PID CONTROL
The output of the three controls is combined and the net resultant drives the rudder. This type of autopilot is also called as PID Auto Pilot.
A Proportional–Integral–Derivative Controller (PID controller) is a control loop feedback mechanism (controller) commonly used in industrial control systems. A PID controller continuously calculates an error value as the difference between a desired set point and a measured process variable. The controller attempts to minimize the error over time by adjustment of a control variable, such as the position of a control valve, a damper, or the power supply.