Analysis And Design Of Fractional-slot Concentrated Winding For Permanent Magnet Synchronous Machines

With the emergence of high-performance permanent magnet materials and magnetically conductive materials,the development of permanent magnet synchronous motors(PMSM)is trending to be lightweight and integrated.Fractional-slot concentrated winding(FSCW)has been widely used in low-speed,high-torque and medium-high-speed motors due to its many advantages such as high torque density,lower copper loss,lower torque ripple,and the capability to apply assembled stator.In applications where torque density is the primary performance indicator,the application of FSCW has become inevitable.It is of great significance to study the design of FSCW and its characteristics of the air gap MMF.The pitch of the concentrated winding is fixed at 1,which makes the winding contain rich spatial MMF harmonics due to the absence of techniques of coil pitch factor to suppress the harmonics,so it affects the overall performance of the motor.So far,researches on FSCW mainly focus on attributes such as torque performance,inductance calculation and so on,and comprehensive studies on the formation of its topological structure and the winding topology expansion is relatively insufficient.In this paper,starting from the basic theory of AC winding,the MMF of single phase and the air gap synthetic MMF are analyzed.Using the theory of slot phase diagram to analyze the design characteristics and topology expansion of doublelayer FSCW,an in-depth analysis is carried out and detailed description is made via specific winding topologies.With the principle of superposition of slot vectors,the basic features of MMF harmonics in an unit motor are analyzed.Then the MMF harmonics of the commonly used FSCW is calculated,and the method of slot vectors superposition combined with the slot phase diagram for the MMF harmonic analysis is summarized.In summing up the winding design and the MMF harmonic analysis method,this paper proposes a five-phase double layer FSCW topology and then the design method of multiphase FSCW with slot phase diagram is summarized.MMF harmonic analysis has been carried out for the above winding and it is reported that PMSMs with this winding configuration are featured with high torque performance.Finally,through Ansys / Maxwell finite element analysis(FEA),a common PMSM is designed to compare the performance of the studied FSCW.When keeping the core unsaturated and the same of the motor effective size,electrical and magnetic load,and the slot fill factor,the performance of MMF harmonic losses and radial force and so on is simulated and compared while 2 typical combinations of poles and slots of FSCW are applied.And output torque ability,torque ripple performance and MMF harmonic losses of the designed 5-phase PMSM with double layer FSCW are also simulated with FEA,and proper optimization is carried out and some advice is proposed for its application.