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[Solved] delay in 0 Torque

Forum 1
(@0torque)
New Member

In the plot below, I use digital torque mode to set torque to 10A, then down to 0A. The solo motor controller quickly reaches the max current, but when I command 0 torque, it takes quite a while to go to 0 current. Why is this? I would like to be able to put the motor in freewheeling mode, no torque and no regen as quickly as possible. To be clear, the point I enter 0 torque is when you see the speed start decreasing. I understand that the speed will not drop to 0 instantly due to inertia, which is what I want. What I worry about is the non 0 current that persists after specifying 0 torque.

Thanks

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This topic was modified 5 months ago by 0torque
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Topic starter Posted : 29/12/2021 7:30 pm
SOLO Team
(@milad)
Chief Member Moderator

Hi @0torque,

Just a couple of notes and questions, first of All, are you using SOLO in Torque mode but in No-Load condition? because usually, the results of Torque control are highly dependant on the load on the shaft of the Motor, but in any case, as you correctly mentioned in torque mode, once you reduce the torque reference, the inertia of the system will play a role in how fast the torque will decrease beside the controller characteristics,  so in our condition what we can do are a couple of things:

1- If you instantly change the direction of rotation to reverse after setting the 0 Torque reference, SOLO will follow the torque reference with the same performance as the times you command it to increase the torque, however, this might be difficult to mimic in the Motion terminal but if you command SOLO in digital or analog mode, you can do that quite fast, The main reason for this once you change the direction, you put SOLO in regeneration mode and it will push out the current out of the motor faster and it will result in faster reduction of the torque, the Momen you chose to change the Direction of rotation will define how much regeneration you will have ( the faster you do the DIR change the more regenerated energy will be fed back into your BUS or Batteries), however, if you go in Speed Mode, all of these actions are controlled automatically and there will be no need to change the direction, but of course, the nature of the control will be very different.

2- Can you share here the Motion Terminal readings ( a full screenshot after pressing read all will be great)

Posted by: @0torque

What I worry about is the non 0 current that persists after specifying 0 torque

by non-zero torque, do you mean the "Iq" that has an offset? because that offset actually defines for you the Zero Torque once the system is under no-load and stable with zero torque reference, you can take into account that offset and adjust your Torque reference to that if you wish.

Let me know if you have any doubts or questions in this regard?

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 : 30/12/2021 8:31 am
Forum 1
(@0torque)
New Member

I am using SOLO in Digital Torque mode with a small flywheel, so once it is up to speed, there is no load other than from the friction in the system. What I would like to do is spin up the flywheel and then at a specific time later, stop adding energy to the flywheel, but also not remove energy from the flywheel as in regenerative breaking.

1) I do not want energy to be fed back into the batteries. I want the motor to stop adding energy, and I also don't want it removing energy

2) Pasted below is a screenshot taken immediately after pressing "read all" in Motion Terminal

Posted by: @milad

by non-zero torque, do you mean the "Iq" that has an offset? because that offset actually defines for you the Zero Torque once the system is under no-load and stable with zero torque reference, you can take into account that offset and adjust your Torque reference to that if you wish.

 

See the screenshot below. In that case I set Torque Reference_Iq to 2 A from Motion Terminal, let the motor reach steady state speed, then set Torque Reference_Iq to 0 A from Motion Terminal. The part I am concerned about is the non-0 Iq reading circled in green which occurs after I set Torque Reference_Iq to 0 A in Motion Terminal. I worry that energy is still moving from the flywheel to the motor or visa-versa whereas I want the flywheel to spin as freely as possible, as if the motor was not attached.

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Screen Shot 2021 12 30 at 10.58.22 AM
This post was modified 5 months ago by 0torque
ReplyQuote
Topic starter Posted : 30/12/2021 4:09 pm
SOLO Team
(@milad)
Chief Member Moderator
Posted by: @0torque

I do not want energy to be fed back into the batteries. I want the motor to stop adding energy, and I also don't want it removing energy

For this, in theory, even if the whole system is turned off and you turn the Motor mechanically and manually the energy of the motor will be fed back to the batteries through the body diodes of the MOSFETs if the generated voltage goes above the battery voltage, however even when SOLO is operational, having effective regeneration highly depends on the Gains of the Current controller and if you put low values for them ( something like 0.1 for current controller Kp and 0.0001 for current controller Ki ) you will have practically no regeneration, however, the more your reduce the current controller gains, the less reactive will be the torque controller and lower will be its performance, pls remember that after changing the current controller gains, a power recycle is required so the new gains can take effect.

image

 

Posted by: @0torque

The part I am concerned about is the non-0 Iq reading circled in green which occurs after I set Torque Reference_Iq to 0 A in Motion Terminal. I worry that energy is still moving from the flywheel to the motor or visa-versa whereas I want the flywheel to spin as freely as possible, as if the motor was not attached.

In this part that you mentioned, it's true that the torque is set to be zero, but still, the Motor is mechanically moving, this will cause the Angle of the rotor to change, and that's why you see some sort of oscillation in the Torque plot ( "Iq" ) since the combination of the measure Angle and the Current inside of the motor forms the "Iq" ( or torque) so if one is changing ( Angle here) the result will not be a fixed value, regarding the Regeneration, you can use the second monitoring plot in Motion terminal and see if the BUS voltage rises or not, since usually if you have Regeneration the Bus voltage can rise above the battery voltage level for short periods specially during brakes

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 : 31/12/2021 2:21 pm
Forum 1
(@0torque)
New Member

Thank for the help. I didn't know about the body diodes in the MOSFET which has cleared things up.

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Topic starter Posted : 31/12/2021 9:43 pm
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