The Study Of Control Strategy For Permanent Magnet Type Bearingless Motor

The permanent magnet type bearingless motor(PMBLM) is the combination of the permanent magnet type AC motor with the electromagnetic bearing. According to the similar structure of the AC motor's stator with the electromagnetic bearing, it embedded the windings which are used to produce suspension force in the electromagnetic bearing into the stator of AC motor, using the flux produced by the suspension windings to change the original flux distribution of the AC motor, making the flux density increase in some part of the air-gap, but decrease in the counter part, then the unbalanced distribution of the flux density will generate suspension force on the rotor towards the direction where the flux density increased, the force realized the suspension of the rotor. The permanent magnet type bearingless motor has been paid close attention due to its potential application prospect in the filed of life sciences, aviation, et al, because of its advantages of frictionless, abvasionless, lubricationless,compact structure and high power capability.The permanent magnet type bearingless motor can be classified in to three types based on the different structure of rotor. These are surface mounted magnet type, inset magnet type and interior magnet type. Compared with the other two types, the surface mounted magnet type has advantages of simple structure, magnet being prone to optimized non-salient electromagnetic characteristics. This paper has made in-depth study on the control strategy of the surface mounted magnet type PMBLM.IN view of the complexity of suspension force model and the nonlinear relationship between suspension force with its control current of the traditional control algorithm based on the motor rotor flux orientation, a decoupling control strategy based on motor air-gap flux orientation was proposed in this paper based on the principle of suspension force production, it found that it can successfully untie the limitation of the rotor flux orientation control strategy.There exists time delay in suspension force of the conventional suspension control system. Based on the feedforward control theory, a feedforward compensation tache of suspension force was introduced in the suspension control system, the time delay in suspension force was successfully eliminated.At last, in view of the problem that the inherent limitation of mechanical displacement sensor influences the motor's suspension characteristics, according to the characteristics that the mutual flux component of suspension windings contains rotor radial displacement information, a rotor radial displacement estimation scheme using the mutual flux component of suspension windings in rotary coordinates was proposed in this paper, it fond that it is able to achieve stable sensorless suspension operation.