Observer Design Method Research Articles

Association between Stress Levels and Functional Dyspepsia among Medical Students During the COVID-19 Pandemic: A Study of Indonesian Christian University

Background: Stress is a problem that often occurs among students. The high incidence of stress in students can interfere with students' effectiveness in carrying out their lecture activities. Stress in students not only affects the quality of learning but can also affect the physical condition of students, one of which is the occurrence of gastrointestinal disorders, one example of which is dyspepsia. Aims: This study aims to determine whether there is a relationship between stress levels and functional dyspepsia in students at the Faculty of Medicine, Indonesian Christian University class of 2020. Study Design: This research uses an observational analytical research design method with a cross-sectional approach. The main data source is primary data obtained through questionnaires taken online via Google Forms. Place and Duration of Study: The research was conducted at the Indonesian Christian University located in Cawang, East Jakarta. Time of research in September 2022. Methodology: The population in this study was 137 students from the Faculty of Medicine, Indonesian Christian University class of 2020. The sample was taken using a simple random sampling technique totaling 103 people determined using the Slovin formula with an uncertainty percentage of 5%. Results: From the results of data collection on 103 respondents who were FK UKI students Class of 2020, around 65% or 67 respondents were identified as having normal stress levels and as many as 64 students (62%) had symptoms of functional dyspepsia. Based on the results of the bivariate analysis, it was found that there was a relationship between the level of stress and the incidence of dyspepsia experienced by FK UKI students class of 2020 with the results of the chi-square test, namely p = 0.003 < sig 0.05 Conclusion: There is a significant relationship between stress levels and functional dyspepsia. This certainly cannot be taken lightly because the incidence of functional dyspepsia can have fatal consequences which can disrupt the sufferer's activities and productivity. Therefore, it is very necessary to manage emotions (stress levels) both by the sufferer himself and with professional help.

Observers for hyperbolic systems with multiple delays in the nonlocal boundary condition and its application to secure image encryption

In this article, we propose a step-by-step observer design for a first-order linear hyperbolic system with multiple delays in the nonlocal boundary condition. In the proposed approach inspired by the backstepping methodology, the observer gains are obtained following seven successive steps. Next, we present the application of this observer design in the context of image encryption. We consider a system where a local nonlinear term causing a chaotic vibration is added to the nonlocal boundary condition with time lags. A synchronization system for this chaotic system can be constructed using the same observer design method. The chaotic states generated by both systems can be used to encrypt and decrypt image data. The time lags, and weight functions included in the nonlocal boundary condition play the role of common encryption keys. By considering a system that includes arbitrarily many delays, this approach allows for a significant increase in the number of common encryption keys compared to conventional methods, resulting in greatly improved communication security.

Zonotopic estimation for asynchronous switched system with application to missile flight system

Interval estimation for asynchronous switched systems is investigated on the basis of zonotope. A particular zonotopic estimation framework that includes center estimation and P-radius estimation is presented. In the light of robust stability theory, an asynchronous robust observer, which is used in the center estimation, is established. And the P-radius estimation is conducted by zonotopic set-membership estimation theory. The proposed framework reduces the conservatism that exists in interval observer design methods. Besides, to maintain a high accuracy, the direct method that disregards order reduction is applied instead of the iterative method in this framework. Finally, the simulation of a missile flight dynamics system is carried out to illustrate the validity of the estimation framework.

Trajectory Tracking Control Based on a Composite Disturbance Observer for Unmanned Autonomous Helicopters under Multiple Disturbances

This paper studies the trajectory tracking anti-disturbance control of unmanned autonomous helicopters (UAHs) under matched disturbances and mismatched ones. Firstly, the six-degrees-of-freedom UAH nonlinear system is simplified via feedback linearization to handle strong coupling, in which the multiple disturbances are composed of modeled disturbances and time-varying bounded ones. Secondly, in order to estimate these disturbances, a new design method of a composite disturbance observer is proposed. On the one hand, for the mismatched disturbances, a normal disturbance observer (DO) combined with a backstepping control are utilized to handle their negative effect. On the other hand, two refined disturbance observers (RDOs) are constructed to estimate the matched disturbances, in which the coupling estimations are involved. Then, by designing two anti-disturbance composite controllers, the boundedness of the tracking errors is guaranteed by using the Lyapunov stability theory. Finally, some numerical simulations are provided to demonstrate the effectiveness and advantage of the proposed control scheme.

