Research On Hybrid Excitation In-Wheel Vernier Motor And Its Control Sytem

The key of agricultural modernization is the modernization of agricultural science and technology.The development of electric tractors(ETs)with the advantages of pollution-free and high-efficiency is one of the effective means to alleviate energy crisis and environmental pollution,realize the harmonious development between human being and nature,realize the modernization of agriculture and animal husbandry.In-wheel direct drive system possesses the merits of simple structure,good fault-tolerant capability and high efficiency.In order to ensure the operation quality of ETs,in-wheel direct drive system should has the performances of high torque density and wide speed adjusting range with high efficiency.Permanent magnet vernier(PMV)motor operates based on the magnetic field modulation principle.So this kind of motor has been attracted more and more attention in EVs and wind energy conversion due to the advantages of low speed and high torque because of the different speed between the armature reactive field and the rotor.However,the excitation field of PMV motor which is produced by PM only is relatively unchanged,so the application of PMV motor in EVs is limited.Supported by the National Natural Science Foundation of China(51677081),a novel hybrid excitation in-wheel vernier(HE-IWV)motor is proposed based on the analysis of operating principle of PMV motor.The proposed motor not only inherits the advantages of low speed and high torque from PMV motor,but also possesses the merits of wide speed adjusting range with high efficiency.The motor configuration,operating principle,electromagnetic performances and control strategy are discussed.The main research content of this thesis can be summarized as follows:1.Based on the operating request of in-wheel drive system,a HE-IWV motor with the advantages of wide speed adjusting range and high torque density is proposed by introducing the idea of hybrid excitation into PMV motor.Because there are two sets of 3-phase AC winding,the proposed motor can operate in three different modes based on the current control of armature winding and functional winding.Using the equivalent magnetic circuit method and the finite element method(FEM),the airgap flux density is calculated,so that the operating principle of different operation modes can be explained.2.According to the basic theory of electrical machinery and the operating principle of PMV motor,the dimension power formula is obtained to achieve the initial design of HEIWV motor.Then,independent parameter optimization method is adopted to decide the finial dimensions of prototype motor based on the influence of key dimensions to motor performances,such as average torque,torque ripple and magnetic field adjusting capability.3.The electromagnetic performances,such as magnetic field distribution,flux linkage,no-load EMF,cogging torque and inductance are calculated and analyzed by the FEM.Based on the analysis of flux density,iron core loss of different parts of the HE-IWV motor is calculated in different operating modes.Also,the corresponding copper loss and the eddycurrent loss of PMs are obtained.So the efficiency of the propose HE-IWV motor in different modes can be calculated.All of the results verify the correctness of motor design.4.The mathematic model of the proposed HE-IWV motor with two sets of 3-phase winding is deduced.Based on the analysis of current limit circle and voltage limit circle,the operation of proposed motor is analyzed,thus discussing the operating principle of HEIWV motor further.Consequently,the speed region based current drive strategy is proposed.5.The simulation model of HE-IWV motor control system is built in Matlab/Simulink,based on which the operation performances of HE-IWV motor in different operation regions are analyzed.The simulaiton results verify the correctness and validity of the established mathematic model and current control strategy.6.Finally,the prototype motor is built and the test platform is established based on d SPACE.No-load EMF in different excitation current,current and torque in different operating modes are tested and analyzed to verify the correctness of theoretical analysis and simulation calculation.