Time Delay Uncertainties Research Articles

Calculation model and uncertainty analysis of projectile explosion position based on acousto-optic compound detection

The random uncertainty of a projectile explosion position at the terminal trajectory makes testing difficult. To solve these problems, this paper proposes a measurement method of projectile explosion position acousto-optic compound detection using acoustic sensors and compound-eye photoelectric detection sensor. A test layout mode is designed in which the compound-eye photoelectric detection sensor is at the center of the square test array, four acoustic sensors are at the four corners of the square test array.The compound-eye photoelectric detection sensor is used as the synchronous triggering device for the projectile explosion acoustic signal. A calculation model of the projectile explosion position is established based on the acousto-optic sensors compound detection test method. The influence of time delay uncertainty, array layout uncertainty and acoustic velocity uncertainty on the projectile explosion position are analyzed. Based on the test array platform, live ammunition tests were carried out, and the test results of the projectile explosion position are consistent with the theoretical calculation and the influence law of uncertainty, which shows the feasibility of the proposed measurement method.

The effects of trade cost components and uncertainty of time delay on bilateral export growth

This paper measures the trends, specifically for exporters, in bilateral trade costs and more specifically for costs associated with policy barriers. The study further examines the effects of different trade cost components on bilateral export flows via the dynamic panel gravity model. Empirical evidence shows that trade costs generally have a declining trend globally, however, in the case of emerging countries, this rate of decline is very low. The costs associated with non-tariff barriers in emerging countries have a greater role in the continuation of higher trade costs, in comparison to tariff barriers' costs. Likewise, the two-steps system GMM model's results suggest that the infrastructure quality, transportation costs, volatility of exchange rate, and uncertainty in time (days) delay are major hurdles in the sustainable growth of exports and indeed have rendered the exports uncompetitive in the world market, those are also sturdily supported by the prediction of the theory.

Polynomial-based Stability Analysis of Modified IMC-PID Controller for Piezoelectric Actuator System in Time Delay Environment

Piezoelectric actuators are widely used in several industrial applications requiring precision positioning. However, the positioning accuracy of this nonlinear actuator is severely limited by physical phenomenon such as hysteresis, uncertainties. Accordingly, to improve the performance of piezo micro–nano positioning system, appropriate control laws are designed to linearize the hysteresis through closed-loop approaches. A modified internal model controller (MIMC) is useful with regard to efficient computational hardware resource utilization when compared with the conventional approach provided the resulting controller is stable. This paper focuses on one such widely used and computationally inexpensive control framework in the form of PID-based MIMC to mitigate hysteretic nonlinearity in piezoelectric actuators with the aim to investigate the time delay uncertainty handling range of the controller. The system stability pertaining to time delay has been analyzed numerically and the maximum delay that the system can withstand without losing its stability, i.e. the delay margin has been determined using polynomial-based approach. It has been found that upon increasing the delay beyond a specific critical value, the controller performance is limited and the system turns unstable. Simulations carried out in time delay environment validate the theoretically achieved results.

Dissipativity Analysis for a Class of Discrete-Time Neutral Stochastic Nonlinear Systems with Time Delay

This paper focuses on the problem of dissipativity analysis for a class of discrete-time neutral stochastic nonlinear systems (DTNSNSs) with time delay and parameter uncertainties. Different from the existing results on this topic of neutral system, a kind of discretizing the neutral system is considered. Firstly, a sufficient condition of the dissipativity, which is dependent on the solution of the Lyapunov–Krasovskii technique and linear matrix inequalities (LMIs), is established. Moreover, the state-feedback controller is designed to guarantee the dissipative performance of the closed-loop system. The effectiveness of the theoretical results is finally demonstrated by a numerical example.

