Study On Direct Torque Control Technology Of Brushless Double-Fed Wind Power Generator

With the development of wind turbine generator system (WTGS) technology, wind turbines with doubly-fed induction generator (DFIG) gradually take the advantaged position and become the most popular WTGS type nowadays for their variable speed constant frequency character. Brushless doubly-fed machine (BDFM) not only has the same character as DFIG, but it has no slip ring, which makes it has lower failure rate and operate more stably. Therefore, the wind turbine with BDFM is taken as the research object and some research is done on its direct torque control (DTC) strategy.First, this thesis analysis BDFM's working principle and researches its mathematical model in the rotor speed d-q coordinate system, and the model is proved correct by tested in MATLAB/Simulink.Secondly, induction machine DTC strategy is applied on BDFM and it is found, through MATLAB/Simulink test, that this strategy is not ideal for controlling BDFM because of the pulse of speed and electromagnetic torque at low speed.Again, in order to realize the optimal control of BDFM, fuzzy control is applied on BDFM's low speed operating state and a fuzzy control based BDFM direct torque controller is developed. Furthermore, to improve the inverter's control ability to machine's voltage, discrete space voltage vector modulation (DSVM) technique is introduced in, as it can increase the number of optional voltage vectors in one control periodic time. It is found, through MATLAB/Simulink test, this controller can remarkably decrease the torque pulse and increase the dynamic character.In the end, the model of wind turbine generation system with BDFM in build in MATLAB/Simulink software, and by simulated respectively at ramp wind condition and random wind condition, it is found that the changes of rotational speed and torque both match the theoretic changes, which further proved the stability of control system and the effectiveness of control strategy.