Study On Magnetic Suspension Permanent Magnet Linear Motor

Friction is one of the most important factor that restrict linear drive systemperformance of numerical control (NC). Magnetic suspension permanent magnet linearmotor is applied to NC，it not only eliminate transmission mechanism but also caneffectively impair the friction of NC, at the same time has many advantages, such as lowpower consumption，simple devices，small size and light weight. The systemic researchworks are done from taking the magnetic suspension permanent magnet linear motor asstudy object under the support by National Natural Science Foundation of China, the keytechnologies of study object are dicussed in this dissertation as follows:To satisfy the requirements of impairing the friction of NC, the magnetic suspensionpermanent magnet linear motor which has two windings in the mover is researched anddesigned. On the basis of analysis the operating principle of motor, analyze the structureand characteristics of armature windings and secondary stator. According to the magneticfield lines can not cross and the minimum reluctance path principle, determine theexistence condition and integral region of leakage fluxes, the calculation model ofinterpolar leakage fluxes of the motor is established, further its validity is verified throughthe comparison of analytical solution and finite element method.The two movement patterns of magnetic suspension permanent magnet linear motormover are straight feed and vertical suspension. As the magnetic field generated by twosets of windings has the same magnetic path in common, the thrust is coupled with thesuspension force. Based on the above features，in order to establish mathematical model ofelectromagnetic forces accurate and intuitive, on the basis of comparison of severalmathematical modeling methods, further modeling of the motor is presented in view of the air gap energy. In order to achieve thrust and suspension force decoupling, a controlmethod is presented that thrust winding id0and suspending windingiq0, furtherelectromagnetic decoupling characteristics of the motor is researched.Based on the coupling of magnetic suspension permanent magnet linear motor, themover is required to realize straight feed and vertical suspension. The idea and principle ofelectromagnetic design are provided in order to meet particularity of the motor. Study ofimpact of suspension windings current and thrust windings current on the air-gap fluxdensity magnetic field is done, the effect of key parameters on performance of actuator isalso investigated, and inductance characteristics are analyzed. On the one hand it confirmsthe correctness of motor design method, on the other hand it provides necessary referencedata and technical base for the experimental prototype design and manufacture.Aiming at the stability of electromagnetic force, the force ripple is made variableseparation for obtaining the major factors that impact the performance of theelectromagnetic force. The method of optimization iron-cored length is adopted to designthe motor for reducing force ripple caused by end effect. In order to reduce force ripplecaused by cogging effect, obtained analytical suspension force ripple model based on BiotSavart law and virtual displacement method, and prove that effect of suspension forceripple after altering permanent magnet configuration, further thrust and suspension forceripple is reduced by applying skewing pole.In the aspect of control strategy of the suspension subsystem, firstly mathematicalmodel of suspension subsystem is established. For improving the tracking performance andthe robustness, a nonlinear H∞robust control strategy is presented. Two controllaw used indescribing nonlinear H∞robust controllers are obtained by defining proper storage function.The results of simulation indicate that controllers can guarantee a good disturbancerestraint as well as the tracks of input signals, the robustness of the suspension subsystemis improved. Finally, the experiment platform of magnetic suspension permanent magnet linearmotor system is built，and some experiments of prototype motor are done. Correctness andfeasibility of theoretical analysis and design method are partly verified through theexperiment results, and foundation of theory and technology is laid on further research onthis kind of machine.