How to change the PID Kp value

[RoyStevens]

I am trying to tune a 28 pole 50V 20 Amp  motor 6 step  with hall sensors. Motor Pilot does not work for me. To get over this I am using STM32CubeMonitor to plot the speed response. I have also tried to change the values through Cube Monitor by writing to PID_SpeedHandle_M1.hdDefkpgain and even though the values change it has no effect on the performance. Changing values (#define PID_SPEED_KP_DEFAULT) in the drive_parameters.h file and recompiling does not work either.

I am only able to change the Kp values by going back to workbench and  completely regenerating the project, which is a time-consuming operation.

I would appreciate some advice - thanks.

[Tinnagit]

you can use a regular variable instead of define and you can change value of that variable.

[RoyStevens]

Thanks for the reply Tinnagit and yes it would be best for this to be a simple variable. I have just spent the last 3 hours trying to change the code to do exactly that, and even with Chat GPT looking over my shoulder I have not been successful. I would be the first to admit that I am not an experienced programmer, but I am trying hard to learn. 

[RoyStevens]

Could someone please explain to me why changing the value of  #define PID_SPEED_KP_DEFAULT) in the drive_parameters.h and recompiling (even using the clean option) has no effect on the Kp used by the controller. I know it does not have any effect as I am measuring the motor phase currents with an oscilloscope. 

I thought that when I changed the Kp value in work bench and then run STM32Cubemx that the header file drive_parameters.h was created and this was solely the information that STM32CubeIde was using.

Clearly it is not that simple. Can someone explain what is going on please.

Thanks

[Tinnagit]

Do you ever try Motor Control SDK (MCSDK) on ST.
Is it work fine?

[RoyStevens]

Yes I am using Workbench 6.2. Motorpilot 6.2 does not seem to be useful for a motor with Hall effect device feedback. 

[cedric H]

Hello @RoyStevens ,

The modification you did is correct. Changing PID_SPEED_KP_DEFAULT is what you have to do. But be careful, this is only the numerator part of the KP, there is also the divider stored int #define SP_KPDIV .

If the divider is huge, then your modification is perhaps too small to make any difference. 

Could you elaborate a bit more about "Motorpilot 6.2 does not seem to be useful for a motor with Hall effect device feedback. " what is the issue you are facing ?

Regards

Cedric

[RoyStevens]

Thanks for the reply, Cedric.

I will revisit Motor Pilot later and give you a careful description of the difficulties I had. 

With regard to Changing the Kp the following is the process I have followed.

I am using 6 step. control.

I am running a PMSM motor on 20 V and have added a 1.0 Ohm resistor in each of the phases so that i can do experiments without accidental excessive current demand. Phase to phase resistance is about 2.8 Ohm.

I am using a Nucleo-G431RB and a X-Nucleo-IHM08M1.

I monitor the current by measuring the voltage across the 1.0 Ohm resistor with an oscilloscope. I have physically locked the rotor. 

in main.c  I use the instruction MC_ProgramSpeedRampMotor1(30/6,0) which is run for  1 second .

In workbench in drive settings, I set  Kp = 32766/8. I set Ki to 0 and Kd =0

After going through the process of cube Mx and cubeIDE I run the motor and measure the current which is about 8.0 Amp peak.

The second test I do is back to workbench  and set Kp = 32766/512  recompile and measure the current which is about 3.0A peak.

Now when I change from        #define SP_KPDIV  512     back to       #define SP_KPDIV 8 in the drive_parameters.h file  and recompile the code there is no change in current. The current peak remains at 3.0 Amp.

I also tried doing a clean build but there is no difference. 

What am I doing wrong? 

Regards

Roy

[RoyStevens]

Ok after writing that and going back to the code I see that for changing the denominator  KPDIV I need to change

SP_KPDIV_LOG(()) also and now it all works. It now makes sense to me.

I expect that in the future I may wish to change Kp and KpDiv in the future on the fly in the main.c while loop, for high torque low speed situations.

I have struggled trying to do   this for hours. Please give me some advice on this.

Thanks

Regards

Roy 

[ADAVE.1 · Accepted solution]

Hi @RoyStevens ,

to change the Kp on the fly, you have to update the parameters hKpDivisor and hKpDivisorPOW2 in the structure PIDSpeedHandle_M1.

For instance, to write 1024 (hKpDivisor=1024 and hKpDivisorPOW2=10)

However, you can easily do that with the Motor Pilot clicking on "advanced parameters" button

Alessio