Novel Strategy to Suppress Commutation Torque Ripple for Brushless DC Motor

Researchers from Tianjin Polytechnic University developed a commutation torque ripple suppression strategy for brushless DC motor in the high-speed region

A brushless DC electric motor (BLDCM) is a synchronous motor powered by DC electricity via an inverter or switching power supply which produces an AC electric current to drive each phase of the motor via a closed loop controller. BLDCM feature high efficiency and excellent controllability, and is widely used in several applications. It has power-saving advantages relative to other motor types. However, inductances in windings of the motor and the occurrence of transient process during the current exchanged between two phases can lead to commutation torque ripple. This in turn increases the vibration and noise of motors.

Now, a team of researchers from Tianjin Polytechnic University designed a commutation torque ripple suppression strategy. The strategy was designed considering the back- electromotive force (EMF) variation for a high-speed region. The back-EMF variation was taken into account to reconstruct a modified smooth torque mechanism. This in turn helped to design a novel torque ripple suppression strategy. The team found that the proposed strategy dynamically regulates the chopping duty cycle compared to conventional strategy, which controls the chopping duty cycle relatively smoothly in the commutation process.

The conventional high-speed commutation torque ripple suppression strategies does not consider the change of back-EMF in the commutation process. The torque sensor TMB307 with measuring range of 10N·m and resolution of less than 0.01N·m was used in the experimental system to measure the output mechanical torque of BLDCM. The proposed strategy enhances the range of speed for commutation torque ripple reduction. This in turn helps to reduce the risk of phase current distortion and optimizes the reliability of the motor operation. The team also deduced the speed range for the normal end of commutation. The proposed strategy can ensure the torque gradient to be zero even under the changing back-EMF during the commutation process. This can help to reduce the commutation torque ripple. The research was published in the journal MDPI Energies on May 20, 2019.

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