Observer-based Control Scheme Research Articles

Extended state observer-based model predictive temperature control of mechanically pumped two-phase loop: An experimental study

Mechanically pumped two-phase loop (MPTL), as an emerging two-phase heat dissipation transformational technique, has made booming progress in some critical but tough cases such as space stations and high-performance chips. However, accurate temperature regulation of MPTL is intractable due to periodic heat load disturbance, measurement noise, and micro-channel boiling nonlinearity. To address these issues, an extended state observer-based model predictive control (ESOMPC) strategy is developed in this paper. To describe the process model, this paper builds an MPTL platform equipped with a micro-channel evaporator, based on which a series of sinusoidal heat load variation is carried out to show the effects on the wall temperature. Open-loop step experiments are then conducted in terms of flow rate of the working fluid so that the process model can be identified and the nonlinearity can be analyzed. Then, the ESOMPC is developed by incorporating the disturbance information in the optimization framework of the MPC. The ESO part is utilized to estimate the unknown disturbances and compensate the nonlinearity of MPTL, and thus enhance the disturbance mitigation property of the MPC algorithm. Finally, the closed-loop experiments verifies the efficacy of the proposed solution, showing smaller temperature fluctuation and shorter settling time than the conventional controller. The results indicate the great potential of the proposed ESOMPC in enhancing the temperature control accuracy of MPTL in terms of thermal management performance.

Observer-Based Backstepping Adaptive Force Control of Electro-Mechanical Actuator with Improved LuGre Friction Model

A dynamic load simulator, which can reproduce on-ground aerodynamic hinge moment of control surface, is an essential rig for the performance and stability test of an aircraft actuation system. In this paper, an observer-based backstepping adaptive control (OBAC) strategy with an improved friction model is proposed to deal with the force tracking problem of an electro-mechanical actuator under the influence of nonlinear friction and lumped disturbances. First, The LuGre friction model is improved by introducing the load effect of electrical linear load simulator (ELLS), and both dynamic and static parameters are identified with experimental data. Then, the ELLS system is divided into a loading subsystem and actuation subsystem for backstepping controller deign. The estimation of the position disturbance is obtained using an extended state observer and used for feedforward compensation for the loading subsystem. To reject the disturbance of friction parameter uncertainties for actuation subsystem, a friction scale factor with a reasonable adaptive updating law is introduced during the friction compensation process. Finally, the stability of the whole closed-loop system is demonstrated using a Lyapunov-based method, and experiments are performed to validate the effectiveness of the developed algorithm.

A novel learning observer-based fault-tolerant attitude control for rigid spacecraft

This paper investigates a learning observer-based fault-tolerant control strategy for a rigid spacecraft attitude system with external disturbance, parameter uncertainty and actuator faults. An adaptive learning observer design approach, which does not require the upper bound information of generalized perturbation, is proposed to estimate the attitude angular velocities and reconstruct actuator faults accurately and quickly. On this basis, a fault tolerant attitude tracking control scheme is developed for spacecraft attitude stabilization by combining the estimation value and backstepping control technique. The stability of the faulty attitude system under the designed fault-tolerant control method is analyzed using Lyapunov framework. Finally, simulations are given to show the effectiveness of the proposed method.

Secure Sampled-Data Observer-Based Control for Wind Turbine Oscillation Under Cyber Attacks

Inspired by the recent surge of interest in security analysis of renewable energies, this article proposes a cyber resilient control framework for large-scale wind parks (WPs) against denial of service (DoS) and deception attacks. A detailed cyber-physical model for a doubly-fed induction generator (DFIG)-based WP is first developed. It is shown that the WP is subject to a stability issue known as the sub-synchronous interaction (SSI). Additionally, two cyber threats in the forms of DoS and deception attack attempt to destabilize the WP from the subsynchronous perspective. To stabilize the WP under the SSI phenomenon and these cyber attacks, an observer-based fuzzy control scheme is proposed which requires only periodic samples of the output. Using a looped-Lyapunov functional (LLF) method for stability analysis, the control and observer gains are computed from the solution of some linear matrix inequality (LMI) conditions. The proposed design framework allows including the desired level of cyber resilience to DoS and deception attacks for computing proper control and observer gains. The effectiveness of the proposed controller against the considered threats is demonstrated via electromagnetic transient (EMT) simulations performed using the EMTP-RV software and a co-simulation platform.

