Due to the asymmetry of the actual back electromotive force (back-EMF), the performance of the conventional commutation deviation correction method degrades in sensor less control of the brushless direct current (BLDC) motor. This Project proposes a high-precision sensor less optimal commutation deviation correction strategy, which considers the asymmetry problems of the back-EMF. Firstly, this Project discusses the optimal commutation issues and the internal power factor angle based commutation deviation correction method. Then, given the issue of the non-sinusoidal phase current integration and the asymmetric back-EMF, a dual improved second-order generalized integrator with a positive sequence component extractor (DISOGI-PSCE) is proposed. The DISOGI-PSCE can effectively deal with the DC component and harmonics in flux linkage and current integration, as well as the asymmetry of the back-EMF. It is performed on a magnetically suspended control moment gyroscope BLDC motor, which verified the effectiveness of the proposed high-precision sensor less optimal commutation deviation correction method.