Simple Output Feedback Controller Research Articles

Robust finite-time output feedback stabilisation for a class of uncertain planar systems with asymmetric output constraints

This paper considers the finite-time output feedback stabilisation (FTOFS) problem for a class of uncertain planar systems with asymmetric output constraints. The presence of unknown control coefficients, unknown measurement sensitivity and asymmetric output constraints makes the system under consideration essentially different from those in the existing related works. By constructing a new barrier Lyapunov function and applying homogeneous system theory, a simple proportional-derivative like finite-time output feedback controller is explicitly constructed, which only utilises the output information. A rigorous proof demonstrates that not only the closed-loop system is finite time stable, but also the requirement of asymmetric output constraint can be achieved. The novelty of the control approach lies in that it is capable to handle the FTOFS problem for uncertain planar systems with or without asymmetric output constraints in a unified manner, without changing the control structure. The efficiency of the proposed theoretical results are confirmed by simulation results.

Krasovskii and shifted passivity based output consensus

Motivated by current sharing in power networks, we consider a class of output consensus (also called agreement) problems for nonlinear systems, where the consensus value is determined by external disturbances, e.g., power demand. This output consensus problem is solved by a simple distributed output feedback controller if a system is either Krasovskii or shifted passive, which is the only essential requirement. The effectiveness of the proposed controller is shown in simulation on an islanded DC power network.

ASPR-based Output Feedback Control with Virtual PFC for Output Tracking

Nowadays, the output feedback control method based on the Almost Strictly Positive Real (ASPR) property gets many attentions and has been researched widely. ASPR models can be stabilized by applying simple output feedback control; so the designed controllers have a simple structure. However, the systems have to satisfy quite strict conditions in order to obtain ASPR-ness, although almost all practical systems do not have the ASPR property. Therefore, for relaxing those conditions, the introduction of a Parallel Feedforward Compensator (PFC) has been proposed. This method can render the resulting augmented system ASPR. Up to now, several PFC design methods have been proposed, and one of them is an adaptive PFC design scheme. This technique has a feature that it can design a PFC automatically by utilizing online data. Furthermore, for the purpose of output regulation, the control design methods with an adaptive PFC have been proposed. Unfortunately, however, in almost all schemes, the discussion on the convergence of actual errors has not been conducted. Therefore, in this paper, introducing a virtual PFC model and an auxiliary input for ensuring ASPR-ness, a new ASPR-based output feedback control method is proposed, and the stability analysis and convergence of the actual error are discussed. Finally, the effectiveness of the proposed method is confirmed via numerical simulations.

Output Feedback Tracking Sliding Mode Control for Systems with State- and Input-Dependent Disturbances

In this paper, output feedback tracking sliding mode control was considered for uncertain multivariable linear systems. The uncertainties included external disturbance, the system state, and control input. A new property of the loop transfer recovery (LTR) observer was first established: the state estimation error of the LTR observer can be made arbitrarily small with respect to state- and input-dependent system uncertainties. Observer-based output feedback tracking sliding mode control using the LTR observer is presented. The proposed sliding mode control approach can maintain the boundedness of the system state and drive the system outputs arbitrarily close to the desired reference outputs; the degree of closeness was determined by a design parameter in the LTR observer. In the proposed approach, the most general and simple observer-based output feedback control formulation was used to achieve global tracking. Simulations with a two-degree-of-freedom (DOF) robotic manipulator application illustrated the claimed properties, and a peaking and chattering reduction technique was demonstrated to protect the actuator.

Robust Adaptive Neural Network Finite-Time Tracking Control for Robotic Manipulators Without Velocity Measurements

This paper proposed a robust finite-time tracking controller with adaptive neural networks for uncertain robotic manipulators without velocity measurements. A simple output feedback controller plus a nonlinear filter is designed to achieve satisfied performance, such as high accuracy, and fast response, which is more convenient and lower cost for robotic manipulators in practice. The adaptive neural networks with finite-time convergence are designed to compensate the uncertainties, which effectively further improve the robustness. The Lyapunov stability theory and geometric homogeneity technique are employed to prove the practical finite-time stability of the whole closed-loop system. Simulations on two-degree robotic manipulators show the effectiveness and robustness of the proposed control strategy.

