Adaptive torque ripple control of permanent magnet brushless DC motors

This paper presents an approach for reducing the torque ripple of permanent magnet brushless DC motors. The technique requires coordination of an outer speed loop with an inner current loop. The inner current loop is responsible for shaping the phase currents during the commutation intervals. The outer speed loop is responsible for commanding the magnitude of the phase currents. It is shown that the speed loop must be sufficiently fast that the commanded phase current is able to respond to potential ripple torque during phase commutation; a simple direct adaptive controller satisfies this requirement. The inner current loop must be able to adaptively change the slope of the commanded current in order to avoid poor current regulation through inverter saturation in the face of large back EMFs. The composite control is able to reduce torque ripple to a level which is dictated by phase ripple currents.