A new alternating predictive observer approach for higher bandwidth control of dual-rate dynamic systems

Dual-rate dynamic systems consisting of a sensor with a relatively slow sampling rate and a controller/actuator with a fast updating rate widely exist in control systems. The control bandwidth of these dual-rate dynamic systems is severely restricted by the slow sampling rate of the sensors, resulting in various issues like sluggish dynamics of the closed-loop systems, poor robustness performance. A novel alternating predictive observer (APO) is proposed to significantly enhance the control bandwidth of a generic dual-rate dynamic systems. Specifically, at each fast controller/actuator updating period, we will first implement the prediction step by using the system model to predict the system output, generating a so-called virtual measurement, when there is no output measurement during the slow sampling period. Subsequently, the observation step is carried out by exploiting this virtual measurement as informative update. An APO-based output feedback controller with a fast updating rate is developed and rigorous stability of the closed-loop system is established. The superiority of the proposed method is demonstrated by applying it to control a permanent magnet synchronous motor system.</p

Continuous nonsingular terminal sliding mode control for nonlinear systems subject to mismatched terms

This paper proposes a continuous nonsingular terminal sliding mode (NTSM) control approach for nonlinear systems subject to mismatched terms in order to achieve finite time exact tracking and disturbance rejection. The controller is constructed using a composite method that utilizes a power integrator and combines the output regulation theory, disturbance observation technique, feedback domination, and sliding mode control technique. The performance analysis demonstrates that the proposed continuous NTSM controller can drive the system output to the desired reference signal in a finite time in the presence of mismatched time-varying disturbances and nonsmoothed nonlinearities in each channel. The finite time Lyapunov theory is utilized to ensure finite-time convergence of the closed-loop system. The simulation results validate the effectiveness of the proposed continuous NTSM controller

Nonsmooth adaptive control for uncertain nonlinear systems: a non-recursive design approach

In this letter, a one-step nonsmooth adaptive controller design framework is proposed the first time for a class of nonlinear systems with general non-parametric uncertainties. By virtue of a novel non-recursive synthesis philosophy, a nonsmooth adaptive stabilizer can be constructed straightforwardly from the system in a possible simplest form, which facilitates practical implementations. In reference to well-acknowledged recursive design based approaches, direct improvements with this new non-recursive methodology include largely reduced synthesis complexity along with an essential detachment of control law design and stability analysis. A numerical example is provided to demonstrate both the simplicity and effectiveness of the proposed algorithm

Event-triggered state feedback control for p-normal uncertain nonlinear systems

The problem of event-triggered control for a class of uncertain nonlinear systems subject to p-norm is investigated in this paper. Note that the input-to-state stability (ISS) assumption related to the measurement error and the assumption on the existence of a stable controller are removed in this paper. With the help of adding a power integrator technique, intermediately control signals are presented to address the uncertainties and nonlinearities of the system under a fixed/relative threshold strategy, which plays an important role in the design of the event-triggered controllers. A rigorous Lyapunov stability analysis method is put forward to verify that all the signals of the closed-loop system are globally uniformly bounded and converge to an arbitrarily small set. Finally, an application of an underactuated mechanical system demonstrates the effectiveness of the designed scheme

Adaptive fixed-time position precision control for magnetic levitation systems

A novel adaptive fixed-time controller (AFTC) based on disturbance compensation technology is proposed to achieve high performance position precision control for magnetic levitation system in this paper. Firstly, the dynamic model of the magnetic levitation system is established and a fixed-time controller (FTC) is designed to realize the closed-loop control. However, this approach usually requires a large switching gain to suppress interference, resulting in chattering. In view of this, the generalized proportional integral observer (GPIO) is introduced to estimate and compensate the time-varying interference, which can not only improve the anti-interference ability, but also reduce the chattering by choosing a smaller switching gain. Nevertheless, these two performance improvements come at the cost of the dynamic response rate. In order to improve steady state performance without sacrificing dynamic performance, an adaptive fixed-time controller based on GPIO is proposed, which has a significant advantage because of the adjustable switching gain. Specifically, when the system state is far from the sliding mode surface, a larger switching gain is adjusted to improve the convergence rate. When the system state is close to the sliding mode surface, a smaller switching gain is adjusted to reduce chattering. Simulation and experimental results demonstrate the superiority of the proposed AFTC-GPIO method qualitatively and quantitatively

Predictor-based periodic event-triggered control for nonlinear uncertain systems with input delay

