Current reference computation for Bearingless Multi-Sector Permanent Magnet Machine: methods and issues

Bearingless Multi-Sector Permanent Magnet Machines integrate the functions of active magnetic bearings and traditional rotating electric machines, enabling simultaneous rotor suspension and torque generation. These machines are particularly advantageous for high-speed applications such as compressors, flywheels, and turbo-molecular pumps, where mechanical wear reduction and operational reliability are critical. However, the strong cross-coupling between torque and radial force control presents significant challenges, especially in the computation of current references from force and torque inputs. This paper reviews two primary methods for current reference computation: Finite Element Analysis and analytical modeling, each offering distinct trade-offs in accuracy, computational efficiency, and interpretability. Two inversion techniques—Decoupled Torque and Force Control, and Pseudo-inverse Calculation—are analyzed for their ability to address the inversion of the current-to-wrench mapping matrix. The study also examines the impact of rotor eccentricity on force generation and proposes compensation strategies, including mechanical loop correction and explicit wrench model adjustment. Advanced control functionalities, such as power-sharing and fault-tolerant operation under open-circuit and short-circuit conditions, are discussed to highlight the maturity and versatility of control systems.