Reduction of the torque ripples in brushless PM motors by optimization of the supply - theoretical method and experimental implementation

This paper deals with the active compensation of the torque harmonics in brushless DC motors. The proposed method consists in analytical computation of the currents whose allow to remove electromagnetic torque harmonics. A first interest of this paper is that, for a given motor, the number of currents harmonics is minimized. Therefore, the maximum frequency of currents is limited, so that practical implementation is easier, A second and important interest is that harmonics multiple of three are not considered for the current computation so that the motor phases can be star-connected and the motor can be fed with a classical three-phase full-bridge inverter and not with three single-phase inverters. The complete methodology of the currents harmonics computation is presented. To illustrate the method, an example of calculation concerning a motor integrated in the wheel of a bicycle is detailed. Then, using a special test bench, the real machine is fed with the optimal currents in order to confirm the possibility of experimental implementation. Finally, experimental measurements concerning the vibratory behavior are proposed and the results obtained with the optimal fed are compared with the ones obtained with a 120° square fed.