Theory And Design Of Fractional Pole-pair Permanent Magnet Vernier Machine

With the development of industry and technology,the demand for high-end servo system in various industries is growing rapidly.As the actuator of servo system,the two key performance indexes of servo motor are torque density and cogging torque.The torque density determines the response speed of the servo system,and the cogging torque directly affects the positioning accuracy of the servo system.Benefit from the simple structure,high torque density,high efficiency and high reliability,permanent magnet motors(PMM)occupy the majority of servo motors.Suffers from the cogging torque,conventional PMM is difficult to adapt to highprecision applications.While the torque density of the ironless PMM is low due to its low flux density,making the servo system very expensive.Permanent magnet vernier machine(PMVM)is a new topology with inherent higher torque density and lower cogging torque compared to the conventional PMM,which brings the PMVM a broad application prospect.However the PMVM still suffers from the cogging torque because there are still teeth on its stator.This limits the application of PMVM in high-end servo field.Based on the PMVM topology,a novel fractional pole-pair permanent magnet machine(FP-PMVM)is proposed to further reduce the cogging torque.The FP-PMVM is studied comprehensively through the theoretical analysis and finite element analysis(FEA).Firstly,the topology and evolution of the FP-PMVM are introduced in this paper.Based on the slot vector diagram,a method to estimate the feasibility of the slot-pole combinations in FPPMVM is induced,as well as the calculation method of the winding factor.Secondly,the cogging torque of the FP-PMVM is divided into the slotting component and the end component,which are optimized by different means.The design process of the FPPMVM is given and the designed FP-PMVM is compared with a conventional PMM,an ironless PMM and a PMVM.It is found that the FP-PMVM has good performance in both electromagnetic and economic aspects.Finally,a prototype of the FP-PMVM is manufactured and tested.The machining errors will lead to some cogging torque harmonics that will not appear in ideal situation.Some of these machining errors are located with the help of theoretical analysis and analytical calculations.The relationship between the cogging torque and the corresponding machining error is studied by the FEA.An error orientation method based on complex frequency domain analysis is introduced,and some errors in the prototype are located by this method...