Fundamental Research On Alterablemagnetic-circuit Variable-flux Permanent-magnet Synchronous Machine

Nowadays,the rare-earth permanent-magnet synchronous machines are widely used in electric drive systems.However,the permanent magnet flux of the traditional rare-earth permanent-magnet synchronous machine is difficult to regulate and the operating speed range is limited.This issue makes the traditional permanent-magnet synchronous machine not adequately meet the requirements of electric vehicles and other applications which frequently change operation conditions and desire wide extended-speed range and high operating efficiency.The magnetization state of lowcoercivity permanent magnets in the variable flux machine can be regulated by applying magnetization or demagnetization pulsing magenetomotive force.And hence the wide extended-speed range and high operating efficiency in high speed region can be achieved.The hybrid permanent-magnet variable flux machine which simultaneously utilizes high-coercivity and low-coercivity permanent magnets is considered as the promising development direction of this type of machine.According to the configuration of two kinds of permanent magnets,the hybrid permanent-magnet variable flux machine can be divided into two types: series topology and parallel topology.A novel alterable-magnetic-circuit variable-flux permanent-magnet synchronous machine(AMC-VFPMSM)is proposed,which solves the problems of narrow magnetic flux regulation range in the series topology and low torque production capability in the parallel topology.Several key problems of the AMCVFPMSM are investigated,and the major research work can be summarized as follows:Firstly,the AMC-VFPMSM is proposed,and both the hysteresis model and the equivalent magnetic circuit model of the machine are established.The magnetic flux regulation principle and the alterable-magnetic-circuit principle of the machine are introduced.The established hysteresis model is employed to predict nonlinear hysteresis characteristics of low-coercivity permanent magnets,and the predicted results are evaluated and verified.When the machine is open circuited,the condition that leakage flux of high-coercivity permanent magnet passing through the flux regulation barrier is equal to zero is given.The magnetic flux regulation range and torque production capability of the AMC-VFPMSM and the typical series-and parallel-topologies are compared by the finite element method.Research results show that the proposed topology can overcome the drawbacks of narrow magnetic flux regulation range in the series topology and low torque production capability in the parallel topology.Secondly,the influence factors of key electromagnetic performances of the AMC-VFPMSM are investigated and the design method of the machine is established.The analytical expressions of the flux regulation magnetomotive force of the AMCVFPMSM are derived,and the demagnetization and re-magnetization magnetomotive forces required for regulating the permanent magnets to specified magnetization state are obtained.The influences of key structural parameters of permanent magnets,rotor and stator,and the magnetic characteristics of the low-coercivity permanent magnet material on the magnetization and demagnetization characteristics,torque production capability and resisting unintentional demagnetization capability of the AMCVFPMSM are investigated.The design method of the AMC-VFPMSM based on analytical equations and finite element method is established.The final design scheme of the machine which can operate in the wide extended-speed range and resist unintentional demagnetization is given,of which the main performances are analyzed.Thirdly,the characteristics and influences of the non-uniform magnetization phenomenon of the AMC-VFPMSM are investigated,and the solution to the nonuniform magnetization problem is proposed.The non-uniform magnetization phenomenon of the low-coercivity permanent magnet in the AMC-VFPMSM is divided into different types,and the corresponding characteristics are also investigated.The influences of the non-uniform magnetization on no-load air-gap flux density,no-load back EMF and electromagnetic torque are analyzed.The uniform magnetization regulation method with the shortest time consumption and not limited by the initial rotor position for the AMC-VFPMSM's magnetization regulation process is proposed.The minimum consumed time of uniform magnetization regulation for the AMC-VFPMSM with various kinds of slot/pole combinations is given.The evaluation indices of the magnetization regulation effect for the AMCVFPMSM are proposed,and the optimal winding arrangement is obtained based on the evaluation indices.Afterwards,the inductance variation law and the operating performances of the AMC-VFPMSM are investigated.The variation of the inductance with magnetization state is analyzed,and the torque characteristics which include the output torque capability,maximum torque current angle,the ratio of reluctance torque to the total electromagnetic torque are investigated.The control principle of the AMC-VFPMSM which can realize high-efficiency and wide-speed operation is established.Based on this principle,the variations of operating speed range,losses and efficiency with magnetization state are investigated.The temperature field calculation model of the AMC-VFPMSM is established.The equivalent modeling methods of stator winding and air-gap are given.Further,the temperature field distribution and the influence of the magnetization state on temperature rise of the AMC-VFPMSM are investigated.Lastly,the prototype of the AMC-VFPMSM is manufactured,and the test platforms of flux regulation performance and operation performance are built.The performances of the prototype are tested and analyzed.The tests of the remagnetization and demagnetization characteristics,inductance parameters,no-load back EMFs and torque performances,the operating speed range and efficiency map of the AMC-VFPMSM in different magnetization states are carried out to verify the theoretical research and simulation analysis.It is found that the permanent magnet flux and the no-load back EMF of the AMC-VFPMSM can be regulated repeatedly in a wide range.The capacity of resisting the unintentional demagnetization is verified.By regulating the magnetization state of low-coercivity permanent magnets,the capacities of extending the operating speed range and improving the efficiency of the AMC-VFPMSM are also verified.