Research On The Key Problems Of Electrical-Magnetic-Thermal For Direct Drive Permanent Magnet Synchronous Motor In Large Pumping Station

Low-speed High-torque Direct Drive Permanent Magnet Synchronous Motor(LHDDPMSM)has the advantages of simple structure,easy maintenance,high efficiency,high power factor,and easy control.Therefore,they are widely used in various large-scale engineering and equipment manufacturing fields.The magnetic stability of permanent magnets(PMs)is the basis for ensuring that LHDD-PMSM can achieve its expected performance during operation.Once the permanent magnet undergoes demagnetization,a series of electrical magnetic thermal problems will occur in the motor.The research object of this paper is the LHDD-PMSM used in a large water delivery pump station.In practical application,it is found that the LHDDPMSM will enter a continuous positive feedback of temperature rise due to the reversible demagnetization of PMs until the temperature rises to a new thermal balance.In the process of achieving new balance,the stator current,loss and heating increase,and the system efficiency decreases.Monitoring the magnetic properties of PMs,limiting their loss and temperature rise,and maintaining stable magnetic performance are effective methods to solve this problem.Therefore,this paper will start from the demagnetization detection,loss analysis,loss reduction research,temperature rise coupling calculation,and heat dissipation improvement research of the PMs,and conduct a systematic analysis of the electro-magneto-thermal key issues of LHDD-PMSM.The main research content is as follows:Firstly,this paper proposes a method for online measurement of back EMF of PMSMs to detect the dynamic magnetic performance of PMs.The back EMF testing method for PMSMs mainly relies on offline testing.The paper first summarizes the shortcomings of existing detection methods.Furthermore,an online test method for the magnetic properties of PMSMs based on the principle of waveform equivalence was proposed,and theoretical analysis,development of practical testing instruments,and experimental verification of equipment detection accuracy were carried out.Then,the developed tester was used to conduct online testing of the magnetic properties of the LHDD-PMSM permanent magnets.And determine the demagnetization state of the PMs based on the experimental results.The research objectives and content have been set for the later research on reducing the losses of PMs in motors and reducing the temperature rise in LHDD-PMSM.Secondly,the losses of LHDD-PMSM for large pumps,especially the eddy current(EDC)losses of PMs,were studied.Firstly,a finite element analysis(FEA)model of LHDD-PMSM for pumps was established,and no-load and rated load simulation were conducted to calculate the various losses of the motor under no-load and rated load conditions.Then,this paper established mathematical models for the iron loss and the EDC loss of the PMs,and analyzed the sources of the losses.Finally,a classification study was conducted on the sources of EDC losses in PMs.The different losses caused by different harmonics were separated,laying the foundation for the later research on EDC loss reduction of the PMs of LHDD-PMSM.Thirdly,based on the study of the source of EDC losses in PMs,a method for reducing EDC losses in LHDD-PMSM PMs for large pumps was proposed and studied.Firstly,considering the structural limitations and driving characteristics of large motors,two electromagnetic improvement schemes for LHDD-PMSM,hybrid structure magnetic slot wedge and rotor magnetic insulation slot,were proposed.A comparative simulation study was conducted in the paper to evaluate its effectiveness in reducing PM losses.Then,based on this,this chapter synthesized these two schemes and proposed an optimized LHDD-PMSM model.Compare it with the original model,the optimized one has a good improvement effect in suppressing EDC losses of PMs.Finally,this paper conducted.temperature rise simulation calculations,experimental verification,and cooling improvement research on LHDD-PMSM for large pumps using magneto-thermal bidirectional coupling.Firstly,a temperature field model was established and coupled magneto-thermal simulation was conducted,and the accuracy of the simulation results was verified by temperature rise experiments of the motor.Secondly,this paper conducted coupling simulation on the optimized model proposed in the previous chapter,and compared it with the original model to verify the effectiveness of the new structure in improving temperature rise.Finally,considering the current engineering application status of LHDD-PMSM for pumps,this paper further studies the effect of increasing cooling air ventilation or reducing cooling air temperature on the heat dissipation of permanent magnets,and compares the improvement effect of the above two methods on the temperature rise of PMs through the simulation model.