Disturbance-observer-based robust control for time delay uncertain systems

A robust control scheme is proposed for a class of systems with uncertainty and time delay based on disturbance observer technique. A disturbance observer is developed to estimate the disturbance generated by an exogenous system, and the design parameters of the disturbance observer are determined by solving linear matrix inequalities (LMIs). Based on the output of the disturbance observer, a robust control scheme is proposed for the time delay uncertain system. The disturbance-observer-based robust controller is combined of two parts: one is a linear feedback controller designed using LMIs and the other is a compensatory controller designed with the output of the disturbance observer. By choosing an appropriate Lyapunov function candidate, the stability of the closed-loop system is proved. Finally, simulation example is presented to illustrate the effectiveness of the proposed control scheme

Adaptive fuzzy tracking control for a class of uncertain MIMO nonlinear systems using disturbance observer

In this paper, the adaptive fuzzy tracking control is proposed for a class of multi-input and multioutput (MIMO) nonlinear systems in the presence of system uncertainties, unknown non-symmetric input saturation and external disturbances. Fuzzy logic systems (FLS) are used to approximate the system uncertainty of MIMO nonlinear systems. Then, the compound disturbance containing the approximation error and the time-varying external disturbance that cannot be directly measured are estimated via a disturbance observer. By appropriately choosing the gain matrix, the disturbance observer can approximate the compound disturbance well and the estimate error converges to a compact set. This control strategy is further extended to develop adaptive fuzzy tracking control for MIMO nonlinear systems by coping with practical issues in engineering applications, in particular unknown non-symmetric input saturation and control singularity. Within this setting, the disturbance observer technique is combined with the FLS approximation technique to compensate for the effects of unknown input saturation and control singularity. Lyapunov approach based analysis shows that semi-global uniform boundedness of the closed-loop signals is guaranteed under the proposed tracking control techniques. Numerical simulation results are presented to illustrate the effectiveness of the proposed tracking control schemes

Sliding mode control for a class of uncertain nonlinear system based on disturbance observer

In this paper, a sliding mode control (SMC) scheme is proposed for a class of nonlinear systems based on disturbance observers. For a nonlinear system, the disturbance that cannot be directly measured is estimated using a nonlinear disturbance observer. By choosing an appropriate nonlinear gain function, the disturbance observer can well approximate the unknown disturbance. Based on the output of the disturbance observer, an SMC scheme is presented for the nonlinear system, and the stability of the closed-loop system is established using Lyapunov method. Finally, two simulation examples are presented to illustrate the features and the effectiveness of the proposed disturbance-observer-based SMC scheme

Design of H∞ synchronization controller for uncertain chaotic systems with neural network

A synchronization controller is designed based on disturbance observer for two uncertain chaotic systems in this paper. The compound disturbance of the synchronization error system consists of non-linear uncertainties and exterior disturbance of two chaotic systems. The compound disturbance observer is proposed based on RBF neural networks and the parameter's update law is given for monitoring the compound disturbance. The output of the compound disturbance observer is used to design synchronization controller. The designed synchronization controller can make the synchronization error converge to zero. Finally, an example is given to demonstrate the availability of the proposed synchronization control method

Maintaining synchronization by decentralized feedback control in time delay neural networks with parameter uncertainties

A decentralized feedback control scheme is proposed to synchronize linearly coupled identical neural networks with time-varying delay and parameter uncertainties. Sufficient condition for synchronization is developed by carefully investigating the uncertain nonlinear synchronization error dynamics in this article. A procedure for designing a decentralized synchronization controller is proposed using linear matrix inequality (LMI) technique. The designed controller can drive the synchronization error to zero and overcome disruption caused by system uncertainty and external disturbance

RLIPC confers cardioprotection against post-ischemic arrhythmia and SCD.

<p><b>A)</b> Quantification of the incidence of different cardiac arrhythmia characteristics and mortality during post ischemia reperfusion in CON (<i>n</i> = 16) and RLIPC (<i>n</i> = 14) rats. Numbers of animals per category are indicated in parentheses. Sinus rhythm, remained in sinus rhythm; AVB, AV block; VT, ventricular tachycardia; SVT, sustained VT (>1min VT); PVT, polymorphic VT; VF, ventricular fibrillation; SCD: sudden cardiac death. *<i>P<0</i>.<i>05</i> and **<i>P<0</i>.<i>01</i> vs. CON. <b>B)</b> Representative surface ECGs from CON and RLIPC rats during reperfusion showing greater severity of arrhythmia in the former. <b>C)</b> Mean VT parameters including the onset time of first VT episode after reperfusion (left) and durations of VT (middle) and the longest episode of VT duration (LVT) (right) for control (<i>n</i> = 16) and RLIPC (<i>n</i> = 14) rats. Rats without VT were indicated as 0 duration. **<i>P<0</i>.<i>01 vs CON</i>, <i>NS</i>: <i>P>0</i>.<i>05</i> between two groups. <b>D)</b> Left, VF incidence during the first 5 minutes of reperfusion for CON (n = 16) and RLIPC (<i>n</i> = 14) rats. Numbers in parentheses indicate the numbers of rats exhibiting VF; right, the starting time of the first run of VF after the onset of reperfusion in CON (<i>n</i> = 16) and RLIPC (<i>n</i> = 14) rats. *<i>P<0</i>.<i>05</i> vs. CON. <b>E)</b> Mean serum K⁺ concentration for CON and RLIPC rats after 20min reperfusion; <i>n</i> = 8 per group. <i>NS</i>: <i>P></i>0.05 between two groups.</p

