Nonlinear Output Feedback Control Research Articles

Output feedback nonlinear control of power system under large penetration of renewable energy sources

This paper deals with the problem of stability analysis and controlling a power system in which a synchronous generator and renewable energy sources supply the power to an infinite bus. Firstly the investigation of the existence of the equilibrium points of the system and their stability is presented. For this problem, we derive a sufficient condition on the renewable energy current for the existence of the equilibrium points. In addition, we analyse the stability of the equilibrium points, and show that there is only one equilibrium points which is stable. These results clarify the impact of the penetration of renewable energy sources on the existence of the stable equilibrium points of the system. Secondly, the focus is made on elaborating an output feedback controller, combining a state observer and a nonlinear control law that stabilises the closed loop system whatever the current of renewable energy sources. Numerical simulations are given in order to show the effectiveness of all theoretical results.

Nonlinear Output Feedback Control of Flexible Rope Crane Systems With State Constraints

When the suspension rope of the crane system is relatively long and its mass cannot be simply ignored compared with that of the payload, or when the crane rope is underwater, it will exhibit flexible characteristics, that is, the bending deformation will occur during swing. Undoubtedly, unreasonable bending deformation of the crane rope will further excite larger-amplitude payload swing, which will seriously influence the efficiency and safety. To this end, for flexible rope crane systems, this paper carries out in-depth analysis and puts forward an effective control method. Specifically, by introducing the concept of lumped mass method and virtual spring, a nonlinear dynamic model is established. Furthermore, in order to solve the problem that velocity signals are not measurable, a nonlinear control strategy, which does not need velocity signals for feedback, is proposed in this paper. Finally, rigorous theoretical analysis and a series of experimental results verify the effectiveness of the proposed control strategy.

Quaternion-based Robust Trajectory Tracking Control of a Quadrotor Hover System

This paper presents a robust nonlinear output feedback control method that achieves three degree of freedom (3-DOF) attitude trajectory tracking of a hover system test bed. The proposed control method formally incorporates dynamic model uncertainty in addition to test bed voltage constraints. To reduce the computational requirement in the closed-loop system, constant feedforward estimates of the input-multiplicative parametric uncertainty are utilized in lieu of adaptive parameter estimates. To eliminate the need for angular rate measurements, the control design employs a bank of dynamic filters, which operates as a velocity estimator in the closed-loop system. A rigorous error system development and Lyapunov-based stability analysis are presented to prove asymptotic 3-DOF attitude trajectory tracking control. Computer simulation and experimental results are also included to illustrate the performance of the attitude control method using the Quanser 3-DOF hover system test bed.

Stabilization of Switched Nonlinear Systems by Adaptive Observer-Based Dynamic Surface Control with Nonlinear Virtual and Output Feedback

This paper presents a new nonlinear output and virtual error feedback control technique for stabilization of switched uncertain nonlinear systems using a continuous differentiable nonlinear feedback function (NFF). The merits of the proposed method are threefold: (i) there is no assumption that the switching signals must satisfy the (average) dwell time, (ii) the feedback amplitude self-adjusts under different state levels to guarantee better dynamic performance using the NFF, and (iii) the number of parameters that needs online tuning is 1, i.e., the proposed control method is computationally inexpensive. Moreover, the closed-loop signals are kept bounded using the rigorously proved Lyapunov and Invariant-set theorems, and the output signal converges to a sufficiently small region around zero by choosing proper design parameters. Finally, simulation and comparative results are given to demonstrate the effectiveness of the proposed method.

Nonlinear adaptive fuzzy output-feedback controller design for dynamic positioning system of ships

This paper develops a nonlinear adaptive fuzzy output feedback controller for dynamic positioning (DP) system of ships in the presence of unmeasured states of ships, unknown dynamic model parameters, unknown time varying environment disturbances and input saturation. It is the first time that all the conditions above are simultaneously dealt with in the DP control design. By combining adaptive fuzzy system and auxiliary dynamic system, a control scheme with high-gain observer is developed via vectorial backstepping method. It is proved that the proposed nonlinear adaptive fuzzy output feedback controller can maintain the ship at desired position and heading with arbitrary accuracy, while guaranteeing the uniform ultimate boundedness of all closed loop signals in the DP system. Finally, simulations are carried on a supply ship to demonstrate the effectiveness of the proposed control approach.

