PID systems inherently require some amount of overshoot in order to stabilize around a target. This often requires adding or subtracting some resultant term in order to shrink the relative error. However, there are many physical applications where the input of the closed-loop system is unidirectional and/or finite.
For example: You use a closed loop control algorithm to launch and perform in-flight adjustments on a model rocket in order to achieve Y target apogee. The rocket can ADD thrust in-flight if it calculates the trajectory to be too low, but it can never SUBTRACT thrust that's already been applied. Thus, vanilla PID (as I understand it) cannot effectively run this control loop.
For my actual application, I'm interested in using pressure transducer feedback alongside a booster pump, in order to boost the volume downstream of the pump up to X target pressure. The system can't easily bleed pressure if the pump overshoots, so as far as the control-loop goes, I can only add pressure.
The easy solution would be do basic on/off "am I there yet?" control. However, I'm more interested in a control loop that produces a curve that asymptotes at X target pressure. So my questions are:
- What is the name of this type of control algorithm (I assume there are a few methods)?
- How does the feedback and relative-error-reduction system work?