Research On Eddy Current Loss Optimization And Temperature Distribution In High Speed Permanent Magnet Generator

Due to the advantages of small size, low noise, fast dynamic response, high power density and high transmission efficiency, the high speed permanent magnet generator (HSPMG) has become a critical equipment in microturbine distributed energy supply system and could meet the requirements of the power system developing towards to the miniaturization and integration. As the’ generation equipment in portable power, HSPMG has been used widely in military, medical and mine rescue. As a mechanical form of uninterruptible power supply(flywheel energy storage), compared with the chemical energy storage, it is friendly with the working environment and has the longer life, so it can be widely used in aerospace, industrial and computer netword services. In the HSPMG, the higher power density could cause the larger losses in unit volume. The high frequency harmonic magnetic field in the air gap could induce the eddy current in the rotor sleeve and permanent magnets, which will cause the eddy current losses and increase the temperature of the rotor directly. Since the permanent magnets working in high temperature environment could be demagnetized, the eddy current losses could directly affect the normal operation of the generator. So it is of significance to have some researches on rotor eddy current losses.According to the special structure of a100kW level HSPMG, including the stator back wound windings and rotor alloy sleeve, the eddy current losses in the rotor sleeve and permanent magnets are studied. Based on the three-dimensional time-stepping finite element method, the rotor eddy current losses are calculated accurately, and the eddy current distribution in the rotor sleeve and permanent magnets could be obtained. Establishing the analytical calculation model of the surface mounted permanent magnet machine, the rotor eddy current loss expression could be derived, and the calculation results are compared with the finite element calculation results. It proves that the analytical method has the advantages of rapidity and universality. Combined with the3D finite element analysis and the analytical calculation method, the influences of the rotor sleeve segmenting in axial direction and the permanent magnets segmenting in circumferential diection on rotor eddy current losses are studied. Based on the above analyses, the principles of the permanent magnet segmenting are obtained.In order to reduce the eddy current losses, the influence of the sleeve materials on generator is studied. The variations of the electromagnetic field, eddy current density and eddy current losses are analyzed, when the electromagnetic property of the sleeve material is given. Based on the theory of harmonic field penetration depth, the copper plating which could reduce effectively the rotor eddy current losses is presented, which is also analyzed compared with the copper shield. The resulets show that the copper plating is a better way to reduce the rotor eddy current losses.The equivalent magnetic circuit model of HSPMG is established. In order to determine the boundary condition of permanent magnets, the iterative method of leakage coefficient is presented. The ferromagnetic material sleeve is adopted in the HSPMG, which could reduce the reluctance of the main magnetic circuit, improve the operating point and material utilization of permanent magnets. Using the vector magnetic potential, the induced noload electromotive forces of the HSPMG with different permeability sleeves are calculated analytically. And therewith the influence of the sleeve permeability on the induced electromotive force is analyed. The adjusting magnetic field character curve of sleeve permeability could also be obtained. Based on the priciple of the magnetic field superposition and the equivalent current sheet of fundamental MMF, the magnetic fields in the air gap and the rotor sleeve are calculated analytically when the generator operating at rated load. According to the Poynting Vector, the generator electromagnetic power transmitting from the rotor to the stator is calculated when the generator adopting different permeability sleeves. And therewith combined with the finite element method, the influence of the sleeve permeability on the generator magnetic field is studied comparatively. The relationship of the operating point of permanent magnets, the main flux and leakage flux is further analyzed. The optimal strategy is presented, which could take advantages of ferromagnetic material sleeve. In addition, the influence of the sleeve conductivity on rotor eddy current losses is also analyzed. According to the theory of the harmonic field penetration depth and the influence factors of the rotor eddy current losses, the variation principles of the eddy current losses with different conductivity sleeves are discovered. The range of the sleeve conductivity of the generator which will generate larger eddy current losses is given.The influence of the three-phase bridge rectifier load on the HSPMG is studied comparatively based on the field-circuit coupling electromagnetic model and the test plat. According to the Fourier transform theory, the voltage harmonics and current harmonics are studied. The content rate of the current harmonics and the current Total Harmonic Distortion(THD) are obtained. In addition, the rotor eddy current losses are ananlyzed comparatively, when the generator connected with the rectifier load and the resistance load respectively. With the same output power, the variations of the output voltage and the power factor of the generator with different loads are further analyzed.The3D coupling field between the fluid and temperature is established based on the calculation of the generator losses. And the influences of the rotor sleeve materials, the rotor structure, the electromagnetic properties of sleeve and the form of the load on the generator temperature field are studied. The temperature variations in different parts of the generator are given when the HSPMG adopts different rotors and loads respectively. The influences on the temperature of permanent magnets are further analyzed, and it is very important for the research on the permanent magnet demagnetizing.