Nonlinear Output Feedback Control for Average Output Voltage of Boost Converters Based on their Discretized Bilinear Model

Nonlinear Output Feedback Control for Average Output Voltage of Boost Converters Based on their Discretized Bilinear Model

Stability of Gaussian Process Learning Based Output Feedback Model Predictive Control

Abstract We present an output feedback nonlinear model predictive control approach that uses a Gaussian process model for prediction. We show nominal stability assuming that the Gaussian process model is able to represent the real process and establish input-to-state stability assuming a bounded error between the real process and the Gaussian model approximation. These results are achieved using a predictive control formulation without terminal region. The approach is illustrated using a continuous stirred-tank reactor benchmark problem.

Saturated output-feedback nonlinear control of a 3-continuous exothermic reactor train

The problem of controlling with saturated output-feedback (OF) temperature control a six-state (concentration-temperature) bistable train of three continuous stirred tank reactors with recycle is addressed. The closed-loop system must operated about the unstable steady-state (SS) by manipulating the coolant temperature on the basis of one of the tank temperatures. The aim is to attain robust closed-loop stability with a control scheme as simple as possible. The constructive combination of advanced and industrial control ideas yields a the behavior of a passive nonlinear state-feedback (NLSF) stabilizing controller can be recovered with an industrial-type proportional-integral (PI) control with anti-windup protection plus criteria to choose the sensor location as well as control gains and limits.

A Separation Principle for Underactuated Lossless Lagrangian Systems

We study under-actuated Lagrangian systems without dissipative forces, augmented by a chain of integrators. For such systems, we solve the open problem of global tracking control via position measurements only; strictly speaking, we establish uniform global asymptotic stability for the closed loop system. As a corollary, we obtain an original statement for flexible-joint robots, which closes a long-standing open problem of output feedback nonlinear control.

Stability of the Small-Scale Interconnected DC Grids via Output-Feedback Control

A decentralized nonlinear model and controller is proposed to stabilize the interconnected small-scale islanded dc grids in the presence of renewable energy sources with proven stability in this paper. The dc interconnected network comprises dc sources along with resistive and constant-power loads (CPLs). Though the dc sources are photovoltaic (PV) in this paper, the proposed controller can be applied to other types of low-inertia intermittent sources as well. All sources and/or CPL loads are connected to the grid through simple dc–dc converters (DDCs) to avoid power electronic complexities. The negative-resistance CPLs can destabilize the grid in the presence of the DDC dynamical components. The decentralized nonlinear output-feedback controller mitigates rapid voltage and power oscillations caused by the disturbances and measurement noises, and stabilizes the grid. Since the proposed output-feedback controller needs only partial knowledge of the local converter states, the number of measure points reduces leading to a simple implementation. Simulation results on a small-scale dc grid are provided to show the performance of the proposed controller.

Fault-Tolerant Control of a Nonlinear System Based on Generalized Fuzzy Hyperbolic Model and Adaptive Disturbance Observer

This paper focuses on the problem of fault-tolerant control for a class of nonlinear systems with unknown nonlinear dynamic. The generalized fuzzy hyperbolic model is used to approximate the unknown nonlinear function. A novel fuzzy adaptive descriptor observer and an adaptive disturbance observer are designed simultaneously to estimate the system state, actuator fault, sensor fault, and disturbance. In this paper, the disturbance is assumed to be generated from an unknown exogenous system. Compared with the existing results, in which the disturbance is generated from known exogenous system, the proposed adaptive disturbance observer is more applicable in practice, since the exogenous system is independent of the controlled system and its parameter matrix is difficult to be measured. Furthermore, using the estimation information, a novel nonlinear dynamic output feedback controller is designed. The controller can stabilize the nonlinear system, which is subjected to the unknown nonlinear dynamic, actuator fault, sensor fault, and mismatched disturbance, simultaneously. Finally, simulation results are provided to illustrate the effectiveness of the proposed techniques.

