Optimal Study Of The Electromagnetic Parameters Of Low-speed High-torque Submersible Permanent Magnet Synchronous Motor

With the development of oil field exploitation,the number of highly-deviated and horizontal wells,viscous and heavy oil wells,sandy and waxy oil wells are increasing.As a new technology,progressing cavity pump(PCP)directly driven by low-speed high-torque submersible permanent magnet synchronous motor(SPMSM)is applied to oilfields gradually.SPMSM is the power source of this unit and its performance has significant effects on the quality and life of this pumping unit,the crude oil output and the production cost.SPMSM is a new kind product developed in recent years,so it will be of great significance to analyze and research the electromagnetic performance of SPMSM and optimize the SPMSM.In this paper,to improve the efficiency and reduce the cogging torque simultaneously,the optimal study of the electromagnetic parameters of SPMSM is carried out.First of all,the design schemes of low-speed high-torque SPMSM are analyzed.Four different slot-pole combinations are selected based on the classification characteristics of PMSM,and a total of eight motor models are studied based on finite element method because the motor models can be classified as closed slot and semi-closed slot.The air gap flux density,back emf,cogging torque,output torque,tooth flux density of the eight motor models are contrastively analyzed.According to the analysis results and making a comprehensive consideration,finally the model with 12 poles and 36 slots is selected for the further optimization design.There are many parameters during the design process of SPMSM and it is difficult to determine the parameters to optimize.The analytic method is used to analyze the loss and cogging torque of SPMSM.The mechanism of production the losses(copper loss,iron loss,stray loss,mechanical loss)and the cogging torque is analyzed,and the function relationships between losses and parameters and between cogging torque and parameters are established.Combined with the design experience for PMSM,eight factors that have effects on loss and cogging torque are identified,and the initial values of the eight parameters are obtained by parametric analysis.Second,the optimization design of SPMSM is carried out.Defining SPMSM is a multi-parameter problem,but not all parameters have a significant influence on motor performance,and there are interaction effects between the electromagnetic parameters.Taking the interaction effects and the confusions between the interaction effects into account,the fractional factorial design out of design of experiment(DOE)is employed for the screening activity,and finally four significant parameters are identified.Because the true function between the performance and design parameters is difficult to obtain,response surface methodology is used to build a second-order analytical model of efficiency and cogging torque,and the quality of the fitted models are estimated.The non-dominated sorting genetic algorithm II(NSGA-II)is used to search for the Pareto-optimal solutions that maximize the efficiency and minimize the cogging torque simultaneously.The production process of the SPMSM causes various tolerances,which has effects on the motor's performance.Also taking efficiency and cogging torque as optimization objectives,the robust parameter design is carried out based on Taguchi's method.The four screened out significant parameters are set as controllable factors,and five error factors are selected and set as noise factors.The orthogonal array including the control table and the noise table is established by using the Taguchi's method.Finite element method is used for the numerical experiments to obtain the signal-to-noise ratio of efficiency and cogging torque.The respective optimal factor combination for maximum efficiency and minimum cogging torque are obtained by the analysis of mean,and the “Pareto optimal factor combination” maximizing efficiency and minimizing cogging torque simultaneously is obtained by the analysis of variance.Finally,according to the optimization results,the detailed design for the SPMSM is completed,and a SPMSM prototype with rated power 9.6 kW and rated speed 150 rpm is manufactured.Both the no-load test and load test are carried out.The motor runs smoothly during testing and both the torque ripple and speed ripple are small.The measured efficiency is close to the theoretical analysis result,which verifies the effectiveness of the optimization design.