Design of a closed-loop controller for mitigation of torque ripple in a brushless DC machine

Brushless DC machines with nonsinusoidal back-emf are often characterized by significant torque ripple that occurs as a result of the interaction of back-emf and stator current harmonics, as well as cogging torque. In this paper, a method of mitigating the torque ripple is described that utilizes closed-loop feedback control. Specifically, the torque ripple produced by a machine is measured using a piezoelectric sensor. The sensor is constructed from polyvinylidene fluoride (PVDF) film, which produces a voltage in response to subtle strains in the motor housing. The sensed torque ripple provides a feedback that is used to determine stator current harmonics utilizing a controller that is based upon cost function minimization. Simulation and experimental results are used to demonstrate the effectiveness of the control technique.