Extended High Gain Observer Research Articles

A High-Gain Observer Approach to Robust Trajectory Estimation and Tracking for a Multi-Rotor Uav

Abstract Using the context of trajectory estimation and tracking for multi-rotor UAVs, we explore the challenges in applying high-gain observers to highly dynamic systems. The multi- rotor will operate in the presence of external disturbances and modeling errors. At the same time, the reference trajectory is unknown and generated from a reference system with unknown or partially known dynamics. We assume the only measurements that are available are the position and orientation of the multi-rotor and the position of the reference sys- tem. We adopt an extended high-gain observer (EHGO) estimation framework to estimate the unmeasured multi-rotor states, modeling errors, external disturbances, and the reference trajectory. We design a robust output feedback con- troller for trajectory tracking that comprises a feedback linearizing controller and the EHGO. The proposed control method is rigorously analyzed to establish its stability properties. Finally, we illustrate our theoretical results through numerical simulation and experimental validation in which a multi-rotor tracks a moving ground vehicle with an unknown trajectory and dynamics and successfully lands on the vehicle while in motion.

Chaotic Secure Communication by Event-Triggered Extended High-Gain Observers

Chaotic Secure Communication by Event-Triggered Extended High-Gain Observers

Active and Reactive Power Control of the Voltage Source Inverter in an AC Microgrid

This paper presents the mathematical model and control of a voltage source inverter (VSI) connected to an alternating current (AC) microgrid. The VSI considered in this paper is six switches three-phase Pulse Width Modulated (PWM) inverter, whose output active and reactive power is controlled in the dq reference frame. The control strategy presented here is state feedback control with disturbance cancellation. This disturbance signal is either provided by a voltage sensor or estimated using a presented extended high gain observer (EHGO). The control strategy without EHGO requires a current sensor and a voltage sensor, and the control strategy with EHGO requires only a current sensor. The EHGO is saving the requirement of a voltage sensor. The stability analysis of the presented control strategy is showing that the error is ultimately bounded in the presence of disturbance, formed due to Pulse Width Modulated (PWM) inverters. The microgrid is simulated using the SimPowerSystems Toolbox of MATLAB/Simulink. The simulation results are also showing the effectiveness of the proposed control strategy, that the output active and reactive power control is achieved with ultimately bounded errors. The comparison of the proposed control with the PI-based control scheme is also presented, and it is shown that better reference tracking with the desired settling time of “0.04 s” is achieved with the proposed control.

Robust bipartite tracking consensus of multi-agent systems via neural network combined with extended high-gain observer

In this paper, the robust bipartite tracking consensus problem for second-order multi-agent systems has been addressed in the presence of lumped disturbances and unknown velocity information. The leader’s dynamics are modeled by uncertain fractional-order equality based on the neural network (NN), and the followers can only obtain the position information of the leader under the signed networks. A novel robust bipartite tracking consensus control scheme is developed by combining the NN approximators, the continuous sliding mode control (SMC) strategy, and the improved extended high-gain observer (EHGO). The improved EHGO is used to compensate for and estimate each agent’s lumped disturbances and unknown velocity information in the controller design process. Moreover, NN is constructed to approximate the velocity and acceleration of the uncertain leader’s dynamics for generating the feedforward signal of controllers, and the adaptive update laws of estimation parameters are generated online based on the Lyapunov function. Finally, the effectiveness of the proposed control strategy is verified by some numerical simulations.

Adaptive output-feedback robust active disturbance rejection control for uncertain quadrotor with unknown disturbances

PurposeIn this research paper, an adaptive output-feedback robust active disturbance rejection control (RADRC) is designed for the multiple input multiple output (MIMO) quadrotor attitude model subject to unwanted uncertainties and disturbances (UUDs).Design/methodology/approachIn order to achieve the desired control objectives in the presence of UUDs, the low pass filter (LPF) and extended high gain observer (EHGO) methods are used for the estimation of matched and mismatched UUDs, respectively. Furthermore, for solving the chattering incurred in the standard sliding mode control (SMC), a multilayer sliding mode surface is constructed. For formulating the adaptive output-feedback RADRC algorithm, the EHGO, LPF and SMC schemes are combined using the separation principle.FindingsThe findings of this research work include the design of an adaptive output-feedback RADRC with the ability to negate the UUDs as well as estimate the unknown states of the quadrotor attitude model. In addition, the chattering problem is addressed by designing a modified SMC scheme based on the multilayer sliding mode surface obtained by utilizing the estimated state variables. This sliding mode surface is also used to obtain the adaptive criteria for the switching design gain parameters involved in the SMC. Moreover, the requirement of high design gain parameters in the EHGO is solved by combining it with the LPF.Originality/valueDesigning the flight control techniques while assuming that the state variables are available is a common practice. In addition, to obtain robustness, the SMC technique is widely used. However, in practice, the state variables might not be available due to unknown parameters and uncertainties, as well as the chattering due to SMC reduces the performances of the actuators. Hence, in this paper, an adaptive output-feedback RADRC technique is designed to solve the problems of UUDs and chattering.

