Effects of Stator Iron Loss and Current-Loop Delay on Copper-Loss-Minimizing Torque Control of BLDCM: Analysis and Improvements

Copper-loss-minimizing torque control (CLMTC) method has been widely studied to reduce electromagnetic torque ripple and minimize copper loss of a brushless dc motor (BLDCM), but still suffers challenges to improve its performance. This paper presents a quantitative analysis of stator iron loss and current-loop delay effects on CLMTC. In the analysis, the iron-loss-included torque equation that only suits for sinusoidal back electromotive force (EMF) is modified to cover the case of nonsinusoidal back EMF. It is concluded that the iron loss effect brings about significant torque generation error and the delay effect leads to torque ripple that increases linearly with the delay angle. Two improvements are proposed, one of which redefines the condition of an optimal motor current vector to compensate for the iron loss effect. The other one aims to suppress the delay effect by preshaping current reference based on delay characteristic of the loop. The improvements can be performed effectively on a microprocessor to realize a better CLMTC method with reduced torque generation error and torque ripple. Both the analysis and improvements are experimentally validated on a 0.95 kW BLDCM setup.