Research On Multi-Excitation-Source Magnetic-Shunting-Rotor Flux-Regulating Technologies Of High-Power-Density Permanent Magnet Synchronous Machines

Electrification has become the characteristic and trend of the advanced transportation.As the power conversion device of electrified transportation equipment,the motor system is the key component.Rare earth permanent magnet synchronous motor(PMSM)has high power density and high efficiency.However,it is difficult to control the magnetic field of permanent magnets once the motor is fabricated.It leads to the problems such as the narrow high-efficiency range,the high back-EMF impulse under the failure of high-speed flux weakening control and the difficulty of demagnetization under fault condition.In this paper,the key research and innovation work aim at the flux-regulating technology of PMSM.The multi-excitation-source magnetic-shunting-rotor flux-regulating technology of high power density PMSM is studied.A new topology of multi-excitation-source magnetic-shunting-rotor flux-regulating PMSM(FRPMSM)is proposed and analyzed.The key technologies of this motor are studied,including the operating principle,the electromagnetic design method,the principle and suppression of loss,the multi-channel cooling method,the structure enhancement method of modular rotor,and the characteristic current tracking control strategy.The main research work of this paper includes the following aspects.The principle and characteristic of PMSM are described.The improvement of power density can be realized by the improvement of speed and torque density.The key factors of high torque density design are to improve the electromagnetic load.The research status of high power density PMSM is summarized from the development of PM materials,motor topology and cooling system.The definition of fluxregulating technology of PMSM and the characteristics of different flux-regulating technologies are concluded based on the PMSMs with rotor excitation.The structure and operating principle of FRPMSM with multi-excitation-source magnetic-shunting rotor are outlined.The development and evolution of the topology are summarized.A new magneticshunting-rotor flux-regulating method and structure is proposed.Based on the mechanism of flux linkage and its influence on the performance,the ratio of different excitation sources is analyzed.The magnetic equivalent circuit(MEC)considering the magnetic saturation and leakage flux distribution is built and illustrated,as well as a fast-calculating software is developed.A 2D equivalent finite element modelling method for the motors with radial/axial flux paths via MEC is proposed.With the proposed modelling method,the computational time is significantly reduced and the calculation accuracy is high.A design procedure of the FRPMSM with multi-excitation-source magnetic-shunting rotor is developed by ultilizing the equivalent fast calculation model and multi-objective optimization method of PMSM,and the electromagnetic design of a 100 kW prototype for electric vehicle is completed.The loss distribution and 3D temperature field of the new multi-excitation-source magnetic-shuntingrotor FRPMSM are studied,and a multi-channel cooling method combining casing water channel and end cover water channel is proposed.The distribution and suppress methods of rotor eddy current loss under different operating conditions are studied.The rotor temperature rise is improved by the multichannel cooling method.The maximum temperature of PM is reduced from 170.1 ℃ to 135.2 ℃ at the peak speed,which improves the high-speed capacity and reliability of the motor.Considering the complex rotor structure of the multi-excitation-source magnetic-shunting-rotor FRPMSM,a comprehensive and systematic analysis is carried out according to the electromagnetic force,high-speed centrifugal force and structure of the motor.The distribution of electromagnetic force is studied and a new structure enhancement method of the modular rotor is proposed.A 3D multi-physics model is established for the analysis of the N-pole magnetic conductor,PM and rotor core stress distribution.The multi-objective optimization analysis of the rotor parameters is carried out.The effectiveness of the modular rotor structure and the analysis method are verified by experiments.The influence of characteristic current on flux-weakening ability and the requirements of inductance characteristics under different working conditions in different motor topologies are summarized.The theoretical analysis method of the inductance characteristics of the multi-excitation-source magneticshunting-rotor FRPMSM is proposed.The inductance variation law is analyzed through the fast analysis equivalent model and 3D finite element model.Based on the inductance variation law and flux linkage regulating characteristics,the characteristic current characteristics are analyzed and the characteristic current tracking control strategy is proposed.The improvement of output power at the high-speed operating mode by the characteristic current tracking control strategy has been validated by the simulated and experimental results.