Hi, We have a vessel whose level is continually ramping up and down between about 20 and 80% in a triangle wave. The output flow is controlled by an onoff valve with a 50% duty cycle, that part of the system is an immutable 'given'. Objective is to control the level so that the high peaks don't overflow the tank, and the low peaks don't empty it. The handle available is a proportional control valve in the feed line.
Normal PID control of the tank level doesn't appear to be suitable because the feed valve is of an unusual type that wouldn't tolerate excessive movement for long. The alternative is some sort of inching control, where you back the feed off when the level gets *too* high, or increase when it gets *too* low. One way to do this would be a PI controller with deadzone on the error, that approach has the advantage that it's a standard algo on our platform. Does anyone have any experience on what sort of tuning settings may be appropriate in a situation like that?
We've considered filtering the level heaps, but that wrecks the dynamic response, and with an integrating process the resulting stability is going to be really marginal.
Any other ideas?
For the purposes of the exercise, can assume that the ramp time one way for the tank level is 5 minutes.
TIA