Output-Feedback Control of Virus Spreading in Complex Networks With Quarantine

In this paper the problem of designing an output-feedback control for the stabilization of the extinction steady-state in a virus spreading process over a complex network with quarantine is considered. Sufficient conditions are established for the choice of those nodes for which sensor information is necessary and those which should be controlled using notions from constructive control theory. A simple output-feedback control is proposed which exponentially stabilizes the extinction state. Numerical simulation results are provided to illustrate the functioning of the proposed control scheme for a scale-free network of one million nodes.

Robust Output Feedback Controller For a Class of Nonlinear Systems with Actuator Dynamics

Abstract This paper addresses a simple robust output feedback controller, which suits a class of nonlinear dynamical systems. It takes into account the dynamics and limitations of the actuator. This setting appears in industrial problems such as flow rate control for hydraulic turbines which is used for speed control, where controller gains tuning is important to avoid violent input signals that could excite unstable dynamics, in addition to the limitation of the actuator in use. A systematic approach is proposed to compute the parameters of a simple control law optimally to minimize the tracking error. This approach is divided into two steps. Firstly, computing bounds on some of the system’s parameters and variables, then solving a nonlinear constrained optimization problem (offline). Stability analysis is carried out to guarantee that obtained parameters stabilize the system while keeping the tracking error below a certain bound. A numerical example is given to illustrate the relevance of the proposed controller.

High Order Sliding Mode Observer-Based Output Feedback Controller Design For Electro-Hydraulic System

A perturbed linear system with property of strong observability ensures that there is a sliding mode observer to estimate the unknown form inputs together with states estimation. In the case of the electro-hydraulic system with piston position measured output, the above property is not met. In this paper, the output and its derivatives estimation were used to build a dynamic structure that satisfy the condition of strongly observable. A high order sliding mode observer (HOSMO) was used to estimate both the resulting unknown perturbation term and the output derivatives. Thereafter with one signal from the whole system (piton position), the piston position make tracking to desire one with a simple linear output feedback controller after canceling the perturbation term.
 The numerical simulation results showed excellent performance of the proposed output feedback controller in forcing the piston position to follow the desired reference position. Moreover, the control effort spent was minimal.

Chaos control for a unified chaotic system using output feedback controllers

This paper presents a new method of controlling a unified chaotic system by using output feedback control strategy. In particular, for an arbitrarily given equilibrium point of a unified chaotic system, we design explicit and simple output feedback control laws by which the equilibrium point is globally and exponentially stabilized. Computer simulations are employed to illustrate the theoretical results.

Output Feedback Attitude Tracking for Spacecraft Under Control Saturation and Disturbance

This paper proposes a class of velocity-free attitude stable controller using a novel finite-time observer for spacecraft attitude tracking, which explicitly takes into account control input saturation to assure fast and accurate response and to achieve effective compensation to the effect of external disturbance as well. First, a novel semiglobal finite-time convergent observer is proposed to estimate the angular velocity in a finite-time under external disturbance. Then, a simple global output feedback controller is proposed by adoption of the designed finite-time observer. Rigorous proofs show that the proposed observer can achieve the finite-time stability and the controller rigorously enforces actuator magnitude constraints. Numerical simulations illustrate the spacecraft performance obtained using the proposed controller.

On-line maximization of biogas production in an anaerobic reactor using a pseudo-super-twisting controller

We consider an apparently oversimplified first order model of an anaerobic digester operated as a CSTR, where the dilution rate is the controlled input and the biogas production rate is the measured output. The parameters of this model are considered slowly time-varying. The output function depends on the only state (the substrate), and at any instant has a unique maximum. We propose a simple output-feedback controller based on the super-twisting algorithm combined with a state machine, which converges in a practical sense to this maximum. The controller was tested by simulations of an anarobic digester, maximizing the biogas production rate, showing very good results.

