Novel Active Disturbance Rejection Control Based on Nested Linear Extended State Observers
For control systems engineers, this offers an incremental improvement to ADRC by addressing bandwidth limitations in disturbance estimation.
The paper proposes a novel active disturbance rejection control (N-ADRC) using a nested linear extended state observer (LESO) to improve disturbance estimation without increasing bandwidth. Simulations show a 69.87% reduction in ITAE tracking error compared to conventional ADRC.
In this paper, a Novel Active Disturbance Rejection Control (N-ADRC) strategy is proposed that replaces the Linear Extended state observer (LESO) used in Conventional ADRC (C-ADRC) with a Nested LESO. In the nested LESO, the inner-loop LESO actively estimates and eliminates the generalized disturbance. Increasing the bandwidth improves the estimation accuracy which may tolerate noise and conflict with H/W limitations and the sampling frequency of the system. Therefore, an alternative scenario is offered without increasing the bandwidth of the inner-loop LESO provided that the rate of change of the generalized disturbance estimation error is upper bounded. This is achieved by the placing an outer-loop LESO in parallel with the inner one, it estimates and eliminates the remaining generalized disturbance that eluded from the inner-loop LESO due to bandwidth limitations. The stability of LESO and nested LESO is investigated using Lyapunov stability analysis. Simulations on uncertain nonlinear SISO system with time-varying exogenous disturbance revealed that the proposed nested LESO can successfully deal with a generalized disturbance in both noisy and noise-free environments, where the Integral Time Absolute Error (ITAE) of the tracking error for the nested LESO is reduced by 69.87% from that of the LESO.