BLDC Hub Motor Controller Issue: High Jerk on Deceleration with 48V 20A Lithium-ion Battery

Thread Starter

Junaid Arshad

Joined Jul 7, 2023
24
Hello everyone,

I'm facing an issue with my BLDC hub motor controller, and I'm seeking expert advice to troubleshoot and resolve it. Below are the details of my setup and the problem I'm encountering:

System Configuration:

  • Motor Type: BLDC Hub Motor, 1500W
  • Control Method: Trapezoidal control
  • Microcontroller: STM32F4
Additional Configuration:

  • Capacitors: I have added capacitors between the three phases of the motor to improve the performance and reduce noise.
Problem Description:

  • Motor Behavior with Lithium-ion Battery (50V, 20A): When I apply throttle, the motor rotates smoothly and performs well. However, when I release the throttle to decelerate, the motor stops abruptly with a high jerk. This behavior is inconsistent and only occurs when using the 50V 20A lithium-ion battery.
  • Motor Behavior with Lead Acid Battery (3.6A): When I test the system with a 3.6A lead acid battery, the motor decelerates smoothly without any jerk, indicating that the issue is likely related to the compatibility or interaction between the lithium-ion battery and the controller.
Suspected Issue:

I suspect that the problem might be related to back electromotive force (EMF) or the battery's high current output, causing the high jerk during deceleration with the lithium-ion battery. The different battery chemistries and current capabilities could be affecting the controller's performance, but I'm not entirely sure how to confirm this or address it effectively.
I would greatly appreciate any insights, suggestions, or recommendations from experts in this community. If anyone has encountered a similar issue with BLDC hub motors, trapezoidal control, or battery compatibility, your guidance would be invaluable.
 

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MisterBill2

Joined Jan 23, 2018
19,054
The problem is that your throttle control is simply sending a lower speed command and the motor is immediately following that command. There are a large number of people who believe that is the way to drive, while others believe that it is the stupidest possible scheme. When you use the low powered battery the motor does not have enough torque to produce that jerk. So what you need is to revise the control so that the trottle control gives the motor a torque command instead of a speed command.
 

Thread Starter

Junaid Arshad

Joined Jul 7, 2023
24
The problem is that your throttle control is simply sending a lower speed command and the motor is immediately following that command. There are a large number of people who believe that is the way to drive, while others believe that it is the stupidest possible scheme. When you use the low powered battery the motor does not have enough torque to produce that jerk. So what you need is to revise the control so that the throttle control gives the motor a torque command instead of a speed command.
Thanks for the help, got your point the throttle simply vary the PWM signal duty cycle with respect to hall sensor input, which vary the speed, If you could further guide how to control the torque instead of varying PWM signal duty cycle.
 

MisterBill2

Joined Jan 23, 2018
19,054
Some motor drive controls have a torque adjustment, at least that was the case 20 years ago. So controlling torque would e done by controlling the power fed to the magnet coils, which is a rather fundamental part of the drive package. So it would require understanding the particular controller package. Quite possibly the drive manufacturer may even have a torque control option available.
 
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