Observer-based Control Scheme Research Articles

Observer-based control for networked Takagi-Sugeno fuzzy systems with stochastic packet losses

This paper addressed the observer-based control problem for Takagi-Sugeno (T-S) fuzzy systems with stochastic packet losses. More specifically, an sampled-data (SD) control technique is introduced to reduce the burden of the limited bandwidth of the network, a general consecutive packet loss model is used to represent the stochastic packet loss behavior between sensor-to-controller and controller-to-actuator, and an observer scheme based on received SD output information is used to obtain the estimated system states. Based on the above scenarios, an exact discrete-time model approach is developed for stabilizing networked T-S fuzzy systems. First, the considered system with the observer-based control scheme is transformed into its discrete-time model such that subsequent analysis will be carried out in the discrete-time domain. On this basis, stability criteria are derived by fully considering the probability distribution of consecutive packet losses. Furthermore, an observer-based controller is designed by introducing some auxiliary matrices. Finally, the correctness and practicability of the designed controller is demonstrated by a mass-spring-damper system.

The Fixed-Time Observer-Based Adaptive Tracking Control for Aerial Flexible-Joint Robot with Input Saturation and Output Constraint

The aerial flexible-joint robot (AFJR) manipulation system has been widely used in recent years. To handle uncertainty, the input saturation and the output constraint existing in the system, a fixed-time observer-based adaptive control scheme (FTOAC) is proposed. First, to estimate the input saturation and disturbances from the internal force between the robot and the flight platform, a fixed-time observer is designed. Second, a tangent-barrier Lyapunov function is introduced to implement the output constraint. Third, adaptive neural networks are introduced for the online identification of nonlinear unknown dynamics in the system. In addition, a fixed-time compensator is designed in this paper to eliminate the adverse effects caused by filtering errors. The stability analysis shows that all the signals of the closed-loop system are bounded, and the system satisfies the condition of fixed-time convergence. Finally, the simulation results prove the superiority of the proposed control strategy by comparing it with the previous schemes.

Observer-Based Single-Sensor Control Schemes for LCL-Filtered Grid-Following Inverters

In the single-sensor grid-following control of <i>LCL</i>-type grid-connected inverters, extended-observers, which behave as &#x201C;virtual sensors,&#x201D; are typically employed for active damping, disturbance rejection, current tracking, and grid synchronization. However, most of the existing observer-based single-sensor control schemes choose grid current as the system measurement and output, and the performance of other combinations is still unclear. Hence, in this article, with the help of impedance modeling and Nyquist stability criterion, a systematic comparative assessment for selecting different measurements and controlled outputs is introduced. In this comparison, the sub- and super-synchronous oscillation issues induced by grid faults, lower current reference, high phase-locked loop (PLL) bandwidth and large grid inductance, are investigated. In addition, two easily overlooked interval stability corollaries are proved, facilitating the system stability analysis. Finally, the correctness of the theoretical analysis is verified by a series of steady-state and transient experimental tests.

Design of Observer-Based Discrete-Type PID Control for Reconstructed Jump Model of Interconnected Power System Under Hybrid Attacks

In this article, observed-based discrete proportion-integration-differentiation (PID) control for multi-area interconnected power systems is addressed under hybrid attacks. Firstly, a reconstructed jump model for interconnected power systems is proposed by taking the circumstance of data packet loss into consideration, which caused by the stochastic transmission delay of sampled data. Then, different from the traditional continuous-type PID control, an observer-based discrete-type PID control strategy is designed for discrete-time power system. Besides, due to the sampled data may be tampered or shield in open communication networks, the hybrid attacks, i.e., deception attacks and denial-of-service attacks, with random manners are considered. Furthermore, an input-to-state stable criterion is derived by constructing appropriate Lyapunov-Krasovskii functionals. Finally, the discrete-type PID controllers and observer are achieved, and the validity of proposed approach are also demonstrated in the illustrative examples section.

