Impedance Modeling of Self-Inductive Displacement Sensor Considering Iron Core Reluctance and Flux Leakage

The inductive displacement sensor has been widely used in active magnetic bearings (AMBs). The excitation frequency of this kind of sensor is usually as high as tens of kHz, so it is significant and cannot be ignored the influence of eddy current effect, hysteresis effect, flux leakage, and excitation frequency on the sensor performance. However, the above influence cannot be studied through the traditional ideal model considering only air gap reluctance. This paper introduced complex permeability to account for the influence of eddy current and hysteresis effects, introduced the flux leakage coefficient to account for the influence of flux leakage, and then established an improved core coil impedance model of self-inductive displacement sensor, and presented a method to calculate the model parameters through experimental results. For the designed self-inductive displacement sensor with a nominal air gap of 1.2 mm, the inductance and AC resistance of sensor core coils under different excitation frequencies and rotor displacements were measured, and then the model parameters were calculated. The improved model predicted the core coil impedance of the same sensor under three different excitation frequencies, and the relative error with the experimental value is no more than 3%. For a self-inductive displacement sensor with a nominal air gap of 1.0 mm, the predicted output voltage and sensitivity have relatively small errors with the experimental results, which verifies the correctness and accuracy of the improved impedance model.