PID paramaters from Simulink to PLC

[Danil]

Hello there!

I'm trying to drive DC Motor with PLC V570 via PWM.  This is for my diploma thesis so I want to do it nice and design PID controller in Simulink Matlab. In PLC I want to do identification of the transfer function for this system with step response. This is the first order system, so it shouldn't be a problem. Than I'm going to use this transfer function in Simulink to find PID parameters. At the end, I got P,I and D parameters from Simulink, and I don't know to transfer them into PLC.

For example for closed loop system with discrete PI controller in ideal form P(1 + I*Ts*1/ (z-1)) (Serial PI) I have P =  1.93, I= 1.86[sec]  Ts = 0.1[sec]

Than in PLC I got

Sample Time = Ts = 0.1[sec] = 10

Integral time = I= 1.86[sec] = 2, because it is defined in units of 1 second,

Proportional band =(1/P)*100% =51.81% = 518 defined in units of 0.1% 

Am I doing this right?

Could anyone please tell me what is the type of transfer function for PID controller is used in PLC Vision V570 (Serial or parallel)? And how do I correctly transfer parameters P, I, D into PID regulator in PLC.

Thank you.   

 

[Joe Tauser]

Danil,

Your P and I parameter conclusions are correct.  As far as getting them into the PLC, read the Help on PID and post a program.  We can help after that. 

As for identifying the transfer function, I don't even know where to start.  You are so far over our heads it's not even funny!  I've never seen PID parameter described to 15 significant digits!

Here is where PID control originally started way back in 1942, if you didn't already know.

https://en.wikipedia.org/wiki/Ziegler–Nichols_method

I haven't looked at a transfer function since I took Control Theory in college 30 years ago.  If you ask some simpler leading questions of us we can probably help you figure out what your transfer function needs to be.

Nowadays, we run the AutoTune function, which measures the response time to the PLC generating a Step Output (100% On).  Then some magic happens and the PID parameters are calculated based on the change in process value and the time required.

If that doesn't work (and sometimes it doesn't) we fiddle with the parameters manually until it behaves.  Often processes have a nonlinear response based on setpoint.  For example, an oven required different PID parameters at 400 degrees than it needs at 800 degrees due to how fast it loses heat to the ambient environment.

Joe T.