Estimation of Magnetic Center Location in Radial Active Magnetic Bearings Through a Pull Test

The misalignment between the mechanical center and the magnetic center in a radial active magnetic bearing can cause serious problems and must be measured before commissioning the machine for field deployment. Once a suspension controller is operating, the misalignment can be estimated from the coil current imbalance. In this paper, we present a method of estimating the misalignment without the need for suspension. Through a simple test where the rotor is pulled to several different directions, the magnetic center can be estimated. For this purpose, a force model that relates the coil current and the force that the rotor experiences is derived. Utilizing this force model, a minimization proble is set up, where the discrepancies between the contact angle measurements and the force angles computed from the force model are minimized. The results of this minimization produce the estimation of the magnetic center. The validity of the method is checked through simulations and experiments.