Research And Design Of Active Magnetic Bearing For High Speed Motors

Since high-speed motors have advantages of wide speed range,compact structure,small inertia and high power density,it has gained more and more attention over the world and also has been widely used in the industry.But the severe wear and heat problems of the bearing system reduce the reliability of high-speed motors,directly limiting the development of high-speed motor.Fortunately,the active magnetic bearing(AMB)can not only stably suspend the rotor but also actively control the dynamic behavior of the rotor,which make it more and more popular in the use of high –speed motor.However,the design of the AMB is a complex process integrated with multiple disciplines.So far,it has not been widely used in the industry.Therefore,it is important to study the design method of the AMB applied to the high-speed motor.This thesis will study the AMB system from the following aspects:Firstly,a detailed comparison of different magnetic bearing topologies are presented.According to the requirements of high-speed motor,the active magnetic bearing(AMB)topology is chosen and analyzed.The structural characteristics of AMB are also studied in detail to create the single degree model.After that,based on equivalent magnetic circuit method,the configuration and fundamental principle of AMB are analyzed and the mathematical model of the radial magnetic suspension force is established.Then,in terms of engineering technology,the performance requirements of the AMB and the size limit of actual machining assembly are taken into account to build the engineering process and design method of the AMB.Based on the multidisciplinary design method including electromagnetic,mechanical and thermal,a magnetic bearing for 200 k W&40000rpm high-speed motor is designed as an example.Finite element method is also used in the design of AMB to prove the effectiveness of the method proposed.In order to fully consider the characteristics of the rotor into the design of the AMB,which is the supporting object of the AMB,the thesis studies the design process of rotor of 200kW&40000rpm high speed motor.The design process include rotor structure selection,material selection,static analysis and dynamic analysis.In addition,considering the existence of the actual eccentricity in the rotor,the transient dynamic analysis is analyzed by the FEA method to predictive dynamics behavior of the rotor.Finally,different topologies of switching power amplifier are compared in detail to select the new half-bridge structure as the switching power amplifier for the AMB,which is chosen based on the lowest cost and the minimum current ripple principle.MATLAB simulation is built to verify the working principle of the new half-bridge structure.What's more,some experiments are designed to verify the feasibility of the topology.