Research On Deadbeat Direct Torque And Flux Linkage Control For Permanent Magnet Synchronous Motor

Permanent magnet synchronous motor(PMSM)is commonly used in AC servo system for its high capability and high performance.Thus,it's of great value to research on improving motor control capability.As we know,the essence of motor control is torque control.Thus,direct torque control(DTC)has been an academic study focus since it was applied in PMSM.The sampling time of system convergence can be calculated by motor discrete time model.As one of predictive algorithms,the deadbeat controller is developed to achieve the desired command trajectories in “one” sample time period with the advantage of simple principle and easy digital realization.To solve extensive torque ripple and poor steady-state performance of the direct torque control system of PMSM,this thesis adopts deadbeat predictive algorithm and attenuates torque ripple by using space vector pulse-width modulation(SVPWM).As a result,both the dynamic and steady-state performances can be improved.Thus,the main work of this thesis is as follows:Firstly,the mathematical model of interior PMSM is established and the whole system of direct torque control of PMSM is developed based on the principle of direct torque control.Secondly,to attenuate the torque ripple and eliminate the steady-state error of the system,SVPWM is combined with DTC which achieves constant switching frequency.At the same time,deadbeat direct torque control algorithm is derived based on motor discrete model and a closed-loop mixed flux linkage observer is designed.Thirdly,different system operations are analyzed under the limited voltage vectors and a torque reference correction is proposed to eliminate the steady-state error caused by inaccurate modeling and parameter variations.Then,the stability analysis is conducted by using the small-signal model of a nonlinear system.Also,maximum-torque–per-flux-linkage(MTPF)algorithm is derived and the flux linkage reference is corrected in this thesis.The improved deadbeat direct torque control system of PMSM is derived by combining torque reference correction with flux linkage reference correctionFinally,the above theoretical investigations are verified via simulation using MATLAB/Simulink and experiments using QuaRC platform.