Observer-based synchronisation control for discrete-time delayed switched complex networks with coding–decoding approach

ABSTRACT In this paper, we investigate the synchronisation control problem for a class of discrete-time switched complex networks with time-varying delays via a coding–decoding-based approach. An observer-based control scheme is proposed for each node by utilising the outputs of complex networks. The data are transmitted in a digital manner and only the sequence of finite coded signals is sent from the observer to the controller. We design a proper coding–decoding procedure for each node to ensure that the closed-loop networks achieve the expected synchronisation performance. By applying the average dwell-time switching strategy and a uniform quantisation approach, some criteria are firstly presented to ensure the detectability of the complex networks. Then sufficient conditions are provided for the existence of desired observer-based controller, guaranteeing the synchronisation of complex networks. Finally, a numerical example is given to illustrate the effectiveness of the obtained theoretical results.

Observer-Based Event-Triggered Boundary Control of a Class of Reaction–Diffusion PDEs

This article presents an observer-based event-triggered boundary control strategy for a class of reaction–diffusion partial differential equations with Robin actuation. The observer only requires boundary measurements. The control approach consists of a backstepping output feedback boundary controller, derived using estimated states, and a dynamic triggering condition, which determines the time instants at which the control input needs to be updated. It is shown that under the proposed observer-based event-triggered boundary control approach, there is a minimal dwell time between two triggering instants independent of initial conditions. Furthermore, the well-posedness and the global exponential convergence of the closed-loop system to the equilibrium point are established. A simulation example is provided to validate the theoretical developments.

Disturbance observer-based nonlinear feedback control for position tracking of electro-hydraulic systems in a finite time

In this paper, a disturbance observer-based backstepping tracking control is designed for an electro-hydraulic actuator (EHA) system to estimate and track reference signals in a finite time. It is assumed that the system is uncertain with unknown upper bounds. Different from the existing ones, the proposed observer can deal with strong uncertainties in which the estimation error converges to an arbitrarily small neighborhood of zero in a finite time. Then, the disturbance observer-based backstepping tracking control is provided to compensate the uncertainties and estimation errors and to guarantee the finite-time tracking of the piston position toward the desired time-varying reference signal. The key idea is to employ a monotonically increasing function associated with the control objective to improve the control performance, where the finite-time boundedness criterion is guaranteed using Lyapunov stability analysis. Finally, the efficacy of the proposed robust scheme for the EHA system with unknown measurement noise is illustrated in numerical simulations as compared to a leading observer-based control strategy in the literature. It is shown that the proposed approach results in more accuracy and faster convergence than that in the literature, making it a qualified alternative approach with noteworthy potential.

Nonlinear disturbance observer-based adaptive nonlinear model predictive control design for a class of nonlinear MIMO system

Model predictive control with less prior knowledge of system uncertainty and external disturbance is a long-standing theoretical and practical problem. In this paper, a solution is presented by proposing a disturbance observer-based adaptive nonlinear model predictive control scheme for a class of nonlinear MIMO systems. Our scheme requires the state and parameterdependent state-space model to linearise the nonlinear system along the prediction horizon. To cope with the unknown system uncertainty, the multiple estimation model and the concept of second-level adaptation [Pandey, V. K., Kar, I., & Mahanta, C. (2014). Multiple models and second level adaptation for a class of nonlinear systems with nonlinear parameterisation. In Industrial and Information Systems (ICIIS), 2014 9th International Conference on (pp. 1–6). IEEE.] technique for the nonlinear system is used. To ensure the boundedness of the estimated parameter, a projection-based adaptive law [Hovakimyan, N., & Cao, C. (2010). L1 adaptive control theory: Guaranteed robustness with fast adaptation. SIAM.] is used. Using a twin-rotor MIMO system (TRMS), the effectiveness of the proposed control algorithm has been verified. Simulation and real-time results show that the proposed control algorithm performs better than the existing control algorithm in the presence of unknown external disturbance and parameter uncertainties.

