Floating Capacitor Suspension Inverter for Parallel Combined Winding Bearingless Motors

Abstract

Recent efforts to improve the performance of bearingless motors have focused on “combined winding” machine designs that use the same coils for torque and suspension force production. While combined winding designs have been successful in increasing the machine performance, they add substantial cost and complexity to the power electronics required for the bearingless drive system. This article presents a bearingless drive concept, which eliminates the additional power electronic hardware requirements for a parallel combined winding design. The resulting drive requires the same hardware components as a traditional, separated winding bearingless motor. The article proposes and explains the design and theory of operation, proposes a simple control implementation, and presents initial validation via simulation results. The theory and design presented are valid for both conventional $p\pm 1$ bearingless motor designs (i.e., bearingless permanent magnet designs) as well as $p_s=1$ bearingless motor designs (i.e., bearingless ac homopolar designs). Experimental results are provided that validate the proposed concept and demonstrate stable levitation of a bearingless motor.