Robust Controller Synthesis and Analysis in Inverter-Dominant Droop-Controlled Islanded Microgrids

This work investigates the problem of controller design for the inverters in an islanded microgrid. Robust μ-synthesis controllers and local droop controllers are designed to regulate the output voltages of inverters and share power among them, respectively. The designed controllers alleviate the need for additional sensors to measure the states of the system by relying only on output feedback. It is shown that the designed μ-synthesis controller properly damps resonant oscillations, and its performance is robust to the control-loop time delay and parameter uncertainties. The stability of a droop-controlled islanded microgrid including multiple distributed generation (DG) units is analyzed by linearizing the nonlinear power flow model around the nominal operating point and applying theorems from linear algebra. It is indicated that the droop controller stabilizes the microgrid system with dominantly inductive tie-line impedances for all values of resistive-inductive loads, while for the case of resistive-capacitive loads the stability is conditioned on an upper bound on the load susceptances. The robust performance of the designed μ-synthesis controller is studied analytically, compared with the similar analysis in an H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> control (benchmark) framework, and verified by simulations for a four DG benchmark microgrid. Furthermore, the robustness of the droop controllers is analyzed by Monte Carlo simulations in the presence of local voltage fluctuations and phase differences among neighboring DGs.

Stability Analysis of Grid-connected Inverter System Containing Virtual Synchronous Generator under Time Delay and Parameter Uncertainty

Virtual synchronous generator (VSG) control is an effective way to increase the equivalent inertia of grid connected inverter system and improve the stability of the power grid. However, the influence of this control on the stability of the whole system with time delay and parameter uncertainty should be researched further. In this paper, the state space model of the whole grid connected inverter system adopting VSG under control time-delay and parameter uncertainty is established. The Lyapunov functional with time-delay is constructed by employing time-delay dependent free weight matrix transformation. Furthermore, Lyapunov stability theorem is used to obtain the more conservative time-delay stability conditions with and without parameter uncertainty, linear matrix inequality is used to calculate the time-delay stability margin of the system under uncertainty, and the influence of the parameters of VSG control on the delay stability margin is analyzed. The validity of the proposed stability analysis and stability margin solution method are verified by simulation examples.

Robust adaptive neural networks control for dynamic positioning of ships with unknown saturation and time-delay

In this paper, a robust adaptive neural networks control based on minimal–parameter-learning (MLP) is proposed for dynamic positioning (DP) of ships with unknown saturation, time delay, external disturbance and dynamic uncertainties. Through the velocities backstepping method, radial basis function (RBF) neural networks and robust adaptive control are incorporated to design a novel controller of which an appropriate Lyapunov-Krasovskii Function (LKF) is constructed to overcome the effect caused by time-delay. Meanwhile, the MLP technology is applied to reduce the computational burden while only one parameter need to be update by an adaptive law. In additional, a robust adaptive compensate term is introduced to estimate the bound of the lumped disturbance including the unknown saturation, unknown external disturbance and the approximate error of neural networks control while the robustness of MLP is improved and the unknown saturation is compensated. The developed control law makes the DP closed-loop system be uniformly ultimately stable which can be proved strictly through Lyapunov theory. Finally, simulations with a guidance law are proposed to demonstrate the validity of controller we developed.

A Robust Steered Response Power Localization Method for Wireless Acoustic Sensor Networks in an Outdoor Environment.

The localization of outdoor acoustic sources has attracted attention in wireless sensor networks. In this paper, the steered response power (SRP) localization of band-pass signal associated with steering time delay uncertainty and coarser spatial grids is considered. We propose a modified SRP-based source localization method for enhancing the localization robustness in outdoor scenarios. In particular, we derive a sufficient condition dependent on the generalized cross-correlation (GCC) waveform function for robust on-grid source localization and show that the SRP function with GCCs satisfying this condition can suppress the disturbances induced by the grid distance and the uncertain steering time delays. Then a GCC refinement procedure for band-pass GCCs is designed, which uses complex wavelet functions in multiple sub-bands to filter the GCCs and averages the envelopes of the filtered GCCs as the equivalent GCC to match the sufficient condition. Simulation results and field experiments demonstrate the excellent performance of the proposed method against the existing SRP-based methods.

