A Study On Independent Control Of The Levitation Subsystem Of Bearingless Induction Motor

The bearingless induction motor, which integrates induction 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: The principle of independent control of levitation subsystem of bearingless induction motor based on U-I model is described in detail. Furthermore, the key problems of airgap flux estimation of drive control winding based on U-I model are analyzed. They are: How to obtain the phase voltage and current of drive control winding; How to get the stator parameters of drive control winding; How to implement the pure integrator algorithm? To acquire the phase voltage and current of drive control winding, this dissertation presents a novel stator voltage estimation method. The stator voltage is reconstructed from the duty cycles and dc link voltage of the voltage source inverter. Therefore, the voltage sensors may be eliminated and the cost of the control system can be reduced. To obtain the stator parameters, this dissertation introduces an on-line stator parameter estimation method, which gains the parameter by solving the least square minimization problem of zero-sequence model. To realize the pure integrator algorithm, this dissertation proposes a novel and simple integration algorithm with a programmable band-pass filter in series with the pure integrator. The lower and upper cut-off frequencies of the band-pass filter are set to the synchronous frequency of induction motor. After the three problems are solved, the performances of independent control of levitation subsystem based on U-I model are investigated in Matlab/Simulink. What's more, the digital control system of bearingless induction motor is constructed. The experimental results verify that the stable operation can be realized under the control strategy introduced in this dissertation.