Fault‐tolerant control of observer‐based H∞ with sensor and actuator faults under two‐step event triggering mechanism

AbstractThis article considers the design problem of observer‐based fault‐tolerant control under three faulty cases: sensor only, actuator only, and both sensor and actuator faults. To save communication resources, the event trigger mechanism method is used for sensor‐to‐observer and observer‐to‐controller transmissions. In this case, the design method of the new observer is given for obtaining estimating both states and faults which are used to design observer‐based fault‐tolerant controllers. In particular, the virtual observer is designed to suppress the effects of faults on the system. As the virtual observer contains unmeasurable system information, the real observer is built on top of the virtual observer to eliminate the unmeasurable information. Finally, the feasibility of the approach is tested with a numerical example.

Fixed-Time Fault-Tolerant Consensus Control for High-Order Nonlinear Multiagent Systems Under Directed Topology

This paper addresses the fixed-time fault-tolerant consensus control problem for high-order nonstrict-feedback nonlinear multi-agent systems under directed topology. A distributed high-order fixed-time observer is proposed to obtain the accurate estimations of the full states of the leader. Different from the fixed-time observer design methods, a much more concise estimate for the upper bound of the convergence time is provided. Based on the fixed-time observer and adding a power technique, a fixed-time tracking protocol is designed for a group of followers subject to unknown nonidentical dynamics and unpredictable actuation faults. It is shown that there is no need to know the information of the nonstrict-feedback nonlinear dynamics, the control gains, and the actuation faults in the control design and implementation completely, which is deemed favorable in practice. Simulation results are provided to validate the effectiveness of the developed control scheme.

Observer design method for nonlinear generalized systems with nonlinear algebraic constraints with applications

This paper proposes a new method to estimate the state of nonlinear generalized systems subject to nonlinear algebraic constraints via H∞ observers. Compared with previous research, the proposed approach relaxes the linear algebraic constraint and the infinite observability, making it applicable to a wider range of generalized systems. The generalized inverse technique for matrices avoids the additional structural requirements caused by the nonlinear algebraic constraints. Moreover, we assume an easier-to-implement rank condition than infinite observability, allowing for the handling of two different observability. Building on the above, the method can be extended to systems with nonlinear outputs after converting them to a suitable form. To validate the effectiveness of the proposed method, we demonstrate three practical applications, including observer designing for electromechanical systems, Lithium batteries, and vehicles.

Internal Model Principle-Based Extended State Observer for the Uncertain Systems with Nonconstant Disturbances

Existing traditional expansion state observers exhibit good tracking performance for constant and low-frequency disturbances. However, their ability to track non-constant disturbances such as ramp and high-frequency harmonics is inadequate. This paper proposes an extended state observer design method based on the internal model principle. This method achieves precise tracking of non-constant disturbances in the system, effectively addressing the issue of disturbance estimation errors in conventional expansion state observers. When applied to control systems, this approach significantly mitigates or suppresses system vibrations caused by non-constant disturbances, thereby enhancing control accuracy. Furthermore, it demonstrates the stability of the controlled system and the active disturbance rejection controller parameters over a wide range of variations. Simulation results indicate that the ADRC controller based on the proposed observer in this paper offers notable advantages, including high tracking accuracy, strong disturbance rejection capability, and good stability, leading to commendable control performance.

Fault Estimation Observers for the Vehicle Suspension with a Varying Chassis Mass

This paper proposes a descriptor Nonlinear Parameter Varying (NLPV) observer for damper fault estimation in vehicle semi-active suspension systems, here considering the highly practical case of a varying sprung mass, which is an open problem. This mass and the control input are treated as known scheduling parameters for the design and implementation of the observers, thus making the structure adaptive. This novel modeling leads to parameter-dependent dynamics and output matrices in the nonlinear parameter-varying formulation. To solve this problem, we extend an existing reduced-order observer design method (following descriptor system modeling) to this new case. Both polytopic and grid-based methods are then considered to compute and implement the problem solutions. The designs are then assessed using frequency-domain analysis and realistic time-domain simulations.