Particle Model Predictive Control: Tractable Stochastic Nonlinear Output-Feedback MPC

We combine conditional state density construction with an extension of the Scenario Approach for stochastic Model Predictive Control to nonlinear systems to yield a novel particle-based formulation of stochastic nonlinear output-feedback Model Predictive Control. Conditional densities given noisy measurement data are propagated via the Particle Filter as an approximate implementation of the Bayesian Filter. This enables a particle-based representation of the conditional state density, or information state, which naturally merges with scenario generation from the current system state. This approach attempts to address the computational tractability questions of general nonlinear stochastic optimal control. The Particle Filter and the Scenario Approach are shown to be fully compatible and–based on the time- and measurement-update stages of the Particle Filter–incorporated into the optimization over future control sequences. A numerical example is presented and examined for the dependence of solution and computational burden on the sampling configurations of the densities, scenario generation and the optimization horizon.

Semi-global output feedback nonlinear stabilization of variable speed grid connected direct drive wind turbine generator systems

The goal of the present work is to achieve nonlinear semi-global output feedback stabilization of variable speed grid connected direct drive wind turbine generator DDWTG systems under wind energy conversion systems to provide the electricity demand for electrical networks. The study will address the sensorless control of variable speed wind energy generation systems, namely optimized rotor speed and direct-axis current control to determine the most appropriate structure and to improve both robustness and reliability of this kind of distributed generators. The proposed nonlinear observer is robust with respect to measurements error and perturbations of the sampling schedule. The simulation results of the case study support the presented main theorem that reflects the effect of measurement errors and the improvement with respect to global convergence properties. The novelty of the present study resides in taking into account the difficulties and control problem complexity that faced the nonlinear output feedback control undergo: (i) the proposed system nonlinearity and loss the observability of sensorless PMSG near the singularity point of the rotor speed; (ii) inaccessibility measurements for all system state variables; (iii) maximum power point tracking of optimum reference angular rotor speed; (IV) magnetizing and demagnetizing direct-axis current at standstill; (V) the proposed semi-global observer has dynamic high-gain design parameter DHGO. The simulation results of variable speed grid connected DDWTG, in general, confirm the main theorem developed under DHGO parameter and lead us to enlarge and prolongation the admissible sampling period using nonlinear Lyapunov stability control techniques.

Passivity control with practically finite-time convergence for large space structures

A nonlinear output feedback control law based on passivity is proposed to reduce the vibration of large space structures. The considered system is assumed to be equipped with collocated actuators and sensors. The concept of practically finite-time stability is first developed to describe the finite-time convergence of a passive system. Then, an output feedback is introduced to drive the trajectories of a passive system into a small set around the origin in finite time. Finally, the proposed control strategy is applied to the vibration suppression of large space structures with distributed thrusters and velocity sensors or torque outputting devices and angular rate sensors. Numerical simulations are conducted to validate the effectiveness of the proposed controller.

Dynamic anti-windup design for a class of nonlinear systems

ABSTRACTThis work addresses the dynamic anti-windup design problem for a class of nonlinear systems subject to actuator saturation. The considered class regards the systems that can be cast in a differential algebraic representation (DAR), such as rational and polynomial systems. Considering that a nonlinear dynamic output feedback controller, which can also be written as a DAR, has been designed to stabilise the nonlinear system disregarding the saturation effects, LMI-based conditions are proposed to compute a stabilising dynamic anti-windup compensator. Two problems are considered: the first one regards the regional internal stabilisation; and the second one, assuming that an energy-bounded disturbance acts on the system, concerns the input-to-state stability. The derived conditions can therefore be incorporated in convex optimisation problems that allow to compute the anti-windup compensator in order to maximise the region of guaranteed asymptotic stability, to maximise a bound on the admissible -norm of the disturbance or even to minimise a bound on the -gain between the disturbance and the output. Numerical examples illustrate the proposed methods.

