Additive Disturbances Research Articles

A Single-Tube Robust Model Predictive Control Method Based on ε-Approximation

This paper aims to solve the problem of the robust model predictive control, the contradiction of the system robustness, and the conservative terminal constraint set range. A robust model predictive control (RMPC) method based on an ε-approximation single-tube set is proposed. We construct a single-tube RMPC structure for linear discrete time invariant systems with additive disturbances. To this structure, we add the state estimation and state feedback to improve the convergence rate. Furthermore, we use the ε-approximation to estimate the terminal constraint set with less conservatism, thus improving the robustness. Then, we conduct a stability analysis of the ε-approximation single-tube RMPC system. The simulation results demonstrate the stability and interference allowance advantages of the proposed method.

Interval Observers for Switched Metzler-Takagi-Sugeno Fuzzy Systems

This paper is concerned with the design of switching observers for nonlinear positive systems, where the basic parameters of the Metzler-Takagi-Sugeno fuzzy models are intervally defined. With consideration of the measurable set of premise variables the associated structure of the switching fuzzy interval observers is proposed for system state estimation to maintain stability and H1 performance level under the influence of norm-bounded additive disturbance. The design conditions take into account the lower and upper bounds of nonnegative system state. A numerical example is included to demonstrate the effectiveness of the developed theory for the condisered class of systems.

Long-term effects of rewetting and drought on GPP in a temperate peatland based on satellite remote sensing data

Rewetting previously drained peatlands restores the critical function of peatlands as long-term carbon storages and sinks currently threatened by climate change and additional human-induced disturbances. Understanding and projecting the restoration process by rewetting, however, currently face a pressing challenge, the lack of consistent and gap-free records of important carbon cycling indicators of peatlands such as the gross primary production (GPP) over long term. In this study, we reconstructed the GPP in a rewetted peatland called Zarnekow (Fluxnet-ID: DE-Zrk) in Germany from 2000 to 2020 by combining long-term satellite observations and limited-term tower-based eddy covariance (EC) measurements based on Random Forest regression models. The R2 between the reconstructed data and EC data was 0.6. The reasonable reconstruction of long-term GPP enabled trend analysis that identified two distinct periods of decreasing/increasing in GPP due to rewetting and droughts. Rewetting in the winter of 2004 and 2005 stabilized GPP after a decreasing period. A drought in 2018 significantly increased GPP, and GPP remained high over the following two years. Furthermore, the month-specific trends show significant seasonality at this site, specifically, an increasing trend over the 21 years in the growing-season months of June to August and a decreasing trend in the other months. The most important variables for satellite-based estimates of GPP at this site include total evapotranspiration, land surface temperature, enhanced vegetation index and near-infrared reflectance vegetation index. Long-term analyses of carbon fluxes through the combination of satellite observations and EC measurements provide crucial insights into the restoration of carbon sequestration functions in rewetted peatlands.

Numerical Study of Instability of Medium Interface During Thermonuclear Combustion of a Cylindrical Shelled Microtarget

The study is limited to two-dimensional disturbances of the interface between media. A computational technology based on the explicit interface separation in the form of one of the lines of a regular grid is used. A method for visualizing spontaneous disturbances at an early stage when they cannot yet be seen on the interface profile is proposed. It is shown that the computer rounding error plays an insignificant role in their formation. For the late stage of the disturbance development, a method for obtaining the profile of the local oscillation amplitude along the interface is proposed. The features of spontaneous disturbance at different stages of its development are studied. It is shown that the spontaneous disturbance tends to grid convergence, at least until the beginning of the process of formation of a quasi-stationary shockless combustion wave. It is shown that during the formation of a quasi-stationary wave and its subsequent motion, an additional spontaneous disturbance arises. The interaction of a specified sinusoidal disturbance having an initial amplitude of up to 0.1 of the wavelength with a quasi-stationary combustion wave is studied. It is shown that the Kelvin–Helmholtz instability is the main mechanism for the development of instability at the nonlinear stage. The combustion wave is not destroyed. The profiles of the oscillation amplitude of the given disturbance are obtained, from which it is possible to extract the universal time-independent part.

