BLDC motor phase Current waveform's at high speed

Thread Starter


Joined Jul 11, 2016
Dear sir/madam,

I have a small doubt in controlling BLDC motor, when motor is operated in 6-step commutation sequence using hall sensors as feedback, phase current shape should be in quasi-square wave.

When i am simulating, Bldc motor logic in Matlab waveforms are generating correctly but in Realtime hardware the waveforms are not in correct shape.

Current waveforms are attached to this thread.

I have tried at low speed also, at that time one commutation step signal is missing every time.

krishna kanth.



Joined Oct 30, 2015
I would say the motor is being miss-commutated. Are you sure the Hall Sensor transition happens exactly at the sector edge? Sometimes the hall sensors are skewed and you would need to schedule the commutation point in time. A way to see whether this is the case or not is to employ a BEMF sensorless commutation algorithm and looking at where the hall sensor activity comes into play. Something tells me it may be happening at an offset such as 15 or 30 degrees. Good luck on your search!


Joined Jul 18, 2013
A way to check the correct hall sensor position is to use a D.B. 'scope and back feed (rotate) the motor and monitor each phase in relationship to the generated wave form.
You tie a 10k resistor to each of the phase leads and connect the ends of each together, this is your 'scope common.
the 2nd channel is the Hall sensor.
See pdf.