Analysis of the segmented displaced trapezoidal winding for self sensing using back EMF waveforms

In our companion paper, the trapezoidal winding is proposed for use as a self bearing motor that is capable of actively controlling motoring torque, radial force and axial thrust Of course, this assumes that sensor signals are available for control of these axes. Conventionally, this is done using encoders and proximity sensors. In this paper the authors propose a self sensing approach that uses the back-EMF waveforms of the trapezoidal winding to estimate the angular, radial and thrust positions of the rotor, as well as rotor speed. Both simulated and experimental results are presented that demonstrate the potential of the approach and identify its limitations when applied to a closed loop feedback system. The experimental results indicate that the x, y, z and θ positions can be completely decoupled and estimated using the phase difference information in the back-EMF waveforms. A test actuator demonstrates that large axial displacements in excess of 5-10mm are achievable with the new actuator layout.