Research on HVDC Supplementary Two-Stage Transient Control and Smooth Switching

HVDC additional transient control is an essential means to elevate the transient stability of AC/DC interconnected systems and the inevitable requirement of intelligent transmission. Two-stage transient additional control and a smooth switching strategy are proposed. By establishing an extended state observer for unbalanced power in the system disturbance, the real-time and accurate estimation of unstable power is realized, and an adaptive emergency power support controller is constructed. The mathematical model of the system is identified by using Total Least Squares-Estimation on Signal Parameters via Rotational Technique (TLS-ESPRIT). Based on the singular value reduction theory, the HVDC additional Active Disturbance Rejection Damping Controller (ADRDC) that can inhibit the low-frequency oscillation of the system is designed. Finally, two switching strategies are designed based on the change in the state of the network fault switch and the change in the power angle oscillation curve. The three-in-feed HVDC system is built in PSCAD, and the simulation analysis is carried out. The simulation results confirm the validity of the proposed method.

On the Stable Solution of the Problem of Compensating Nonsmooth Additive Disturbances with the Help of Feedback Laws

On the Stable Solution of the Problem of Compensating Nonsmooth Additive Disturbances with the Help of Feedback Laws

Attributing a Causal Agent and Assessing the Severity of Non-Stand Replacing Disturbances in a Northern Hardwood Forest using Landsat-Derived Vegetation Indices

Non-stand-replacing disturbances are major drivers of northern hardwood forest dynamics, but are more challenging to characterize using satellite imagery than stand-replacing events. This study proposes a hurdle approach in which disturbance causal agents are first attributed to permanent sample plots that were either partially harvested, had sustained damage from an ice storm or remained undisturbed during the observation period, reaching an overall accuracy of 82.9%. Ordinary least square regression was then used to develop disturbance-specific models to assess the severity of partial harvests and damage from ice storms, with r-squared values of 0.57 and 0.59, respectively. The disturbance-specific models included a different set of predictors, confirming the importance of attributing a causal agent to a disturbance before assessing its severity. The sequence of models was implemented regionally to produce severity maps for two disturbance events, revealing within-stand variability in the severity that could be useful for the planning of future silvicultural actions. Although the proposed models offer acceptable performance, more research is needed to include additional disturbance agents and develop models that better capture the small variations in the spectral reflectance caused by low-severity disturbances, especially in the case of low-intensity partial harvests.

Reduction of Auto-Power Procedure Influence on the Photovoltaic Inverter On-Board Bus System Caused by Pulsed Loads

The article presents an on-board power system designed for ships, aviation, and space vehicles using energy from photovoltaic panels. The power structure includes both DC and high-frequency AC power buses. As a result of pulse loads, this system is exposed to disturbances that cause electronic systems to reboot. To reduce the effect of the appearance of secondary disturbances in the AC bus to which the photovoltaic converter is connected, a new control strategy has been proposed. This strategy improves the operation of the proportional resonant regulator that controls the AC bus current by making the reference values linearly dependent on the DC bus voltage. A prototype of such a system was designed in the laboratory. The FPGA control board was pulse-disturbed, leading to start the auto-power procedure, and additional disturbances were observed in the AC bus for the standard system. Reduction in the impact of these disturbances was achieved using the proposed control method by reaching a limitation of the bus current in dynamic states caused by the auto-power on process from 280% to less than 100% of the steady-state value. Experimental results verified the validity of the proposed method.

Cooperative control of a platoon of connected autonomous vehicles and unconnected human‐driven vehicles