Fixed-time synchronization of memristor chaotic systems via a new extended high-gain observer

Memristor based chaotic oscillators are often chosen for secure communication owing to their interesting feature. In chaos-based secure communication applications, synchronization is a central issue. Most of synchronization methods proposed in the literature are asymptotic. In practice, it is desirable that synchronization be established in a user predefined time. This paper provides new developments in the design of filtered extended high-gain observer dedicated for prescribed-time synchronization of memristor chaotic systems used in a master-slave based secure communication process subject to channel noise. The proposed prescribed-time extended filtered-high gain observer is constructed on the basis of a time-dependent coordinates transformation based on modulating functions which annihilate the effect of initial conditions on the synchronization time. Simulations performed on a numerical example illustrate the efficiency of the proposed approach.

In-Flight Actuator Failure Recovery of a Hexrotor Via Multiple Models and Extended High-Gain Observers

We study an in-flight actuator failure recovery problem for a hexrotor UAV. The hexrotor may experience external disturbances and modeling error, which are accounted for in the control design and distinguished from an actuator failure. A failure of any one actuator occurs during flight and must be identified quickly and accurately. This is achieved through the use of a multiple-model, multiple extended high-gain observer (EHGO) based output feedback control strategy. The family of EHGOs are responsible for estimating states, disturbances, and are used to select the appropriate model based on the system dynamics after a failure has occurred. The proposed method is theoretically analyzed and validated through simulations and experiments.

Output feedback control design using Extended High-Gain Observers and dynamic inversion with projection for a small scaled helicopter

This paper presents the output feedback control design for a tracking problem of a small-scale helicopter in the presence of uncertainties. The dynamics of the helicopter is an underactuated mechanical system and the form of control inputs is nonaffine. A time-scale approach is suggested to cope with underactuated mechanical systems to overcome lack of the number of inputs. A newly developed dynamic inversion with projection is used to deal with nonaffine control inputs to increase the region of attraction as compared to linearized inputs, i.e., an affine control input form and to deal with actuator’s constraints and peaking in estimates from an Extended High-Gain Observer. The Extended High-Gain Observer is employed to quickly estimate model uncertainties and external disturbances. The singular perturbation method is used to analyze the stability of the closed-loop system in a multi-time scale structure. Based on the stability analysis, the design procedure for the proposed algorithm is presented for practical implementation. The effectiveness of the proposed control algorithm is shown via numerical simulations as well as experimental tests with a small-scale helicopter in an outdoor environment.

Multi-time-scale 3-D coordinated formation control for multi-underactuated AUV with uncertainties: Design and stability analysis using singular perturbation methods

This paper is concerned with a multi-underactuated AUV three-dimensional (3-D) formation control method with a multi-time-scale structure in the presence of uncertain nonlinearities and environmental disturbances. First, a double-layer independent position-velocity fixed topology is adopted to overcome the drawback of narrow bandwidth of underwater communication. Then, an extended high-gain observer (EHGO) is utilized to provide compensation to uncertain nonlinearities and environmental disturbances. Moreover, the consensus theory is incorporated with an integral sliding mode controller to guarantee that the multi-underactuated AUV system can track the desired trajectory while maintaining the predefined formation. In addition, based on the analysis for the whole formation control system, the extended high-gain observer is on the ultra-fast time scale, the integral sliding mode controller is on the fast time scale, and the system state converges to the desired state on the slow time scale. Such multi-time scale structure allows independent analysis of the dynamics in each time scale, and the singular perturbation method is effectively utilized to establish the exponential stability of the equilibrium. Finally, simulation results are presented to illustrate the control performance.

Nonaffine Helicopter Control Design and Implementation Based on a Robust Explicit Nonlinear Model Predictive Control

Control design for a helicopter is a challenging problem because of its nonaffine inputs, its underactuated characteristics, and highly coupled dynamics. To solve a control problem of the helicopter under model uncertainties and disturbance present environments, an explicit nonlinear model predictive control (ENMPC), a dynamic inversion (DI), and an extended high-gain observer (EHGO) are combined in a multi-time-scale fashion. The multi-time-scale scaled structure and the ENMPC provide the framework of the control design, the DI deals with nonaffine control inputs, and the EHGO estimates the unmeasured system states and uncertainties. The proposed control design is discretized to be implemented on a small-scale helicopter. The successful outdoor experiments with the proposed control implemented on autopilot hardware demonstrate the validity of our approach in the presence of model uncertainties and wind disturbances.

