Position sensing is one of the crucial parts of the active magnetic bearing (AMB) system. The printed circuit board (PCB) eddy current position sensor is a new type of position sensor for the AMB system, which makes a compact structure, high sensing quality, and is low cost. In this article, an improved driver circuit is proposed for this new sensor. The driver circuit includes an excitation circuit and signal conditioning circuits. A crystal oscillator circuit with a power stage is used to provide the excitation coil with a stable excitation source of high stability and good precision of frequency. The analog demodulation circuit is designed for signal conditioning circuits to extract the rotor displacement information from the sensing coil outputs. Compared with the state-of-art driver schemes, the proposed method reduces the circuit complexity and cost. Accordingly, the experimental results show that the designed sensor has good linearity and sensitivity, and it can ensure AMB stable operation at the rated speed.

This article proposes a rotor position and speed estimation method for the interior permanent magnet synchronous machine (IPMSM) in the full-speed range. The proposed method is implemented in the synchronous rotating frame. Based on the voltage equation of the IPMSM in the synchronous rotating frame, a single-variable optimization problem is formulated to solve the rotor position at each current sampling step. After that, the solved position is fed into a phase-locked loop observer to obtain the estimated rotor speed and smooth out the estimation. The proposed position and speed estimation methods are effective from standstill to high speed, and no estimation algorithm switching is needed during speed variation. Details about the convexity of the optimization problem, the effects of parameter mismatch and sampling noise, and the solving method of the problem are discussed. Finally, experiments are conducted in both steady and dynamic situations to validate the effectiveness and robustness of the proposed algorithm.

This paper applies two different analytical methods, i.e., the perturbation method and superposition method, to calculate the magnetic flux density distribution and the magnetic force of the active magnetic bearing (AMB) with the rotor eccentricity. These two methods are thoroughly analyzed, compared and validated by the finite element model (FEM). The perturbation method is theoretically complex while the superposition method is intuitive. The valid range of the superposition method is larger than the perturbation method. However, the superposition method requires longer computation time. The main contribution of this paper is assessing the effectiveness of two analytical methods for predicting the AMB performance with the rotor eccentricity and giving a comprehensive guideline for engineers to choose the proper analytical method to design AMB.