Understanding BLDC Motor Control: Position, Speed, and Current

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Discussion Overview

The discussion revolves around the control of Brushless DC (BLDC) motors, specifically focusing on position, speed, and current (torque) control. Participants share their experiences and challenges with BLDC motor controllers, including technical details about motor operation and control strategies.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant questions whether the output of the speed controller should indeed serve as the input for the current PID controller in a closed-loop system.
  • Another participant discusses the relationship between torque and current, suggesting that torque is proportional to current and load, and poses a scenario to illustrate this relationship.
  • A different participant mentions that current supplied to a BLDC motor controls its speed and describes a method of controlling current through chopping the driver.
  • One participant notes that the torque of a BLDC motor can be affected by speed, indicating that low speeds may result in a loss of torque.
  • Another participant highlights the difference between typical BLDC motors that use Hall sensors and those that use Hall ICs, indicating a need for more information about the specific motor in question.
  • Several participants express a need for additional information regarding the motor's specifications and control methods, including inquiries about the motor's pin configuration and data sheets.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the control of BLDC motors, with some agreeing on the importance of current control while others highlight differences in motor types and control methods. The discussion remains unresolved regarding specific control strategies and the implications of different motor configurations.

Contextual Notes

Participants mention various assumptions about motor operation, including the role of Hall sensors and the specific characteristics of the motors they are working with. There is a lack of consensus on the exact control methods and relationships between torque, current, and load.

Who May Find This Useful

This discussion may be useful for individuals interested in BLDC motor control, including students, hobbyists, and engineers working on motor control systems or related projects.

bagavac
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Hi guys,

I'm developing a BLDC motor controller with load. I've bought a Maxon E40 motor . But some things i can't figure out:

I want to control position, speed and current (torque). I use PID controller to do it. In the closed loop system the output of the speed controller should be input of current PID controller.

questions:

1) is this above true?

2) is it true that the torque and current are propotional also with the load?

example: If the torque constant is 2Nm/A and my load is 1Nm i need 0,5A to move the load? or is the torque constant only propotional on no loaded motor...?

btw: why is it needful to controll the current?
 
Last edited:
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BLDC motor in printer

I am studying about BLDC motor.
My teacher gave me a BLDC motor which is in printer machine.
however I don't how to control.
It has 11 unknown outputs.(its seems to be use HALL IC 4 pins)
I have some pic about my motor but i don't how to post.
If there is anyone knowing about it.give ur opinion.
Thanks you very much.
 
bldc motors are a bit complicated. there's some tutorial around the web explaining how BLDC's work. Last i work on it few months back, the current supplied controls the speed of the motor. current is controlled by chopping the driver or somewhat essentially shutting it on/off. i was using A3936.

a BLDC motor typically has 8 connector. 3 for each motor phase, 3 for hall sensor (1 sensor for each phase), 1 power supply Vcc for sensor, 1 gnd for sensor.

yes the output of the hall sensor goes back to the input. you get the timing from the motor poles through the hall sensor. from this timing, # of motor poles etc you can find the rpm of your motor. based on this result, you compare with what speed you want (ie: your speed corresponds to some timing). Increase/decrease your current to get that speed.

I got mine to work but I'm not sure if it works right. Mainly because torque is also a factor of current and speed. if you go too slow, you lose torque. So if you want to use brushless and run slow, you have to use a gear to down convert the speed.

hope this helps
 
He.Thanks your opinion.
I controlled a typical BLDC motor as you say.
but the BLDC motor in printer is differ form a typical motor.
while a typical motor uses HALL sensors ,my BLDC motor uses HALL IC.
He.I can send you some info abt my BLDC motor?
Give me your email to contact!
Ok!thanks for ur help!
 
what is the chip? Can you look at the data sheet for the chip. More information is required. What are your 11 pins,
 
hi.i don't know how to decribe.
it will be more convient if we can contact each other by email.
are you ok?
 

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