Research On The DTC System Of Brushless Doubly-fed Machines Based On Fuzzy Theory

The Brushless Doubly-fed Machine (BDFM) can be operated in synchronous mode andasynchronous mode which has simple structure and dependable fastness. So it takes itsadvantages in the large-sized speed adjustment system，and the control strategies which aresuitable for induetion motor all can be used to control the brushless doubly-fed machine.Direct torque control (DTC) technology has newly developed from the middle of80’s of lastcentury. It uses stator flux-oriented. This method controls the motor torque and flux directlywhich makes the motor torque response rapid.Firstly, this paper reviews the history of the development of BDFM, expounds thesignificance of BDFM, analyses the research status of BDFM and outlooks the futureapplication prospects of BDFM. Then the structure of stator and rotor, speed,steady-state characteristics and operation modes of BDFM are analysed, d-q axismathematical model of BDFM is derived, the simulation model of BDFM is built underMatlab/Simulink. And taking advantage of this model to simulate and analyse itsopen-loop characteristics, in order to verify its correctness.The basic theory of DTC strategy of BDFM is discussed according to the model ofBDFM, the optimized space voltage vector switching table of the DTC strategy is deduced,and the zero-voltage vector is lead into. zero-voltage vector make torque keeping invariant,decrease action frequency of switching devices and improve control performance of thesystem. Based on the established BDFM model, combinating the DTC strategy, the directtorque control system of the BDFM is built. The status of DTC strategy of BDFM with orwithout zero-voltage vector is simulated respectively, in order to reflect the advantage of thezero-voltage vector.The torque pulsation of traditional DTC strategy is relatively large, so fuzzy control isintroduced into the DTC system of BDFM in this paper, the simulation models of flux andtorque calculator, electromagnetic torque hysteresis, stator flux linkage hysteresis, sectorchoice and fuzzy controller of BDFM have been set up under the MATLAB/Simulink. Thesimulation of DTC control strategy with space vector modulation and fuzzy controlarepresented which demonstrate the fundamental theory of DTC control strategy for BDFM. TheDTC of fuzzy control and traditional control strategy are compared, the simulation resultsshows that fuzzy control strategy can decrease torque pulsation, improve dynamic and staticperformance of systems.