Simulation And Experiment Of Sensor-less Control Strategy For A Doubly-fed Induction Wind Power Generator

Towards the end of 20th and beginning of the 21st centuries, interest has risen in the search and development of using renewable alternative energy sources. Among the renewable alternatives, wind energy has an important potential role, and wind power farms are becoming widely used all over the world. Variable speed generation systems show higher energy capturing and better converting efficiency than the fixed speed systems. The doubly-fed induction generator (DFIG) provides flexibility of operation in sub-synchronous and super-synchronous speeds both in the generating and motoring modes, thus making DFIG suitable for variable speed generating system such as wind power.At first, this thesis introduced the current technologies of wind power around the world. The operation principle of the variable-speed-constant-frequency (VSCF) wind energy generation system is analyzed according to the model of the wind turbine. The mathematical model of the DFIG is established, a stator-flux-oriented control scheme for power control is derived. The structure of the pluse-width-modulation (PWM) converter is given. The control strategy for the grid-side converter is also introduced.This thesis analyzes the implementation of the sensor-less vector control strategy for a DFIG. The knowledge of rotor position is necessary to realize the vector control. However, a position encoder increases the failure rate of the system. Therefore, sensor-less algorithm is desirable. A PQ-power rotor position observer is described in this thesis, which indirectly makes use of the functional relationship between the rotor and stator currents. This control strategy overcomes the drawback of available sensor-less speed/position estimation schemes, which failed at the synchronous speed. The proposed algorithm has wider speed range, and easier to design and implement. The same control performance is achieved by using the proposed sensor-less control.Finally, a experimental system based on DSP was established. Experimental evaluation is carried out to test the proposed position observer, the performance of the DFIG system in steady and transient state in sub-synchronous and super-synchronous speeds are studied, the validity is demonstrated by the simulation and experiment.