Luenberger Observer-Based Microgrid Control Strategy for Mixed Load Conditions

In this paper, a Luenberger observer-based microgrid control strategy is proposed to enhance the power quality of microgrids, when the grid loads are mixed and strongly non-linear. To improve performance under this condition, a Luenberger observer is designed for three phase power grids. On the basis of the observer, the components of different frequencies and sequences of voltages and currents are obtained accurately. The virtual impedance of different frequencies and sequences is designed, which makes the equivalent line impedance meet the power-sharing condition, reducing the fundamental negative sequence voltages and harmonic voltages. The active power droop equation, meanwhile, is proposed, where the bus voltage is modified. The value range of virtual impedance is discussed in the complex frequency domain. The proposed control strategy does not require any communication lines, so the hardware structure is simplified. The simulations and experiments are provided to verify the effectiveness of the proposed method.

Event-triggered controller design for LTI systems: A distributed interval observer-based approach

This paper investigates the distributed event-triggered control design problem for networked linear time-invariant (LTI) systems with partially measurable states, in the presence of bounded external disturbances. A distributed interval observer-based event-triggered control scheme has been proposed, the main features of this scheme lie in a) designing a novel distributed interval observer to deal with the unknown states and bound disturbances problem; b) proposing a distributed feedback control method using interval estimation information, the partially measurable limitation has been solved; c) introducing a decreased time-varying function with dead-zone modification to avoid the Zeno behavior. Moreover, sufficient conditions for the stability of closed-loop systems are given in the Lyapunov sense by using matrix inequalities and transmission strategy. Finally, the uniformly ultimately bounded stability and Zeno behavior avoidance of the proposed approach have been numerically demonstrated.

Disturbance Observer-Based Tracking Controller for Uncertain Marine Surface Vessel

In this study, a novel control framework is proposed to improve the tracking performance of uncertain marine vessels which work in enhanced sea states. The proposed control strategy is based on incorporating a fixed-time nonlinear disturbance observer (FTNDO) in a fixed-time convergent backstepping control. More specifically, the FTNDO is developed to reconstruct the total uncertainties due to the system uncertainty and unknown time-varying exterior disturbances. In comparison with the existing disturbance observers, the FTNDO guarantees that the estimation errors will converge to the origin within a predefined time even if the initial estimation errors tend toward infinity. This feature is quite important in the closed-loop system stability analysis as the separation principle does not hold in nonlinear systems. Besides, it does not require the restricting assumption that the upper bound of the lumped uncertainty or its time derivative has to be bounded or known. A backstepping control with a compensation control part is then designed to make the tracking errors converge to the origin within a finite time regardless of initial tracking errors. The compensation control is developed by means of the estimated signal and applied to totally reject the total uncertainty. The global fixed-time stabilization of the closed-loop system is investigated through the Lyapunov stability criterion. Numerical simulation results conducted on an uncertain marine surface vessel confirm the superior control performance and efficiency of the planned method in comparison with the existing disturbance observer-based tracking control strategies.

Sliding Mode Observer-Based Finite Time Control Scheme for Frequency Regulation and Economic Dispatch in Power Grids

In this brief, a novel sliding mode (SM) observer-based scheme is proposed to achieve frequency regulation and economic dispatch (ED) in power grids composed of interconnection of generators and load buses. The ED problem is addressed in two steps. Assuming only the voltage phase angles are measured, in the first step a network of heterogeneous SM observers, suitably interconnected in a distributed fashion, is created to estimate both frequency deviations and unknown power levels associated with each bus. In the second step, the observer scheme is coupled with an SM control strategy which is able to reach the optimal value of the control input in each generator bus in finite time. The scheme is assessed via the IEEE 39 bus benchmark, and a comparison with existing control methods is provided.

