How do you deal with the trade-offs and constraints of control logic systems?

I have found an often missed consideration is who will be the end user, what are his resources to maintain the system after commissioning, what spare parts do they already have, systems already in service at their site, long-term training plan for new systems. OEM vendors have a vested interest not to look these details that affect total cost of ownership and future availability and maintainability. Quite often what is an awesome technical solution gets unplugged and put in the corner simply because the end user either doesn't have the training, or management support to take the time to effectively use a great solution and it becomes a nuisance.

Well put. The future migration plans also come into play. Is this a system needed as an interim solution until funding is available to upgrade related systems, or is it intended to be a final long-term solution with expandability, and parts available in 10 years.

You must involve operations in the development and testing, especially the HMI. Getting a key operator involved in some project decisions will provide buy-in and a great opportunity to extend the training of the new system. Granted they probably do not know much about the tools, but good operators know their process.

A natural trade-off exists between control effort and state error, but one can potentially minimize this with an adequate understanding of system dynamics, including both plant and disturbance models. Then, one can optimize to resolve a minimum-effort reference trajectory, taking advantage of stable/unstable manifolds, periodicity, equilibrium points, and even chaotic features of motion. Model-based controllers avoid excessive control effort due to their predictive quality (e.g., MPC, MRAC). For systems with unknown dynamics, iterative/adaptive (e.g., Jacobian learning) and data-driven methods (e.g., DMD and its variants) are available. Thus, Dynamics and Controls go hand-in-hand!

Take advantage of any virtual controller tools and external connections. Tail to mouth (wired or virtual) simulation should go as close as possible to the raw input and final output as possible. Hours and days of site startup issues can be avoided by simple closed loop testing. As with the last paragraph, get a good operator involved in the test.

Commissioning and start-up of the new or modified system is always a big undertaking. Usually there are a small amount of logic or instruments that that don't actually function or respond the way the design teams envisioned. This can occur as well when going live with the actual process start-up and initial (mostly) stable process operations. Again very important to have operations support during the site checkout & functional testing, a lead operator being preferred. Also important to fully train the operators on the new system.

So many vendors use a different team to develop the logic than the ones that actually start it up. The design team MUST be involved in the commissioning if you want to close the loop on improving the control systems and experience for your programmers/engineers.

Documentation and as-builds are not fun to do & take a lot of time to do correctly. But they will save yourself or your team trying to figure it out in the middle of a weekend night with operations or plant management asking why the system isn't working. Do system documentation and as-builts assuming it will be you out there that weekend night.