A Study On Control Strategy Of Bearingless Induction Motors

The bearingless motor which integrates motor and magnetic bearing, has the function of rotation and self-levitation. It has been the focus of research work on high speed motor since 1990,s.This dissertation focuses on the basic theory of independent control of levitation subsystem of bearingless induction motor. The main contents are as follows:As the independent control algorithm of levitation subsystem in bearingless induction motor is based on U-I model, in order to solve the pure integral problem that exist in it, a novel arithmetic of motor flux estimation was proposed in this paper. It was made up of a high-pass filter and a coordinate transformation. The cut-off frequencies of the high-pass filter are set to the synchronous frequency of induction motor. This arithmetic can effectively eliminate the direct current bias and original phase problem without importing range and phase error in the flux.This paper also introduces the direct torque control to the bearingless induction motor decoupling control. However, as the stagnant control was applied to the flux and torque in the traditional direct torque control algorithm, there is no current feedback loop and the current as well as the torque have big ripples. In this paper, small signal model is used to analyze the influence of torque current ripple on the Maxwell force and a SVPWM direct torque control algorithm is studied further. The outputs of torque PI modulator and flux PI modulator are flux phase and range increments respectively and a regulator for phase angle increment is adopted to solve the disturbance problems in torque loop and flux loop. Besides, the THD of SVPWM is analyzed as well as the design of proportional relationship between the voltage of DC bus and the duty of SVPWM is optimized in this paper.In this paper, one-phase open loop fault tolerant schems of inverter in DTC system and SVPWM system are studied respectively on bearingless induction motor. Based on DTC strategy, stable suspending of bearingless induction motor is realized under the four-swich three-phase inverter system with fault tolerant. In SVPWM control system, a switch status form of SVPWM using fault talerant is designed and a novel estimation algorithm of phase voltage is studied. With this new algorithm, the voltage sensor is saved and prolems which it brings can be eliminated simultaneously, thus the bearingless induction motor can suspend steadily.As complicated configuration and communication delay problems are brought by using double DSP, the delay errors of air gap flux in conmunacations between the dual DSP are analysed. Thus the scheme of controlling dual windings of bearingless induction motor using single DSP (TMS320f2812) is proposed. The hardware and software configuration of the control system are optimized.