Observer-Based PID Control Strategy for the Stabilization of Delayed High Order Systems with up to Three Unstable Poles

In this paper, a new method to manage the stabilization and control problems of n-dimensional linear systems plus dead time, which includes one, two, or three unstable poles, is proposed. The control methodology proposed in this work is an Observer-based Proportional-Integral-Derivative (PID) strategy, where an observer and a PID controller are used to relocate the original unstable open-loop poles to stabilize the resultant closed-loop system. The observer provides an adequate estimation of the delayed-free variables and the PID uses the delay-free variables estimated by the proposed observer. Also, step-tracking is achieved in the overall control scheme. Necessary and sufficient conditions are presented to ensure closed-loop stability based on the open loop parameters of the system. The observer-based PID strategy considers five to seven constant parameters to obtain a stable closed-loop system. A general procedure to implement the proposed control strategy is presented and its performance is evaluated by means of numerical simulations.

Disturbance observer-based robust coordination control for unmanned autonomous helicopter slung-load system via coupling analysis method

This work studies the robust coordination control for a strong coupled and under-actuated unmanned autonomous helicopter (UAH) slung-load system subject to external disturbances. Firstly, disturbance observers are designed to obtain the disturbance estimations, and a dynamic coupling matrix is introduced to describe the coupling relationships between the UAH system and the slung-load system. Secondly, based on the proposed coupling matrix, a disturbance observer-based coordination control scheme is designed for the position system of the UAH and the slung-load one by using hierarchical sliding mode control. Thirdly, an improved controller is designed for the attitude system of the UAH by combining the backstepping control, disturbance observer, and dynamic surface control, in which the detrimental coupling is suppressed while the beneficial one is retained to improve control performance. Especially, the stability for the overall closed-loop system is guaranteed based on Lyapunov stability theory. Finally, some simulations are presented to show the effectiveness and advantage of the proposed control scheme.

Fault-tolerant trajectory tracking control for unmanned surface vehicle with actuator faults based on a fast fixed-time system

In this paper, an observer-based fixed-time tracking control strategy is presented for unmanned surface vehicles (USVs) with model uncertainties, external disturbances, and actuator faults. Firstly, as the theory foundation, a fast fixed-time stable system that has a shorter settling time than the existing systems is proposed. According to this system and the motion characteristics of an USV, a fast fixed-time disturbance observer is developed to obtain the unknown effects caused by lumped uncertainties. By combining the estimated knowledge and a nonsingular fast fixed-time terminal sliding surface, a robust fast fixed-time trajectory tracking controller is designed for the USV. According to Lyapunov stability theory, the fast fixed-time convergence of the proposed controller is proved. Finally, the simulation results demonstrate the effectiveness of the developed control scheme.

Takeoff and Landing Control of a Hybrid Aerial Underwater Vehicle on Disturbed Water’s Surface

This article proposes a disturbance observer-based nonlinear control strategy for the accurate takeoff and landing control of a novel hybrid aerial underwater vehicle, Nezha III, subjected to wave and wind. The approach consists of the dynamic surface controller (DSC) and the nonlinear disturbance observers (NDOs). The problem is first modeled with full consideration of diverse external forces, including the capsizing buoyant moment, the added mass effect, and wave and wind loads. The DSC forms the base of the controller and benefits the tracking behavior by handling the nonlinearity of the system. Meanwhile, the integrated NDOs enhance the robustness of the closed-loop system by estimating the unmeasurable external forces. The proposed method is proved theoretically to stabilize the vehicle when it tracks the reference trajectory across different media in the presence of environmental disturbances. Finally, the proposed controller is tested numerically by challenging it under the wind and wave disturbances. The results show the controller makes Nezha III achieve successful takeoff and landing on the disturbed water’s surface in spite of the hazardous environment, which strongly evidence the outstanding performance of the proposed method.