The influence of pharmacological inhibitors on ST elevation in rats.

<p><b>A)</b> The change of ST height in the absence (-) or presence (+) of liver I/R preconditioning stimulus when applying GSK-3β inhibitor SB216763 (<i>n</i> = 6–9 per group). <i>NS</i>: <i>P>0</i>.<i>05</i> among groups. ST height for control group is repeated from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0165123#pone.0165123.g002" target="_blank">Fig 2</a> for comparison. C, control; R, RLIPC; SB, SB216763. <b>B)</b> The change of ST height in the absence (-) or presence (+) of liver I/R preconditioning stimulus when applying ERK inhibitor U0126 (<i>n</i> = 6–9 per group). <i>NS</i>: <i>P>0</i>.<i>05</i> among groups. ST height for control group is repeated from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0165123#pone.0165123.g002" target="_blank">Fig 2</a> for comparison. C, control; R, RLIPC; U, U0126.</p

Experimental protocols.

<p><i>A</i>ll groups were subjected to 5-min left main coronary artery occlusion followed by 20-min reperfusion except for the sham-operated group. Remote liver ischemia preconditioning (RLIPC) was induced by four cycles of 5 min of liver ischemia with 5 min intermittent reperfusions. Pharmacological inhibitors (SB216763 and U0126) were administered as a bolus 30 min prior to myocardial ischemia. Two baseline values were recorded: Baseline 1, ten minutes stabilization after instrumentation, and Baseline 2, twenty-five minutes post liver I/R stimulus.</p

RLIPC phosphorylates ERK1/2 and GSK-3β post cardiac IR injury.

<p><b>A)</b> Left, Western blots of ventricular phosphorylated ERK1/2 and total ERK1/2 isolated from sham, control and RLIPC rats after 20 minutes of reperfusion; right, band density of p-ERK/ERK (<i>n</i> = 6–8 per group). ***<i>P<0</i>.<i>001</i> vs. RIPC. <b>B)</b> Left, Western blots of ventricular phosphorylated GSK-3β(Ser9) and total GSK-3β isolated from sham, control and RLIPC rats after 20 minutes of reperfusion; right, band density of p-GSK-3β(Ser9)/GSK-3β (<i>n</i> = 6–8 per group). ***<i>P<0</i>.<i>001</i> vs. RIPC.</p

The influence of pharmacological inhibitors on cardiac ERK and GSK-3β phosphorylation status in rats.

<p><b>A) Upper panel,</b> Representative western blots of phosphorylated ERK1/2 and ERK1/2 isolated from CON and RLIPC rats in the presence or absence of pharmacological inhibitors. CON, control; RLIPC, remote liver ischemia preconditioning. <b>Lower panel</b>, Quantification of p-ERK/ERK protein band density; <i>n</i> = 6–12, each group. S, sham-operated group, C, control; R, RLIPC; SB, SB216763; U, U0126. ***<i>P<0</i>.<i>0001</i> compared with RLIPC (by One-way ANOVA). All other group comparisons showed <i>P>0</i>.<i>05</i>. <b>B) Upper panel,</b> Representative western blots of phosphorylated GSK-3β(Ser9) and total GSK-3β isolated from control and RLIPC rats in the presence or absence of pharmacological inhibitors. <b>Lower panel</b>, Quantification of p-GSK-3β(Ser9)/GSK-3β protein band density; <i>n</i> = 5–10, each group. S, sham-operated group, C, control; R, RLIPC; SB, SB216763; U, U0126. ***<i>P<0</i>.<i>0001</i> compared with RLIPC (by One-way ANOVA). All other group comparisons showed P>0.05. <b>C) Upper panel,</b> Representative western blots of phosphorylated GSK-3β(Tyr216) and total GSK-3β isolated from control and RLIPC rats in the presence or absence of pharmacological inhibitors. <b>Lower panel</b>, Quantification of p-GSK-3β(Tyr216)/GSK- 3β protein band density; <i>n</i> = 6–9, each group. S, sham-operated group, C, control; R, RLIPC; SB, SB216763; U, U0126. All group comparisons showed <i>P>0</i>.<i>05</i>.</p