Speed-sensorless voltage & frequency control in autonomous DFIG based wind energy systems

This paper investigates the application of the hysteresis current control technique to control the voltage and frequency of a variable speed-constant frequency autonomous DFIG based wind energy system by using Direct Voltage Control method. The DFIG feeds an isolated R-L load. A diode bridge rectifier and a power electronics converter (called rotor side converter) having common dc link is connected between the stator and rotor of the DFIG. The control strategy uses the speed-sensorless control for the rotor side converter designed for low-to-medium wind speeds. To regulate the voltage and frequency at stator terminals, the error between the actual rotor currents and the reference rotor currents is given to the hysteresis controller. The reference currents are obtained by the direct voltage control technique. The control pulses for the rotor side converter are supplied by the hysteresis controller which is operated on the error signal. A 2 MVA Wind energy system is designed by using DFIG prototype in MATLab/Simulink. Simulation outcome obtained from the 2 MVA system are presented and discussed in this paper.