Disturbance observer-based fuzzy adaptive optimal finite-time control for nonlinear systems

This paper investigates the issue of disturbance observer-based fuzzy adaptive optimal finite-time control in light of the backstepping approach for strict-feedback nonlinear systems with bias fault term and full state constraints. Considering that external disturbance and bias fault signal can affect the stability of control and control quality, a disturbance observer is constructed to track the external disturbances and bias fault online. A disturbance observer-based finite-time control strategy is proposed to achieve optimized control by utilizing the fuzzy logic system approximation-based adaptive dynamic programming method under the critic-actor framework. The purpose of the critic is to evaluate control performance and the role of the actor is to execute control behaviour. In addition, it is proved that the proposed fuzzy adaptive optimal finite-time scheme not only realizes all signals in closed-loop system are bounded, but also ensures that system states are restricted within specific sets. Finally, simulation results are shown to demonstrate the effectiveness of the proposed control strategy.

Prescribed-time extended state observer and prescribed performance control of quadrotor UAVs against actuator faults

The detection and accommodation of actuator faults in control systems have received considerable attention. However, the existing fault-tolerant control techniques typically require complex and computationally intensive algorithms, and the settling time cannot be pre-assigned offline, which limits the practical applicability of these techniques. To address these problems, this paper proposes a prescribed-time fault-tolerant tracking control scheme for accommodating actuator failures in quadrotor unmanned aerial vehicles. First, a prescribed-time nominal controller is developed to precisely track the desired position in the absence of actuator faults. Subsequently, an extended state observer is developed to precisely estimate the uncertainties derived from actuator failures. Using the estimated values, a prescribed-time tracking control scheme is designed for the position subsystem, based on the prescribed performance control technique. In addition to having a simple structure, the proposed controller relaxes the limits that both the settling time and desired transient- and steady-state performances cannot be pre-assigned. Similarly, an observer-based prescribed-time tracking control scheme is established for the attitude subsystem under actuator failures. Numerical simulations are performed to validate the effectiveness and robustness of the proposed control method.

선형 파라미터 변형 시스템에 대한 이벤트-트리거 외란 관측기 기반 강인 제어

In this paper, an event-triggered disturbance observer-based robust control strategy is proposed for linear parameter-varying systems. In the proposed control strategy, the disturbance observer estimates the plant’s states and external disturbances, and the robust tracking controller uses the estimated values to compensate for the external disturbance. The scenario of the transmission of the estimated values from the disturbance observer through shared networks was considered. An event-triggered observer scheme was proposed to reduce communication resources while ensuring the stability of the closed-loop system. A stability analysis was performed by considering external disturbances. The simulation results demonstrated that the output follows the desired value, compensating for external disturbances.

Radio Frequency Cavity’s Analytical Model and Control Design

Reduction or suppression of microphonic interference in radio frequency (RF) cavities, such as those used in Electron Linear Accelerators, is necessary to precisely control accelerating fields. In this paper, we investigate modeling the cavity as a cylindrical shell and present its free vibration analysis along with an appropriate control scheme to suppress vibrations. To this end, we first obtain an analytical mechanical dynamic model of a nine-cell cavity using a modified Fourier-Ritz method that provides a unified solution for cylindrical shell systems with general boundary conditions. The model is then verified using the ANSYS software in terms of a comparison of eigenfrequencies which prove to be identical to the proposed model. We also present an active observer-based vibration control scheme to suppress the dominant mechanical modes of the cavity. The control system performance is investigated using simulations.

Active control for system with multiple microchannel heat exchangers using disturbance observer

To prevent flow maldistribution and imbalanced temperature, a disturbance observer-based control strategy is presented for microchannel cooling systems with multiple heat exchangers. A disturbance observer is designed using the extended Kalman filter for estimating the states and disturbance. The performance of the observer is validated using experimental data from a pumped liquid cycle testbed. Disturbance observer-based control is applied to systems with two and three heat exchangers. The findings demonstrate that the wall temperatures and the temperature differences for the heat exchangers could be maintained at the desired values. When the heat exchangers are subjected to heat loads in the form of square, sinusoidal, and sawtooth functions, the temperature fluctuation could be suppressed by 60%-80% and the temperatures could be maintained at the same values. Our research demonstrates that the proposed control strategy has acceptable accuracy and robustness for the system with multiple heat exchangers undergoing various operating situations.

