CodeWarrior for MCUのトピックRe: PID constants

PID constants

binukannur — Sat, 30 May 2015 05:08:48 GMT

Hai,

Iam using HCS08 and codewarrior studio. I implemented a PID algorithm for a generator speed control by valve control using stepper motor. Here Iam measuring rpm of generator with hall effect sensor as a feedback.

It works fine, but in this algorithm I changed my Kp,Ki,Kd constants in different conditions. ie nearest of setpoint I changed these constants to get fine values and if there is a big difference changed to get large error value.

My question is , can i change PID constants in running condition? Is it favourable ?

Re: PID constants

trytohelp — Tue, 02 Jun 2015 13:06:23 GMT

Hi,

To investigate the problem we need more info.

What is the development tool version you're using ?

Please can you provide us to code or example code showing the behavior ?

Have a great day,
Pascal
Freescale Technical Support
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Re: PID constants

binukannur — Wed, 03 Jun 2015 04:44:16 GMT

Hai,

Iam using Code Warrior Development studio V.10.6, and controller MC9s08DZ128.

Here is the bit of code we want to investgate.

if(count > (rpm_setpoint-4) && count <(rpm_setpoint+4))//fine tune PID constants when setpoint reached

{

PID=PID_Compute(0.5,0.2,0.01,1,-5,5);//kp, ki, kd, dt(time intervell) , outmin, outmax

}

else

{

PID=PID_Compute(1,0.5,0.25,1,-20,20);//kp,ki,kd,dt,outmin,outmax

}

//////////////////////////////////////////////////

count -- it is the feedback value .here it is generator RPM input

rpm_setpoint --- set point

PID_Compute---- PID function

PID---- it is the output

outmin,outmax -- Iterm minimum and max value.

In the first loop , PID value is small and in the second loop PID value is high compared to first.

So if there is a large error the second loop will run and faster the adjustments.

Re: PID constants

kef2 — Wed, 03 Jun 2015 06:55:36 GMT

What do you do to PID integral when you change PID constants? If close to the right anti windup control is implemented, then at least you should recalculate PID integral every time you change PID constants. IMO it is totally wrong to change PID constants (constants!) on the flight.