MRAS observer for sensorless direct active and reactive power control of DFIG based WECS with constant switching frequency

This paper presents a sensorless direct active and reactive power control (DPC) of grid connected DFIG using back to back PWM voltage source converters in the rotor circuit, the sensorless DPC has been proposed to overcome the drawbacks of large power ripple and variable switching frequency in classical LUT DPC. In this approach two vectors are applied during one control cycle and their periods are obtained in a very simple way. The stator active and reactive powers are made to track references using hysteresis controllers without including any synchronous coordinate transformations. A switching table is used to directly determine the first active vector, and to improve the system robustness with constant switching frequency a second null vector is also chosen, exhibits lower power ripples and better harmonic performance of stator and rotor currents. A sensorless method is implemented for detection of the rotor position based on the comparison between actual and estimated rotor currents. It has some similarity to the model reference adaptive system (MRAS) approach, but a hysteresis comparator is used instead of a proportional integral (PI) controller. Simulation results on a 2 MW DFIG system are provided to demonstrate the effectiveness and robustness of the proposed control strategy.