# Is the PID just an outdated control method and state-space is superior?

So I've been wondering this for a while; is PID just a simple but slightly outdated control method / isn't state-space (SS) a far superior method in pretty much every way?

SS allows for MIMO, PID just SISO. SS allows for non-linear models, PID does not do non-linear models. SS allows you to see and control the states of your system, this is kind of lost in the laplace transform of PID... So given this; why do I encounter PID everywhere? Is it simpler and cheaper and good enough if it works?

I've asked this question to my mechatronic systems design professor, but I did not really find his answer all that satisfying: "State space is not going to do magic if loopshaping way of designing PID reaches its edge. State-space is time domain to design linear control while loopshaping is frequency domain. With both you can design PID."

His research group is focused on the high-tech side of things, and has made a 'fractional order' PID controller toolbox (FLOreS - Fractional order loop shaping MATLAB toolbox, essentially you place a bunch of zeros and poles close to each other to mimic something which is between e.g. s^1 and s^2). In any event, I think he might be biased so I wish to get some perspective.

• PID is simple and works adequately for a range of applications. There are masses of classical and modern control algorithms which will be better for any single specific application. Feb 5, 2021 at 23:48
• PID control (so-called three term controllers, which typically have upwards of 30 parameters in commercially available implementations) may well be overused, but they get the job done for many single loop applications. PID is easy to explain to beginners too, i.e. understand a little calculus but not frequency domain. As you say, state space is for multi dimensional applications, IMO. More difficult SISO situations are solved with more customized forms, pole placement etc // also state space is not necessarily time domain, I wouldn't agree with that // fractional order is a cool technique too Feb 6, 2021 at 0:34
• A big chemical company I know of has about 100,000 closed-loop controllers in the various systems at their main plant. Imagine designing a sophisticated MPC controller for each of them. In fact, 90 % are PID controllers because it's a) good enough b) very easy to design. Only the top level control is done with sophisticated control algorithms. Feb 6, 2021 at 11:20