BLDC Motor - Finding out how many Pairs of Poles and the difference with PMSM

In summary: V.In summary, it seems that the power board is overheating and not able to deliver the rated current or voltage.
  • #1
Vatech
54
7
TL;DR Summary
I have a 3 Phase low voltage BLDC but i have a problem of driving it using a Nucleo microcontroller combined with a extension board
Hello Community,
i have BLDC motor with General parameters are 3 Phase motor with 4 Poles, 36V, 7.3A rated current, 4000RPM rated speed.
you can check datasheet on link below
The first question is how many Pair of Poles does this motor have? 2 or 4?
For example the motor bellow
1618981792465.png

https://www.omc-stepperonline.com/download/57BLR110-36-01.pdf

//For those who want to get depper into the problem :
I am using a Nucleo-F401RE combined with the extension board X-NUCLEO-IHM08M1 in order to run the BLDC motor as shown on link below. General parameters are 3 Phase motor with 4 Poles, 36V, 7.3A rated current, 4000RPM rated speed.

The power board is configured in FOC mode, following the official documentation.
I use the ST Motor Profiler to generate the motor profile.
The problem is that the power board overheats in first seconds of Run.
First calibration is “successful” although it stops at 3000RPM as maximum speed and torque is very low.

At the end of calibration I am not able to recalibrate or use the “play” function to run the motor because the PowerBoard is overheated, ALTHOUGH I get no overheating error as feedback.

If I let the Board cool down some minutes, then I am able to run the board for some seconds until overheating protection stops the motor at about 80C.
No load is added on motor

I have added heatsink with the only difference getting some more seconds of run
On the STM32 NUCLEO board: JP1 open, JP5 (PWR) on E5V side, JP6 (IDD) closed.
On the X-NUCLEO-IHM08M1 expansion board: J9 open, JP3 closed.

jumpers: JP1 and JP2 closed, J5&J6 on the 3-Sh side. Removed capacitors C3, C5 and C7
In motor profiler I tried different number of pole pairs, lower RPM, much lower current (1A) again with no success.

Any idea what could be the issue?
 
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  • #2
4 poles = 2 pole pairs.

I'm not familiar with any of your specific hardware.

Do you have a multimeter? can you check that the motor is actually getting the rated voltage and current?

It seems that the drive is not able to deliver enough power - though the specs show that it should. If it's getting too hot and shutting down, it's likely too much current for the drive to handle. Similarly, if the motor is not reaching it's rated speed and torque (I assume you are just eyeballing the torque from the acceleration?), that sounds like it's not getting enough voltage and current.

Have you tried 6-stepping?

Is the motor running at a more or less constant speed when it shuts off or is it trying to accelerate?

Are there control parameters you can dial back - (acceleration, PID, etc)?
 
  • #3
Vatech said:
Summary:: I have a 3 Phase low voltage BLDC but i have a problem of driving it using a Nucleo microcontroller combined with a extension board

The power board is configured in FOC mode
What about startup? Isn't there a start mode? What frequency are you sending to the motor?
 
  • #4
Another thought.

The rated voltage/current are likely rms values; peak are sqrt(2) higher. I think you aren't giving your motor enough power. Software thinks it should be pushing up to 4krpm, but tops out of power at the rms values.

speed is proportional to voltage. limiting voltage to rms -> 4krpm/sqrt(2) ~2800rpm, close to the 3krpm max you are seeing.
 
  • #5
onatirec said:
4 poles = 2 pole pairs.

I'm not familiar with any of your specific hardware.

Do you have a multimeter? can you check that the motor is actually getting the rated voltage and current?

It seems that the drive is not able to deliver enough power - though the specs show that it should. If it's getting too hot and shutting down, it's likely too much current for the drive to handle. Similarly, if the motor is not reaching it's rated speed and torque (I assume you are just eyeballing the torque from the acceleration?), that sounds like it's not getting enough voltage and current.

Have you tried 6-stepping?

Is the motor running at a more or less constant speed when it shuts off or is it trying to accelerate?

Are there control parameters you can dial back - (acceleration, PID, etc)?
The driver was configured for FOC mode and i didn’t have the replacement capacitors to configure it back to 6-step. On Friday i received a new board and i will configure it on 6-step mode and i will let you know the results.

I believe that something must be wrong with the mosfet - power synchronization between the poles. They might get instant activated between different pole pairs during each period. There are control parameters, i tried reducing the current even to 1A and it just run for some more seconds.
When i measured voltage it was at 35.6V which is correct
 
  • #6
The main problem is the overheating. I added the rated current starting from 7.3A and testing wven 1A.
I let the peak current to be calculated by software.
 

1. What is a BLDC motor and how does it work?

A BLDC (brushless DC) motor is an electric motor that uses a permanent magnet rotor and electronically controlled commutation to produce motion. Unlike traditional DC motors, BLDC motors do not use brushes to switch the direction of current flow. Instead, they use a control circuit to switch the current to different windings on the stator, allowing for smoother and more efficient operation.

2. How do you determine the number of pairs of poles in a BLDC motor?

The number of pairs of poles in a BLDC motor can be determined by counting the number of poles on the stator and dividing by two. For example, if a motor has 12 poles on the stator, it would have 6 pairs of poles.

3. What is the difference between a BLDC motor and a PMSM?

While both BLDC and PMSM (permanent magnet synchronous motor) use permanent magnets in their construction, the main difference is in the control method. BLDC motors use electronic commutation while PMSM motors use a mechanical commutator. PMSM motors also typically have a sinusoidal back-EMF (electromotive force) waveform, while BLDC motors have a trapezoidal back-EMF waveform.

4. How can I determine the optimal number of pairs of poles for my BLDC motor?

The optimal number of pairs of poles for a BLDC motor depends on the specific application and performance requirements. Generally, having more pairs of poles can provide smoother operation and higher torque, but it also increases the complexity and cost of the motor. A trade-off must be made based on the specific needs of the application.

5. Can a BLDC motor be used in both high-speed and low-speed applications?

Yes, BLDC motors are versatile and can be used in both high-speed and low-speed applications. The speed of a BLDC motor is determined by the frequency of the electronic commutation, which can be adjusted to suit different speed requirements. However, the torque output may vary at different speeds, so the motor should be selected based on the specific speed and torque requirements of the application.

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