Multiple Input Multiple Output (MIMO) interfering PID loops

Projects General Guidance
1

Hey all,

This is a grossly complicated issue, and I'm mostly wondering if someone has already implemented a solution like this in one of their projects..

Basically, I have 2 PID loops which will be interfering with each other, and I'm curious as to how I can ensure stability within the system. I'll have an ultrasonic humidifier feeding humid air into a room, and an evaporative cooler feeding cold air into that same room. They each have differing humidity and temperature with respect to each other. The goal is to have a steadystate at the highest humidity and lowest temperature that the system will allow.

I was planning on using Node Red, which has some PID nodes to help simplify things, but god damn is it still way over my head..

I'm hoping I can take the input and output of say Input 1 on Output 2 and Input 2 on Output 1 to determine the transfer function for both of the additional feedback loops G_P1-2 and G_P2-1, but there's some funky Laplace Transform stuff going on as well.

Anyway, if someone has worked on this already, some advice would be greatly appreciated.

Thank you for your time!

2

Although I can answer your question I refuse because of your language.

1 Like
3

Well, you'd be the first across several automation forums who could or would be willing to give an algorithmic solution to an Nth dimensional MIMO system.

4

Just do the math. If it seems hard, question your assumptions. PID is second order and linear.

Better yet, don't waste your time. Write some simple code that does not assume "loop interference" and see if it works.

5

I immediately thought that if he used alah, someone would hunt him down.

6

I immediately thought that if he used all-ah, someone would hunt him down.

I tried a different spelling but the forum wouldn't allow.

7

This is basically the answer lol...

The system is not necessarily LTI, which further complicates the MIMO.

Just attempting to reduce interference for now.

8

Hi,
How low a temperature?
Relative or Absolute Humidity?

Air with 80% Relative Humidity at 5C carries less water than 80% Relative Humidity at 25C

What is the application?

Thanks.. Tom.. :smiley: :+1: :coffee: :australia:

9

Or the coupling is too weak to matter.

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