Research On Three-Segment Series-parallel Magnetic-Circuit V-Shape Variable-Flux Machine System

With the advantages of high efficiency and high power density,permanentmagnet synchronous machine(PMSM)is the dominant drive motor for electric vehicles.However,the permanent magnet(PM)magnetic field of PMSM is difficult to adjust,which leads to the limited speed-expansion range and relatively low highspeed-region efficiency.To enhance the wide-speed operation performance of PMSMs,the variable-flux machine(VFM)with adjustable air-gap magnetic field is proposed by domestic and foreign scholars.The VFM has the advantages of wide speed-expansion range and high efficiency at high speed region.A novel threesegment series-parallel magnetic-circuit V-shape variable-flux machine(TSSPVVFM)is proposed in this thesis.The problems of the small regulation range of magnetization state(MS)in traditional series scheme,and the relatively low output torque in traditional parallel scheme are solved.In this thesis,investigations are carried out focusing on the key problems of TSSPV-VFM.And the main contents are as follows:Firstly,the topology of TSSPV-VFM is proposed,and the speed-expansion principle based on magnetization-regulation is illustrated.The proposed topology is compared with typical VFMs.The equivalent magnetic circuit model of the machine with high accuracy is established,by which the air-gap fluxes under different magnetization currents and structural parameters are analyzed.Accordingly,a preliminary analysis of the magnetization-regulation ability of the machine is given.The proposed topology is compared with typical series and parallel VFMs in the aspects of the electromagnetic torque,magnetization-regulation ability and PM stability.The comparison results show that the proposed topology is able to combine the advantages of series and parallel VFMs,and balance the electromagnetic torque and magnetization-regulation range.Secondly,the influence laws of key parameters on TSSPV-VFM performances are analyzed,and the research on the non-uniform magnetization of PMs is carried out.The influence laws of PM relative position,magnetic-pole dimensions and rotor magnetic-bridge dimensions on electromagnetic torque,magnetization-regulation ability and PM stability are investigated.And the restrictive relationship of different structural parameters for machine design is analyzed.The special schemes with the parallel Al Ni Co placed on the both sides of magnetic pole are compared with TSSPVVFM to prove the advantage of the proposed three-segmented scheme.The nonuniform magnetization of TSSPV-VFM is analyzed,and the distribution law of the flux density of middle Al Ni Co is obtained based on the equivalent magnetic-circuit model.An accurate finite element modeling method is proposed,and a scheme which can ameliorate the non-uniform magnetization is also presented.Thirdly,the magnetization-regulation characteristics,torque characteristics,speed-expansion ability and loss characteristics of TSSPV-VFM are analyzed.With the magnetization current limit considered,the maximum magnetization-regulation range of the machine is analyzed.The variation laws of electromagnetic torque,maximum-torque current angle and PM stability versus current and MS are investigated.And the torque-speed regions under different MSs are analyzed.According to the influence laws of d-axis current and MS on q-axis voltage,the essential reason that the toque region at high speed reduces with the decreasing MS is clarified.The distribution laws of copper and iron losses under different operation conditions and MSs are analyzed.According to the loss characteristics and torquespeed regions at different MSs,the MS-selection principle of the machine for the whole operation region is obtained.Afterwards,the maximum torque per ampere(MTPA)control method with variable MS based on Gauss process regression(GPR),and speed control method based on typical MSs are proposed.The mapping relation between electromagnetic torque and machine parameters is reflected by the established GPR model,and the hyperparameters of the covariance function is optimized.Accordingly,the fast and accurate predictions of the MTPA current angle under all MSs are achieved.The efficiency characteristics under different MSs are investigated,and the abilities of improving speed range and high-speed efficiency of the machine are verified.The speed control method based on typical MSs is proposed,by which the machine can maintain relatively high efficiency,and the maximum torque-speed region is guaranteed at the same time.The frequent switching of MSs is also avoided.Finally,a TSSPV-VFM prototype is manufactured,and the test platform is built to test the electromagnetic performances.To verify the theory and simulation analyses,the magnetization-regulation characteristics and anti-demagnetization ability of the magnetic pole are tested.And the experiments about the torque characteristics,loss characteristics and efficiency characteristics of the machine are carried out.The proposed topology is proved to be able to regulate the air-gap magnetic field,so as to realize the expansion of speed range and the improvement of high-speed-region efficiency.