Nonlinear Observer-based Control Research Articles

Output Feedback Passivity-Based Controller for Microalgae Cultivation

Microalgae are microscopic plants existing in aquatic environment. They can be used in the production of high value compounds and they have promising opportunities in energy production, wastewater treatment and fixation of carbon dioxide. In this context, the control of the cultivation requires a special attention in order to obtain high amounts of biomass. The control of microalgae cultivation is approached from passivity-based control perspectives. The proposed controller solves set point tracking and stabilizes the control loop by the passivity properties. Moreover, in order to obtain the process state variables from the measurement output, which are used in the control law, a nonlinear observer with guaranteed stability of estimation error dynamics is proposed. The design of the nonlinear controller and the observer is based on the Droop model, describing the dynamic behaviour of the microalgae process in a practical way. Finally, the performance of the nonlinear observer-based controller is shown by simulation.

Development of Linearizing Feedback Control with a Variable Structure Observer for Continuous Stirred Tank Reactors

This paper deals with the design of an observer-based nonlinear control for continuous stirred tank reactors (CSTR). A variable structure observer is constructed to estimate the whole process state variables. This observer is basically the conventional Luenberger observer with an additional switching term used to guarantee the robustness against modeling errors. The observer is coupled with a nonlinear controller, designed based on input-output linearization for controlling the reactor temperature. The asymptotical stability of the closed-loop system is shown by the Lyapunov stability theorem. Finally, computer simulations are developed for showing the performance of the proposed approach.

Full-order nonlinear observer-based excitation controller design for interconnected power systems via exact linearization approach

This paper presents a novel full-order nonlinear observer-based excitation controller design for interconnected power systems. Exact linearization approach of feedback linearization is used to design the nonlinear observer when the power system is fully linearized. The excitation control law is derived for the exactly linearized power system model. The observed states of power system are directly used as the input to the controller where the control law does not need to be expressed in terms of all measured variables. A single machine infinite bus (SMIB) system is used as test system and all the states are observed for SMIB system. To validate the effectiveness of the proposed control scheme on a large system, a benchmark 3 machine 11 bus system is also simulated. Simulation results show the accuracy and performance of observer-based nonlinear excitation controller by comparing with the exact linearizing controller where the control law is expressed in terms of all measured variables.

Multi-machine power system stability improvement using an observer-based nonlinear controller

Control and operation of electric networks undergo several changes due to growing energy coming from renewable sources and demanding power quality standards. New dynamic load features also pose a challenge to grid designers. In addition, economic reasons, an increasing demand and remote generation push transmission lines to their stability limits causing oscillation modes to become more lightly damped. In this context, controllers and devices are used to enhance the performance of the new power systems. In this work, an observer-based controller to improve stability in power systems, by using the excitation of synchronous generators, is introduced. The strategy goal is to attain maximum damping injection and to increase the transient stability, while good voltage regulation performance is maintained. The proposed strategy presents two important features from the implementation point of view. First, the controller only needs sensing currents and rotor speed, and second, previous knowledge of network parameters and topology is not required. Several comparisons in multi-machine scenarios with current power system stabilizers are presented. These studies confirm the viability and the performance improvement when conventional solutions are replaced by the proposed approach.

Observer-Based Nonlinear Feedback Controls for Heartbeat ECG Tracking Systems

The analysis and design of observed-based nonlinear control of a heartbeat tracking system is investigated in this paper. Two of Zeeman’s heartbeat models are investigated and modified by adding the control input as a pacemaker, thereby creating the control-affine nonlinear system models that capture the general heartbeat behavior of the human heart. The control objective is to force the output of the heartbeat models to track and generate a synthetic electrocardiogram (ECG) signal based on the actual patient reference data, obtained from the William Beaumont Hospitals, Michigan, and the PhysioNet database. The formulations of the proposed heartbeat tracking control systems consist of two phases: analysis and synthesis. In the analysis phase, nonlinear controls based on input-output feedback linearization are considered. This approach simplifies the difficult task of developing nonlinear controls. In the synthesis phase, observer-based controls are employed, where the unmeasured state variables are estimated for practical implementations. These observer-based nonlinear feedback control schemes may be used as a control strategy in electronic pacemakers. In addition, they could be used in a software-based approach to generate a synthetic ECG signal to assess the effectiveness of diagnostic ECG signal processing devices.

GPI observer-based non-linear integral sliding mode control and synchronisation of uncertain chaotic system

An output feedback control scheme for a class of triangular chaotic systems in the presence of system uncertainties, unknown disturbances, parameter perturbations and measurement noises is proposed in this paper. A high gain general proportional integral (GPI) observer is used for the accurate linear estimation of the error states, non-linear endogenous and exogenous disturbances from the noisy output signals of the system, and then a non-linear integral sliding mode controller with active disturbance cancellation is proposed for the tracking control and synchronisation of the chaotic systems. The uncertain Gesino chaotic system is used to validate the proposed control method and the convincing numerical results illustrate the proposed method is effective to deal with various system uncertainties only based on the utilisation of the input-output data.