Observer-Based Path Tracking Controller Design for Autonomous Ground Vehicles With Input Saturation

This paper investigates the problem of path tracking control for autonomous ground vehicles (AGVs), where the input saturation, system nonlinearities and uncertainties are considered. Firstly, the nonlinear path tracking system is formulated as a linear parameter varying (LPV) model where the variation of vehicle velocity is taken into account. Secondly, considering the noise effects on the measurement of lateral offset and heading angle, an observer-based control strategy is proposed, and by analyzing the frequency domain characteristics of the derivative of desired heading angle, a finite frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$H_{\infty}$</tex> index is proposed to attenuate the effects of the derivative of desired heading angle on path tracking error. Thirdly, sufficient conditions are derived to guarantee robust <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$H_{\infty}$</tex> performance of the path tracking system, and the calculation of observer and controller gains is converted into solving a convex optimization problem. Finally, simulation examples verify the advantages of the control method proposed in this paper.

ESO-based adaptive event-triggered load following control design for a pressurized water reactor with samarium–promethium dynamics

Conventional control systems used in nuclear reactors rely on real-time information transmission between the controllers and the actuators, which is unnecessary and imposes a heavy communication burden. To this end, this paper proposes an extended state observer-based adaptive event-triggered control (ESO-AETC) scheme for the load following problem of a pressurized water reactor (PWR) in the presence of uncertainties and limited communication resources. Different from most of the previous controllers presented in the literature, the samarium–promethium dynamics are considered in the constructed PWR model in this paper. Based on the PWR model with the load-dependent parameters and the samarium–promethium dynamics, an ESO, which can estimate lumped uncertainties and unmeasured system states including the relative density of the delayed neutron precursor, the average fuel temperature, the xenon concentration, the iodine concentration, the samarium concentration, the promethium concentration, and the total reactivity, is designed. With the help of the ESO and the event-triggered techniques, an AETC scheme is developed to avoid the real-time communication in the controller-to-actuator channel of the PWR system. It is rigorously proved that the control error can converge to any prescribed residual set in a finite time according to Lyapunov stability theory, excluding the Zeno behavior. Finally, simulation studies involving comparisons with existing works, estimation performance verification, and sensitivity analysis are conducted to assess the proposed ESO-AETC scheme. Simulation results reveal that (1) relative to the pre-existing model-free controller (MFC) and the disturbance observer-based sliding mode controller (DO-SMC), the proposed ESO-AETC scheme is found to provide better load following performance with at least 56.12% lower maximum absolute error (MAE), at least 15.05% lower integral absolute error (IAE), and 87.58% reduced communication resources in the controller-to-actuator channel, (2) the ESO possesses strong estimation capability for system states and lumped uncertainties, and (3) the proposed ESO-AETC scheme yields a low sensitivity with respect to the change of the controller parameters.

Security control scheme for cyber-physical system with a complex network in physical layer against false data injection attacks

In this paper, based on finite-frequency domain H∞ control techniques, security control issues are investigated for a cyber-physical system (CPS) suffering from false data injection (FDI) attacks on sensors and actuators, where the real system in the physical layer is a complex network system. First, for each subsystem of the complex network system, an H∞ proportion integral (PI) observer is designed to estimate the system states and attack signals on the sensors and actuators simultaneously. Second, a state feedback controller with attack compensation is proposed using the estimates of the attack signals and the states. Thus, an observer-based security control strategy against FDI attack is set up and the stability analysis is accomplished by frequency domain H∞ control techniques. Finally, a simulation example is given to illustrate the better performance of the proposed methods compared with the traditional H∞ method.

