Firstly the mathematical model of brushless DC motors (BLDCM) is introduced in this paper. The commutation process of brushless DC motors is analyzed in the two-phase αβ stationary coordinate by using coordinate transformation. The energy conversion relationship of brushless DC motors is obtained in the two-phase αβ stationary coordinate, the restrictive condition for reducing the torque ripple is derived during the commutation process in the αβ coordinate. The modulation method for shortest commutation time without the commutation torque ripple is obtained. The commutation is transferred the two components control, one is applied to control the toque and the other is used to control the commutation time. The complicated circuit equations during the commutation are avoided to solve, obtaining the clearer physical concept and the restriction condition with no torque ripple during the commutation. Find another new idea to study the commutation torque ripple of the brushless DC motor. Finally, the feasibility and effectiveness of the method are verified by experiments.