Research On Model Predictive Control Without Weight Coefficient Of Three-level Permanent Magnet Synchronous Motor With Optimized Duty Cycle

Permanent magnet synchronous motor(PMSM)has been widely used in industrial robots,rail transit and other fields because of its simple structure,small moment of inertia and high power density.At the same time,due to its low voltage harmonic content and relatively simple topology,NPC three-level inverter has been widely used in various topologies of multilevel inverter.However,due to the problems of midpoint potential fluctuation and increasing the calculation burden of the system,how to effectively control it has become a research hotspot.In addition,in the high-performance control system of PMSM,model predictive torque control(MPTC)has also attracted more and more attention because of its fast dynamic response and multi-objective control.However,it is also difficult to adjust the weight coefficient and unstable control performance.Therefore,aiming at the above problems,this thesis focuses on PMSM,model predictive control(MPC),weight coefficient elimination and neutral point potential control.The main contents include:(1)Firstly,the mathematical model of PMSM is established in three different coordinate systems,and then the working principle of NPC three-level inverter and MPC is introduced in detail.(2)The design method of PMSM three-level MPTC system is studied.On this basis,aiming at the imbalance of three-level neutral point potential,the constraints of neutral point voltage and stator current limiting are added to the value function to improve the PMSM three-level MPTC system,so that the improved PMSM three-level MPTC system has better neutral point potential control ability.(3)Aiming at the problems of large amount of calculation and the need to adjust the weight coefficient of the improved PMSM three-level MPTC,a model predictive flux control(MPFC)algorithm with no weight coefficient is designed.By replacing the electromagnetic torque and stator flux control in MPTC with stator flux vector control,the cumbersome weight coefficient adjustment process in traditional MPTC is omitted.On this basis,the neutral point potential control strategy and fine vector partition strategy are combined to effectively reduce the computational burden of the system and improve the control performance of PMSM three-level unweighted MPFC system.(4)Aiming at the defect that the duty cycle link in the traditional duty cycle control strategy with zero vector as the second action vector can not fully play its role,an improved modulation duty cycle control strategy is designed.By calculating the duty cycle of three optional vectors in the sector respectively and selecting the best vector combination,the computational burden of the system is further reduced.Combined with PMSM three-level unweighted MPFC,the improved modulation duty cycle MPFC system has less torque and flux ripple,and the suppression of neutral point potential is more rapid and stable.After simulation analysis,the PMSM three-level non weighted MPFC system designed in this thesis reduces the torque and flux ripple of the system and improves the control performance of the system without omitting the weight setting process of the traditional PMSM three-level MPTC system.Compared with PMSM three-level non weighted MPFC system,the improved modulation duty cycle MPFC system designed on this basis not only further increases the neutral point potential control ability,but also effectively improves the control effect of torque and flux,which verifies the superiority and reliability of the control strategy.