A new sensor-less voltage and frequency control of stand-alone DFIG based dead-beat direct-rotor flux control-experimental validation

Abstract

The paper presents a new sensor-less voltage and frequency control method for a stand-alone doubly-fed induction generator (DFIG) feeding an isolated load. The proposed control approach directly regulates the magnitude and angle of the rotor-flux vector rather than controlling rotor currents or voltages as in classic field oriented control (FOC). To accurately regulate the magnitude and frequency of stator voltage, two separate closed-loop based PI regulators are employed to evaluate the reference signals of the rotor flux vector magnitude and angle, respectively. As the proposed control strategy directly regulates the rotor flux vector in the rotor frame, this helps effectively in avoiding the use of rotor speed/position sensors or computationally intensive rotor speed estimators. Furthermore, the stator current measurements are not required to evaluate the load power requirement, considerably reducing the control implementation cost for the system. Furthermore, the proposed control strategy has the ability to operate in both sub-synchronous and super-synchronous speed modes without the need to identify the operating speed range. Since the method only requires knowledge of rotor resistance, it is extremely simple to use and virtually parameter-independent. To evaluate the performance, effectiveness and robustness of the new controller, extensive simulation and experimental tests of a 3-kW laboratory generator are accomplished for different operating conditions. Additionally, a performance comparison with the classic FOC strategy is made, from which the superiority of the proposed control is clearly confirmed.