Showing papers on "Variable structure control published in 2006"

On designing of sliding-mode control for stochastic jump systems

Abstract: In this note, we consider the problems of stochastic stability and sliding-mode control for a class of linear continuous-time systems with stochastic jumps, in which the jumping parameters are modeled as a continuous-time, discrete-state homogeneous Markov process with right continuous trajectories taking values in a finite set. By using Linear matrix inequalities (LMIs) approach, sufficient conditions are proposed to guarantee the stochastic stability of the underlying system. Then, a reaching motion controller is designed such that the resulting closed-loop system can be driven onto the desired sliding surface in a limited time. It has been shown that the sliding mode control problem for the Markovian jump systems is solvable if a set of coupled LMIs have solutions. A numerical example is given to show the potential of the proposed techniques.

Sliding Mode Disturbance Observer-Based Control for a Reusable Launch Vehicle

Abstract: The nation's goals to replace the aging Space Shuttle fleet and pursue exploration of our solar system and beyond will require more robust, less costly launch vehicles and spacecraft. This paper presents a novel Sliding Mode Control approach, Sliding Mode Control driven by Sliding Mode Disturbance Observers with Gain Adaptation, for the reusable launch vehicle (RLV) flight control system design as a way to improve robustness to many phenomena such as modeling uncertainties and disturbances, while retaining continuity of control without using high control gains. Due to the robustness to external disturbances (including wind gusts), mission guidance trajectories and modeling uncertainties, the proposed flight control system design also can reduce cost by requiring less time in design cycle and preflight analyses. This design is applied to Terminal Area Energy Management and Approach/Landing (TAL), a flight regime that has had little research effort in recent years. The multiple-loop, multiple time-scale design features low order disturbance observers that rely only on knowledge of the bounds of the disturbance. A gain adaptation algorithm is included in the disturbance observer design that provides the least gain needed for existence of the sliding mode. High fidelity 6 DOF computer simulations of the X-33 technology demonstration sub-orbital launch vehicle for nominal and severe wind-gust tests demonstrate improved performance over a more conventional, classical control system design.

Sliding mode control with PID sliding surface and experimental application to an electromechanical plant.

Abstract: In this study, a sliding mode control system with a proportional+integral+derivative (PID) sliding surface is adopted to control the speed of an electromechanical plant. A robust sliding mode controller is derived so that the actual trajectory tracks the desired trajectory despite uncertainty, nonlinear dynamics, and external disturbances. The proposed sliding mode controller is chosen to ensure the stability of overall dynamics during the reaching phase and sliding phase. The stability of the system is guaranteed in the sense of the Lyapunov stability theorem. The chattering problem is overcome using a hyperbolic function for the sliding surface. Experimental results that are compared with the results of conventional PID verify that the proposed sliding mode controller can achieve favorable tracking performance, and it is robust with regard to uncertainties and disturbances.

Coordination of active steering, driveline, and braking for integrated vehicle dynamics control

Abstract: An integrated vehicle dynamics control system which aims to improve vehicle handling and stability by coordinating active front steering (AFS) and dynamic stability control (DSC) subsystems is developed in this paper. The DSC subsystem includes driveline-based, brake-based, and driveline plus brake-based DSC subsystems. The influence of varying forward speed and lateral acceleration on the lateral vehicle dynamics is investigated first. The AFS controller, which is used to improve vehicle steerability in the low to mid-range lateral acceleration, and the DSC controller, which manages to maintain vehicle stability during extreme driving situations, are then designed by using the sliding mode control (SMC) technique and phase plane method respectively. Based on the two independently developed controllers, a rule-based integration scheme is proposed to optimize the overall vehicle performance by minimizing interactions between the two subsystems and extending functionalities of individual subsystems. Computer simulation results confirm the effectiveness of the proposed control system and the overall improvements in vehicle handling and stability.

Advances in variable structure and sliding mode control

Abstract: Mathematical Developments and VSC.- Higher Order Sliding Modes.- Sliding Modes for Matched and Un-Matched Uncertainty.- Observation and Identification.- Discrete-Time Sliding Modes.- Applications.

