controlled as a whole i.e. a multi-input-multi-output (MIMO) system and a fixed PWM at 5 kHz is used to generate the gating signals of the two back to back converters. The system is tested for both sub-synchronous and super-synchronous speed and the simulation results obtained with Sim Power System (SPS) and Simulink of Matlab implementation of the controller proved the effectiveness of the control strategy.