Zero Sequence Power Contribution on BLDC Motor Drives. Part I: A Theoretical Investigation

Brushless direct current (BLDC) motors are permanent magnet machines that develop trapezoidal phase back electromotive forces (back-EMFs). The interaction of back- EMFs and stator currents compose the main torque source in permanent magnet motors and most of the current waveforms considered in the literature to supply the BLDC do not exploit the full potential of the back-EMF harmonics to produce smooth torque with high efficiency. In this Part I paper, the instantaneous power theory in stationary space is applied to deduce the stator current waveshape, called 3D petal-wave current, able to produce smooth torque with full interaction with back-EMF harmonic content. Also, a comparative analysis is carried out to elucidate its superiority in relation to other possible current supply strategies. Among the benefits, the 3D petal-wave current stands out for its reduction in the copper power loss in about 13% compared to the conventional square-wave current supply strategy.