In this paper we investigate the problem of predictor-based periodic event-triggered control for a class of nonlinear uncertain systems subject to input delay. When only sampled-data output is available, a novel predictor-based continuous-discrete observer is first designed to estimate system state, and an event-triggered controller is second proposed to globally exponentially stabilize the nonlinear uncertain system. Under the proposed control method, the effects of input delay and sampling of output can be considerably compensated thanks to prediction technique. As a byproduct, the Zeno behavior is avoided in nature since the proposed event-triggering mechanism is detected in the form of discrete-time. Some sufficient stability conditions on maximum allowable sampling period and input delay are presented by using feedback domination technique and small-gain argument

Disturbance observer-based autonomous landing control of unmanned helicopters on moving shipboard

In this paper, the autonomous landing control issue on moving shipboard is investigated for unmanned helicopters subject to disturbances. The issue is studied by stabilizing the error system of the helicopter and the shipboard. The landing process is divided into two phases, i.e., homing phase, where a hierarchical double-loop control scheme is developed such that the helicopter is forced to hover synchronously at a certain altitude over the shipboard, and landing phase, where a composite landing control scheme is proposed such that the helicopter lands vertically on the shipboard in synchronization with its attitudes. The velocity and acceleration information of the shipboard as well as lump disturbances is estimated through joint state and disturbance observers. The estimates are then incorporated into the baseline feedback controller, formulating composite active anti-disturbance landing control schemes. A continuous terminal sliding mode control method is proposed for the feedback controller design, which not only effectively mitigates the chattering of the control action, but also simplifies the design process of the controller. Numerical simulations demonstrate the effectiveness and superiorities of the proposed control schemes

A model-based unmatched disturbance rejection control approach for speed regulation of a converter-driven DC motor using output-feedback

The speed regulation problem with only speed measurement is investigated in this paper for a permanent magnet direct current (DC) motor driven by a buck converter. By lumping all unknown matched/unmatched disturbances and uncertainties together, the traditional active disturbance rejection control (ADRC) approach provides an intuitive solution for the problem under consideration. However, for such a higher-order disturbed system, the increase of poles for the extended state observer (ESO) therein will lead to drastically growth of observer gains, which causes severe noise amplification. This paper aims to propose a new model-based disturbance rejection controller for the converter-driven DC motor system using output-feedback. Instead of estimating lumped disturbances directly, a new observer is constructed to estimate the desired steady state of control signal as well as errors between the real states and their desired steady-state responses. Thereafter, a controller with only speed measurement is proposed by utilizing the estimates. The performance of the proposed method is tested through experiments on dSPACE. It is further shown via numerical calculations and experimental results that the poles of the observer within the proposed control approach can be largely increased without significantly increasing magnitude of the observer gains

Reduced-order GPIO based dynamic event-triggered tracking control of a networked one-DOF link manipulator without velocity measurement

In networked robot manipulators that deeply integrate control, communication and computation, the controller design needs to take into consideration the limited or costly system resources and the presence of disturbances/uncertainties. To cope with these requirements, this paper proposes a novel dynamic event-triggered robust tracking control method for a one-degree of freedom (DOF) link manipulator with external disturbance and system uncertainties via a reduced-order generalized proportional-integral observer (GPIO) . By only using the sampled-data position signal, a new sampled-data robust output feedback tracking controller is proposed based on a reduced-order GPIO to attenuate the undesirable influence of the external disturbance and the system uncertainties. To save the communication resources, we propose a discrete-time dynamic event-triggering mechanism (DETM) , where the estimates and the control signal are transmitted and computed only when the proposed discrete-time DETM is violated. It is shown that with the proposed control method, both tracking control properties and communication properties can be significantly improved. Finally, simulation results are shown to demonstrate the feasibility and efficacy of the proposed control approach. </p

Finite-time path following control for small-scale fixed-wing UAVs under wind disturbances

By integrating the finite time control technique and finite-time disturbance observers together, the finite-time three-dimensional path following control problem for small-scale fixed-wing UAVs subject to external wind disturbances is investigated in this paper. The external wind disturbances are estimated through finite-time disturbance observers and the estimates are then incorporated into the finite-time feedback controller such that a composite control scheme is proposed. Under the proposed control scheme, the closed-loop system possesses not only faster convergence rate but also stronger disturbance rejection ability and better robustness, which is the main contribution of the paper. The effectiveness and superiorities of the proposed composite control scheme are demonstrated by numerical simulations. </p