Smooth switching design/implementation of the active disturbance rejection control

Although active disturbance rejection control (ADRC) has demonstrated promising results in many applications, in some safety critical applications e.g. power plant, unmanned aerial vehicle, etc., it is often reluctant to switch from an existing control algorithm, either the traditional PID controller or other advanced control algorithms, to a new one. If the switching between the control algorithms can be made seamless, many more opportunities may open up. In this paper, the problem of making the switching to the ADRC smooth is studied. Previous attempts to solve the problem are not thorough enough, since only a second order system was addressed. A very simple and effective method is proposed based on analysis to make the transition seamless. The solution is very general, and can be applied to system of any order or even system with time-delay. At the core of the solution is the initialization of the "total disturbance".