Robust active disturbance attenuation control of an uncertain quadrotor

PurposeThe aim of this research is to design a robust active disturbance attenuation control (RADAC) technique combined with an extended high gain observer (EHGO) and low pass filter (LPF).Design/methodology/approachFor designing a RADAC technique, the sliding mode control (SMC) method is used. Since the standard method of SMC exhibits a chattering phenomenon in the controller, a multilayer sliding mode surface is designed for avoiding the chattering. In addition, to attenuate the unwanted uncertainties and disturbances (UUDs), the techniques of EHGO and LPF are deployed. Besides acting as a patch for disturbance attenuation, the EHGO design estimates the state variables. To investigate the stability and effectiveness of the designed control algorithm, the stability analysis followed by the simulation study is presented.FindingsThe major findings include the design of a chattering-free RADAC controller based on the multilayer sliding mode surface. Furthermore, a criterion of integrating the LPF scheme within the EHGO scheme is also developed to attenuate matched and mismatched UUDs.Practical implicationsIn practice, the quadrotor flight is opposed by different kinds of the UUDs. And, the model of the quadrotor is a highly nonlinear underactuated model. Thus, the dynamics of the quadrotor model become more complex and uncertain due to the additional UUDs. Hence, it is necessary to design a robust disturbance attenuation technique with the ability to estimate the state variables and attenuate the UUDs and also achieve the desired control objectives.Originality/valueDesigning control methods to attenuate the disturbances while assuming that the state variables are known is a common practice. However, investigating the uncertain plants with unknown states along with the disturbances is rarely taken in consideration for the control design. Hence, this paper presents a control algorithm to address the issues of the UUDs as well as investigate a criterion to reduce the chattering incurred in the controller due to the standard SMC algorithm.

An Output Feedback Based Robust Saturated Controller Design for Pavement Sweeping Self-Reconfigurable Robot

Mobile robots play a crucial role in cleaning, maintenance, and surveillance applications. This article advocates for the use of a novel robust output feedback based path following controller, for a class of self-reconfigurable mobile robot under actuator saturation. The reconfigurability property of such platforms is captured via an uncertain Euler-Lagrange dynamics. The proposed control framework estimates the unmeasurable states and the uncertain dynamics terms through two extended high gain observers, whereas the actuator limits are honored via a fast dynamic compensator. The closed-loop stability is analyzed via contraction theory, which, compared to the conventional Lyapunov based approaches, avoids the requirement of arbitrarily large controller and observer gains. Such a feature is of particular interest in view of actuator saturation. The experimental results with PANTHERA self-reconfigurable robot validate the effectiveness of the proposed technique over the state of the art.

Continuous PID-SMC based on improved EHGO for robot manipulators with limited state measurements

This paper focuses on the robust output feedback tracking control for n-DOF (degree-of-freedom) robot manipulators with limited state measurements. An improved extended high-gain observer (EHGO) is designed to estimate the unavailable states as well as the system uncertainty and disturbance. A novel control framework combining the improved EHGO and continuous PID-sliding mode controller (PID-SMC) is proposed. The Lyapunov approach is used to prove the effectiveness of the EHGO. Moreover, the stability and convergence of the closed-loop system are confirmed through the singular perturbation theory. Numerical simulation and experimental results are presented to show the performance of the proposed control scheme.

Extended High Gain Observer-Based Sliding Mode Control for an Electro-hydraulic System with a Variant Payload

This paper presents a robust control regarding position control of an electro-hydraulic rotary actuator (EHRA) system under the presence of the lumped uncertainties such as the variant payload, the unknown friction, and the uncertain parameters. The proposed control is developed on a high order sliding mode control (HOSMC) and an extended high gain observer (EHGO). In detail, the HOSMC is derived to not only reduce the chattering effect but also guarantee the stability for the EHRA. In addition, the EHGO is used as a disturbance estimator to compensate the lumped uncertainties. Consequently, it helps to improve control performance. Furthermore, the stability and robustness of the whole system are theoretically proved by a Lyapunov approach. The proposed control is practically implemented through both the co-simulation between AMESIM and MATLAB, and the experiments. The results are compared to other controllers to exhibit the effectiveness of the proposed control with the lumped uncertainties.

Active suspension control by output feedback through extended high-gain observers

The paper addresses extended high-gain observer (EHGO) design for a vehicle suspension system. The different way from previous reports is that a regional input-to-state stabilization (including exponential stabilization) controller is presented. To pursue this aim, first the original suspension dynamical equation is transformed into a normal form. And then, a feedback linearization controller is designed as the state feedback control, which makes the closed-loop system regionally input-to-state stable. Based on this, the output feedback control by using EHGO is proposed. The stability of the singular perturbation system composed by the state closed-loop system and the scaled error equation is demonstrated. Simulation examples are illustrated, which validate that provided small high-gain parameter the output feedback control will recover the performance of RISS under state feedback control and the responses of suspension performance behave better than those under the later.

