A Study on Output Torque Analysis and High Efficiency Driving Method of BLDC Motor

BLDC motors has the high efficiency, high power density, low acoustic noise, and low maintenance cost due to the removal of the mechanical commutators and brushes. It is known that BLDC motor is operated ideally, when a rectangular shape phase current is injected at the flat part of back-EMF waveform. Assuming that the field flux and armature current are constant, it has been argued that the output torque of the ideal BLDC motor is constant, but the feature of BLDC motor operation that the stator flux of the BLDC motor is not rotated continuously is not considered. In this paper, 2-step voltage control method based on the output torque analysis result according to the rotor position of BLDC motor is proposed to improve efficiency of BLDC motor. The proposed control method aims to maximize the output torque by changing current waveform through an input voltage control according to rotor position.