Disturbance Observer

Disturbance observer is an inner-loop output-feedback controller whose role is to reject external disturbances and to make the outer-loop baseline controller robust against plant's uncertainties. Therefore, the closed-loop system with the DOB approximates the nominal closed-loop by the baseline controller and the nominal plant model with no disturbances. This article presents how the disturbance observer works under what conditions, and how one can design a disturbance observer to guarantee robust stability and to recover the nominal performance not only in the steady-state but also for the transient response under large uncertainty and disturbance

Yet Another Tutorial of Disturbance Observer: Robust Stabilization and Recovery of Nominal Performance

This paper presents a tutorial-style review on the recent results about the disturbance observer (DOB) in view of robust stabilization and recovery of the nominal performance. The analysis is based on the case when the bandwidth of Q-filter is large, and it is explained in a pedagogical manner that, even in the presence of plant uncertainties and disturbances, the behavior of real uncertain plant can be made almost similar to that of disturbance-free nominal system both in the transient and in the steady-state. The conventional DOB is interpreted in a new perspective, and its restrictions and extensions are discussed

Development of a Novel Disturbance Observer Based Fractional Order PD Controller for a Gun Control System

Motion control of gun barrels is an ongoing topic for the development of gun control equipment (GCE) with excellent performances. In this paper, a novel disturbance observer (DOB) based fractional order PD (FOPD) control strategy is proposed for the GCE. By adopting the DOB, the control system behaves as if it were the nominal closed-loop system in the absence of disturbances and uncertainties. The optimal control parameters of the FOPD are determined from the loop-shaping perspective, and the Q-filter of the DOB is deliberately designed with consideration of system robustness. The linear frame of the proposed control system will enable the analysis process more convenient. The disturbance rejection properties and the tracking performances of the control system are investigated by both numerical and experimental tests, the results demonstrate that the proposed DOB based FOPD control system is of more robustness, and it is much more suitable for the gun control system with strong nonlinearity and disturbance

Robust control stability using the error loop

The paper briefly formulates the error loop as a tool for designing robust stability control systems in front of structured and unstructured uncertainties. The error loop indicates that a tool for accommodating such uncertainties is the noise estimator, which is the unique feedback channel from plant to control. It is shown that the causality constraint preventing perfect cancellation of causal uncertainties (unknown disturbance), makes also control law to play a role, offering a further degree of freedom. Employing asymptotic expansions of the closed-loop transfer functions, simple, explicit design formulae derive from stability inequalities: they relate closed-loop eigenvalues to model parameter and requirements. A simple example is provided from a ball and beam plan

Disturbance-Observer-Based PBC for Static Synchronous Compensator under System Disturbances

© 2019 IEEE. Passivity-based control (PBC) relies on an accurate mathematical model and thus its performance will be degraded by the weak robustness against parameters uncertainties, modeling error, and external disturbances. Moreover, it cannot achieve zero tracking error of the steady-state current under parameter uncertainties and modeling error. This paper proposes a novel disturbance-observer-(DO) based PBC (DO-PBC) for static synchronous compensator (STATCOM) to achieve better stability and dynamic performances against disturbances. A DO that has been introduced into the PBC current loop is used to compensate system disturbances, which can improve the robustness of the control system and eliminate the steady-state tracking error. Moreover, the proposed DO-PBC provides faster responses in handling various kinds of disturbances. Then, the detail design process, stability and robustness analysis, and parameters tuning method are investigated and presented. Also, the proposed method is simple to be implemented by the separation principle. The performance comparisons among the proportional integral, the conventional PBC, and the proposed DO-PBC are carried out to show the effectiveness of the proposed method against disturbances and the precise current tracking, via simulation tests and experimental tests based on a down-scale laboratory prototype experiment of 380 V STATCOM

Thermal control for the liquid metal coolant circulation loop

The target complex facility (TC-1 facility) located at University of Nevada, Las Vegas (UNLV), is serving the fundamental research of thermal-hydraulics and corrosion test of liquid metal coolant lead bismuth eutectic (LBE). A stable thermal condition is the basis for the TC-1 facility to operate and target coolant LBE to circulate throughout the loop made of the main components of TC-1 facility, TC-1 loop. The proper thermal process of the TC-1 loop critically comprises a smooth heating phase, the main intention of which is to warm all the loop components and melt solid LBE; a stable temperature maintenance phase, which is to maintain the TC-1 loop temperature around the setting point to make sure target coolant circulates efficiently for long lime; and a cooling phase, which to make sure coolant be stored inside a certain component drainage tank as solid state after the circulation finishes; The current thermal control scheme for the TC-1 loop has a very low efficiency. Under the current control, many problems happen to the important temperature maintenance phase. For example, heating zones\u27 temperature of the TC-1 loop vibratos seriously, some heating zones\u27 vibration range is much bigger than accepted, and to the worst some zones\u27 temperature vibrato outside the setting range. All these problems affect inversely the further research of hydraulics and corrosion of liquid metal coolant; In this thesis, the system identification method has been used to identify system mathematical model. Based the identified system models, different control schemes are studied and demonstrated. Current control scheme of band temperature control is investigated again, then two new thermal control schemes are proposed for the TC-1 loop, one of which is a hybrid scheme of proportional-plus-integral-plus-derivative control scheme (PID control) and ON/OFF control, the other is a disturbance observer (DOB) based PID-ON/OFF control scheme; Moreover, the performance of the current control scheme and proposed control schemes is demonstrated for the nine heating zones separately as well as a simulator furnace by simulation method through SIMULINK toolbox under the MATLAB environment. Finally, guided by the obtained simulation results, many experiments corresponding to these different control schemes for the heating zones of the TC-1 are performed on the furnace using the commercial National Instrumental LABVIEW; The obtained experimental results from the simulator can be used as a guideline and reference for the further experiments in the TC-1