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a developing system in BLDC motor control

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smilechou

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bldc motor sensors

hi all guys
i'm developing a system of bl dcmotor with avr microcontrolor
now i have some problem to be solved.
because the motor has 3 hall sensors,i want to caculate the motor speedby compute frequency value of the sensor pulse.but i can't think out a perfect algorithm.
in addion i compare the real speed value with desired_speed and the via PID tuning, output the PWM width to the motor drive part to change the voltage of motor,further change the speed of it,now i select ATmega64 as controlor,and IR2130 as motor drive through a 3 phase inverter bridge supply,here eager for your opinion,any words hopful.thanks
smilechou
 

best microcontroller bldc motor

Hello smilechou,

A word of warning. Hall sensors are OK to get adecuate switching sequence, but I think they not very usefull to use its output as real speed in the PID algorithm, specially at low speeds.
You could code something like a speed predictor between hall sensor pulses, but it is a potential source of inestabilities. It's better to get speed from a encoder if you have one.
Hope this helps
Best regards
 

developing system control

Check out this IC MC33035 from ONSemi conductor
It will make your software easy and better because that IC directly controls the BLDC depending on Hall Sensors and the Input from Microcontroller.
 

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bldc control

jorgito said:
Hello smilechou,

A word of warning. Hall sensors are OK to get adecuate switching sequence, but I think they not very usefull to use its output as real speed in the PID algorithm, specially at low speeds.
You could code something like a speed predictor between hall sensor pulses, but it is a potential source of inestabilities. It's better to get speed from a encoder if you have one.
Hope this helps
Best regards
Click to expand...

Why can't a digital hall sensor's output be used as real speed by counting pulses ?
I'm using hall sensor to control bldc motor- is it not going to be reliable?

thanks
 

bldc algorithm

Hello coochip,

My concern is about stability, not reliability, specially at low speed. Getting a speed sample a few times each revolution may introduce a time delay or lag in the control loop. A common symptom could be high current ripple, acustic noise emission and reduced efficiency.
Hope this helps.
Best regards
 

Sorry if it sounds silly, but how would getting a speed sample few times every revolution introduce a time delay in control loop?
 

Coolchip,
Is not silly, is a good question.
If the effect I mention is or not important in your velocity or position loop may depend on your bandwidth, control algorithm and power stage.
Sampling a signal and using that value until you get the next sample implies a delay. And we are no taking into account the additional calculation delay. Obviuosly, all this only matters if speed is not constant.
I have a paper, by Robert van der Kruk and John Scannell (more than 15 years old and practically illegible), where authors address this question. Maybe you could get something similar searching for authors.
Best regards
 

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