Is it correct to say that 'the current' drawn by a BLDC motor is the same as the current from any single phase at a given time (assuming they are all balanced/equal in magnitude)?
I came across this diagram describing the characteristic shape of a BLDC current waveform:
From this diagram, it seems that the current is roughly flowing through one phase at a time, with only a tiny amount of overlap. What this doesn't look like is three sinusoidal waveforms 120° out of phase – a situation where the total current is more easily understood and calculated.
What is convention here?
Best Answer
Motor line current is just the peak of any individual phase's current. Notice that in any of the six commutation steps, one phase always has no current, while the other phases have equal and opposite current (well, they should, the rounded leading edges in your diagram are wrong). This makes sense, as the phases are Y-connected so the current must always flow into one phase and out of another (in BLDC motors, one phase is always idle).