ADRC Can Reject Unbounded Disturbance*

Active disturbance rejection control (ADRC) is a hot issue of control theory, whereas bounded total disturbance is thought to be necessary for ADRC working. This paper constructs an counter example, in which the total disturbance equals the external disturbance and has unbounded value and derivative. Simulations and analysis illustrate ADRC can reject the disturbance and track step reference without steady-state error. Thus, the bounded total disturbance assumption is unnecessary for ADRC.