A PWM harmonics elimination method in simultaneous estimation of magnetic field and displacements in bearingless induction motors

Abstract

In this paper, a novel estimation method of both revolving magnetic field and rotor radial displacements is proposed. Four auxiliary windings, i.e., search coils, are wound around the stator teeth in an induction type bearingless motor. The coils are connected to a high frequency voltage source. The middle point voltages between two search coils are processed with simple analog circuits to obtain radial rotor displacements. These middle point voltages are affected by harmonic voltages generated by a general-purpose PWM inverter connected to motor terminals. Thus, two methods of noise elimination are proposed and tested. The theoretical analysis and the successful experimental results validate the proposed approach.

Overview of Bearingless Induction Motors

“…So far, various types of motors have been put forward as bearingless motors, such as synchronous reluctance [3,4] and switched reluctance types [5,6], induction type [7,8], surface mounted permanent magnet (PM) [9,10], inset PM [11], interior and buried PM types [12], Lorentz slotless type [13,14], consequent-pole type [15,16], and brushless DC type [17,18]. Among these types of bearingless motors, the bearingless induction motor is being actively researched and developed around the word since it possesses the following advantages.…”

Research on Dynamic Decoupling Control Method of Three-phase Bearingless Induction Motor

“…But, the motor with magnetic bearings has a series of disadvantages, such as: longer rotor shaft, higher magnetic suspensions cost, difficulty to over speed, etc. [1,2]. Based on the comparability in configuration between magnetic bearing and conventional motor stator, the bearingless motor is proposed, which embeds the windings of magnetic bearing in the stator slots along with the conventional motor windings.…”

“…Bearingless motor is a newly type of electric machinery, which not only has the function of conventional motor, but also has the self-suspension function. Compared with the motor with magnetic bearings, the bearingless motor has a series of advantages, such as shorter rotor shaft, higher critical speed, being applicable to super-high speed and long time running [1][2][3][4][5][6]. Bearingless control technology can be used to all kinds of AC motors [1][2][3].…”

“…Bearingless induction motor not only has the advantages of other bearingless motors, but also has the compact and robust structure, then owns broad application prospects [1,[4][5][6][7][8]. But, there exist complex electromagnetic coupling relations within bearingless induction motor.…”

Digital control system design and analyses of a 3-phase bearingless induction motor

“…Recently, aiming at some kind of bearingless motor, research has been conducted on sensorless technology and unbalance vibration control technology [4,10,11]. The control system of the bearingless motor is an integrative automatization system, which integrates the theories and technologies of automation, motion control, power electronics, and computer control.…”