Observer-based nonlinear control of power system using sliding mode control strategy

This paper presents a new transient stabilization with voltage regulation analysis approach of a synchronous power generator driven by steam turbine and connected to an infinite bus. The aim is to obtain high performance for the terminal voltage and the rotor speed simultaneously under a large sudden fault and a wide range of operating conditions. The methodology adopted is based on sliding mode control technique. First, a nonlinear sliding mode observer for the synchronous machine damper currents is constructed. Second, the stabilizing feedback laws for the complete ninth order model of a power system, which takes into account the stator dynamics as well as the damper effects, are developed. They are shown to be asymptotically stable in the context of Lyapunov theory. Simulation results, for a single-Machine-Infinite-Bus (SMIB) power system, are given to demonstrate the effectiveness of the proposed combined observer–controller for the transient stabilization and voltage regulation.

Observer-based nonlinear control law for a continuous stirred tank reactor with recycle

This paper proposes new results concerning the problem of the control of a continuous stirred tank reactor with recycle. The novelty of the proposed results consists of a new nonlinear observer-based controller which is found by means of recent results of differential geometry for time-delay nonlinear systems, without using linear approximations of the model. Local convergence of the system state to the arbitrarily chosen operating point is theoretically proved. The significance of the proposed control law is shown by many simulations, which show high performances with any initial conditions, even at the start-up, and with critical cases of mismatched parameter values.

Stabilizing Nonlinear Control Using Damper Currents Sliding Mode Observer of Synchronous Generator

In this article, a new observer-based nonlinear controller for excitation control of synchronous generator is presented. First, a nonlinear sliding mode observer for the synchronous machine damper currents is developed. Second, the existence of a control law for the complete seventh order model of a generator, which takes into account the stator dynamics as well as the damper effects, is proved by using the theory of Lyapunov. The stabilizing feedback law for the power system is shown to be Globally Exponentially Stable (GES) in the context of Lyapunov theory. Simulation results, for a single-Machine-Infinite-Bus (SMIB) power system, are given to demonstrate the effectiveness of the proposed combined obsever-controller for the transient stabilization and voltage regulation.

Absolute Stability for a Class of Observer-based Nonlinear Networked Control Systems

摘要: 主要考虑了基于观测器的Lurie网络化控制系统的绝对稳定性问题. 由于采用了基于观测器的反馈控制器, 传感器到控制器的网络诱导时延和控制器到执行器的网络诱导时延不再能合并到一起处理. 首先通过状态增广方法将Lurie网络化控制系统建模为一个多时滞的Lurie系统, 然后利用Newton-Leibniz公式和添加自由权矩阵的方法给出了时滞依赖的稳定性条件. 在此基础上, 给出三种求解控制器和观测器增益矩阵的方法. 此外, 还分别给出了被控对象存在范数有界不确定性和结构不确定性时系统的鲁棒稳定性条件及鲁棒控制器设计方法, 所有得到的结果都是以线性矩阵不等式的形式给出的. 便于利用线性矩阵不等式工具包进行求解. 最后, 通过两个仿真算例说明了方法的可行性和有效性. 关键词: 网络化控制系统 / 观测器 / Lurie系统 / 线性矩阵不等式 / 稳定性 / 时延

Finite difference-based output feedback control for a class of nonlinear systems with sampling time-delay

Within the full linearization framework, the continuous-time observer-based nonlinear control should be determined by solving the implicit, nonlinear ordinary-differential-equation (ODE). To construct the discrete-time nonlinear control, the calculus of finite difference is used such that the finite difference-based output feedback control scheme can be straightforward synthesized since the higher-order difference term is truncated. The nonlinear control methodology with the one-time-delay-ahead prediction effort can ensure the stable output regulation under the specification of nonlinearity bounds. Through the discrete-time Lyapunov function analysis, the presented corollaries show that the sampling time-delay and nonlinearities effects dominate the closed-loop stability and performance. Finally, the proposed control method is successfully demonstrated on an exothermic chemical reactor system with the sampling time-delay and inlet perturbations.

Exponential Observer-Based Stabilization for a Class of Affine Nonlinear Systems

In this paper, we investigate the problem of stabilizing a class of nonlinear affine systems by using the generalization of Gronwall-Bellman lemma with two control laws : first a nonlinear state feedback and second a nonlinear observer-based control. The obtained closed-loop stability is exponential.

Adaptive observer-based non-linear stochastic system control with sliding mode schemes

In this paper, an adaptive sliding mode observer is designed to reconstruct the states of non-linear stochastic systems with uncertainties from the measurable system output and the reconstructed states are employed to construct a sliding mode controller for the stabilization control of complex non-linear systems. It takes the advantages of the sliding mode schemes to design both the observer and the controller. The convergence of the observer and the globally asymptotical stability of the controller are analysed in terms of stochastic Lyapunov stability, and the effectiveness of the control strategy is verified with numerical simulation studies.

