Research On Direct Force Control Of Permanent-magnet Type Bearingless Motors

Compared with other type of bearingless motors, the permanent magnet type bearingless motor, due to its simple structure, absence of excitation windings, high power factor, high power density and high efficiency, can be widely used in the developing industry applications of flying wheel for energy storage, spindle machines, sealed pumps, centrifuge pumps, compressor, high speed micro-harddisk drive technology, etc.This dissertation focuses on the control strategies of permanent magnet type bearingless motors. Most of fulfilled studies are shown as follows:First, a profound theoretical analysis on mechanism of magnetic levitation for a permanent magnet bearingless motor is presented and its mathematical model is also analyzed. In order to conquer the limitations in the previous strategy of rotor flux field-oriented vector control, with the reference of direct torque control of conventional permanent-magnet synchronous motor, a novel direct force control algorithm based on space vector pulse width modulation method is proposed to directly control magnetic levitation fore inside bearingless motors. The results from parallel simulations between the traditional control strategy and the direct force control strategy suggest successful suspension in steady state as well as transient state and confirm the validity and availability of this new control arithmetic.An experimental platform of digital control system for real-time control is designed and realized on the DSP2407 for this new control strategy. A flyback switching accessorial power is designed and realized on the TOPSwitch. The results from no-load and load experiments suggest successful suspension of this new control strategy. In order to find the characters of the two control strategies, design some experiments such as static accuracy, sudden change in the speed, transient suspension.Simplifying the displacement-loop, the off center displacement is regulated by one PID controller to generate the synthetic suspension force, so one PID controller is reduced, the control system is two closed loop based on displacement and flux linkage which possess of the virtues of the two control strategies.