Three-Axis Inductive Displacement Sensor Using Phase-Sensitive Digital Signal Processing for Industrial Magnetic Bearing Applications

Abstract

Non-contact rotor position sensors are an essential part of control systems in magnetically suspended high-speed drives. In typical active magnetic bearing (AMB) levitated high-speed machine applications, the displacement of the rotor in the mechanical air gap is measured with commercially available eddy current-based displacement sensors. The aim of this paper is to propose a robust and compact three-dimensional position sensor that can measure the rotor displacement of an AMB system in both the radial and axial directions. The paper presents a sensor design utilizing only a single unified sensor stator and a single shared rotor mounted target piece surface to achieve the measurement of all three measurement axes. The sensor uses an inductive measuring principle to sense the air gap between the sensor stator and rotor piece, which makes it robust to surface variations of the sensing target. Combined with the sensor design, a state of the art fully digital signal processing chain utilizing synchronous in-phase and quadrature demodulation is presented. The feasibility of the proposed sensor design is verified in a closed-loop control application utilizing a 350-kW, 15,000-r/min high-speed industrial induction machine with magnetic bearing suspension. The inductive sensor provides an alternative solution to commercial eddy current displacement sensors. It meets the application requirements and has a robust construction utilizing conventional electrical steel lamination stacks and copper winding.

Driver Circuit Design for a New Eddy Current Sensor in Displacement Measurement of Active Magnetic Bearing Systems

“…The dynamic property of the sensor is determined by the dynamics of the amplitude detector and the anti-alias filter before ADC [20], and it is given by…”

The Influence of Magnetic Field of AMB on Eddy-Current Sensor Operation

“…The magnetic support system of a high-speed machine rotor usually consists of an electromechanical actuator, a control unit, amplifiers and sensors [ 15 , 16 , 17 , 18 , 19 , 20 ]. The electromechanical actuator is intended to support a high-speed rotor and generate electromagnetic force, providing its stable operation.…”

“…Non-contact and noise-tolerant sensors are an essential part of control systems in magnetically suspended high-speed machines [ 17 ]. Two types of sensors are typically used in the AMB systems, namely induction sensors and displacement sensors.…”

“…Two types of sensors are typically used in the AMB systems, namely induction sensors and displacement sensors. Induction sensors have good potential but are difficult to use because they must be mounted in the bearing air gap [ 17 , 18 ]. On the other hand, displacement sensors are more expensive and introduce some design limitations, but their configuration and assembly are simpler than in the case of induction sensors.…”

“…For this reason, displacement sensors are typically used in AMB systems [ 15 , 16 , 19 , 20 , 21 , 22 ]. In typical AMB levitated high-speed machine applications, the displacement of the rotor in the mechanical air gap is measured with commercially available eddy-current-based displacement sensors [ 16 , 17 , 19 , 20 , 21 , 22 ]. In recent years, these sensors have gained increasing scientific attention [ 23 , 24 , 25 , 26 , 27 , 28 ] due their wide range of applications in health [ 29 ], aerospace [ 30 ] and automotive [ 31 ] fields.…”