Two observer-based nonlinear control approaches for temperature control of a class of continuous stirred tank reactors

In this paper, two nonlinear observer based controllers for temperature control of a continuous stirred tank reactor in which a special class of parallel exothermic reactions take place are proposed. A reduced order nonlinear observer is constructed to estimate the concentration in the reactor. The observer is coupled with two nonlinear controllers, designed based on two well-known techniques, namely input–output linearization and backstepping for controlling the reactor temperature. For dampening the effect of observer error dynamics, a compensating term is used in each control law. The asymptotical stability of the closed-loop system is shown by the Lyapunov's stability theorem. The effectiveness of the proposed controllers has been demonstrated through computer simulations.

Nonlinear State Estimation and Generic Model Control of a Continuous Stirred Tank Reactor

The goal of this paper is to develop a nonlinear observer-based control strategy for a jacketed continuous stirred tank reactor (CSTR). The nonlinear adaptive state estimator/observer (ASE/ASO) is designed based on a model structure that mainly consists of an energy balance equation. In this observation approach, reactor concentration is considered as an imprecisely known extra state (augmented state) with no dynamics. Despite significant process/model discrepancy, the proposed state observer estimated adequately the states of the simulated reactor. Mainly due to the design simplicity, negligible computational effort and fast convergence, the observer is recommended for online implementation. The generic model controller (GMC) has also been synthesized for the example reactor. The nonlinear GMC scheme receives the required information about the reactor concentration from the ASE for calculating the controller responses. Simulation experiments have been carried out to investigate the superior performance provided by the proposed GMC-ASE algorithm compared to the conventional proportional integral (PI) controller.

Nonlinear Observer-Based Control of Load Transitions in Homogeneous Charge Compression Ignition Engines

This paper presents a model-based nonlinear feedback controller designed to regulate the crank angle at 50% fuel burned (thetasCA50) for a gasoline homogeneous charge compression ignition engine model during load transitions. The regulation of the combustion timing is based on manipulating the charge temperature through internal dilution, which is achieved by controlling the lift of a secondary opening of the exhaust valve, also known as the rebreathing lift. The nonlinear feedback controller developed is based on a positive semidefinite Lyapunov function using a simplified control model which contains only the cycle-to-cycle temperature dynamics. The nonlinear feedback controller depends on measurement of the combustion timing thetasCA50 and estimation of the temperature at intake valve closing. Closed-loop simulation of the full-order engine model shows that the nonlinear feedback controller, along with a nonlinear observer, is able to regulate the combustion timing thetasCA50 by stabilizing the temperature dynamics during load transitions. The closed-loop system with the observer-based feedback controller is shown to be robust to some classes of model uncertainty and measurement noise through simulation and an estimate of the region of attraction

Image-guided Control of Flexible Bevel-Tip Needles.

Physicians perform percutaneous therapies in many diagnostic and therapeutic procedures. Image guidance promises to improve targeting accuracy and broaden the scope of needle interventions. In this paper, we consider the possibility of automating the guidance of a flexible bevel-tip needle as it is inserted into human tissue. We build upon a previously proposed nonholonomic kinematic model to develop a nonlinear observer-based controller. As a first step for control, we show that flexible needles can be automatically controlled to remain within a planar slice of tissue as they are inserted by a physician; our approach keeps the physician in the loop to control insertion speed. In the proposed controller, the distance of the needle tip position from the plane of interest is used as a feedback signal. Numerical simulations demonstrate the stability and robustness of the controller in the face of parametric uncertainty. We also present results from pilot physical experiments with phantom tissue under stereo image guidance.

Robust controller for synchronous generator with local load via VSC

The objective of this paper is to design a nonlinear observer-based excitation controller for power system comprising a single synchronous generator connected to an infinite bus with local load. The controller proposed is based on the using first singular perturbation systems concepts and then Sliding Mode Control technique combining with Block Control Principle. To reduce “chattering” a nonlinear observer with estimation of the mechanical torque and rotor fluxes is designed. This combined approach enables to compensate the inherent nonlinearities of the generator and to reject external disturbances.

Observer-based nonlinear control of a torque motor with perturbation estimation

This paper presents an observer-based nonlinear control method that was developed and implemented to provide accurate tracking control of a limited angle torque motor following a 50Hz reference waveform. The method is based on a robust nonlinear observer, which is used to estimate system states and perturbations and then employ input-output feedback linearization to compensate for the system nonlinearities and uncertainties. The estimation of system states and perturbations allows input-output linearization of the nonlinear system without an accurate mathematical model of nominal plant. The simulation results show that the observer-based nonlinear control method is superior in comparison with the conventional model-based state feedback linearizing controller.

Torque Control in Harmonic Drives with Nonlinear Dynamic Friction Compensation

This paper proposes a nonlinear observer-based controller designed to compensate for friction in harmonic drives with hysteresis. Hysteresis in a harmonic drive is described by a nonlinear differential equation representing the combination of nonlinear stiffness and nonlinear friction. Nonmeasurable friction is derived using a nonlinear observer to provide asymptotic stability and position tracking. The performance of the proposed system is confirmed by computer simulation.