DRV10983: Motor speed does not reach expected value

Hi Vishnu,

thank you for your response. Increasing the programmed resistance enables a higher speed. With a programmed resistance of 0.291 ohm i can achieve about 2800rpm.

But disabling the software current limit does not help. The motor is running into a lock current at approx the same speed. I implemented a logging of the current that can be read from the current register. With the current log I store the highest current that was measured from the controller, by reading the current register continously. The maximum value i get there before the controller runs in a current lock is approc. 1,4A. The continous current when it spins with 2800rpm is 0.4A.

Do you have any further advice what we can do? Or do we just need to increse the programmed resistance?

Kind regards,
David

Just a quick update after further testing:

it is possible to reach high speed (about 3600rpm) with the software current limit disabled. I tried different parameters for Rm and found finally a parameter that spins the motor at that speed. Nevertheless the controller runs into a current lock if I further increse the speed.

But we would need an even higher speed for our application. Is there something else that can be adjusted? Or does the controller not offer the posibility to run a motor with such a low phase resistance at higher speed?

Kind regards,
David

Hi David,

What is the electrical frequency at 3600 rpm? This device can only support up to 1000 Hz. 3600 rpm seems to be a low number but I want to make sure it is less than 1000 Hz. Can you adjust the lead time?

Regards,

Vishnu 

Hi Vishnu,

the electrical frequency is 600Hz for 3600rpm. Therefor it should be not a problem to control the motor?

With lead time you mean the Commutation Advance Timing?

Kind regards,
David

David,

Yes, it shouldn't be a problem at 600 Hz. Yes again for the Commutation advance timing. 

Regards,

Vishnu

Hi Vishnu,

thank you for your advice.

With the following paramerts programmed and software current limit disabled, we reach now about 4100rpm:

Rm:0.387 Ohm
Kt: 18.3 mV/Hz
tSetting: 220 µs

We found this parameters by testing. Is there an advice how to tune the motor, when tuning according to the Tuning Guide does not give the desired result? Or is in that case searching for working parameters by experimental testing the only way how to find them?

These parameters seems to be very sensitive. Changing one of these paramers by a bitvalue of 1, the max speed (before it runs into a current lock) decreases significantly. Therefor the question if there is a better approach for finding maybe other parameters, than offer the same or better performance?

Kind regards,
David

David,

What fault is getting triggered when you try to go above 4100 rpm? What is the motor phase current at 4100 rpm? I want to see if there is any room to increase the motor speed. Would be great if you could share the screenshot of phase current during steady state operation at 4100 rpm and when you try to increase the speed above 4100 rpm.  

Regards,

Vishnu

Hi Vishnu,

i can share the values of the current measurement readout with you. We implemented the DRV10983 in our own PCB design with a AtMega Microcontroller to controller the DRV10983 and therefor can´t use the TI Software for tuning.

We get a Lock0 (Lock detection current limit) from the FaultCode Register. When we look at the values we read out from the current regsiter we have current values in the range of 0,7-1,1A.

But what suprises me, is that we get a max current measured at some time of almost 6A. For the max current we continously read out the current register with during operation, and safe the highest measured value in a variable. With each readout we reset the max current value. But each time we read it from the microcontroller, we get the same value of almost 6A. It seems like short current peaks occure during operation. Even when we do not accelerate the motor we get this high max current.

Any advice what we can test, improve or implement?

Kind regards,
David

David,

I will get back to you by tomorrow. 

Regards,

Vishnu

David,

Thanks for your patience! I wouldn't recommend reading current from the motor current register because this does not give accurate results. Can you use a  current probe to read the current from any one of the motor phases? If the steady state current at 4100 rpm is close to 2A then we have reached the max limit and there is no room for improvement. 

Regards,

Vishnu

Good day Vishnu,

thank you for your reply.

We measured now the current with an external probe. But we see here a max current of 0.7A for the speed of 4100rpm. Nevertheless if we go faster, we run into the lock current.

Regards,
David

David,

If you are using an oscilloscope, can you share the screenshot of the phase current plot when the speed goes above 4100 rpm? We've had similar issues in the past with motors having very low phase resistance. Unfortunately, there's nothing much that can be done if you still see issues after tuning the lead time and increasing the phase resistance. 

Regards,

Vishnu 

Hi Vishnu,

so it seems we would have to take another controller to reach higher speeds. Would be the MCF8316 a suitable alternative? Can this controller low phase resistance better?

Kind regrads,
David

David,

Yes, MCF8316A will be a good candidate for this motor. 

Regards,

Vishnu