Comprehensive Multi-Physics Design Of Large-Power High-Speed Permanent Magnet Electrical Machines

High-speed permanent magnet electrical machines have found broad applications due to their advantages such as high power density and high efficiency.Focusing on the multiphysics comprehensive design of high-power and high-speed permanent magnet motors,the following studies are carried out:In terms of motor modeling,two improved models,in time and frequency domain,respectively,are proposed for the high-speed permanent magnet machines.The proposed models can take the significant rotor eddy current reaction effect into account,so that harmonic currents can be calculated accurately under harmonic voltage excitation.The improved time-domain model can account for the influence of rotor eddy current reaction field on the stator flux linkage,by introducing virtual short-circuit windings on the rotor.The parameters of the rotor virtual windings are obtained through standstill frequency response tests.The improved frequency-domain model can account for the stator flux linkage induced by the rotor eddy currents,by introducing the concept of stator-rotor comprehensive inductance.Analytical model of the stator-rotor comprehensive inductance is established,so that fast and accurate calculation can be conducted.When calculating the rotor eddy current field,the influence of Bessel function type on the numerical stability is revealed.In terms of electromagnetic analysis,the influence of converter power supply on motor performance is evaluated,regarding both the fundamental and the harmonic components.At the fundamental level,the fundamental operating point of the motor is calculated,based on the fundamental motor parameters,as well as the control strategy under the converter capacity constraints.At the harmonic level,the pulse width modulated(PWM)voltage waveforms under the switching frequency constraint are derived.Then,the voltages are substituted into the improved frequency-domain model,so as to calculate the armature current harmonics.Moreover,computational model of iron loss,copper loss,and rotor eddy current loss under harmonic excitation is established,achieving fast and accurate calculation of the electromagnetic losses under converter power supply.In terms of temperature and fluid field analysis,a three-dimensional lumped parameter thermal network model of the motor is established.For the airgap fluid flow problem,a surrogate model is established to calculate the convection heat transfer coefficient and air friction loss,based on the computational fluid dynamics(CFD)analysis results of a set of airgap dimensions and temperatures.The proposed thermal network model employing airgap surrogate model enables fast and accurate calculation of the motor temperature.In terms of rotor strength analysis and retaining sleeve design,the analytical model for surface-mounted permanent magnet rotor is established.Then,the ultimate stress conditions of the rotor are analyzed.Based on the study above,an analytical method for calculating the minimum sleeve thickness is proposed,with the materials utilized near their strength limits.Confronting the practical problem of interference fit machinability,the proposed method is further improved to take the assembly constraints into account,which enables rapid design of rotor sleeves for the surface-mounted permanent magnet electrical machines.In terms of rotor dynamics analysis,both analytical and finite element models are established to analyze the critical speeds,and the influence factors are investigated.Based on the finite element analysis results of rotors with different dimensions,a surrogate model is established to calculate the key critical speeds of the rotor.In this way,fast and accurate calculation of the dynamic performance of the rotor-bearing system is achieved.By integrating the multi-physics models above,and considering the mutual influence between physical fields with temperature iteration,a fast multi-physics model for the highspeed permanent magnet motors is established.After determining the optimization parameters,constraints,and objective,the model is applied to large-scale optimization of the key motor dimensions.As a result,the maximum local temperature rise of the motor is effectively suppressed,and the efficiency is improved.A high-power high-speed permanent magnet motor prototype with the rated power of 300 kW and rated speed of 26 krpm is designed and manufactured,and the relevant experiments are conducted.The no-load and load experimental data are analyzed and compared with the design values,proving the effectiveness of the fast multi-physics analysis method proposed in this thesis.