A torque ripple suppression circuit for brushless DC motors based on power DC/DC converters

This paper demonstrates a method of using a DC-DC boost conversion circuit to suppress the commutation torque ripple of a brushless DC (BLDC) motor with rectangular flux distribution. The commutation torque of a BLDC motor is depending on the commutation transient line current. To calculate the line current accurately, the phase resistance is taken into account, and the phase currents rising and falling speed are compared. Furthermore, it is proved that the line current will maintain constant if the DC voltage is lifted in the commutation period. The desired voltage is even higher than the supplied DC link voltage, if the back EMF is higher than two fifths of the input DC voltage. A super-lift Luo-converter is employed to increase the input voltage. The required waveform of the transient voltage is accomplished by changing the parameters of the power DC/DC converter based on the mathematical modeling for the proposed circuit. And the torque ripple is under control. The control stratagem for the torque ripple suppression is described in the paper and its reliability is testified by the simulation and experiment results.