A novel twelve-step sensor-less control for torque ripple reduction in brushless DC motor

The large torque ripple and decrease of the output torque of brushless DC motor (BLDCM) with sinusoidal back EMF are caused by the current commutation between two phases of the motor. It is the six step 120° drive that is suitable for the motor with an ideal trapezoidal back EMF. This is the significant drawback which will deteriorate the performance of the drive system in high performance and high efficiency applications. To solve the problem, this paper proposes the novel algorithm using novel twelve step sensor-less control to reduce torque ripple and increase of the output torque of BLDCM with sinusoidal back EMF. The proposed algorithm has two commutation process. In the two phase conducting period, rotor position is estimated to control speed of BLDCM. In the three phase conducting period, the slope of duty ratio considering the phase current variation ratio is applied from the calculations of no load duty and load duty according to speed and load conditions of BLDCM. The theoretical basis of the algorithm and individual definition of the control block is explained. The effectiveness of this proposed control is verified by the simulation and experiment according to the comparison of the output characteristics between the traditional and proposed control.