A simple fault tolerant control for input/output asynchronous sequential machines

This paper presents a fault tolerant controller for asynchronous sequential machines subject to unauthorized state transitions caused by adversarial inputs. The input/output machines are considered where direct access to the machine’s state is unavailable. If the asynchronous machine satisfies some condition on transition feature and reachability, we can design a simple output feedback controller that needs neither a state observer nor output bursts. Despite insufficient knowledge of the current state, the proposed controller automatically counteracts any transient fault so that the closed-loop system can maintain the normal input/output behavior.

Power-Level Control for MHTGRs with Time-Delay in Helium Temperature Measurement

The modular high temperature gas-cooled reactor (MHTGR), which has the inherent safety feature, high thermal efficiency and satisfactory economic feasibility, can be applied for electricity and process heat production. Power-level control is an important technique for providing both the stable operation and load-following performance. Since the coolant temperature sensors of an MHTGR are usually installed near the primary side of the corresponding steam generator, there must be time-delay effect in the feedback loop of the coolant temperatures. Moreover, the measurement signal transducing may also induce time-delay effect. Therefore, it is meaningful to give the power-level control design method by considering this time-delay effect. In this paper, a simple output-feedback power-level control is proposed for the MHTGRs by using the delayed measurement signal of average reactor coolant temperature. In the aspect of theoretical analysis, a sufficient condition, under which it is well guaranteed that this newly-built power-level control is a globally asymptotic stabilizer, is firstly given. In the aspect of verification, numerical simulation results not only verify the feasibility of the theoretical results but also show the relationship between the performance and values of parameters of this novel power-level controller. The meaning of this work lies in two aspects. The first one is deeply revealing the relationship between the closed-loop stability and values of the controller parameters. The second one is giving the approach of designing a simple and effective power-level control strategy to suppress the negative influence induced by the time-delay in the feedback loop of the coolant temperatures.

Closed loop Identification of Quadruple Tank System using an Improved Indirect Approach

The well known, indirect method of closed loop identification is difficult to apply for multivariable systems owing to its two step procedure of first identifying the loop sensitivities which are then used in the second step to estimate the plant dynamics. In this paper, we propose an improved indirect method of closed loop identification that exploits (i) simple proportional output feedback control law and (ii) inherent dynamic relationships that results from the implementation of this control law to estimate the plant dynamics in a single step. In the proposed methodology, we used state-space parameterization of the open loop dynamics for both the plant and the loop sensitivities so as to accomodate multivariable systems. The use of the simple proportional output feedback control law in the proposed methodology obviates the need for inverse filtering using the loop sensitivities which could be a problem for large multivariable systems. Since, the proposed methodology involves a single open loop identification between the dither and the output, other problems of noise-output correlation are also not seen. The proposed methodology is demonstrated by a simulation study on a benchmark Quadruple Tank system proposed by Johansson (2000). The simulation results presented in this paper shows the effectiveness of the proposed method for system identification.

A simple output-feedback controller for fed-batch cultures of microbial strains with overflow metabolism

An output-feedback controller is proposed for fed-batch cultures of microbial strains exhibiting overflow metabolism, i.e., cultures where cell strains may produce inhibiting metabolites when excess substrate is fed. The control objective is therefore to control the substrate feed rate in order to remain near the optimal substrate concentration during the whole culture. The proposed controller uses measurements of an output signal that can be calculated from on-line process data and determines the necessary dilution rate to maintain the output near its local, time-varying, maximum at all times. The controller is hybrid, combining a proportional plus integral controller with antiwindup, modified so that the error signal used in the feedback may change its sign according to a state machine which keeps track of whether the control action should be positive or negative. The transition is made smoothly to avoid chattering and based on an auxiliary variable which follows the local output maximum. Partial proof of convergence is given and simulations of the model of a yeast production system show the applicability of the proposed strategy.