Distributed formation control for multiple quadrotor UAVs under Markovian switching topologies with partially unknown transition rates

This paper addresses distributed formation control for a group of quadrotor unmanned aerial vehicles (UAVs) under Markovian switching topologies with partially unknown transition rates. Instead of the general stochastic topology, the graph is governed by a set of Markov chains to the edges, which can recover the traditional Markovian switching topologies in line with the practical communication network. Extended high gain observers (EHGOs) are constructed with a two-time-scale format to deal with the issue of nonlinear input coefficients, so that there could be a higher estimation precision of the system uncertainties. To impel multiple quadrotor UAVs to achieve a predesigned formation shape, a modified integral sliding mode (ISM) control protocol is proposed here with a multi-time-scale structure, which allows independent analysis of the dynamics in each time scale. The stability proof for the system state space origin is derived from the singular perturbation method and Lyapunov stability theory. In addition, the introduced ISM controller can deal with the time varying desired references with the bounded accelerations and is robust to the disturbances. Finally, simulations on six quadrotor UAVs are given to verify the effectiveness of the theoretical results.

Hamiltonian Structure-Based Robust Station-Keeping for Unstable Libration Point Orbits

In this work, a controller for spacecraft station-keeping in an unstable libration point orbit was designed based on the Hamiltonian structure of the system. The proposed controller exploits the inherent Hamiltonian structure of the system, and therefore the performance of the controller can be easily adjusted while ensuring the stability of the closed-loop system. A filtered extended high-gain observer was also designed to compensate for the performance degradation of the controller due to external disturbances and model uncertainty. The filtered extended high-gain observer includes an integral state feedback to alleviate navigation error amplification due to the high gain of the observer. The global convergence of the proposed observer was demonstrated, and the tracking error was ultimately bounded to the reference libration point orbit by applying the Hamiltonian structure-based controller. The performance of the proposed controller and observer was demonstrated by numerical simulation of the Earth–Moon system.

Decentralized robust tracking control for 2-degree of freedom planar robot manipulator subject to disturbances and uncertainties

In this study, a novel decentralized exact tracking control approach for 2-degree of freedom (DOF) planar robot manipulators with disturbances and uncertainties has been proposed. The main idea of the proposed method is to partition the whole robot manipulator into single joint and lumped disturbance. A well designed extended high gain observer (EHGO) is adopted to observe the lumped disturbance of each joint, which includes coupling, load disturbance and uncertainty, and so forth. Rather than coping with the robot manipulator as a whole, the proposed method is locally designed to compensate the estimated coupling and stabilize the internal states of a single joint. By doing that, each joint can be virtually decoupled from the whole robot manipulator and functions in a relatively independent way. When joints are interconnected, the stabilization of the whole robot manipulator would be obtained by only guaranteeing the localized stability of individual joint. The theoretical analyses are rigorously conducted by utilizing Lyapunov stability theorem. Simulation results illustrate the effectiveness of the proposed control scheme.

Cooperative Semiglobal Robust Output Regulation of Non-Introspective Nonlinear Agents With Partial Normal Form and State-Dependent High-Frequency Gain

This paper investigates cooperative semig-lobal robust output regulation problem for a class of non-introspective nonlinear multiagent systems. Each agent of this class is allowed to have a partial normal form , instead of only the conventional normal form, with a state-dependent high-frequency gain. Besides, all agents are unaccessible to the controller states of their neighbors. In this setting, if the uniform detectability assumption in the sense of [25] is satisfied, then a robust distributed regulator can be designed with the employment of a distributed nonlinear internal model and a novel distributed extended lower-power high-gain observer, such that the numerical implementation problem is solved and the regulated output of each agent asymptotically converges to the desired reference input robustly with guaranteed domain attraction.

An extended observer-based robust nonlinear speed sensorless controller for a PMSM

ABSTRACTThis work focuses on the problem of observer-based robust speed sensorless control of a 3-phase permanent magnet synchronous motor (PMSM). Nonlinear design techniques are employed for designing robust speed controller and observer that are able to withstand the effects of modelling uncertainties and load variations. A new cascaded observer scheme is proposed comprising a continuous sliding mode observer (SMO) and an extended high-gain observer (EHGO). The proposed cascaded observer reduces chattering, exhibits reasonable insensitivity to modelling inaccuracies and is capable of withstanding errors due to the finite boundary layer of continuous SMO. For the robust speed control, an integral sliding mode controller is designed that yields fast and accurate speed tracking performance even in the presence of bounded uncertainties and external disturbances. The complete scheme has been evaluated using simulations and experiments.