A digital optimal controller for VSCF wind generators

A design technique for a class of gain-scheduling adaptive controllers for a variable-speed constant-frequency (VSCF) wind generator system using wound rotor induction generators with a AC/DC/AC rotor link is discussed. The controller will affect the system performance by controlling the firing angle of the rotor circuit inverter at different wind speeds. For wind speeds above the rated level, the generator will tend to be overloaded, and the output is controlled to keep the stator current close to its rated value to prevent machine overloading. When the wind speed is lower than the rated value, the generator is driven below its rated speed, and there is no danger on the generator from excessive currents. The generator speed will then be controlled so that the generator output is maximized. The control action is derived in an optimal state feedback form based on a digital linearized system model at various operating points. The operating points are chosen to cover the entire range of system operation between cut-in and cut-out wind speeds. Results obtained using a simulated system are presented in order to show the effectiveness of the proposed controllers.<>