AbstractBy using kinematic state information obtained through vehicle‐to‐vehicle communications, connected autonomous vehicles (CAVs) can drive cooperatively to alleviate shockwave propagation associated with traffic disturbances. However, during the transition to full autonomy, CAVs and human‐driven vehicles (HDVs) will coexist on the road, creating mixed‐flow traffic. The inherent heterogeneity and randomness in human driving behavior can generate additional disturbances in the traffic flow. Further, HDVs without communication functionality (unconnected HDVs) can cause the control performance of CAVs to degrade by negatively impacting platoon formation. To proactively mitigate the negative impacts of HDVs in mixed‐flow traffic, this study proposes a cooperative control strategy with three components for platoons consisting of CAVs and unconnected HDVs: (i) a number estimator for estimating the number of HDVs between two CAVs, (ii) a kinematic state predictor for predicting the kinematic states of HDVs, and (iii) a multi‐anticipative car‐following controller (i.e., control strategy using kinematic state information of multiple preceding vehicles) for CAVs to maintain string stability and desired time headway. To initialize the proposed strategy, the number estimator is developed using a deep neural network (DNN). Then, a DNN‐based kinematic state predictor predicts the kinematic states of HDVs for CAVs to enable multi‐anticipative car‐following control. The multi‐anticipative car‐following controller is implemented using an extended intelligent driver model‐guided deep deterministic policy gradient algorithm, which ensures safety, string stability, and traffic efficiency. The effectiveness of the proposed control strategy is validated through numerical experiments using NGSIM data. Results indicate that the proposed strategy can produce accurate estimations of the number and the kinematic states of HDVs between CAVs. Further, it can achieve string stability while maintaining smaller time headways, compared to car‐following models used for training guidance under different market penetration rates of CAVs, which significantly improves traffic smoothness and mobility.

Aerodynamic configuration and control optimization for a novel horizontal-rope shipborne recovery fixed-wing UAV system

Efficient UAV performance and a perfect recovery system are required to achieve the safe and reliable shipborne recovery of fixed-wing UAVs, which is essential for expanding their marine applications. In this study, taking an automatic horizontal-rope shipborne recovery (aHRSR) system as the recovery platform, a joint optimisation method of fixed-wing UAVs combined aerodynamic configuration and control optimisation was investigated. First, the distribution of a dynamic system was adopted to attain aerodynamic optimisation. A wing-mounted double-engine pull (WMDE-PULL) configuration was developed based on the slipstream effect. Compared with the tail-mounted single-engine push (TMSE-PUSH) configuration, the WMDE-PULL configuration could significantly enhance the lift and low-speed characteristics and eliminate the disturbances from the reaction torque of the single-engine propeller. This aerodynamic optimisation method evidently improved the control accuracy of the controller. To offset the comprehensive disturbance under complex conditions at the sea, including the internal disturbance of the additional torque and external disturbance of the wake, the acceleration feedback method was implemented for the inner loop attitude of the original controller. The optimised controller had good robustness and stability. Several experiments were conducted for the recovery of the optimised UAV on the aHRSR system, and a recovery success rate of 100% was achieved. The results show that the joint optimisation method of fixed-wing UAVs is valid and practical, and the recovery scheme of an optimised fixed-wing UAV on an aHRSR system provides practical reference for shipborne recovery.

Lie-brackets-based averaging of affine systems via a time-delay approach

In this paper, we study input-to-state stability (ISS) of affine systems with a small parameter ɛ>0 and additive disturbances in the presence of state-delays. We present a time-delay approach to Lie-brackets-based averaging, where we transform the system to a time-delay (neutral type) one. The latter has a form of perturbed Lie brackets system. The ISS of the time-delay system guarantees the same for the original one. We present a direct Lyapunov–Krasovskii (L–K) method for the time-delay system and provide sufficient conditions for regional ISS. Further we apply the results to stabilization of linear uncertain systems under unknown control directions using the bounded extremum seeking controller with measurement delay. In contrast to the existing results that are all qualitative, we derive constructive linear matrix inequalities for finding quantitative upper bounds on ɛ and the time-delay that ensure regional ISS of the original system and on the resulting ultimate bound. Numerical examples illustrate the efficiency of our method.

