Magnetic Circuit Modeling Of Self-inductive Displacement Sensor In Full Air Gap

As a new type of high-performance bearing,active magnetic bearing has been more and more widely used in mechanical engineering,life science,aerospace and other fields.The active magnetic bearing needs to continuously adjust the electromagnetic force applied on the rotor to realize the stable suspension of the rotor according to the real-time rotor displacement signal detected by the displacement sensor.Therefore,the performance of displacement sensor is one of the key factors that determine the performance of active magnetic bearing.Among many non-contact displacement sensors,the inductive displacement sensor has been widely used in active magnetic bearing because of its strong anti-interference ability,high sensitivity,good linearity,good real-time,easy to manufacture and integrate,and many other advantages.Aiming at the problem that the traditional principle model of the commonly used self-inductive displacement sensor still has great deficiencies in performance prediction,this paper summarizes a sensor magnetic circuit modeling method based on the theory of electromagnetic field and circuit and the research results of existing literature.The complex permeability is introduced to consider the effect of eddy current and hysteresis in the sensor core on the magnetic field and core reluctance,the leakage coefficient is introduced to reflect the effect of leakage on the magnetic field and air-gap reluctance,and the excitation frequency is taken into account,the magnetic circuit model and improved impedance model of self-inductive displacement sensor are established.In order to study the variation of the inductance and resistance of the core coil of the self-inductive displacement sensor with the displacement and frequency,an eight-pole radial self-inductive displacement sensor with a nominal air gap of 1.2 mm was designed,the variation of the inductance and resistance of the core coil with rotor displacement is simulated by ANSYS finite element software at the excitation frequency of 20-100 kHz.In addition,based on the static performance experimental platform of the sensor,the inductance and resistance of the sensor core coil at different excitation frequencies and different rotor displacement are measured.Based on the experimental data,the parameters in the impedance model of the core coil of the self-inductive displacement sensor and their variation rules are obtained.Then the model is used to predict the inductance and resistance of the sensor core coil at three different excitation frequencies.The relative error between the predicted value and the experimental value is not more than 3.1%.Finally,the improved impedance model,traditional principle model and finite element simulation are used to calculate the output voltage,sensitivity and linearity of the sensor.Compared with the experimental results,the prediction error of the improved impedance model is less than 3.81%,the prediction error of the finite element simulation is about 32.32%,and the prediction error of the traditional principle model is more than 182.06%.The improved impedance model can accurately reflect the weakening effect of excitation frequency on the output voltage and sensitivity of the sensor,while the traditional principle model and finite element simulation cannot accurately reflect the impact of excitation frequency on the output performance of the sensor.The improved impedance model of self-inductive displacement sensor established in this paper can accurately reflect the variation of the inductance and resistance of the coil,output voltage and sensitivity of the sensor under different excitation frequencies,which has important theoretical significance,and provides an important reference basis for the design and performance optimization of the sensor,which has high engineering value.