Sliding-mode control for dc-dc converters with constant switching frequency

Abstract: A new approach implementing the sliding-mode controller is proposed for dc-dc converters. The equivalent control input is used as the system control input, which results in a duty cycle regulation control system. As designed, equivalent control input is maintained at a value between 0 and 1, similar to the desired duty cycle value. Thus, constant switching frequency can be achieved under changes of state conditions. Two sliding-mode controllers based on this method are designed for positive output elementary Luo converter. Traditional small-signal analysis is applied to study the close-loop system performance under proposed approach. Audio-susceptibility, control-to-output transfer functions and output impedance are derived on the basis of the small-signal model. It is shown that the proposed sliding-mode control approach retains the advantages of traditional sliding-mode control, as well as achieve constant switching frequency, which is decided by the input saw-tooth waveform. Results of the experiment are reported for both controllers and they verify the theoretical analysis.

A Sliding-Mode Antiswing Trajectory Control for Overhead Cranes With High-Speed Load Hoisting

Abstract: This paper proposes a sliding-mode anti-swing control foroverhead cranes. The objective of this study is to realize ananti-swing trajectory control with high-speed load hoisting. Asliding-mode anti-swing trajectory control scheme is designedbased on the Lyapunov stability theorem, where a sliding sur-face, coupling the trolley motion with load swing, is adopted fora direct damping control of load swing. The proposed controlguarantees asymptotic stability while keeping all internal signalsbounded. In association with a new anti-swing motion planningscheme, the proposedcontrol realizes a typical anti-swing trajec-tory control in practice, allowing high-speed load-hoisting mo-tion and sufficient damping of load swing. The proposed con-trol is simple for a real-time implementationwith high-frequencysampling. The effectiveness of the proposed control has beenconfirmed by experiments. 1 Introduction Over the past two decades, considerable research has beenperformed for the anti-swing control of overhead cranes [1-11].However, the manual control of an experienced crane opera-tor is still more effective than a computerized anti-swing con-trol. An experienced crane operator controls the crane alonga typical anti-swing trajectory that consists of an acceleratingzone, constant-velocity zone, and decelerating zone, frequentlywith high-speed load hoisting in the accelerating and decelerat-ing zones. This implies that the research in the anti-swing con-trol should address the following control criteria. First, the anti-swing control should be solved as a trajectory control. Second,high-speed load hoisting should be allowed in the acceleratingand decelerating zones. Finally, sufficient damping should beguaranteed for rapid suppression of load swing.This paper proposes a new sliding-mode anti-swing controlfor overhead cranes. An anti-swing trajectory control scheme,allowing high-speed load-hoisting motion, is designed basedon sliding-mode control [12]; the proposed control guaranteesasymptotic stability while keeping all internal signals bounded.The proposed control provides a direct damping mechanism forthe load swing control. In association with a new anti-swingmotion-planning scheme [11], the proposed control realizes atypical anti-swing trajectory control in practice, enabling high-speed control of load hoisting and sufficient damping of loadswing. Moreover, the proposed control is simple for a real-timeimplementation with easy gain tuning. The effectiveness of theproposed control is shown with control experiments.The remainder of this paper is organized as follows. In Sec-tion 2, a dynamic model of an overhead crane is described. InSection 3, a model-based anti-swing trajectory control schemeis designed based on sliding-mode control. In Section 4, theproposed control is evaluated through experiments. Finally, inSection 5, the conclusions are drawn for this study.1 Copyright

Adaptive stabilizing and tracking control for a nonlinear inverted-pendulum system via sliding-mode technique

Abstract: Since the system behaviors of a dual-axis inverted-pendulum mechanism including actuator dynamics are highly nonlinear, it is difficult to design a suitable control system that realizes real-time stabilization and accurate tracking control at all times. In this paper, an adaptive sliding-mode control system is implemented to control a dual-axis inverted-pendulum mechanism that is driven by permanent magnet synchronous motors. First, the energy conservation principle is adopted to build a mathematical model of the motor-mechanism-coupled system. Moreover, an adaptive sliding-mode control system is developed for stabilizing and tracking control of the dual-axis inverted-pendulum system, where an adaptive algorithm is investigated to relax the requirement of the bound of lumped uncertainty in the traditional sliding-mode control. In addition, numerical simulation and experimental results show that the proposed control scheme provides high-performance dynamic characteristics and is robust with regard to parametric variations, various reference trajectories, and different initial states.