A Novel Interaction Controller Design for Robotic Manipulators With Arbitrary Convergence Time

In this brief, robot-environment interaction control problem of n-link robotic manipulator system without force sensors is investigated. At first, a novel sliding mode (SM) based two-layer adaptive force observer is proposed to estimate the robot-environment interaction force. In comparison with the most existing force observers, the proposed force observer ensures arbitrary-time convergence of the observer errors and relaxes assumptions on the external force. Moreover, an admittance controller is developed to ensure exact trajectory tracking within arbitrary time. It is mathematically proved that both trajectory tracking errors and force estimation errors will converge to zero at any setting time. Finally, numerical simulations and comparisons show that the proposed force observer-based control scheme can provide superior interaction performance.

Observer-based adaptive fuzzy finite-time tracking control of switched nonlinear systems

In this article, we investigate the finite-time output feedback control issue for switched nonlinear systems. In the design procedure, fuzzy logic systems are used for identifying the unknown functions in switched nonlinear systems. A common state observer is constructed such that the unmeasured states can be measured. Based on the framework of the backstepping algorithm, an observer-based finite-time adaptive tracking control strategy is proposed via the common Lyapunov function approach. The stability analysis process confirms in detail that all the closed-loop signals are bounded under arbitrary switchings and the tracking error can converge to a small neighbourhood of the origin after a finite period of time. In order to verify the feasibility of the proposed control scheme, a numerical simulation example is shown in this paper.

Observer-based robust gain-scheduled control for semi-active air suspension systems subject to uncertainties and external disturbance

In this paper, an observer-based robust gain-scheduled control scheme is designed for a semi-active air suspension (SAAS) system subject to uncertainties and external disturbance. Since the air spring in SAAS system is a highly nonlinear component and its stiffness relies on the spring interior pressure and displacement, an air spring model is constructed based on aerothermodynamics theory. Aiming at comprehensive and simplified expression of air spring nonlinear dynamics, the air spring model is expressed as linear-parameter-varying (LPV) form and further integrated into a quarter car semi-active air suspension model. To identify system states under the noisy condition with lower cost, a LPV-Kalman filter is proposed to estimate the states which are difficult to be measured or physically unmeasurable in the semi-active air suspension. With the proposed observer, a robust gain-scheduled controller is developed to overcome complex nonlinear dynamics, actuator uncertainties and external disturbance. To realize a better transient response, the control law is improved by constraining eigenvalues of the closed-loop system in desired linear matrix inequality (LMI) region. At last, simulations and experiments are conducted to illustrate the effectiveness of proposed control scheme in a quarter car test rig.

Observer-based quantized control for discrete-time switched systems with infinitely distributed delay

This paper studies the globally almost surely exponential stabilization of discrete-time switched systems (DSSs) with infinitely distributed delay. On account of the limitation of communication resources in the actual environment, a novel class of observer-based quantized control scheme is designed that incorporates the quantization of three kinds of signals: the measurement output, the state of observer, and the measurement output of observer. By employing S-procedure and some matrix inequality techniques, an algorithm is given to design the controller parameters. To reduce the conservativeness of the obtained results, new multiple Lyapunov–Krasovskii functionals (LKFs) with negative terms are proposed to deal with the infinitely distributed delay and mode-dependent average dwell time (MDADT) switching based on transition probability (TP) is introduced to study the stabilization of DSSs with both stable and unstable modes. It is worth highlighting that the improved stabilization conditions for DSSs can release the restriction on the length of dwell time (DT) of stable and unstable subsystems. Finally, a simulation example is presented to demonstrate the validity of the proposed method.