Performance Analysis And Structure Optimization Of A Series Magnetic Circuit Hybrid Permanent Magnet Memory Motor

Permanent magnet synchronous motor(PMSM)has been widely used in many fields such as ships,aerospace,new energy vehicles and so on because of its high power density and high efficiency.However,the permanent magnet magnetic field of traditional permanent magnet synchronous motor is not easy to adjust.Negative straight axis current is injected to control the weak magnetic field to offset the increasing back EMF.However,the copper consumption is proportional to the square of the current,the additional weak magnetic current will lead to a large amount of copper consumption,which will reduce the control accuracy of the drive system.Limited by the current capacity of power electronic inverters,the increase of weak magnetic current will inevitably reduce the output torque current,thus reducing the output torque capacity of the motor.A series magnetic circuit hybrid permanent magnet memory motor(SMC-HPM-MM)is studied in this thesis.The high coercive force permanent magnet guarantees the strong air gap magnetic density of the motor.The air gap magnetic density can be adjusted by controlling the pulse current to change the magnetization level of the low coercive force permanent magnet.The motor demagnetizes the low coercive permanent magnet in the high speed range,eliminates the continuous weak magnetic current,expands the speed range and improves the comprehensive efficiency of the motor.The specific research contents include the following aspects:Firstly,the Preisach hysteresis model of magnetic materials is studied,and an analytic Preisach hysteresis model is established by designing the distribution function.Then the topology of SMC-HPM-MM is given.According to the equivalent magnetic circuit of the motor,the magnetization process of AlNiCo permanent magnet in the motor is analyzed.Finally,the mathematical model of SMC-HPM-MM is established,and the basic working principle of the motor is analyzed.Secondly,according to the main performance indicators of SMC-HPM-MM,the main dimensions of the motor are determined.The stator structure of SMC-HPM-MM is determined by theoretical analysis,including pole-slot ratio,stator slot and stator winding.At the same time,the leakage phenomena at the end of high coercive permanent magnets are studied.It is pointed out that the cross-section area ratio of the two permanent magnets is an important factor affecting the leakage phenomena at the end of high coercive permanent magnets.When calculating the sizeof permanent magnets,the cross-section area ratio of the two permanent magnets can be taken as a constraint condition to reduce the leakage phenomena at the end of high coercive permanent magnets fundamentally.Thirdly,the SMC-HPM-MM finite element simulation model is established,and the electromagnetic performance of the motor under the positive and negative magnetization states of AlNiCo permanent magnet is analyzed.At the same time,through the analysis of the generating mechanism of cogging torque,a method combining stator tooth opening counter groove with rotor opening hole is proposed to restrain the cogging torque of SMC-HPM-MM.The effectiveness of the method is verified by finite element simulation.Then according to the inductance characteristics of AlNiCo permanent magnet under different magnetization States,the special inductance characteristics of the motor with straight axis inductance larger than that of the quadrature axis inductance are obtained by adding built-in magnetic barrier to reduce the quadrature axis inductance.When the motor is running at low speed,the direct axis current greater than zero is used to obtain positive reluctance torque and then the working point of AlNiCo permanent magnet is improved.Therefore,the torque performance of the motor at low speed is optimized and the reliability of the motor is improved.Finally,the appropriate control strategy is selected,according to the inductance characteristics of SMC-HPM-MM with built-in magnetic barrier,and the torque-speed relationship and efficiency of the motor under different magnetization states of AlNiCo permanent magnet are calculated by finite element simulation,which verifies the wide speed regulation performance of SMC-HPM-MM.