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BLDC Motor Hall Encoder Issue

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Jerryxm

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I'm trying to control a BLDC motor with a microcontroller board and three MOSFET half-bridges and am running into issues with the Hall encoder outputs from the motor. I'm using the three Hall sensor inputs to determine when to commutate the motor in the usual six step sequence. The problem I'm having is that the Hall sensor inputs don't transition cleanly--they bounce a few times and that's screwing up the commutation code, which is causing the motor to run roughly.

Below is a scope capture of one of the Hall inputs (channel 4--the purple trace). Is this sort of bouncing typical of Hall sensors on BLDC motors? What's the best approach to handle this? The MCU is a Microchip PIC32MK100MC, which is the motor control MCU in the PIC32 family. Oddly, its Hall encoder support doesn't seem to have any noise filtering capability.

scope_1.png
 

KlausST

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Hi,

It's a good idea to use a low pass filter and a schmitt trigger to get clean signals.
Especially with sensible signals and high current switching applications.

I don't think you will see the same behaviour with all BLDC motors ... it's more a question of wiring, decoupling and PCB layout.

Klaus
 

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