Dynamic observer‐based fault estimation and fault‐tolerant control for switched stochastic systems with multiple faults

AbstractThe fault estimation (FE) and fault‐tolerant control (FTC) problems are studied for the switched system with sensor fault, actuator fault, and stochastic noise. The dynamic FE observers are used to reconstruct the system states and faults at the same time. Differently from the classical observer design method, in the process of observers design, both the output information and its derivative are introduced to improve the estimation performance, especially in the case of the systems subject time‐varying fault. Based on the coordinate transformation, the output derivative is not appeared in the observers, which means that the proposed dynamic observers can be used for the cased that the output derivative is unmeasured. Utilizing the estimate information, the observer‐based FTC scheme is given. For any switching signal, the linear matrix inequality (LMI) conditions are provided, which can ensure that the entire system is mean‐square exponentially stable (MSES). Finally, simulation examples show the effectiveness of the observer and controller.

Intermediate observers based robust fault estimation for multi-agent systems under communication constraints via switching scheme

This paper addresses the problem of robust fault estimation for multi-agent systems (MASs) under communication constraints. Taking into account the possible data packet loss (DPL) in the information interaction of each subsystem, MASs are remodelled as switching systems by introducing a variable sampling strategy. Then, using the local information among agents, a novel intermediate observer design method based on switching scheme is proposed to estimate faults of MASs. Combining Lyapunov’s criterion and linear matrix inequality, sufficient conditions for the intermediate observer to be exponentially stable and have H ∞ performance against bounded disturbances and the DPL are given. Finally, some simulations are provided to verify the effectiveness of the proposed method.

Unknown input observer for Takagi-Sugeno implicit models with unmeasurable premise variables

<p>Recent years have seen a great deal of interest in implicit nonlinear systems, which are used in many different engineering applications. This study is dedicated to presenting a new method of fuzzy unknown inputs observer design to estimate simultaneously both non-measurable states and unknown inputs of continuous-time nonlinear implicit systems defined by Takagi-Sugeno (T-S) models with unmeasurable premise variables. The suggested observer is based on the singular value decomposition approach and rewritten the continuous-time T-S implicit models into an augmented fuzzy system, which gathers the unknown inputs and the state vector. The exponential convergence condition of the observer is established by using the Lyapunov theory and linear matrix inequalities are solved to determine the gains of the observer. Finally, the effectiveness of the suggested method is then assessed using a numerical application. It demonstrates that the estimated variables and the unknown input converge to the real variables accurately and quickly (less than 0.5 s).</p>

A globally exponentially stable observer for torque estimation with only position measurement

A novel estimation scheme for joint torque information is constructed by observer design method in the case that force/torque/velocity/acceleration sensors of manipulator are not available. Based on generalized dynamic scaling function and scalar filtering, the globally exponentially stable observer for torque estimation with only position measurement is presented in this article. The main contribution lies in the development of the classic Nicosia observer with performance improvements and significant order reduction compared to the existing results. Comparative simulations demonstrate the effectiveness and superiority of the proposed scheme.

Continuous‐discrete high gain observer design with PI output predictor

SummaryIn this article, a continuous‐discrete high gain observer with a proportional integral (PI) output predictor structure is designed for a class of nonlinear systems subject to sampled‐delayed data measurements. To counteract the effect of the well‐known sensitivity of the high gain observer to the noise measurements, a novel PI output predictor structure is proposed. The uniform ultimate boundedness (UUB) of the proposed observer is demonstrated by means of Lyapunov function and small gain method. The effectiveness of our proposed observer is demonstrated through numerical simulations and performances comparison with previous observer design methods in the literature.

Fault Estimation Observer Design for Markovian Jump Systems With Nondifferentiable Actuator and Sensor Failures.

This article addresses the simultaneous actuator and sensor fault estimation (FE) problem for a class of Markovian jump systems (MJSs) with nondifferentiable actuator failures. In order to overcome the difficulties brought by the nondifferentiable actuator failures, we construct an extended vector composed of states, sensor faults, and disturbances, where the derivatives of actuator failures are not required in this augmented system. Then, two novel observer-based approaches are developed for the augmented descriptor system to cope with the FE problem. The first one is a reduced-order FE observer, where the actuator failures can be estimated by the algebraic input reconstruction strategy. The second one refers to an iterative learning observer (ILO) design method, which can obtain the accurate FE result by integrating the estimations in the iterative processes. The two proposed FE observer design methods can avoid the sliding surface switching problem produced by sliding-mode observers in the area of MJSs. Finally, a practical example of the F-404 aircraft engine system is presented to show the validity of the proposed FE observer design techniques.

