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Field Weakening with BLDC Motors

Forum 1
(@virtualbruno)
Active Member

Does the SOLO controller support Field weakening to increase the base speed? Our application only requires low torque at higher speeds but be able to speed up to prevent sudden acceleration from the load. 

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Topic starter Posted : 23/09/2021 3:15 pm
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SOLO Team
(@milad)
Chief Member Moderator

Hi @virtualbruno,

Posted by: @virtualbruno

Does the SOLO controller support Field weakening to increase the base speed?

Up until now with the firmware 0x000B009 release we are not supporting field weakening, however, it will be added in future releases, but just out of curiosity, what is the max speed that you want to operate in? and in general what is the interval of the speed that your system should perform on?

-BTW, it will be great if you can share the datasheet of your motor so we can have look at it for a better undrestanding.

Regards
Milad

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Posted : 23/09/2021 3:59 pm
Forum 1
(@virtualbruno)
Active Member

Thanks Milad for the quick response. We have not yet picked the motor. There is no ideal choice as we have to use what's available in the commercial market. It will either be a scooter motor ( a bit heavy ) or a bicycle motor ( a bit too large ).

Regardless of the wheel diameter the speed over somewhat rough and uneven terrain must reach 17 to 20mph at full torque and up to 32mph offering little resistance to being pushed. However regenerative breaking should work at all speeds down to zero. Our battery voltage is 12S and should be able to absorb the energy to keep the voltage below the controller rating. 

Most likely we will acquire several motor types as its very difficult to obtain realistic specifications from offshore suppliers.

 

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Topic starter Posted : 23/09/2021 4:24 pm
SOLO Team
(@milad)
Chief Member Moderator

@virtualbruno

Ok great, let me clarify one thing, as you might know, Field-Weakening is used when you want your motor to surpass its nominal speed at a cost of reduction of torque ( this might be a big price for your type of application), this method is usually used for ultra-high-speed solutions so that they want to reach to very high speeds up to 2-3X of the nominal speed of the motor itself while the torque reduction is not an issue like FANs or some sort of drones...

For your application ( you know absolutely better than me) it might not be needed to surpass the nominal speed of the motor, and as long as this hypothesis is true you can safely use normal FOC that SOLO offers without the need to field weakening, so through this method SOLO will guarantee ( as long as your motor torque supports) to keep the speed steady at the reference. ( of course with fine-tuned gains).

Posted by: @virtualbruno

However regenerative breaking should work at all speeds down to zero. Our battery voltage is 12S and should be able to absorb the energy to keep the voltage below the controller rating. 

SOLO operates in 4 quadrant mode and it feeds back the regenerative energy if available by the motor back to the batteries, again here you need to make sure your battery system really can absorb that much energy instantly or you need to store them on some capacitor bank and use them later...

Posted by: @virtualbruno

Most likely we will acquire several motor types as its very difficult to obtain realistic specifications from offshore suppliers.

this is a wise choice, I also offer to use a motor with sensors equipped with either Hall sensors or Encoders, as they are better for low-speed operations compared to sensorless. (SOLO offers both).

Let me know if you have anything else in mind.

Milad

If you found the answers helpful and you could solve your problems, please kindly verify here to help others in the future.

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Posted : 23/09/2021 4:39 pm
Forum 1
(@virtualbruno)
Active Member

@milad Specifically: your current firmware using HALL sensors, FOC and 4-Quadrant control what will happen if current limit is very low near zero, when the load tries to accelerate the motor beyond maximum base speed? will the controller simply allow the motor to freewheel as if it had a mechanical clutch? Like going down a steep hill, no braking force desired until the user changes the current limit. Currently we are using high end servo's ( Dynamixel from Robotis ) with Coreless DC motors and they can do this overspeed and soft controlled braking very well. We need to move to higher power hence the interest in your controllers. Its important that we know this so we can pick the right Kv motor rating.

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Topic starter Posted : 23/09/2021 5:58 pm
SOLO Team
(@milad)
Chief Member Moderator

@virtualbruno

Posted by: @virtualbruno

will the controller simply allow the motor to freewheel as if it had a mechanical clutch?

Yes, if the current limit is very low or near zero, the motor will freewheel, but there might be regeneration if the motor is going downhill fast enough, but I think that's not going to be an issue for you.

Posted by: @virtualbruno

Its important that we know this so we can pick the right Kv motor rating.

fine, if you selected a motor, I'd be happy to have a look at it.

Regards
Milad

 

 

If you found the answers helpful and you could solve your problems, please kindly verify here to help others in the future.

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Posted : 23/09/2021 6:24 pm
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