The torque ripple of brushless DC motor (BLDCM) generated during the commutation process seriously limits the applications in high precision system, such as aviation and aerospace. By analyzing the cause of the torque ripple, a modified singleended primary inductor converter (SEPIC) topology of BLDCM drive system is presented, in which a capacitor in parallel with a diode circuit is embedded. Compared to classical SEPIC converters, high static gain and low switching voltage stress can be achieved. Meanwhile, the voltage is adjusted according to the speed of the motor during noncommutation period. As a result, the back electromotive force (EMF) is proportional to the DC input voltage, thereby, the torque ripple is suppressed. The experimental results show that the proposed topology can be effectively applied to BLDCM drive system, and significantly reduce the commutation torque ripple under different operating speeds.