Rotor on cone-shaped active magnetic bearings with three-phases power drivers

This paper presents the modeling, the control design and the experimental results obtained on a rotor suspended by means of cone-shaped active magnetic bearings controlled by an innovative three-phases drive technique. The machine reproduces a turbo-compressor group of a conditioning unit used in high performance jet aircrafts. The conical geometry of magnetic bearings allows to perform a compact design of actuation stage which is composed of only four pairs of electromagnets instead of five of conventional cylindrical solution, resulting of great interest for the application in small machines. The modeling phases of the system are illustrated along with the drive technique and control design procedure. The mechanical subsystem has been reproduced starting from the finite element (FE) model, reduced to its first bending modes. The electromechanical interaction has been modeled considering each electromagnet as a two-port element (electrical and mechanical) exerting a force expressed as function of displacement and current in equations linearized around the working point. The control design takes into account the axial and radial coupled actions of the actuators and performs a SISO decentralized technique with five PID filters. The overall system results to be compact in the actuation subsystem as well as in the power divers equipment, being this performed with an innovative technique based on a three-phases configuration to drive a couple of electromagnets instead of standard H-bridge configuration. The control and drive schemes are presented and the reference generation for power drivers switches is illustrated in details. This approach allows to save 25% of power electronics components and reduce losses on the switches although the design phases result quite more complex than classical solutions. The paper concludes on the exposition of experimental results aiming to validate and prove the correctness of drive technique and control design approaches.