The following is based on an excerpt from Chapter 14 that I contributed to PID Control in the Third Millennium: Lessons Learned and New Approaches (Vilanova and Visioli 2012).
Special algorithms can be designed to deal with measured load disturbances at the process input, setpoint changes, and disturbances at the process output (e.g., noise). Often neglected is the overriding requirement that controllers in industrial applications must be able to deal with unmeasured and unknown load disturbances at the process input. Fortunately, the proportional-integral-derivative (PID) controller excels at this load disturbance rejection. An estimate of the current and best possible load rejection as a function of the process ...