Adaptive Control of Grid-Connected Inverters With Nonlinear LC Filters

Distributed generation is an effective solution to clean, reliable, and cost-efficient energy supply. In this framework, inverters play a key role as energy converters. Accordingly, this article investigates the utilization of nonlinear inductive–capacitive (LC) filters for grid-connected inverters. Nonlinear LC filters are made of inductors with nonlinear B–H curves, which makes them have a smaller volume, less dissipation loss, and lower cost. The main drawback of using these filters, however, is their nonlinear current-dependent characteristics. To harness the undesirable impacts of nonlinear filters on the system performance, an adaptive observer-based control scheme is developed in this article. The proposed controller is based on a concurrent estimation of nonlinear inductor values, capacitor voltages, and grid-side currents. Based on its fast adaptation to plant changes, this scheme provides an improved stability margin and an inherent resonant damping characteristic under grid impedance uncertainty. Compared with the conventional approaches, this method requires no extra sensors. A comparative simulation and experimental analysis, based on a three-phase 7-kW inverter, is provided to validate the efficacy of the proposed control strategy.

Capability Exploration of Extended-State Observer-Based Control Under the Uncertain Case of Disturbance and Actuator Saturation

Considering a class of nonlinear systems subject to actuator saturation and uncertain control input, this article explored the control capability of an extended-state observer-based active disturbance rejection controller in the presence of disturbances and uncertainties. First, the actuator saturation is handled with the convex hull in the extended-state observer-based control scheme, and an ellipsoid invariant set inside the domain of attraction for control systems is obtained using the Lyapunov method. Second, the enlargement problem of the invariant set is also studied, which illustrates that the convex hull of the ellipsoid invariant sets is also an enlargement invariant set. Finally, comprehensive comparisons with existing methods on a brushless dc motor demonstrate the stronger capability of the designed controller on disturbance rejection and actuator saturation. The results show that the disturbance offset and performance index (integrated time and absolute error and integral absolute error) are about half of the classical proportional–integral–derivative(PID) and double-integral sliding-mode control, or the disturbance rejection capability is about twice in this case.

Leader-Follower Asymptotic Consensus Control of Multiagent Systems: An Observer-Based Disturbance Reconstruction Approach.

In this article, a leader-follower asymptotic consensus control strategy is developed for a class of linear multiagent systems (MASs) with unknown external disturbances and measurement noises. First, the preconditions, the minimum phase condition (MPC) and observer matching condition (OMC), are discussed in detail, and an equivalent result under these two preconditions is given. In this way, the corresponding results from Corless and Tu (1998) are improved. Meanwhile, a reduced-order observer is designed for a constructed augmented system to estimate the system states and noises of each agent. Next, with the help of a traditional interval observer, a novel unknown disturbance reconstruction method is developed, and the reconstruction can converge to the unknown disturbance asymptotically and decouple from the control input. The subsequent asymptotic consensus is accomplished by utilizing an observer-based control scheme, with its design satisfying the so-called separation principle. Finally, two simulation examples are given to verify the effectiveness and show the advantages of the proposed methods.

Observer-Based Event-Triggered Composite Anti-Disturbance Control for Multi-Agent Systems Under Multiple Disturbances and Stochastic FDIAs

This article aims to investigate the security consensus and composite anti-disturbance problems for a class of nonlinear multi-agent systems subjected to stochastic false data injection attacks (FDIAs) and multiple disturbances under a directed communication topology. To attenuate and reject of the negative effects of two types of disturbances, a disturbance observer (DO) is designed to counteract the disturbance produced by exogenous system, and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {H}_\infty $ </tex-math></inline-formula> control method is adopted to attenuate the bounded errors and variables caused by the other type of disturbances and FDIAs simultaneously. To ensure the consensus performance of MASs, an observer-based control strategy is designed, and a novel adaptive compensation technique is proposed to not only evaluate the upper bounds of the unknown but bounded disturbances but also improve the accuracy of the state observer. Furthermore, a novel event-triggered mechanism (ETM) without requiring continuous communication among neighboring agents is developed to reduce the controller update frequency and the communication burden. Meanwhile, Zeno behavior is excluded. Finally, numerical simulations are provided to verify the availability of the designed method. Note to Practitioners—In multi-agent systems, network security is very important. For example, in smart power grid systems, it is necessary to use the method of state estimation to observe the system to guarantee its safe operation. However, the measured value of the instrument may be affected by FDIAs in the transmission process, thus changing the result of state estimation and causing misjudgment of the system. Similarly, in multi-vehicle systems, FDIAs may destroy the location information of vehicles and cause serious accidents. In addition, the system will be subjected to different types of disturbances in practice, thus reducing the performance of the system. In view of the threat of FDIAs and disturbances to the MAS, a composite anti-disturbance method and an observer-based control strategy are proposed. Meanwhile, to avoid the limitation of communication bandwidth in reality, a novel ETM is developed to save network resources.

