Design And Research On High-speed Permanent Magnet Synchronous Machine Used On Flywheel Storage System

As an energy storage device, the flywheel offers some attractive advantagesover conventional chemical batteries for electric vehic les, including higher energydensity, higher power density, longer cycling life, reduction of maintenance and lesspollution to the environment. The M/G is a key component of the flywheel systembecause the energy conversion from the electrical form to the mechanical during thecharge mode and from the mechanical form to the electrical during the dischargemode happens inside the M/G. Thus, the efficiency of the energy conversion processmainly depends on the performance of the M/G. Hence, one of the ways to improveeffic iency and energy density of the flywheel energy storage system is to design ahigh efficiency and high speed M/G unit.This thesis deals with the issues associated with the design of high-speed, hightorque-density permanent magnet machines which operate in a vacuum environment.High speed machine overheating and mechanical constraints become a main issue tothe machine designer and hence several iterations have to be performed.Firstly considering the background and the design index of application, theoverall scheme of motor is researched. In designing high speed permanent magnetmachines, particular emphasis is made on the interaction (and conflict) ofelectromagnetic fields, thermal fields and mechanical constraints in finding anoptimum machine structure for minimum magnet temperature and best overallefficiency. The dynamic model of the flywheel rotor-bearing system is built. Inorder to insure the safety of the flywheel system, its critical speeds and modal shapesare calculated.Core loss calculation is an important issue in design of high speed permanentmagnet motors. For an accurately calculation, magnetic field analyses in stator coreare performed and a comprehensive consideration rotating magnetization methodand the harmonic magnetic fie ld is used to calculate the core loss of high speedmotor. The causes of rotor eddy current loss are studied. At the same time, the finiteelement method are used to analysis the effects of slot opening width, air gap length,retaining sleeve material and thickness on the rotor eddy current loss drastically.The water cooling system is analyzed by CFD. According to the machineapplication and size characteristics, the spiral water structure is choose as the bestappropriate water cooling structure. An equivalent thermal network model of avacuum environment motor is established and the radiant heat resistance betweenthe stator and rotor is calculated using iterative method.Through the study on material temperature sensitivity, the impact of motor performance is analyzed. The influence of the relationship between electromagneticload distribution in efficiency and thermal property was described and the differentof design method of a40kW machine which operates at speeds up to60krpm,comparing a slotted to a slot-less stator topology are researched. At last, high-speedPMSM transient temperature rise properties is researched and the efficiency andthermal property are compared in slot motor and slot-less motor.