| In recent years,in-wheel motors have been increasingly used in electric vehicles(EV)which are characterized with simplifying the complex chassis structure,improving the energy utilization.Normally,most in-wheel motors use a permanent magnet synchronous motor(PMSM)due to its advantages of high torque density,good fault tolerance and so on.Considering the structure of the outer rotor with the surface mounted permanent magnet(PM)not only consumes more PM materials,but also is poor in field-weakening capacity.The PM is magnetized radially and uniformly arranged in the middle of the iron pole,the iron is magnetized to the S-pole and the PM is magnetized to the N-pole to form the consequent-pole.The most prominent performance of the consequent-pole permanent magnet in-wheel motor(CPM)is the flux-weakening capability,and the winding inductance is a key parameter for the fluxweakening capability and can affect the output torque significantly.Hence,the analysis on the characteristics of the winding inductance is very important for the CPM.In addition,the research on inductance can enhance control precision and improve control method.This paper takes the inductance of this motor as the research object,the relation between the inductance and the internal structure of the CPM is analyzed and the main content is divided into the following three parts.Firstly,the structures of conventional and CPM and their equivalent magnetic circuits(EMC)are compared,then the CPM with 48 slots 40 poles and 36 slots 32 poles are established.Due to the different periodicity of the inductance between the two motors in an electric period,the inductance of the 48 slot 40 pole motor is bipolar in an electrical period,the maximum and minimum occur twice.However,the inductance of the 36 slot 32 pole motor is unipolar within an electrical period,the minimum(or maximum)appears once.The equivalent magnetic circuit method(EMCM)is used to establish the EMC suitable for the CPM based on the flux-lines distributions of the finite element analysis(FEA).The relationship between the inductance and the internal structure of the motor is analyzed and the expressions of the equivalent magnetic resistance of the CPM at different positions are summarized.Secondly,to study the general rules of the inductance about this kind of the CPM,several models of the CPM with different number of slots and poles are established and the inductance are simulated.Including 9 slots 10 poles,12 slots 14 poles,15 slots 14 poles and 15 slots 16 poles.The regularity of the inductance periodicity,sinusoidal degree and the relation with the internal structure of the CPM are summarized.Also,the simulation shows that the pole-arc coefficient will affect the periodicity of the inductance.With the increase of the amplitude of the second harmonic,the inductance will become bipolar.It lays a foundation for the expansion and application and performance optimization of this kind of CPM.At last,two prototypes of 48 slots 40 poles and 36 slots 32 poles are made,and a set of platform is built to test the prototype.Since the inductance will be affected by the test frequency,the test frequency of the CPM are selected through experiments.The phase-inductance is measured since the winding inductance of the CPM is not easy to be measured directly.The experiments fully verify the validity of the simulation and theoretical calculation,and show the rationality of the FEA and the EMCM. |
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