Research On Reverse-Salient Hybrid Permanent Magnet Motor Used For Electric Vehicle And Its Control Strategy

In recent years,with the rapid development of electric vehicle(EV)industry,users have put forward higher requirements for the driving performance of EVs.As a key driving component,the drive motor will directly determine the driving performance of the EV.Due to its simple and reliable structure,high power density and high efficiency,permanent magnet(PM)motors have been widely applied in various fields.However,because the rotor is generally excited by rare-earth materials with high remanence,it is difficult to adjust the air gap magnetic field,which limits its application in electrical driving systems with high requirements of speed adjustment range and operating efficiency.Thus,the method of designing a wide speed range and high efficiency drive motor and high-reliability control system needs further research.In addition,the price of rare-earth PM materials soared,and the cost of motor production increased.To solve the above problems,a reverse-salient hybrid permanent magnet motor(RSHPMM)topology is proposed.Then,its operating principle,structural feasibility,optimization,electromagnetic performance and control strategy are analyzed.The main contents are as follows:First,the operating characteristics of PM drive motors are investigated and the relationship between distribution of multiple operating conditions and design parameters of the electrical driving system is summarized.Based on the proposed motor topology,the daxis and q-axis equivalent magnetic circuit models are established to analyze the feasibility of the proposed rotor structure to realize the reverse-salient characteristic.In order to make the EV have better driving performance,the drive motor and transmission system are optimized by multi-objective optimization and single-parameter scanning method respectively.In this paper,a two-dimensional Pareto front diagram containing three optimization objectives is given to improve the efficiency of multi-objective optimization.Then,the optimal value of the design variables is determined by the actual operation requirements of the drive motor.The transmission ratio is analyzed based on the new European driving conditions(NEDC).According to the operation efficiency of the electric drive system and actual driving requirements of the EV,the final transmission ratio is determined,so that the drive system can maintain a high power density and operation efficiency in the full speed range,which can effectively improve the maximum utilization of on-board energy.The electromagnetic performances of the RSHPMM are compared and analyzed with the conventional V-shaped permanent magnet motor by finite element method.The electromagnetic performances mainly include air-gap magnetic density,no-load back-EMF,d-q-axis inductance characteristic,torque characteristic,flux-weakening and speed expansion ability.The simulation results show that the RSHPMM has a wider speed expansion range,lower torque ripple,and higher operating efficiency in the high-speed region compared to the conventional motor.In order to verify the feasibility of the design of the motor structure,the irreversible demagnetization risk of the permanent magnet,the mechanical and thermal characteristics are also analyzed.The simulation results verify the rationality of the topology design.Finally,a prototype is manufactured for no-load test verification,the amount of rare-earth permanent magnet used in RSHPMM is only 44% of that of the conventional motor,and the experimental results agree well with the simulation results.According to the operation characteristics of the RSHPMM,a flux-weakening control strategy based on stator flux linkage comparison is proposed to make the stator current vector shift to the second quadrant.Considering that the control strategy can also realize the speed expansion when the motor runs in the second quadrant,the current status switching from flux-intensifying magnetizing current to flux-weakening does not need to change the control strategy,which avoids the control system from an unsteady state,which can realize the stable operation control in the full speed range of the RSHPMM.Then the software and hardware of the control system are designed,the load experiment platform of the prototype is built to verify the load capacity of the prototype.