Research On Optimization Design And Control System Of Bearingless Permanent Magnet Synchronous Motor

As the key for the modernization of the equipment manufacturing industry,CNC machine tools are widely used in equipment manufacturing industries of aerospace,automobiles,ships,and power generation.As the key component of the CNC machine tool,the performance and quality of the electric spindle affect the machining accuracy and reliability of the entire CNC machine tool directly.Traditional mechanical bearings need to be lubricated and sealed due to friction and wear,which cannot meet the requirements of high-speed operation of electric spindles.Although the non-mechanical contact operation of the stator and rotor can be achieved by using magnetic bearings instead of mechanical bearings,the axial length of the system is increased,and the critical speed and output power are restricted.As a new type of motor that integrates magnetic bearing technology and permanent magnet synchronous motor technology,two sets of windings including torque windings and suspension force windings are embedded in the stator slots of the bearingless permanent magnet synchronous motor(BPMSM).The stable suspension operation of the BPMSM can be realized by exciting the currents of the same frequency in two sets of windings with a difference of 1 in the number of pole pairs.Because the BPMSM possesses the advantages of no friction and wear,no lubrication,long life,high efficiency,and high power density,applying it to drive high-speed electric spindles can greatly improve the performance of electric spindles.In this dissertation,the BPMSM is taken as the research object,and its working principle,mathematical models,structure optimization design,control strategy,sensorless control technology and digital control system are studied.The main works and achievements are as follows:1.The research background and significance of bearingless motors are described,and the development overview of bearingless motors is introduced.The research status of structural optimization design,mathematical model,control strategy and sensorless control method of BPMSM are emphatically summarized.Finally,the development trend of the BPMSM is analyzed.2.Based on the analysis of the electromagnetic force existing in BPMSM including Maxwell force and Lorentz force,the principle of suspension force generation is explained.The virtual displacement method is used to derive the suspension force and electromagnetic torque mathematical models of the surface mounted BPMSM and interior BPMSM,and the analytical expressions of the parameters in the surface mounted BPMSM suspension force mathematical models are obtained.However,the analytical expressions of the parameters in the interior BPMSM suspension force mathematical models are difficult to obtain.In order to solve this problem,a parameters measurement method of the interior BPMSM suspension force mathematical models is designed.3.The initial design of the stator,rotor and winding structure of the interior BPMSM is carried out.The average torque,torque ripple,average suspension force and suspension force ripple are set as the optimization goals,and 9 parameters that affect the stator slot shape and the permanent magnet structure are selected as the optimization parameters.The sensitivity analysis method is used to distinguish the 9 parameters to be optimized into significant parameters and non-significant parameters.The single-objective optimization based on parameter scanning method is carried out for non-significant variables.The experiment is carried out using the finite element analysis software according to the experimental design of Box-Behnken Design.The response surface method is used to establish the regression equations between the significant parameters and the 4optimization goals.The obtained regression equations are set as the fitness functions,and the multi-objective particle swarm optimization algorithm is used to optimize the significant parameters.The Pareto front of the average torque and torque ripple,and the Pareto front of the average suspension force and suspension force ripple are obtained.Taking the intersection of the two Pareto optimal solution sets,the optimal solutions of the significant parameters are obtained.Finally,a finite element simulation model is constructed to verify the performance of the optimized interior BPMSM.The analysis results show that the proposed BPMSM multi-objective optimization design method can significantly improve the overall performance of the motor and reduce the time required for optimal design.4.In order to solve the integral drift and hysteresis of the traditional flux observer,a direct torque control method based on the phase-locked loop flux observer is designed to improve the torque control performance of the BPMSM.The traditional displacement control method is a double closed-loop control method of displacement and current.This method controls the suspension force indirectly,so it has the problem of slow response speed of the suspension force.In order to improve this defect,the direct suspension force control algorithm under the eccentric displacement coordinate system is designed to realize the double closed-loop control of displacement and suspension force,and improve the response speed and anti-interference ability of BPMSM displacement control.A simulation model is constructed in MATLAB/Simulink to verify the performance of the proposed direct torque and direct suspension force control strategies.The results show that the designed direct torque control method based on the phase-locked loop flux observer can accurately observe the torque,and the observation result is not affected by the operation speed.The designed direct suspension force control method under the eccentric displacement coordinate system has a fast response speed of suspension force and strong antiinterference ability.5.The stable operation of BPMSM is inseparable from the accurate sensing of speed and displacement signals,which are usually obtained by mechanical sensors such as photoelectric encoders and eddy current displacement sensors.However,the measurement errors of mechanical sensors are sensitive to the temperature and electromagnetic noise,and implementation of the mechanical sensors increases the cost and volume of the system and reduces the reliability of the BPMSM.In order to overcome these problems,a speed and displacement sensorless control algorithm of BPMSM based on model reference adaptive system is designed.The BPMSM itself is used as a reference model,and the current equation containing the parameters to be estimated is used as an adjustable model.The speed and displacement adaptive laws are derived based on Popov's superstability theory.Finally,a simulation model is constructed in MATLAB/Simulink to verify the proposed speed and displacement sensorless control method.The results show that the proposed sensorless control method has high detection accuracy and good anti-interference ability.6.According to the results of multi-objective optimization design,a BPMSM prototype is manufactured.Based on the design of BPMSM hardware system and software system,a BPMSM digital control experiment platform is constructed.The prototype is researched on the experimental platform.The speed and suspension performance experiments of BPMSM are carried out to verify the proposed control method.The results show that the constructed digital control system has the advantages of fast response speed and strong anti-interference ability.The proposed control algorithm can realize the sensorless operation of BPMSM and improve the suspension operation performance of BPMSM.