Smart Current Limitation Technique for a Multiphase Bearingless Machine with Combined Winding System

This paper presents a current limitation technique for a multiphase bearingless machine featuring a combined winding system. This winding structure allows each machine phase to produce both suspension force and motoring torque. Compared to more conventional systems where two separate windings are adopted for the force and torque generation, the combined winding one leads to higher compactness and simpler manufacture. The main challenges with the combined winding configuration consist of decoupling the force and torque generation and designing a proper current limitation algorithm. The former topic has been already tackled and presented in previous publications, instead the latter will be addressed in this paper. In particular, the so called smart limitation technique will allow to prioritize either the suspension force or the torque generation. In this paper the priority is given to the rotor levitation, hence the suspension force rather than the torque is essential. The technique can be extended to give priority to the torque generation in further work and can be applied to any multiphase bearingless machine with similar winding structures. Finally, simulation results and experiment validation are provided.