| High-speed permanent magnet synchronous motors(PMSM)are widely used in fuel cell air compressors,flywheel energy storage,and micro gas turbines due to its simple structure,high force-energy density,and no excitation loss.However,the high-speed rotor itself has no starting winding,and there are permanent magnet braking torque and dry friction torque,which lead to difficulty in starting.At present,low-speed open-loop and high-speed closed-loop mixed control methods are commonly used for starting,but low-speed open-loop control will generate a large starting current,and even current overload,which will caus demagnetization and motor damage.Therefore,it is urgent to develop a high-speed permanent magnet synchronous motor with a self-starting capability in the low-speed segment—a permanent magnet hysteresis motor.In this paper,a permanent magnet ring+hysteresis column rotor structure was designed.Firstly,the composition design and performance prediction of the material AlNiCo for the rotor effective layer were carried out from the microscopic level.Secondly,the strength of the rotor was calculated under actual working conditions,and finally the self-starting performance analysis was analyzed.The main contents and conclusions are as follows:(1)The composition of the existing AlNiCo materials was designed.On the basis of the original AlNiCo composition,the high magnetic phase was added,and the high magnetic phase pure iron was insulated and coated by aluminum oxide.The phase structure,phase change,solidification and heat treatment of the newly designed AlNiCo material were analyzed by thermodynamic theory.The random particle distribution model was established based on the Monte Carlo method,and the static magnetic field,transient magnetic field and high-frequency harmonic field were analyzed respectively.According to the phase transformation analysis,the newly designed AlNiCo underwent amplitude modulation decomposition of a-phase and disappearance of γ-phase at 730℃,which was consistent with the existing AlNiCo material.In order to avoid the precipitation of y-phase,730℃ was chosen as the material heat treatment temperature.According to the analysis of static magnetic field and transient magnetic field,it can be seen that the magnetic flux density of the soft magnetic phase treated by insulating coating technology is obviously reduced under the transient magnetic field.At 300℃,its Poisson’s ratio is 0.3-0.34,and the change amplitude is 0.04,which can provide a basis for the application of permanent magnet hysteresis motor.By comparing the eddy current loss of AlNiCo materials with and without insulation coating treatment under high frequency harmonic field,it is found that the eddy current loss of materials can be reduced by 18.4%-13.8%within 2000 Hz after insulation coating treatment.(2)In order to ensure the safe operation of the permanent magnet ring hysteresis column rotor under high-speed operation conditions,the rotor strength without considering temperature effect and considering temperature effect were analyzed respectively.Based on the thick-walled cylinder theory,the analytical formulas for the displacement field and stress field of each part were derived respectively,and the stress of each part for the two structures was compared and analyzed.Under the working condition of rated power of 10kW and rated speed of 120kr/min,the accuracy of analytical calculation was verified by finite element method.The results show that the carbon fiber layer in the proposed four-layer new rotor structure has an expected result,resulting in the vibration of the stress state of the hysteresis column and the permanent magnet ring in the three-layer structure.For the four-layer rotor structure,the magnetic-thermal-solid coupling method was used to analyze the rotor strength considering the temperature effect,and the influence of the fit tolerance and the thickness of the protective sleeve on the rotor stress distribution was studied.The results show that when the motor is unloaded,the maximum temperature inside the rotor is 25.67℃;when the current is loaded with 50A,the maximum temperature inside the rotor is 165.9℃.At this temperature,the maximum radial stress of the rotor occurs at the fitting,and the maximum tangential stress appears at the protective sleeve,all of which conform to the safe use range of materials.The increase of the matching amount increases the prestress of the rotor,which affects the rotor stress distribution.The increase in the thickness of the protective sleeve will increase the loss of the rotor,thereby increase the temperature of the rotor,and then caus the stress of each part for the rotor to increase in a certain extent.(3)The finite element method was used to analyze the starting characteristics of the highspeed permanent magnet hysteresis motor.Firstly,the air-gap flux density waveform and the back electromotive force(EMF)waveform are analyzed when the motor is no-load;Secondly,the starting speed,torque and current of the motor under no-load,load and full load were compared and analyzed.The results show that the motor structure does not need any starting auxiliary system,nor does it need to consider the initial position.It has the characteristics of fast starting and good stability.The motor can enter the stable operation stage in 50ms when it is noload;when the motor is fully loaded,it can also enter the synchronous stable stage in 60ms,and finally stabilizes in 100ms.By analyzing the influence of three different kinds of proportions for the permanent magnet and hysteresis column on the starting characteristics of the motor,it can be obtained that the contents of the two are closely related to the starting characteristics.The more the permanent magnet proportion,the greater the instantaneous current of the motor starting,and the smaller the current after stability.Among the three groups of proportions,the motor with a hysteresis column radius of 10mm and a permanent magnet thickness of 3mm has the best starting characteristics. |
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