Dual Field-Oriented Control of Bearingless Motors with Combined Winding System

Field-oriented control has become a standard method to generated drive torque in permanent magnet excited synchronous drives with high efficiency. In this work, a similar control approach is proposed for radial suspension force generation in bearingless drives with combined winding system. Combined windings sets generate both motor torque and suspension force in each phase depending on the rotor angle. This allows increased efficiency, simpler manufacture and higher compactness compared to separated winding systems. However, in this case the decoupling of force and torque, which is necessary for proper bearingless operation, has to be achieved in the control scheme. Using transformations into two different rotating coordinate systems is proposed in this work to solve this issue. Hence, for full bearingless motor operation, two different field-oriented control schemes of the same structure have to work in parallel, one for force generation and the other for torque generation. The necessary phase currents are finally superposed. Thus, well proven and state-of-the-art industrial procedures can be used to implement the control scheme for a bearingless permanent magnetic motor, similar to a standard electric motor.