Virtual CNC system. Part I. System architecture

Abstract: The paper presents a comprehensive virtual simulation model of a realistic and modular CNC system. The Virtual CNC architecture represents an actual CNC, but with modular feed drives, sensors, motors, and amplifiers. The CNC software library includes a variety of trajectory interpolation and axis control laws. Constant, trapezoidal and cubic acceleration profiles can be selected as a trajectory generation module. The control laws can be selected ranging from a simple PID to complex Pole Placement, Generalized Predictive Control or Sliding Mode Controller with friction compensation. When the Virtual CNC is assembled, its performance can be tested using frequency and time domain response analyses, which are automated. The Virtual CNC includes both analytical tuning methods for linear controllers, as well as Fuzzy Logic based expert auto-tuning system for Adaptive Sliding Mode Control. The paper includes detailed experimental verification of the Virtual CNC.

Underactuated ships follow smooth paths with Integral actions and without velocity measurements for feedback: theory and experiments

Abstract: Steering a ship along a desired path with a prescribed forward speed is a vitally important issue in many offshore applications. This paper presents a global controller that forces a ship without a sway actuator to follow a reference path and without velocity measurements for feedback. Nonlinear damping terms are also included to cover both low- and high-speed applications. Integral actions are added to the controller to compensate for a constant bias of environmental disturbances. Experimental results on a model ship illustrate the effectiveness of the proposed method.

Swarm Tracking Using Artificial Potentials and Sliding Mode Control

Abstract: In this paper, we present a stable and decentralized control strategy for multi-agent systems (swarms) to capture a moving target in a specific formation. The coor-dination framework uses artificial potentials to take care of both tracking and formation tasks. First, a basic controller is designed based on a kinematic model. After that, sliding mode control technique is used to force the agents with general vehicle dynamics to obey the required motion. Finally, specific potential functions are discussed and corresponding simulation results are given.

On Discretization of Continuous-Time Terminal Sliding Mode

Abstract: In terminal sliding-mode control, the system states are brought to the origin in finite time using the concept of sliding-mode control. Though the theory of terminal sliding mode is well studied for continuous time systems, a discrete-time terminal sliding mode concept has not been investigated. This note analyses the applicability of terminal sliding-mode control in the discrete-time framework and discusses the problems involved in the discretization of continuous-time terminal sliding mode. The note also suggests a method to approach the discrete-time terminal sliding-mode control problem

Systematic control of an electropneumatic system: integrator backstepping and sliding mode control

Abstract: This paper presents a synthesis of a nonlinear controller to an electropneumatic system. Nonlinear backstepping control and nonlinear sliding mode control laws are applied to the system under consideration. First, the nonlinear model of the electropneumatic system is presented. It is transformed to be a nonlinear affine model and a coordinate transformation is then made possible by the implementation of the nonlinear controller. Two kinds of nonlinear control laws are developed to track the desired position and desired pressure. Experimental results are also presented and discussed

Discrete sliding mode control of systems with unmatched uncertainty using multirate output feedback

Abstract: Systems with uncertainties and disturbances are common in practice. In some cases, these disturbances are unmatched. Moreover, in most cases the entire state information is also not available for control purpose. This note proposes a control algorithm for achieving quasi-sliding mode in discrete-time linear time-invariant (LTI) systems with bounded unmatched uncertainties. A multirate output feedback based strategy is used for this purpose. The proposed algorithm is illustrated through an example.

