Efficient and stable operation of bearingless motors using a Hall sensors arrangement method for angle detection with less magnetic interference

This paper describes a Hall sensors arrangement method of bearingless motors to reduce the effect of magnetic flux from windings on rotor angle detection. The arrangement method needs no additional magnets or no sophisticated controls, and focuses on the combination of poles/slots and the placement of Hall sensors. An angle error caused by windings contains components of offset from DC current and harmonics from PWM ripple current. It is known that the detected angle error shifts the direction of suspension force generated in the XY plane and sometimes have a negative impact on radial suspension performance. This paper also shows that the interference from current can destabilize rotation control and cause divergence of speed oscillation. Results of FEM and simulation using block diagrams show the proposed method effectively reduces the effect of current on the angle error, and both rotation control and suspension control can be improved.