Research On Demagnetization Of Line-start Permanent Magnet Synchronous Motor In Compressor

Line-start permanent magnet synchronous motor in compressor has a large starting current,the armature reacts violently during the starting process,and the permanent magnet has the risk of demagnetization.Considering the manufacturing cost of the motor,this type of motor can use ferrite instead of DdFeB during the design stage,through proper design of the rotor structure,the performance of the motor can be made close to that of pure DdFeB motor.However,the biggest problem with this design idea is the demagnetization of the permanent magnet.This paper takes a 2-pole 15 kW line-start permanent magnet synchronous motor in compressor as an example to study the demagnetization of permanent magnets.The paper first introduces the research status of line-start permanent magnet synchronous motor and permanent magnet demagnetization at home and abroad,then analyze the working principle of the motor and the material characteristics of the permanent magnet,and gives the specific parameters of the permanent magnets used in this paper.Then use the finite element simulation method to design and analyze the line-start permanent magnet synchronous motor in compressor,according to the different magnetic properties of NdFeB and ferrite,four rotor structures have been preliminarily designed,and the no-load and load conditions of each rotor structure motor are simulated and analyzed,it is found that the ferrite scheme motor can be close to the DdFeB scheme motor in steady state performance under reasonable design,and its cost performance is more advantageous.At the same time,the paper introduces the method of using the finite element software to analyze demagnetization and find the specific demagnetization area and demagnetization rate of the permanent magnet,analysis the demagnetization of four rotor structure motors,it is found that the ferrite motor has poor resistance to demagnetization and it is difficult to meet the design requirements of the motor.Considering the poor anti-demagnetization performance of the ferrite scheme motor and the low cost performance of the NdFeB scheme motor,the paper focuses on the hybrid permanent magnet scheme motor,analyze the steady-state performance and demagnetization of the motor,it is found that the hybrid permanent magnet scheme motor can improve the demagnetization of permanent magnets under the condition of higher cost performance.Then study the demagnetization of the motor from the design point of view,study the influence of the arrangement,specifications and relative position of the permanent magnet on the demagnetization of the motor,and also study the effect of the rotor slot shape and the number of rotor slots on the demagnetization of the motor.At the same time,a rotor structure with non-uniform arrangement of rotor bars is given,and the anti-demagnetization ability of the motor is greatly improved under this structure.At the end of the paper,the hybrid permanent magnet scheme motor is taken as theobject to study the influence of various factors on the demagnetization during the use of the motor,the effects of load conditions,moment of inertia,initial rotor position,and initial phase angle of the voltage on the demagnetization of the motor are studied separately during normal starting,and the better values of each factor are given.Then analyzes the impact of voltage fluctuations during starting and the sudden changes in load on the motor demagnetization during operation.Finally,analyze the demagnetization of the motor when it started at low or high temperature conditions.The work in this paper has certain guiding significance for the research and production practice of this type of motor.