Abstract
Among various tools implemented to counteract undesired effects of time-varying uncertainties, disturbance observer (DOB)-based controller has gained wide popularity as a result of its flexibility and efficacy. In this paper, a low-order DOB that is capable of compensating for the effects of a biased harmonic disturbance, as well as plant uncertainties is presented. The proposed low-order DOB can asymptotically estimate a harmonic disturbance of known frequency but unknown amplitude and phase, by using measurable output variables. An analysis carried out by using the singular perturbation theory shows that the nominal performance of the system can be recovered from a real uncertain system when the observer gain is sufficiently large. The observer gains that result in the performance recovery of the real uncertain system are obtained from the stability condition of the boundary-layer system. To test the performance of the proposed observer, computer simulations with a numerical example and laboratory experiments using a DC motor system have been carried out. The experimental results show that the proposed low-order DOB-based control scheme can provide enhanced performance.
Highlights
Throughout all industrial systems, regardless of all measures taken to design an effective controller that can achieve nominal performance, unforeseeable factors, such as unmodeled plant dynamics, system parameter variations, and external time-varying disturbances inevitably give rise to system performance deterioration
This paper designs a low-order disturbance observer (DOB) to deal with a biased harmonic disturbance based on measurable output information
The proposed DOB can be implemented with a low dynamic order according to a rank factorization result of a matrix related to the unmeasurable system states
Summary
Throughout all industrial systems, regardless of all measures taken to design an effective controller that can achieve nominal performance, unforeseeable factors, such as unmodeled plant dynamics, system parameter variations, and external time-varying disturbances inevitably give rise to system performance deterioration. The robustness of a control system has become a crucial quality and various methods have been proposed to guarantee the robustness of control systems [1,2]. Among these methods, disturbance observers (DOBs) have been widely studied [3]. Disturbance observers (DOBs) have been widely studied [3] By using this method, any previously designed controller, which can achieve the desired performance under nominal conditions, can be modified into a robust controller by adding a DOB. Enabling the recovery of nominal control performance of any exiting controller through disturbance compensation.
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