Research On Winding Switching And Pulling-into Synchronization Of Pole-changing Line-start Permanent Magnet Synchronous Motor

Line-start permanent magnet synchronous motor(LSPMSM)not only has the advantages of wide operation range,economic reliability,but also has the advantages of high power factor,small volume,light weight and so on.Therefore,it has been widely studied and developed rapidly.But it has poor start-up capability,because of the existence of braking torque and pulsating torque.A novel 6/8 pole-changing LSPMSM was studied in this paper,the 6-pole winding is energized at the beginning of starting process,then the electrical source is switched to the 8-pole winding at suitable time,which reduces the braking torque and pulsating torque,and the start-up capability of the motor has been improved.The following research works have been carried out in this paper for this 6/8 pole-changing LSPMSM:First,the structure of the motor,and the work principle of the pole-changing method were introduced and analyzed,the structure of novel 6/8 pole-changing winding,and the main parameters of the motor were also illustrated.The novel 6/8 pole-changing winding was compared with traditional pole-changing winding,it was found that the 6/8 pole-changing winding is more simple and convenient to control winding switching than the traditional pole-changing winding.Next,the torque and magnetic field of the 6/8 pole-changing LSPMSM and the 8-pole LSPMSM in starting process were compared and analyzed,and the finite element simulation(FES)mode was established and analyzed to prove the superiority of the 6/8 pole-changing LSPMSM,by comparing the braking torque,pulsating torque and locked torque in starting process of this two motors;Then,the winding switching process of the 6/8 pole-changing LSPMSM was studied.The motor starting with its 6-pole winding,the steady operation is working with its 8-pole winding,it has the process of winding switching in which the 6-pole winding is disconnected from the power supply and the 8-pole winding is energized.The different winding switching states,including switching speed,the voltage differences between the applied voltage and the induced electromotive force of 8-pole winding,the load torque,the moment of inertia,have effects on speed fluctuation,torque fluctuation,impact current,pulling into synchronization and the demagnetization of permanent magnet.Based on the two methods of MATLAB/Simulink dynamic simulation mode and finite element method(FEM),the dynamic behavior of winding switching process was studied to find a favorable switching time.Last,after winding switching,there is still a pulling into synchronization process.Based on that the start-up capability has been improved by pole-changing starting method,the method of reducing the rotor resistance was adopted to improve the pulling into synchronization capability.By comparing the critical moment of inertia that the motor can drive before and after reducing the rotor resistance,it is proved that the pulling into synchronous capability of the motor is obviously improved.