Research On Control Strategy Of PMSM Driven By Three-phase Eight-switch Fault-tolerant Inverter

Because the Permanent Magnet Synchronous Machine(PMSM)has the advantages of high efficiency and convenient maintenance,it is widely used in agricultural production and other fields.Therefore,permanent magnet synchronous motor control will become an inevitable trend in the field of control systems.At present,the drive motor control system of the voltage source inverters mainly include:two-level and three-level Neutral-Point-Clamped(NPC)inverters.The three-level NPC inverter has the advantages of low electromagnetic interference and small switching loss,while the two-level inverter is not so obvious.If a part of the bridge arm of the three-level NPC inverter fails,the motor control system will also fail,and the system will no longer be able to operate normally.It may even affect the safe operation of the entire system and cause unnecessary losses.The inverter is the most prone to failure in the AC control system with higher performance.Therefore,fault-tolerant control of the system is of great significance.Through years of research,a fault-tolerant control scheme for a three-level NPC inverter has been discovered.Compared with other fault-tolerant systems,this solution has a simpler structure,but also has a lower cost and higher load capacity.In recent years,Model Predictive Torque Control(MPTC)has been paid more attention.MPTC constraint processing ability is better.It can obviously reduce the torque ripple,reduce the Total Harmonic Distortion(THD)of current,and improve the performance of the system.Therefore,this thesis uses MPTC to control the Three-Phase Eight-Switch Fault-Tolerant Inverter(TPESFTI)motor system.The research content of this thesis has the following aspects:(1)In this thesis,first of all,the problem of voltage imbalance is studied and analyzed in detail,and combined with the working process of the system,a mathematical model of TPESFTI and PMSM is constructed.Secondly,in order to reduce the amount of calculation,this thesis constructs a PMSM drive system model predictive control system for a three-phase eight-switch capacitor inverter.(2)In order to reduce the amount of calculation and other issues,this thesis also proposes the MPTC strategy under fast vector selection.At the same time,in order to achieve the purpose of improving the system's dynamics and robustness,the sliding mode speed regulator is designed.(3)In order to deal well with the chattering phenomenon,the advantages of sliding mode control and fractional differential theory are put together,and then the dq rotating coordinate system method is used to determine the input quantity as stator current and stator voltage.Then a fractional sliding mode observer is constructed to estimate the speed,accuracy and real-time of the system's speed control.(4)Three types of observers are designed for the synchronous motor system of TPESFTI.At the same time,considering the problems of unbalanced voltage in MPTC calculation,the optimal minimum objective function is designed.