Philipp Bühler

Unbalance compensation using generalized notch filters in the multivariable feedback of magnetic bearings

Unbalance of magnetically levitated rotors causes undesirable synchronous vibrations which may lead to saturation of the magnetic actuator. To avoid this problem we propose a generalized narrow-band notch filter which is inserted into the multivariable feedback without destabilizing the closed loop. The parameters of the generalized notch filter strongly depend on the inverse sensitivity matrix evaluated at rotational speed. This matrix is easily measured a priori and stored in a look-up table. It is shown that a decentralized notch is feasible for weakly gyroscopic rotors. The proposed notch filter approach has advantages in terms of run-time complexity and analytical verification of closed-loop stability. Results from the implementation of the proposed unbalance compensation in industrial magnetic bearing systems are included.

New results for self-sensing active magnetic bearings using modulation approach

The concept of self-sensing active magnetic bearings (AMBs) is to eliminate the position sensors and estimate the position of the levitated object by measuring the bearing coil current. The main interest of this approach consists in reducing production costs and hardware complexity. Although the idea of self-sensing itself is not new and research has been carried out for years in this topic, it still remains a challenge. Many self-sensing methods have been proposed in literature, however they are all very delicate to realize. For this reason, there is still no industrial application for self-sensing magnetic bearings. This paper investigates the realization of a self-sensing AMB suitable for industrial use. The system must be robust and relatively low cost. In order to do that, this work explores a self-sensing configuration based on the current amplitude modulation. This approach is applied to an AMB test rig using reference sensors.