Research On Finite Control Set Model Predictive Torque Control Of Permanent Magnet Synchronous Motor

Permanent magnet synchronous motor(PMSM)is widely used in wind power generation,numerically controlled machine tool,new energy vehicles and other equipment manufacturing fields due to its advantages of high efficiency,simple structure and small size.The rapid development of manufacturing industry requires higher and higher motor control accuracy,and more advanced control strategies are needed.Model predictive control(MPC)has been developed from industrial production,which can flexibly control various objectives.The application of MPC to the motor speed control system can make the motor have excellent dynamic and steady-state performance.In this thesis,the MPC is combined with the traditional direct torque control technology to ensure the stable operation of permanent magnet synchronous motor,improve its steady-state performance,and simplify the control system structure.Firstly,the structure of PMSM is introduced,and the basic equation of PMSM is derived by coordinate transformation theory.The working principle of direct torque control and the three main components of predictive model,rolling optimization and feedback correction in MPC strategy are discussed respectively.Based on the above theory,the finite control set model predictive control(FCS-MPTC)model is constructed,and a weightless FCS-MPTC model is designed for the problem of cumbersome design of weight coefficients in FCS-MPTC.The simulation results show that the simplified model can meet the stability requirements of the system.Then,aiming at the problem that permanent magnet synchronous motor is easy to be out of step under high load,the causes of motor out of step caused by traditional direct control are analyzed,and a FCS-MPTC strategy based on load angle limitation is adopted.By analyzing the operating characteristics of load angle,the limit of load angle is added in the design of MPC evaluation function,and the system simulation model is built to simplify the prediction process.By comparing and analyzing the simulation results,it is verified that the FCS-MPTC strategy with load angle limitation under high load can make the motor run stably.The FCS-MPTC built has good steady and dynamic performance under different working conditions.Finally,the problems of larger torque and flux ripple of FCS-MPTC are studied.FCSMPTC driven by two-level inverter can only select voltage vectors with fixed amplitudes in six directions,and only one voltage vector works in each control cycle,which will cause large torque and flux ripples in the system.In this thesis,the concept of duty cycle is introduced,and the FCS-MPTC model based on duty cycle is built,which realizes the control of voltage vector amplitude and reduces the torque ripple to a certain extent.Since the duty cycle FCS-MPTC first selects the voltage vector most in line with the evaluation function and then calculates the duty cycle,it cannot be guaranteed that the combination of voltage vector and its duty cycle is the best choice in a certain control cycle.To address this problem,an improved duty cycle FCSMPTC strategy is adopted to predict each voltage vector and its duty cycle.According to the evaluation function,the optimal voltage vector and its duty cycle combination are selected to ensure the minimum torque and flux ripple of the motor.Through the simulation analysis of FCS-MPTC,duty cycle FCS-MPTC and improved duty cycle FCS-MPTC,the results show that the improved duty cycle FCS-MPTC has good steady-state and dynamic performance under different working conditions.