| The existing transmission system composed of asynchronous motor + mechanical gearbox has the advantages of simple structure and low cost,but it also has the disadvantages of low transmission efficiency and poor environmental friendliness,especially the phenomenon of wear,gluing and broken teeth of mechanical gears,which also causes the problems of poor reliability and high maintenance cost of the transmission system.With the development and transformation of material science,especially rare earth permanent magnet materials,it is possible to replace the above mechanical and electrical transmission mode with rare earth permanent magnet motor + rare earth permanent magnet gear;among which the transmission efficiency of rare earth permanent magnet motor replacing asynchronous motor can be increased by 4% ～ 5%;the rare earth permanent magnet gear can realize the contactless transmission,so it does not need the necessary lubricating oil for the mechanical gearbox,and there is no wear or tooth breakage.However,the manufacturing of high torque density permanent magnet gear is very difficult.Taking Field Modulated Permanent Magnetic Gear(FMPMG)as an example,because of its three-layer rotor and two-layer air gap,especially the manufacturing difficulty of the modulation ring which is composed of magnetic conducting material and non-magnetic conducting material,resulting in FMPMG is still in the experimental stage.Based on the field modulated principle of FMPMG,this paper presents a Field-modulated Permanent-magnet Gear Motor(FPGM)structure,which can directly integrate the structure of the modulation ring into the stator core and realize the integration of the permanent-magnet motor and the permanent-magnet gear.In order to make a significant difference between FMPMG and FPGM,the FPGM proposed in this paper is written in bold italics,that is,FPGM.The proposed FPGM has the same structure as the existing permanent magnet motor(or asynchronous motor),with only one layer of air gap,one layer of stator and one layer of rotor,but it realizes the variable speed output of similar mechanical gearbox.It can not only replace the above "asynchronous motor + gearbox" transmission mode,but also solve the problems of manufacturing difficulty and high process cost of FMPMG and its modulation ring.In this paper,the following research work is carried out around the proposed FPGM.(1)In order to establish the theoretical calculation model of FPGM transmission ratio,the analytical model of air gap magnetic field of permanent magnet with staggered magnetic poles is established in polar coordinates,and it is transformed into Laplace equation and Poisson equation which can be solved under specific boundary conditions.According to the change law of permeability of the modulation ring,the modulation function of the modulation ring to the air gap magnetic field is derived,and Fourier transform the analytical solution and modulation function of the air gap magnetic field,the logarithm of the poles of the harmonic magnetic field of the permanent magnet is obtained,finally the variable speed transmission condition and transmission ratio of FPGM are obtained.(2)To replace the permanent magnet field,the stator windings must be symmetrical.Therefore,this paper designs the fractional slot winding and the integral slot winding according to this criterion by using the slot number phase table and makes a comparative analysis.The results show that although there are many harmonics in the fractional slot winding,they can produce the same number of harmonics as the pole number of the permanent magnet field,which is beneficial to the field modulated.(3)The static finite element analysis model of the initial FPGM is established and its magnetic field is analyzed.It not only verifies the correctness of the analytical model of transmission ratio generated by stator winding magnetic field and rotor permanent magnet magnetic field,but also verifies that the amplitude of air gap magnetic field generated by fractional slot winding is larger than that generated by integral slot winding,which makes FPGM have better mechanical operation characteristics.(4)Because the fractional slot winding will produce more harmonic magnetic field after being field modulated,it is easy to produce cogging torque and unbalanced magnetic force.Based on the energy method,this paper analyzes the relationship between the parameters affecting the cogging torque of FPGM,and obtains the conclusion that the cogging torque of fractional slot winding is smaller by comparing the cogging torque of fractional slot winding and integral slot winding.In addition,the finite element analysis also show that the magnitude of cogging torque is about 1.8 Nm,which is far less than the rated torque of 32 Nm.(5)The analytical expression of the unbalanced magnetic force of FPGM is given by using the Maxwell tensor method,and the static eccentric,dynamic eccentric and inherent unbalanced magnetic force are given by combining with the finite element analysis method.The results show that the inherent unbalanced magnetic force of FPGM is very small,and the larger unbalanced magnetic force can be produced under the static and dynamic eccentric conditions.(6)In order to make the FPGM prototype have better output characteristics,the influence of structural parameters such as the height,duty cycle,air gap width and the thickness of permanent magnet on the key indexes such as the air gap magnetic field,back EMF,current,loss and power factor of FPGM is analyzed by using the finite element method,and the optimized FPGM structural parameters are obtained.Through the finite element analysis of the optimized FPGM,it is shown that the optimized FPGM has better performance and can save more permanent magnet materials than the initial design parameters.(7)The prototype was trial manufactured and an experimental platform was built to analyze the rotating speed,torque,efficiency,and power factor of the prototype at different frequencies and loads,the experimental results show that the variable speed output can be stable under different load conditions.The measured rated efficiency is about 84%,and the power factor is about 0.93.The transmission ratio obtained by the experiment is consistent with that obtained by the analytical calculation and the finite element calculation,which verifies the correctness of the theoretical analysis and the finite element analysis of the harmonic magnetic field in this paper. |
