IMC101T Low Speed Performance

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SBitney
Level 1
Level 1
5 replies posted 5 sign-ins First reply posted
Hi,

I’m trying to develop a motor controller that can drive a particular BLDC motor between 0 and 300RPM using an IMC101T.
I’m getting good results at the higher speeds, but I’m having real troubles at the low speeds

At speeds below 25RPM I’m either getting very jerky movement, but with minimal torque, or just twitching and no rotation. I’ve seen the same motor running at these very slow speeds, so I know the motors themselves can handle it.

I had assumed this was due to flux angle estimation, but I’ve since moved to using hall sensors and the performance is the same.

I’ve had some better luck voltage control mode instead of speed control, but that has its only problems.
Mainly that the Vd register seems to be limited to 102V, so I can’t get to max speed, only to about half, and that I’ve so far been unable to find a way to reverse the motor direction in voltage control mode.

I have very little experience or expertise in motor control, so there might be something obvious that I’m missing.
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5 Replies
SBitney
Level 1
Level 1
5 replies posted 5 sign-ins First reply posted
Another problem with the voltage control mode is how hard it's driving the motor.
Things start getting pretty warm under voltage control, where as under speed control they didn't get warm at all, not even under a modest load.
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Casey
Employee
Employee
50 replies posted 25 replies posted 10 replies posted
SBitney wrote:
Another problem with the voltage control mode is how hard it's driving the motor.
Things start getting pretty warm under voltage control, where as under speed control they didn't get warm at all, not even under a modest load.


Hello,
Have you checked out the motor tuning guide in the Software Reference Manual (last section)?
I would say this a good first step, you should check your current sensing.
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SBitney
Level 1
Level 1
5 replies posted 5 sign-ins First reply posted
Thanks for the suggestion.

The tuning guide wasn’t that useful as it seems to be mostly focused on single shunt arrangements, but it did point me in the right direction.

I increased the shunt resistances to try and increase the signal up away from the noise, and now I’ve getting stable speeds down to around 10RPM.

However, I’m still getting no torque at these low speeds, and any force on the motor will cause it to stall.
Is there any way increase the power at low speeds?
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User19241
Level 2
Level 2
10 replies posted 5 replies posted 5 questions asked
I have the same issue with high mechanical loads at start-up on my motor. It helped me to knock-up to 100% the low speed current question 14....but still not adequate.
And upping the rated current question helped...but now I'm at the limit before wizard calc warning.
I've tried some aspects of the tuning guide without much help.


I'm going to try using my hall sensors on the motor. What I/O pins did you use? I have Q=2 hall sensor lines but the wizard is a little confusing as to what I/O pins are chosen.
Initially I thought it was off JP2 connector as AIN3 and AIN4.

I have a suspicion that just to handle the load at low speed/start-up, that I might need to go to the next higher current rated Infineon IGBT driver IC. That way I can up the motor rated current without the wizard balking a warning in the calculation section.
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snget2
Moderator
Moderator
Moderator
5 sign-ins First like received 25 replies posted
Hello dwissel

EVAL-M1-101T does not support hall sensors. We will have another evaluation board, EVAL-M1-101TF which does. This board will be released by the end of October, 2020.

While EVAL-M1-101T uses the IMC101T-T038 which supports digital Halls, the board itself does not. In order to use hall sensors, we need to add a pull-up, and RC filter components for each DHALL channel. And the cap needs to be close to the pin. If not done correctly, then it ends up noise susceptible. We recommend using the EVAL-M1-101TF when available.
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