Research On Brushless Doubly-Fed Machine And Its Direct Torque Control Strategy

Motor is important device that achieve the energy conversion between mechanical and electrical, which is the main power source in modern transmission field, and plays an impor-tant role in industrial production and daily life. According to statistics, the en-ergy consumption of motor drive system for about70% of the total nation generating capacity, among which 90% were consumed by AC motors. AC motor has become major electrical equipment, therefore, it is profound significance that study of new type of AC motor and effi-cient AC control technology.Brushless Doubly-Fed Machine (BDFM) is a new type motor, which has two stator windings—power winding and control winding, and rotor has the function of pole modulation, which achieve the energy transfer between windings. BDFM has the features of brush motor and brushless motor, and it has advantages that less capacity inverter, high power factor, sim-ple motor structure, high reliability. In addition, BDFM can run in the asynchronous, syn-chronous, doubly-fed and power generation state, it is a multifunctional motor. BDFM can be used in large pumps, wind speed and wind power generation which has broad application prospects.Based space vector pulse width modulation (SVPWM) for direct torque con-trol(SVM-DTC), in which control voltage is synthesized according to the size of the flux and torque error, and can increase the inverter switching frequency as fast as sampling fre-quency, response of flux and torque controllers quickly and without static error to track the given signal. SVM-DTC is an improvement of conventional direct torque control.This paper analyzed the basic principals of BDFM, summarized the basic principles of BDFM electromagnetic design, and derived the equivalent circuit model and'the dynamic model. A simulation model of BDFM was build in Matlab/Simulink, the dynamic simulation was executed, from which the dynamic simulation characters of BDFM was obtained and the simulation results were analyzed. By the research of DTC for BDFM and SVPWM, the simu-lation model of DTC system for BDFM, DTC system for BDFM based on SVPWM strategy were build. By the analy of simulation results, DTC for BDFM based on SVPWM strat-egy can track closer to the circular flux shape, reduce startup speed fluctuations, signifi-cantly reduces torque ripple, strengthen the ability of against load disturbances and signifi-cantly improved the static and dynamic performance.