The Design Of Variable Frequency Speed Control In Wide Speed Range Of 4-Pole Induction Motor

With induction motor being more and more widely applied into test bench,original 2-pole motor generally has large frame size because rated speed of load is far away from maximum speed,which is hard to meet market demand for volume and economy.Now domestic 4-pole motor can reduce frame size but can't reach speed above 3000 rpm.Therefore,the research of 4-pole with speed above 3000 rpm has a high economic value and practical significance.The load type of test bench in this paper is constant torque and constant power,and speed range by frequency control is 0-850-3200 rpm.To reduce frame size to 400 from 450,it try to use 4-pole motor solution instead of 2-pole motor then recalculate electrical parameter and redesign mechanical structure.Changes of the number of poles will cause temperature rise,magnetic flux density and current density beyond the limit.For this issue,this paper use finite element software to establish motor mesh model and choose existing stator and rotor slot to carry out magnetic circuit analysis and calculate magnetic flux density and current density.Moreover,according to speed control characteristic for constant torque and constant power load,it chooses appropriate cooling type to describe performance characteristic curve.At the same time,it analyses high harmonics in induced electromotive force and its weakened methods,and finally it use finite element software to simulate and verify.Winding design is based onthe magnetic potential star diagram and the phase division method to draw out the connection diagram,equivalent diagram and expansion diagram of each phase winding.Finally they are summarized into the total winding diagram according to manufacture process requirements.Considering the influence of harmonics of the frequency converter,the harmonic spectrums of three-phase current of the motor are simulated by the finite element software according to the Fourier series principle,and respectively calculate temperature rise and loss of motor under sinusoidal wave and converter supply,which can intuitively compare and analyze harmonic influence on temperature rise and loss of motor.In order to solve the problem that the 4-pole motor can not reach3200 rpm,this paper use 2-pole rotor structure to replace original 4-pole rotor structure.Then,it chooses appropriate bearing type as per speed requirements and combined load,and calculates its operating temperature and service life.Then it establishes segmented finite element model as per bearing and rotor dimensions,and calculated critical speed.Finally,it simulates the vibration rate of the stator yoke and stator tooth tip by finite element model and obtains the radial and tangential vibration spectra.The simulation results show that new rotor structure can fulfill maximum speed requirement.Finally,a series of experiments on the motor are carried out including temperature rise test,noise test and vibration test.The experimental results show that the motor can not only meet electrical performance,temperature rise limit and noise limit but also can meet maximum speed and vibration requirements.