Design of a wide-area damping controller to tolerate permanent communication failure and time delay uncertainties

The wide-area damping controllers showed to be effective in improving the damping ratio of the low-frequency oscillation modes. This controller requires remotes signals sent by Phasor Measurement Units located in different positions of the power system and, then, these signals are highly susceptible to communication time delays, failures and cyber-attacks that may compromise controller performance. This paper presents a procedure based on particle swarm optimization to tune the parameters of the central controller. Considering a set of operating conditions, the proposed procedure will search the central controller parameters that maximize the damping ratio of all eigenvalues of the linear model. A strategy to deal with permanent communication channel failures and time delay uncertainties in a given interval will be included in the proposed model and procedure. Then, the resulting central controller will present robustness to multiple operation conditions of the power system, to time delay uncertainties and to permanent failure of the channels of the controller. The proposed procedure was carried out in the IEEE 68-bus system and the performance of the designed controller was evaluated by modal analysis and time-domain nonlinear simulation.

Scattering Transformation Based Wide-Area Damping Controller of SSSC Considering Communication Latency

This paper presents a new design of a scattering transformation-based wide-area damping controller for static synchronous series compensator (SSSC) to enhance power system stability in the presence of communication latency. The proposed control approach is comprised of a classical structure in addition to two scattering transformation ports. These ports are inserted between the power system and the wide-area damping controller (WADC) to regulate the signal exchange. Since the WADC is a centralized controller, the time delay imperfections are considered in the design stage. The proposed controller design is formulated as an optimization problem where the controller parameters are optimized using the particle swarm optimization (PSO) algorithm. The proposed controller improves the system damping performance due to the achieved time delay compensation. The proposed controller's effectiveness is demonstrated by implementing the controller in several case studies under different disturbance scenarios. The proposed controller performance is benchmarked with the classical WADC based on the lead-lag structure. The results confirm the robustness of the proposed WADC against time delay uncertainty. The proposed controller's efficacy is confirmed to reduce the time delay, resulting in better power system stability.

Time-Varying Boundary Layer Based Iterative Learning Control for Nonlinearly Parametric Time-Delay Systems With Arbitrary Initial Errors and Iteration-Varying Reference Trajectories

In this paper, the tracking problem for a class of nonlinearly parametric time-delay systems with arbitrary initial state errors and iteration-varying reference trajectories is studied. An adaptive iterative learning control scheme is developed by using Lyapunov approach. A time-varying boundary layer is constructed for removing the zero initial error condition, which is necessary in normal iterative learning control algorithms. The time-varying nonlinearly parametric uncertainties and time-delay uncertainties are well compensated by using parameter separation technique, signal replacement mechanism and robust strategy. As the iteration number increases, the state tracking error asymptotically converges to a tunable residual set. In the end, a simulation example further verifies the theoretical results.

A Method Based on Linear Matrix Inequalities to Design a Wide-Area Damping Controller Resilient to Permanent Communication Failures

One of the main advantages of the wide-area measurement systems in the small-signal stability of the electric power systems is to use synchrophasor data from the phasor measurement units (PMUs) for the operation of a central controller, or wide-area damping controller (WADC), to improve the damping ratio of the low-frequency oscillation modes. However, cyber-attacks in the PMU measurements can lead to permanent communication failure of the WADC channels and, therefore, the dynamic performance of the power system can be damaged. Besides, the signals for this controller are from different locations and thus they present time delays that can also damage the power system dynamic performance. This article introduces a method based on linear matrix inequalities to design a WADC robust to power system operation uncertainties, time-delay uncertainties, and permanent communication failure of the WADC channels. The proposed method was applied and evaluated in the IEEE 68-bus system by modal analysis and time-domain nonlinear simulations.