Numerical Investigations of Laminar Separation Bubbles Under the Influence of Periodic Gusts

Direct numerical simulations were performed to investigate the behavior of laminar separation bubbles subject to vertical gusts in an airfoil flow. Oscillating boundary-layer flows containing gusts—including unsteady pressure gradients—were prescribed via boundary conditions as well as forcing terms on a domain located in the upper rear section of a natural laminar flow airfoil. For this hybrid approach, unsteady Reynolds-averaged Navier-Stokes (URANS) simulations of the entire flowfield were carried out in conjunction with the so-called disturbance velocity approach, providing transient boundary conditions for the direct numerical simulation. A steady-state reference case with a Reynolds number of is compared and validated with results from wind tunnel experiments. Results of simulations at four different gust frequencies at the same amplitude , each with and without additional disturbances to the boundary layer introducing oblique resonance, are presented and discussed in this paper. The time-dependent behavior of convective instability modes is evaluated by using the continuous wavelet transform and linear stability theory with an unsteady extension. Furthermore, the contribution of the absolute instability—which appears to be larger in the case of oscillating flow compared to the steady-state case—is discussed. Lock-in effects are identified at high gust frequencies.

Reprint of: Formulation and estimation of stochastic frontier production function models

Previous studies of the so-called frontier production function have not utilized an adequate characterization of the disturbance term for such a model. In this paper we provide an appropriate specification, by defining the disturbance term as the sum of symmetric normal and (negative) half-normal random variables. Various aspects of maximum-likelihood estimation for the coefficients of a production function with an additive disturbance term of this sort are then considered.

On the Stable Solution of the Problem of Compensating Nonsmooth Additive Disturbances with the Help of Feedback Laws

The problem of the feedback control of a system of ordinary differential equations, nonlinear in phase variables, subjected to the effect of an unknown nonsmooth disturbance is discussed. The problem consists of constructing a control action formation law that guarantees compensation for a nonsmooth disturbance; i.e., it guarantees that the phase trajectory (as well as the rate of its change) of the given system follows the prescribed phase trajectory (as well as the rate of its change) for any admissible realization of the disturbance. Two cases are considered. In the first case, admissible disturbances are constrained by instantaneous restrictions, and in the second case, any function that is an element of the space of Lebesgue measurable functions summable with the square of the Euclidean norm can be an admissible disturbance. The problem is solved under conditions of inaccurate measurement at discrete times of the phase states of both systems. In the presence of instantaneous restrictions on disturbances, the problem is also solved by measuring some of the phase states. Algorithms for solving this problem, oriented towards computer implementation, are designed that are resistant to information interference and computational errors. Estimates of the rate of convergence of the algorithms are given.

Anti-disturbance attitude quantized control of flexible spacecraft via a triggering and quantization joint dynamic event-triggered mechanism

This article investigates the problem of dynamic event-triggered anti-disturbance attitude quantized control based on the Takagi-Sugeno fuzzy method for flexible spacecraft, where multiple disturbances and parameter uncertainties are simultaneously considered. First, by employing the Takagi-Sugeno fuzzy model to represent the nonlinear disturbances with additional disturbance, a disturbance observer based on the Takagi-Sugeno fuzzy model is constructed under the unmeasurable premise variables to estimate the unknown nonlinear disturbances. Furthermore, a flexible vibration observer is formatted. Subsequently, a dynamic event-triggered mechanism with the quantization parameter is introduced, which can obtain a trade-off between quantization density and event-triggered frequency on the condition that the system stability is ensured. And an event-triggered anti-disturbance quantized controller is constructed, which can make up for Takagi-Sugeno fuzzy modeling disturbances and reject parameter uncertainties and other bounded disturbances. To guarantee the bound of the closed-loop signals, some sufficient conditions are obtained. At last, the efficiency of the suggested control strategy is illustrated via the simulation results.

An integral‐differential combined type event‐triggered model predictive control for perturbed linear systems

AbstractAn integral‐differential combined (IDC) type event‐triggered model predictive control (ET‐MPC) strategy is constructed for linear time‐invariant (LTI) systems in this paper. Compared with the standard ET‐MPC method, the proposed MPC algorithm is developed based on an IDC type event‐triggering mechanism (ETM), which takes both the integral and change rate of the error between the optimal prediction and the real state into the consideration for the construction of the triggering condition. In this way, the dynamic performance can be considered more comprehensively, for effectively reducing the calculation and communication burdens of the ET‐MPC method. In addition, an improved robust constraint is used to deal with additive disturbances, and the dual‐mode control method is employed in the development of the strategy. Then the parameter conditions guaranteeing the iterative feasibility of the proposed algorithm, the closed‐loop stability of the LTI system, and the avoidance of Zeno behavior are given. Finally, two simulation examples demonstrate the effectiveness of the algorithm.

