A Novel Method to Reduce Toque Ripple with Variable dc-link Voltage

There exists commutation torque ripple (CTR) when the brushless DC motors (BLDCM) run under the square-wave mode. The torque ripple may cause vibration and noise. To overcome the problem, this paper presents a novel variable structure boosting unit to acquire regulation function of the dc-link voltage for reducing the torque ripple and achieving smooth electromagnetic torque. In the method, the variable structure boosting unit is charged by the trigger switch in the normal conduction period (NCP) and is used to achieve boosting dc-link voltage in the commutation period (CP), which remains the non-commutation phase current steady to obtain free-ripple electromagnetic torque. The variable structure boosting unit is composed of several discrete components and the design cost is low. The PI controller is used both in the NCP and CP, the controller switching is avoided accordingly. The proposed structure boosting unit is verified with different load condition and the experiment results show the proposed method exhibits superior steady performance. The presented unit is tested under loading condition and it shows desirable performance. Moreover, the frequency spectrum of the electromagnetic torque is analyzed, and results shows the boosting unit can diminish the 6nf harmonics effectively.