Research On Permanent Magnet Synchronous Motor Based On Variable Magnetic Reluctance Field Adjustment

Permanent magnet synchronous motor (PMSM) which takes the advantages of small capacity, light weight, high efficiency and good control characteristics gets more and more applications in each field in recent years. However, the excitation of PMSM cannot be adjusted which make PMSM take a narrow constant power operation range and limit the applications. Flux weakening for traditional PMSM is accomplished by increasing the d-axis current and utilizing the armature reaction. But this method brings more copper loss, reduces the effiency of the driving system and takes the risk of demagnizting inreversibly. So taking further research on the motor structure which has wide constant power operation range and flux weakening method is still an important topic of motor and control field at the present time.We firstly present a scheme of a variable magnetic reluctance PMSM (VMRPMSM) based on the field adjustment. We formulate the structure of the VMRPMSM and then build the no-load equivalent magnetic circuit model. We calculate magnetic reluctance of each component in the magnetic circuit and research on the magnetic reluctance of the nonmagnetic conductor and the variable rule between the magnetic reluctance and the shape of the nonmagnetic conductor; then we analze the flux weakening principle of VMRPMSM according to magnetic circuit calculation of the airgap magnetic flux and the phasor diagram of the flux weakening process for the motor.The position of the permanent magnet in the slot determines the magnetic reluctance which passed by the magnetic flux produced by the permanent magent. But the position of the permanent magnet is dicided by the resultant force on the permanent magnet. We analyze the centrifugal force and friction force in turn and emphasize on the electromagnetic force. We build the force model of the permanent magents and analize the electromagnetic force that the permanent magents are in different position of the slot. We use finite element method to research on the variable rule of the electromagnetic force from the aspects of permanent magnet position, the shape of nonmagnetic conductor, motor saturation, charge magnetism length of PM, PM material performance and airgap length, especially for the effecto of the nonmagnetic conductor to the electromagnetic force.In the process of speed vaiation, we analyze the motion law of permanent magnet in the slot and the regulating performance of the airgap magnetic field based on the difference analysis of force on permanent magnet between the raising and reducing speed of the motor. We research on the relationship between the no-load air gap magnetic density and the back electromotive force (EMF) and s which is the distance between the main and sencondary permanent magnets, and analyze the difference of in the raising and reducting speed process of the motor, and test in the prototype. We use finite element method to simulate the result of flux weakening and research on the performance in the flux weakening process.The permanent magnet of the new PMSM divides into two parts in the PM slot, which is different from the traditional PMSM, and we analyze the interpolar leakage coefficent and inductance in order to design the new PMSM better. We analyze the influencing factor of leakage flux according to the definition and research on the variation law of the interpolar leakage coefficent from the aspects of airgap length, magnetic bridge length, PM size, PM movement, the shape of nonmagnetic conductor and PM material. We research on the influencing factor of inductance according to the formular and the magnetic flux distributions in different excitations and use finite element method to research on the variation law of inductance from the aspects of thickness of PM, magnetic bridge size, current satruration, the shape of nonmagnetic conductor and PM movement. Based on the analysis of parameters we research on the effect of parameters variation of the motor to the flux weakening performance.The theoretical analysis and the experimental research indicate that the variable magnetic reluctance PMSM based on the magnetic field adjustment take the features of easy flux weakening control method, easy speed adjustment and high system efficiency which provides a new and effective programme for increasing the performance of speed regulation for the PMSM driving system.