Smooth dynamic output feedback control for multiple time-delay systems with nonlinear uncertainties

The dynamic output feedback control problem is considered for a class of systems with multiple time delays and nonlinear uncertainties. Based on the control input matrix and output matrix, we decompose the system into two subsystems. The dynamic compensator is designed for the first subsystem, and then the output feedback controller is constructed based on the compensator and the second subsystem. By using the introduced new Lyapunov–Krasovskii functional, we show that the solution of the resultant closed-loop system converges exponentially to an adjustable bounded region. Compared with the previous works, the developed controller in this paper is memoryless and smooth, which only uses the system output. The control design conditions are relaxed because of the developed dynamic compensator. The result is further extended to the general nonlinear case. The corresponding dynamic nonlinear output feedback control method is proposed. Finally, simulations are performed to show the potential of the proposed methods.

A comparative study of semi-active control strategies for base isolated buildings

A comparative analytical study of several control strategies for semi-active (SA) devices installed in baseisolated buildings aiming to reduce earthquake induced vibrations is presented. Three force tracking schemes comprising a linear controller plus a “clipped” algorithm and a nonlinear output feedback controller (NOFC) are considered to tackle this problem. Linear controllers include the integral controller (I), the linear quadratic regulator (LQR) and the model predictive controller (MPC). A single degree-of-freedom system subjected to input accelerograms representative of the Portuguese seismic actions are first used to validate and evaluate the feasibility of these strategies. The obtained results show that structural systems using SA devices can in general outperform those equipped with passive devices for lower fundamental frequency structural systems, namely base-isolated buildings. The effectiveness of the proposed strategies is also evaluated on a 10 storey base-isolated dual frame-wall building. The force tracking scheme with an integral controller outperforms the other three as well as the original structure and the structure equipped with passive devices.

Nonlinear Adaptive Output-Feedback Controller Design for Guidance of Flexible Needles

In this paper, a control methodology is proposed for guiding and stabilizing flexible bevel-tip needles to an arbitrary planar slice. The proposed controller is an adaptive version of the previously proposed nonlinear output feedback controller, which was built upon the well-known nonholonomic kinematic model of needle steering. On the grounds that such a model is subject to parametric uncertainty, an adaptive controller is necessary for adjusting the model parameters. In addition, a nonlinear observer is required due to the existence of some unmeasurable state variables. Although the original form of the studied system is linearly parameterized, its canonical form is not, preventing the application of conventional adaptive control schemes. In this paper, a nonlinear adaptive control methodology is proposed and applied to the guidance problem of steerable needles. Through simulation results, it is illustrated that the proposed methodology greatly outperforms the existing feedback linearization-based approach.

Output feedback dynamic surface controller design for airbreathing hypersonic flight vehicle

This paper addresses issues related to nonlinear robust output feedback controller design for a nonlinear model of airbreathing hypersonic vehicle. The control objective is to realize robust tracking of velocity and altitude in the presence of immeasurable states, uncertainties and varying flight conditions. A novel reduced order fuzzy observer is proposed to estimate the immeasurable states. Based on the information of observer and the measured states, a new robust output feedback controller combining dynamic surface theory and fuzzy logic system is proposed for airbreathing hypersonic vehicle. The closedloop system is proved to be semi-globally uniformly ultimately bounded (SUUB), and the tracking error can be made small enough by choosing proper gains of the controller, filter and observer. Simulation results from the full nonlinear vehicle model illustrate the effectiveness and good performance of the proposed control scheme.

Using Inverse Nonlinearities in Robust Output Feedback Guaranteed Cost Control of Nonlinear Systems

This paper extends the result of an earlier paper on constructive robust nonlinear output feedback controller design, which is based on the use of IQCs and minimax LQG control. In this paper, in addition to copies of the nonlinearities, we include copies of the inverses of the nonlinearities in the controller. Consequently more IQCs are exploited in the design procedure, which gives a smaller bound on the closed-loop cost function than the earlier result.