Observer-based robust model predictive control of switched nonlinear systems with time delay and parametric uncertainties

In this study, an observer-based robust model predictive control scheme is proposed to control a class of switched nonlinear systems in the presence of time delay and parametric uncertainties under arbitrary switching. Constructing an appropriate Lyapunov–Krasovskii functional in conjunction with an infinite horizon cost function, sufficient conditions are obtained to guarantee the asymptotic stability of the closed-loop switched system in terms of linear matrix inequalities depending on the time delay, the upper bounds of uncertain parameters, and the Lipschitz constant of subsystems. To model the uncertainty of the system, the parametric uncertainty is used to reduce the computational burden and the conservatism of the method. In the proposed method, a predictive state observer and an observer-based controller are synthesized via an online optimization problem to minimize the upper bound of the cost function, while handling the constraints. Finally, the obtained results are validated using practical and numerical simulations.

Semi‐active control of air suspension with auxiliary chamber subject to parameter uncertainties and time‐delay

AbstractSuspension systems are critical to the ride comfort and handling stability of vehicles, but traditional passive suspensions fail to achieve optimal performance in the two aspects. Semi‐active suspension controller changes the suspension stiffness or damping to improve the ride comfort and handling stability, which has the potential advantages of low energy consumption and high reliability. In this paper, the model of an air spring with an auxiliary chamber and a variable throttle orifice is proposed and the semi‐active control strategy of air suspension is carried out. The parameters of the air spring with auxiliary chamber are optimized to improve the performance when the control system fails and to increase the basic performance for semi‐active control. Based on the linear matrix inequality approach to robust H∞ control, the semi‐active control strategy of the air suspension is studied, in which parameter uncertainties and time delay are considered to improve control robustness. An inverse model of the air spring is then established to calculate the area of the variable throttle orifice, by which the desired control force is tracked accurately. Finally, the effectiveness of the semi‐active control system of the air suspension is verified by numerical simulation. Comparing with the passive suspension, not only under nominal parameters, but also with parameter uncertainties, time delay, and both parameter uncertainties and time delay, the semi‐active control system proposed in this paper has good control performance as well as is strong robustness to parameter uncertainties and time delay.

Electric vehicles participation in load frequency control based on mixed H2/H∞

Besides being new loads that would call for further capacity from fossil-fuel based Conventional Sources (CS), managing Electric Vehicles (EVs) smartly i.e. using Vehicle-to-Grid (V2G), holds the opportunity to be used for Load Frequency Control (LFC). However, there exists uncertainty in available dispatch capacity and time delay linked to charging/discharging control of individual EVs. Assessing this uncertain capacity and related delay of its response for LFC is presented first in this paper. Next, for the EVs participating in multi-objective LFC (V2G) along with CSs, a robust mixed H2/H∞ controller based on static output feedback is adopted. The system stability, i.e. bounding frequency and tie-line power to their nominal values in the presence of internal and external disturbance, is ensured by providing better reference tracking to both EVs and CSs. Case studies of a single and three-area system with EVs are tested for LFC, where the efficacy of the mixed H2/H∞ is also endorsed by the comparison with only H∞ controller. The results showed that the EVs and the adopted controller can respond effectively to the scenarios i.e. load variation, parameters uncertainties, effects of dead bands and time delays of both controller and EVs aggregator responses. It caused a decrease in the capacity burden on CS while this study open ways for the future grid to be pollution-free.

Model-Free Adaptive Control of pH Value of Wet Desulfurization Slurry under Switching of Multiple Working Conditions

In limestone-gypsum wet flue gas desulfurization process, the change process of pH value of slurry in absorption tower is a typical nonlinear system with time delay and various uncertainties, so it is difficult to establish an accurate mathematical model of slurry pH control process. According to the pH control process of the slurry of wet flue gas desulfurization process, a model-free adaptive control algorithm based on compact form dynamic linearization (CFDL-MFAC) is designed to realize the tracking control of the pH value of the slurry. Due to various interference factors in the pH control process of slurry in absorption tower, it is easy to cause jump change of control system parameters and even structure. Therefore, a model-free adaptive control algorithm based on switching strategy is proposed in this paper. According to different working conditions, several model-free adaptive controllers are established. The stability of the algorithm is analyzed for the two cases of fixed system parameters and jumping system parameters. It was found that the model-free adaptive controller based on the switching strategy can switch multiple controllers under the condition of system parameter jump, so as to realize the fast tracking control of the slurry pH value of the system absorption tower under different working conditions. Through this method, the overshoot can be reduced and the control quality can be improved.

