Research On Variable Speed System Of Doubly Fed Motor And Its Excitation Controller

Doubly-fed electric machine is a new type of eletric machine which combines the advantages of the traditinoal induction machine and synchronous machine. Not only it can fulfill the need of general mechanical variable speed system,but also can supply reactive power to power system by modulating the frequency and phase of the rotor current. Besides, it can be used in variable speed constant frequency power generation. Doubly-fed electric machine can be operated as super-synchronous speed generator, super-synchronous speed motor, sub-synchronous speed generator and sub-synchronous speed motor. It has better behavior and higher efficiency, which is provided with wide prospects of industrial application. This paper processes some research on the doubly-fed wound rotor induction machine system. Firstly, based on the mathematical model of doubly-fed machine, the model in the synchronous M-T reference frame is built by the vector transform technique. The applications of different vector oriented models are compared and a vector control system is established in the synchronous M-T reference frame oriented by the rotor field. Then, the characteristics of active power,reactive power,electromagnetic torque on the steady state are analyzed. Aimed at the requirement of motor sided excited controller, three applicable converters are compared, and a matrix converter is attempted which is based on double space vector modulation technique and semi-natural two-step commutation strategy. A method which is used to solve the chaos problem of the commutation strategy during the connection zones of conjoint sectors is proposed. Their correctness is proved on the Matlab/Simulink simulation. Following,based on matrix excited controller, a vector control variable speed system is established. The simulation results under various conditions certify the feasibility and validity of the whole control system proposed in this thesis. In the end, the whole hardware configuration and partial software flow on the doubly-fed machine vector control variable speed system is set forth.