Stability Improvement of Parallel-Connected Inverters Under Very Weak Distorted Grid Using Observer-Based Incremental Control Scheme

Stability Improvement of Parallel-Connected Inverters Under Very Weak Distorted Grid Using Observer-Based Incremental Control Scheme

Observer-based Periodic Event-triggered Boundary Control of the One-phase Stefan Problem

The Stefan problem models the phenomenon of phase transition between a liquid and a solid as the time evolution of the temperature profile of a liquid-solid material and its moving interface. This paper provides a novel observer-based periodic event-triggered boundary control (PETBC) strategy for the one-phase Stefan problem using the position and velocity measurements of the moving interface. We propose a method to convert a specific class of continuous-time dynamic event-triggers that require continuous monitoring to periodic event-triggers that only require periodic evaluation. We achieve this result by finding an upper bound on the underlying continuous-time event-trigger between two successive periodic evaluations. We provide an explicit criterion for choosing a sampling period for periodically evaluating the event-trigger. The control input is updated only at events indicated by the periodic event-trigger and is applied in a zero-order hold fashion between two events. We establish the closed-loop system well-posedness along with certain model validity conditions under the proposed PETBC. Further, we prove that the exponential convergence to the setpoint under continuous-time event-triggered boundary control (CETBC) is preserved under the proposed PETBC. We provide simulation results to validate the theoretical developments.

Observer-Based Asynchronous Communication and Adaptive Control Protocols With Intermittent Updating and Interaction

This paper focuses on the distributed observer-based synchronization control of multi-agent systems (MASs) over wireless networks. Unlike existing works mostly focusing on the communication reduction of control sides, a perception-based data reduction and transmission approach is proposed to design an asynchronous communication and control mechanism, which can avoid continuous inter-agents communications for both the communication as well as control sides. Then, an observer-based asynchronously distributed controller with intermittent updating and interaction based on the proposed perception-based data-reduction communication scheme. The criteria of new data transmission of communication triggering strategy and control triggering strategy are developed, respectively. Moreover, it is further extended to develop an observer-based asynchronous projection-type adaptive control strategy for online self-tuning of parameters. Theoretical analysis shows that the proposed two asynchronous communication and control strategies not only ensure that all agents stabilize to their initial average state without requiring any global information, but also ensure the reduction of both communications and controller update frequencies. An example is demonstrated to verify the theoretical analysis.

Adaptive event-triggered fuzzy control for hot strip finishing mill via a disturbance observer-based method

In this paper, a disturbance observer-based adaptive event-triggered control scheme is proposed for hot strip finishing mill against the problem brought by the interstand tension and the looper angle. Firstly, a standard backstepping method is adopted to the design of control scheme with the consideration that the interstand looper possesses particular structure of the dynamic model. Then, via selecting a suitable gain function, the unknown disturbance can be estimated well by the disturbance observer. Meanwhile, it is noted that the looper current control has very fast dynamics when generating the looper torque. Therefore, the actuator torque can be viewed as directly related to the control signal. In addition, since the strip tension fluctuation has an effect on width and thickness, it will be dampened until larger than looper angle fluctuation. Furthermore, unknown nonlinear terms generated by the process of finishing mills can be approximated by linear functions integrated by fuzzy logic systems. The proposed event-triggered control scheme is used to guarantee the Lyapunov stability and performance requirements of the overall system. The effectiveness of the proposed controller is illustrated in simulation results and application.