Investigation of Unmeasured Parameters Estimation for Distributed Control Systems

The problem of unmeasured parameters estimation for distributed control systems is studied in this paper. The Takagi–Sugeno fuzzy model which can appropriate any nonlinear systems is employed, and based on the model, an observer-based fuzzy H∞ filter which has robustness against time-delay, external noise, and system uncertainties is designed. The sufficient condition for the existence of the desired filter is derived in terms of linear matrix inequalities (LMIs) solutions. Moreover, the underdetermined estimation problem in which the number of sensors available is typically less than the number of state variables to be estimated is specifically addressed. A systematic method is proposed to produce a model tuning parameter vector of appropriate dimension for the estimation of the filter, and the optimal transformation matrix is selected via iterative solution to minimize the estimated error. Finally, a simulation example for turbofan aeroengine is given to illustrate the effectiveness of the proposed method, and the estimated error is less than 2.5%.

Fixed Low-Order Wide-Area Damping Controller Considering Time Delays and Power System Operation Uncertainties

This paper presents a procedure for the design of a Wide-Area Damping Controller (WADC) towards improving the low-frequency oscillation modes of the power system considering uncertainties in both nominal power system operation condition and time delay on the WADC communication channels. A set of possible operating conditions is linearized around their equilibrium points and used for the construction of the uncertainty model of the system. The lower and upper limits of the time delay are also included in the set. The WADC operation requires remote signals provided by Phasor Measurement Units and highly susceptible to failures or cyber-attacks that may compromise the controller performance. The proposed procedure evaluates in each stage if the resulting controller presents robustness to communication channel permanent failure. Modal analysis and time-domain nonlinear simulations were conducted in the IEEE 68-bus power system.

Robust optimal control and identification of adaptive cruise control systems in the presence of time delay and parameter uncertainties

This article deals with the robust optimal control and identification of uncertain adaptive cruise control systems. Both measurement delay and engine’s lag are investigated in system modeling and control design. The control structure consists of two steps. In the first step, by using a new approach, the uncertain parameters of longitudinal dynamics of each vehicle is identified. Afterwards, at the second step, by using the relative position and velocity measurement with respect to ahead vehicle, a robust control against size changing of platoon is presented to assure the internal stability, string stability, and safety of heterogeneous vehicular platoons. A cost function involving important metrics internal stability, maximum overshoot, and settling time is introduced, and the particle swarm optimization algorithm is used to find the optimal values of control parameters minimizing the cost function. It will be shown that the proposed robust controller guarantees the internal stability, string stability, and safety of adaptive cruise control systems in the presence of measurement and parasitic delays. Several simulation results are provided to show the effectiveness of the proposed approaches.

Wireless sensor network model with uncertain delay and packet loss based on intelligent fuzzy system

The utilization of fuzzy logic in WSNs is demonstrated to be a promising procedure since it permits joining and assessing various parameters in an effective way. Fuzzy logic is a decent methodology because of the execution prerequisites can be effectively supported by sensor hubs, while it can improve the general system execution. This paper studies the robust H∞ control considering time delay and packet loss related uncertainty in wireless sensor network system based on the basic theory of intelligent fuzzy systems. The model of a wireless sensor network with questionable time lag and packet loss is given first. The stability of the system is proved by the augmented Lyapunov functional and the linear matrix inequality (LMIs) method, with its demonstrated H∞ property. In order to solve the uncertain time delay and packet loss, the memory robust H∞ controller is proposed based on LMIs. Numerical examples and simulation results examines the potency of the presented method in solving the delay and packet loss of wireless sensor networks as well as the accuracy and precision of the system.