A Rotor Displacement Estimation Method for Magnetic Bearings with Direct Measurement of the Ripple Current Slope

In this paper, a method to estimate the position of the rotor supported by active magnetic bearings (AMBs) is proposed, which is based on the direct estimation of the ripple current slope of the coil driven by a switched power amplifier. Firstly, the current equation of the stator coil applied with PWM voltage was derived. Then a method to measure and estimate the current slope with the rising or falling edge of the ripple was presented, and the position of the rotor could be obtained further with the estimated current slope. Finally, experiments were carried out on a test rig and the results showed good accuracy of the estimated position in static. This method is simple to be implemented with modern DSPs or FPGAs, and can simplify the design of the AMB control system.