Nonlinear Stability and Control of Gliding Vehicles

Abstract: In this thesis we use nonlinear systems analysis to study dynamics and design control solutions for vehicles subject to hydrodynamic or aerodynamic forcing. Application of energy-based methods for such vehicles is challenging due to the presence of energyconserving lift and side forces. We study how the lift force determines the geometric structure of vehicle dynamics. A Hamiltonian formulation of the integrable phugoidmode equations provides a Lyapunov function candidate, which is used throughout the thesis for deriving equilibrium stability results and designing stabilizing control laws. A strong motivation for our work is the emergence of underwater gliders as an important observation platform for oceanography. Underwater gliders rely on buoyancy regulation and internal mass redistribution for motion control. These vehicles are attractive because they are designed to operate autonomously and continuously for several weeks. The results presented in this thesis contribute toward the development of systematic control design procedures for extending the range of provably stable maneuvers of the underwater glider. As the first major contribution we derive conditions for nonlinear stability of longitudinal steady gliding motions using singular perturbation theory. Stability is proved using a composite Lyapunov function, composed of individual Lyapunov functions that prove stability of rotational and translational subsystem equilibria. We use the composite Lyapunov function to design control laws for stabilizing desired relative equilibria in different actuation configurations for the underwater glider. We propose an approximate trajectory tracking method for an aircraft model. Our method uses exponential stability results of controllable steady gliding motions, derived by interpreting the aircraft dynamics as an interconnected system of rotational and translational subsystems. We prove bounded position error for tracking prescribed, straight-line trajectories, and demonstrate good performance in tracking iv unsteady trajectories in the longitudinal plane. We present all possible relative equilibrium motions for a rigid body moving in a fluid. Motion along a circular helix is a practical relative equilibrium for an underwater glider. We present a study of how internal mass distribution and buoyancy of the underwater glider influence the size of the steady circular helix, and the effect of a vehicle bottom-heaviness parameter on its stability.

Rollover prevention for heavy trucks using frequency shaped sliding mode control

Abstract: Control and handling of heavy commercial vehicles carrying liquid cargo are influenced by liquid movement within the partially filled tank. During steering and braking maneuvering tasks, the truck may exhibit unstable behavior at lateral acceleration levels of 0.3 g to 0.4 g [m/s2]. The fluid slosh forces and dynamic load transfers in the lateral and longitudinal directions and parametric uncertainties caused by moving liquid cargo affect the overall dynamics of the vehicle. To solve a physical problem about the minimal excitation of the slosh dynamics associated with the longitudinal and lateral excitation of the vehicle, dynamic sliding surface design combined with recursive backstepping algorithm is introduced. Compensator dynamics are introduced in the sliding mode through a class of switching surfaces which has the interpretation of linear operators such that the resulting closed-loop system retains the insensitivity to uncertainties in the sliding mode while minimizing the excitation of flexible mod...

Sampled Data Quasi-Sliding Mode Control Strategies

Abstract: Sampled-data (SD) variable structure control systems (VSCS) with quasi-sliding mode (QSM) are treated in this paper as a logical extension of VSCS with ideal sliding mode (SM). The most of well-known SD QSM control algorithms are derived by starting from reaching law approach. The problems of robustness to uncertainties, loads and unmodeled inertial dynamics are considered and some methods to solve these problems are presented. An example that illustrates SD QSM VSCS properties is given.

Spacecraft vibration suppression using variable structure output feedback control and smart materials

Abstract: A hybrid control scheme for vibration reduction of flexible spacecraft during rotational maneuvers is investigated by using variable structure output feedback control (VSOFC) for attitude control and smart materials for active vibration suppression. The proposed control design process is twofold: design of the attitude controller using VSOFC theory acting on the hub and design of an independent flexible vibration controller acting on the flexible part using piezoceramics as sensors and actuators to actively suppress certain flexible modes. The attitude controller, using only the attitude and angular rate measurement, consists of a linear feedback term and a discontinuous feedback term, which are designed so that the sliding surface exists and is globally reachable. With the presence of this attitude controller, an additional independent flexible control system acting on the flexible parts is designed for further vibration suppression. Using the piezoelectric materials as actuator/sensor, both single-mode vibration suppression and multimode vibration suppression are studied and compared for the different active vibration control algorithms, constant-gain negative velocity feedback (CGNVF) control, positive position feedback (PPF) control, and linear-quadratic Gaussian (LQG) control. Numerical simulations demonstrate that the proposed approach can significantly reduce the vibration of the flexible appendages and further greatly improve the precision during and after the maneuver operations.

Variable Structure Control for Interval Systems

Abstract: A variable structure control method is proposed for a class of interval systems. In terms of linear matrix inequalities (LMIs), a sufficient condition is given for the existence of linear sliding mode surface guaranteeing asymptotic stability of the reduced-order equivalent sliding mode dynamics. An LMI parameterization of such sliding mode surface is designed and a switched feedback control strategy is accordingly given to drive the system state trajectories reach the sliding surface. Finally, the simulation example shows the effectiveness of proposed method.