On the design and synthesis of limit cycles using switching linear systems

This article deals with the design and synthesis of limit cycles for a class of switched linear systems. This work is motivated by an application in the context of electrical networks, but the methodologies can be applied in other engineering fields as well. Several methods for the design and synthesis of limit cycles are presented. Based on a monodromy matrix associated with a periodically switched system, a design method and two feedback strategies are developed. The first strategy is based on linear feedback design using pole placement. The second strategy is based on the observation that certain state-dependent switching strategies can be implemented by means of a simple nonlinear output feedback controller. Advantages of this latter strategy are not only the ease with which the switching strategy can be implemented, but also the fact that classical techniques may also be used to ascertain the stability of the resulting limit cycle. Our next contribution is the development of a novel frequency domain-based approach to limit cycle design. This approach is based on the observation that the existence of certain limit cycles can be deduced from an infinity of circle criteria generated by a family of periodic systems. By making use of recent results, this observation can be used to develop a one-parameter spectral search to deduce the approximate frequencies of feasible limit cycles. Having selected a frequency of oscillation, one may then make use of the aforementioned nonlinear elements to realise a switching strategy that generates a stable limit cycle with given frequency and amplitude. Examples are given to illustrate the effectiveness of the approaches presented.

A Nonlinear Tracking Controller for Voltage-Fed Induction Motors With Uncertain Load Torque

In this paper, a new adaptive output feedback control scheme for the full-order (voltage-fed) model of the induction motor is presented. The proposed algorithm uses measurements of the stator currents and rotor speed and achieves global asymptotic convergence of the rotor speed and flux magnitude to their desired (time-varying) references. The distinguishing feature of the proposed scheme, which makes it appealing from a practical viewpoint, is that it consists of a simple output feedback control law, which is derived using standard arguments pertaining to Hamiltonian systems and passivity-based control. In order to make the scheme robust to load torque variations, an adaptation mechanism is added, which yields asymptotic estimates of the unknown load torque, and a rigorous stability proof for the resulting cascaded closed-loop system is provided. The efficacy of the proposed controller is verified via simulations and experimental tests.

The output feedback control for uncertain nonholonomic systems

This paper considers the problems of almost asymptotic stabilization and global asymptotic regulation (GAR) by output feedback for a class of uncertain nonholonomic systems. By combining the nonsmooth change of coordinates and output feedback domination design together, we construct a simple linear time-varying output feedback controller, which can universally stabilize a whole family of uncertain nonholonomic systems. The simulation demonstrates the effectiveness of the proposed controller.

Output feedback control strategy of parallel hybrid filters

In this paper, the authors propose a novel control strategy of active hybrid filters. The adopted hybrid filter consists of an active filter and a passive filter connected in parallel. The power rating of the converter is reduced compared with simple active filter. The control is introduced to allow active filtering of load harmonics and active damping of passive filter connected in parallel with the active filter. When connected in power grid, the complete system is adjusted to prevent risk of resonance as well as harmonic filtering. A complete modeling of the system is achieved using a simple structure and effective corrector is developed. An important characteristic of the proposed control scheme is that it results in a simple static output feedback controller. Complete simulation of the system validates efficiency of the control law.

Robust regulation of anaerobic digestion processes

This paper deals with the problem of controlling anaerobic digestion processes. A two-step (i.e. acidogenesis-methanization) mass balance model is considered for a 1 m3 fixed bed digester treating industrial wine distillery wastewater. The control law aims at regulating the organic pollution level while avoiding washout of biomass. To this end, a simple output feedback controller is considered which regulates a variable strongly related to the Chemical Oxygen Demand (COD). Numerical simulations assuming noisy measurements first illustrate the robustness of this control procedure. Then, the regulating procedure is implemented on the considered anaerobic digestion process in order to validate and demonstrate its efficiency in real life experiments.