Analysis of equivalent‐input‐disturbance‐based control systems and a coordinated design algorithm for uncertain systems

Abstract

The control method based on the equivalent‐input‐disturbance (EID) estimator and the Luenberger state observer has received much attention in recent years. However, the property of EID‐based control systems is still not well investigated. A number of design procedures were proposed but lacked sufficient theoretic justification. In this article, the two‐degree‐of‐freedom nature of an EID‐based control system is revealed. Specifically, the reference‐tracking is determined by an outer loop, while the disturbance rejection and robustness is determined by an inner loop consisting of the EID estimator and state observer. The bandwidth constraints on the inner loop are analyzed for plants having zeros or poles in the open right‐half plane by using the Bode and the Poisson integral formulas. These analyses provide a theoretic justification for conventional design procedures. Further, a coordinated design algorithm is provided for the EID‐based uncertain control systems. In addition, a comprehensive comparison of the EID‐based and the disturbance observer (DOB) based control systems is conducted in the system design aspect. Lastly, comparative studies of the EID‐based and DOB‐based control methods are given for various types of plants to validate the developed design algorithm.

Robust control of pantograph‐catenary system: Comparison of 1‐DOF‐based and 2‐DOF‐based control systems

“…where the superscripts i = 1, 2 are for the 1-DOF-based and 2-DOF-based control systems, respectively. As explained in [28], we have K 2 e3 (s)G n (s) = K 2 e2 (s). Then, the transfer functions G i yr (s) from r (s) to y(s) and G i yd (s) from d e (s) to y(s) are given as follows:…”

Converter inlet temperature control in flue gas acid‐making process based on equivalent input disturbance and model prediction

“…According to Figure 3, we can consider the system as a two-layer structure of the outer loop and inner loop. 34 When the EID estimator and state observer in the inner loop are properly constructed, the dynamic uncertainty and external disturbance of the controlled plant can be mostly eliminated, so the design of the state-feedback controller only needs to consider the nominal plant. Therefore, an EID based control system has 2-DOF nature.…”

Iterative Design Algorithm for Robust Disturbance-Rejection Control

“…where the angular frequency ω r is the bandwidth of the low-pass filter F(s) and determined by the disturbance-rejection control design. However, when there exist tight constrains on control bandwidth [19] or specific performance requirements on the middle-frequency range, a general filter is necessary. Superior to the conventional EID one, the GEID approach is able to estimate disturbances of a more general frequency range by a general filter.…”

“…In engineering practice, it is difficult to obtain a precise mathematical model of a physical system, owning to parameter perturbations, modeling errors, unmodeled dynamics, and other factors. Moreover, as explained by [19], the uncertainties impact the disturbance-rejection control performance. So, it is vital and necessary to design a robust controller with a prescribed disturbance-rejection performance index.…”