Maximum-Likelihood State Estimators in Probabilistic Boolean Control Networks.

This study addresses state estimation problems for probabilistic Boolean control networks (PBCNs). Compared with deterministic Boolean networks, PBCNs have the stochastic switching in logical update functions in the state equation. Consequently, statistical analysis is required to estimate unavailable states, which induces an optimization problem called maximum-likelihood estimation. This article mainly focuses on two scenarios: 1) state estimation from partially measured state and 2) state estimation from output data, meaning observer design. The resulting optimization problems are solved using efficient algorithms based on dynamic programming. Concurrently, Dijkstra-type algorithms, which solve equivalent shortest path problems, are also proposed using best-first search. Furthermore, both the proposed algorithms derive novel observer design methods for PBCNs. The proposed algorithms are evaluated with practical estimation problems aiming to the sensor reduction and applied to gene regulatory networks of apoptosis and Lac operon.

Distributed Interval Estimation Methods for Multiagent Systems

This article focuses on the study of distributed interval estimation for networked multiagent systems. For a multiagent system, it has many agents that could build an interconnection topology. For a distributed interval observer, it has many subobservers designed for the corresponding agents. Each subobserver contains two kinds of observer gains: one is determined based on the traditional observer design method and the other one is designed by using the information from the neighborhood. To construct distributed interval observers, two methods are proposed in this article. The first method combines the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$H_{\infty }$</tex-math></inline-formula> technique with reachability analysis. This method reduces the constraint of design conditions and improves the accuracy of the estimation. However, it needs additional computation. The second one employs the monotone system theory and has no requirement on computation. Finally, two examples are used to compare the two methods.

Zonotopic state bounding for 2-D systems with dynamic event-triggered mechanism

This paper investigates the problem of zonotope-based state estimation for 2-D systems represented by both the Fornasini–Marchesini local state–space (FMLSS) model and the Roesser model with dynamic event-triggered mechanism (ETM) where the exogenous disturbance and measurement noise are assumed to be unknown-but-bounded (UBB). First, considering the different characteristics of these two models, we design different dynamic ETMs for both FMLSS type and Roesser type respectively. A zonotopic set-membership estimation approach is proposed for the considered 2-D system to obtain the estimation interval. Then, three optimal observer design methods are proposed for different scenarios. In addition, the relationship of the proposed criteria is further discussed between the 2-D augmented error FMLSS system and the 2-D augmented error Roesser system considered in this paper. Finally, simulation results are given to illustrate the effectiveness of the proposed methods.

Fractional-Order Sliding-Mode Observers for the Estimation of State-of-Charge and State-of-Health of Lithium Batteries

Lithium batteries are widely used in power storage and new energy vehicles due to their high energy density and long cycle life. The accurate and real-time estimation for the state-of-charge (SoC) and the state-of-health (SoH) of lithium batteries is of great significance to improve battery life, reliability, and utilization efficiency. In this paper, three cascaded fractional-order sliding-mode observers (FOSMOs) are designed for the estimation of SoC by observing the terminal voltage, the polarization voltage, and the open-circuit voltage of a lithium cell, respectively. Furthermore, to calculate the value of the SoH, two FOSMOs are developed to estimate the capacity and internal resistance of the lithium cell. The control signals of the observers are continuous by utilizing fractional-order sliding manifolds without low-pass filters. Compared with the existing sliding-mode observers for SoC and SoH, weaker chattering, faster response, and higher estimation accuracy are obtained in the proposed method. Finally, the experiment tests demonstrate the validity and feasibility of the proposed observer design method.

Design of an event-triggered joint adaptive high-Gain observer for a class of nonlinear system with unknown states and parameters

In this paper, an event-triggered joint adaptive high-gain observer design method is proposed for a class of nonlinear systems that are characterized by an unknown parameter entering the system state equations. The main difficulty in the observer design is that the event-triggered mechanism (ETM) is affected by variable delayed-sampled data and the system’s unknown parameter. To overcome this difficulty, a closed-loop output predictor is incorporated into the design of the event-triggered mechanism to compensate for the sampling and the delay affecting the system outputs. To prevent the Zeno phenomenon, and to guarantee the exponential convergence of the observer, an exponential decay factor is considered in the ETM. The effectiveness of our proposed observer is demonstrated through numerical simulations, experiments and performances comparison with previous works in the literature.