Self-Sensing Algorithm for Active Magnetic Bearings; Using Direct Current Measurements

In the field of active magnetic bearings (AMBs) the self-sensing theme attracts attention due to the ongoing drive for compact integration and cost reduction. Self-sensing makes use of the AMB’s actuator to sense the position and to convert electrical energy to mechanical energy. The aim of the direct current measurement method (DCM) is to reduce phase shift produced by demodulation methods used in the past. The DCM self-sensing scheme makes use of a specific PWM switching method, which enables the estimation of the rotor position by only measuring the power amplifier ripple current. The DCM technique also has the added benefit of less sensitivity for cross-coupling effects. In this paper the PWM switching method, the method used to extract the current ripple and scaling are discussed. Simulations are done on a transient AMB model which resembles the physical system and practical results are obtained from the practical implementations.