Robust adaptive control design of nonlinear systems with input delay

AbstractIn this paper a robust adaptive controller for a class of uncertain nonlinear systems is developed with additive disturbance and unknown time‐varying input delay. The control law is composed of a Desired Compensation Adaptation Law (DCAL) based feedforward term for the adaptation of uncertain plant parameters and two robust feedback terms based on the integral of the past control to compensate the input delay. The sufficient conditions on controller gains and limit on delay bound are derived through stability analysis by choosing suitable Lyapunov‐Krasovskii functionals which gives a globally uniformly ultimately bounded (GUUB) tracking. The performance of the controller is evaluated by performing simulation on a two link robot manipulator system for different values of the input delay.

INSTRUMENT FOR MEASURING PULSATION CHARACTERISTICS IN TURBULENT FLOWS

The paper considers the design of a two-component strain gauge construction for measuring pulsation characteristics in turbulent flows.
 The analysis is carried out and the shortcomings of the existing sensor models and their influence on the reliability and accuracy of the experimental results are shown. The limited frequency range of such sensors is also emphasized.
 The design of the previous types of sensors is based on a plate on which wire or film strain gauges are glued. In such models, the main part of the perceiving hydrodynamic pressure goes to the formation of stresses in the elastic plate, and only a small part (up to 4%) - to create stresses in the strain-sensitive elements. Such sensors require an increase in the size of sensitive elements, this causes an additional disturbance in the flow, which in turn also reduces the accuracy of the measurement.
 The use of glue in the design of the sensor is associated with adverse effects such as creep and aging of the glue.
 The proposed sensor used strain gauges in the form of constantan wires stretched parallel to each other, which helped to get rid of elastic plates and glue, and also reduced the size of the sensing element.
 A construction of the sensor is shown and its design is described.
 The sensor has a free vibration frequency in water of more than 300 Hz, which is more than an order of magnitude higher than the frequency of water flow oscillations. This allows a more accurate measurement of pulsation characteristics.
 The principle of operation of the strain gauge is considered.
 The presence in the construction of four correspondingly located tensile strands made it possible to measure the longitudinal and transverse components of the pulsation velocities in turbulent flows.

Secure Control Design for Networked Control Systems With Nonlinear Dynamics Under Time-Delay-Switch Attacks

A continuous controller is developed for a centralized network control system (NCS), which is composed of agents with nonlinear dynamics subject to a time-delay-switch (TDS) attack and additive disturbances. Since the state tracking error is unmeasurable during TDS attacks, controllers cannot use the state tracking error to coordinate the NCS. Therefore, a novel error signal is designed to address this unique challenge and enable the NCS to achieve a formation control objective. Furthermore, a TDS attack mitigation strategy is developed, which uses both learning- and model-based approaches to estimate an agent’s state for TDS attack detection and compensation. Lyapunov–Krasovskii functionals are used in the stability analysis to prove that the tracking errors converge to a steady-state residual, which is a function of the system uncertainty and TDS attack properties. The leader–follower formation control problem for unmanned aerial vehicles based on a pure pursuit guidance law is selected for a simulation study to validate the performance of the proposed method.

Impact Analysis of Intercell Interference in Cellular Networks for Navigation Applications

This article studies the intercell interference (ICI) effects in cellular networks for navigation applications. This is achieved through the derivation of an analytical expression for a cellular navigation receiver postcorrelation signal-to-noise power ratio (SNR) in the presence of multiple asynchronous cells. It reveals that in addition to the channel power, the cell loading rate and data modulation order for the interfering cells also play important roles in affecting the received signal quality of the desired cell. Furthermore, the time-of-arrival (TOA) estimation and positioning accuracy degradation due to the ICI is characterized by the Cramer–Rao and Ziv–Zakai lower bounds based on the derived postcorrelation SNR. Simulations are performed to verify the theoretical expressions and the results indicate that the ICI term can be treated as an additional Gaussian disturbance for characterizing the TOA estimation accuracy in cellular navigation receivers.