Proportional Controller (P Controller)
A proportional controller is the simplest closed-loop structure, producing an output directly proportional to the error: the output is the gain times the error. When the error is large it moves fast, as the error gets smaller it moves slowly. By its nature it leaves a small permanent error in steady state, and this error decreases as the gain increases.
Its behaviour is intuitive: while far from the target the actuator moves fast, as it gets closer it slows down and settles softly. This reduces the shock and the overshoot on step commands.
- High gain: fast response, small permanent error, but a risk of oscillation and overcurrent.
- Low gain: stable but lazy; slow to answer a load change.
- Integral action is needed to bring the permanent error completely to zero; that means moving to a PI or PID structure.
On the GS740-3P the position control is done with a P controller and the command is applied with a soft ramp. This choice suits the application: what is aimed at is not a fast servo response but a repeatable throttle position that does not strain the cable and the joint. The very small remaining position error is negligible next to the mechanical free play of the throttle lever.
Context in which this term is used: Electronic speed and throttle control on a diesel engine