Deadbeat Direct Torque Control Strategy Of Permanent Magnet Synchronous Motor In Full Frequency Range

Permanent magnet synchronous machine(PMSM)is widely used in high performance AC drive system because of its high efficiency,simple structure,high power factor and good torque control performance.Current vector control is general method to control permanent magnet synchronous motor.Due to not directly control the torque,there exist problems on torque response and parameter adaptability.In recent years,direct torque control is gradually applied to the control of permanent magnet synchronous motor.It needs to overcome large torque ripple because of using the traditional hysteresis torque control,and unfixed switching frequency of inverter.In this thesis,deadbeat predictive control is incorporated in the direct torque control scheme,and the reference torque and reference flux are reasonably planned to reduce the torque ripple and improve the dynamic response performance in the full frequency running range.Firstly,through establishing the mathematical model of PMSM,this thesis describes the principle and system realization of PMSM vector control based on rotor field orientation and direct torque control respectively,which describe a theoretical basis for the deadbeat direct torque control research and the comparison between different control methods.Secondly,considering the disadvantages of current loop bandwidth limitation,deadbeat predictive control is used to calculate voltage vector directly according to the inverse model of motor to control torque and improve the dynamic response performance.By combining SVPWM strategy with deadbeat direct torque control,the switching frequency of inverter is fixed and the torque ripple is reduced.At the same time,the stator current observer for deadbeat direct torque control is designed,and the stator flux and torque are estimated.Thirdly,the reference current is reasonably distributed in the whole speed range of the motor,and the reference torque is compensated and regulated correspondingly.Under the limit condition of maximum inverter voltage and maximum motor current,the optimal weakening flux and the maximum feasible torque references are planned.The DC bus voltage utilization of the inverter is improved by over modulation strategy,and the voltage output range is expanded.The torque output is maximized in the full frequency running range.Finally,the performance of the PMSM direct torque control system in the full frequency range and the robustness against the change of motor parameters are verified by simulation experiments,and some valid results could be obtained by comparison with the vector control based on rotor field orientation.