Research On Novel Axial-Radial Hybrid Flux Permanent Magnet Machine

Permanent magnet synchronous machine(PMSM)has advantages of high efficiency,high power factor,playing an important role in national economy.The research of PMSM is of great significance to the “dual carbon strategy” and national energy security.Compared with traditional radial flux permanent magnet machine,axial flux permanent magnet machine has attraced the world’s attention due to the andvantageds such as compact structure and low ratio of length and diameter.However,the circumference at the inner diameter of the stator is shorter than that at the outer diameter.In order to ensure the coil embedding,the inner diameter is usually left with a large margin,which causes the insufficient utilization of space.Benefit from the combination of radial flux and axial flux,hybrid flux permanent magnet machine can can improve the spatial utilization of spece.In this paper,a novel axial-radial hybrid flux permanent magnet machine with modular T-type stator core is proposed to improve the space utilization and torque density.The main achievements can be summarized as follows:The structures of traditional radial flux permanent magnet machine and axial flux permanent magnet machine are summarized,and a novel axial-radial hybrid flux permanent magnet machine is proposed.The machine consists of two rotor-disks,a stator with of Ttype core,and an inner rotor.The T-type stator core combines with the rotor-disk and the inner rotor to form the axial-radial hybrid flux path,which improves the internal space utilization of the machine.Aiming at the characteristics of small actual coil pitch caused by the arrangement of fractional slot concentrated winding,the concepts of concentrated effect and the layered effect are proposed,and the influence on winding coefficient is summarized.The analytical expression of the stator magnetomotive force is derived.The influence of the concentrated effect and the layered effect on the harmonic magnetomotive force is analyzed.The influence on the magnetomotive force is verified by the finite element simulation.For the character of complex three-dimensional magnetic circuit,a dimension-reducedtransformation analysis method is proposed.The basic electromagnetic relationship and the main size equation of the hybrid flux permanent magnet machine are derived.Based on the idea of “magnetic circuit equivalence” and the principle of constant magnetic potential and reluctance,the model dimension is reduced from 3D to 2D.The simulation time is greatly decreased.The main parameters such as slot-pole combination,armature diameter ratio,stator tooth width,pole-arc coefficient,and thickness of permanent magnet are optimized,and the preliminary electromagnetic scheme is determined.Three-dimensional finite element simulation shows that the calculation error in flux linkage and average torque is less than 3%,which proves the accuracy and effectiveness of the proposed analysis method.In order to improve the torque quality of novel axial-radial hybrid flux permanent magnet machine,the core material,magnet skew technology and multi-objective optimization are studied.Diffirent materials are compared,and the influence on the performance is analyzed.In view of the characteristics of dual-axial-rotor,an asymmetric bidirectional magnet skewing technology with the effect of magnet skewing and phase shifting is proposed.Different skew modes,skew angles and phase shift angles are researched.With the objectives of high average torque,low torque ripple and high efficiency,the mathematical surrogate model is established.The NSGA-II algorithm is used to optimize the multi-objective of the machine and the final electromagnetic scheme is determined.Compared with the traditional radial flux flux permanent magnet machine and axial flux permanent magnet machine,the proposed axial-radial hybrid flux permanent magnet machine has higher torque density.For the final scheme,scheme checking,prototype development and experimental research are carried out.The temperature rise and mechanical strength of the machine are checked to ensure the reliability of machine.Aiming at the difficulty of machine assembly caused by axial magnetic tension between stator and rotor,a prototype assembly scheme of shaft-end alternate-interlocking is proposed to ensure accuracy.The experimental platform is built to measure the parameters of the prototype,and a series of prototype experiments are carried out.The experimental results verify the superiority of the proposed axial-radial hybrid flux permanent magnet machine in terms of torque density.The effectiveness of the proposed method in machine design is also verified.