Influence of current waveshape on motoring performance of the slotless permanent-magnet machine Torus

The Torus machine is a double-sided, axial-flux, disc-type, permanent-magnet, brushless machine which may be operated as either a generator or a motor. Its particularly short axial length and good power-to-weight ratio is being exploited in a number of generator applications and there is now fairly widespread activity in the study of this machine topology both as generator and as a motor. As the Torus machine is equipped with single or double layer, full pitch uniformly distributed windings its open circuit EMFs are far from sinusoidal. During these studies it was recognised that torque per ampere could be increased by matching the current waveshape to that of the trapezoidal EMF, adopting the principle of instantaneous current regulation which has been successfully exploited in field-oriented control of induction machines. An investigation of improved methods of current regulation is reported based upon a 2.5 kW, 24 V, 9-phase machine previously developed as a generator