Allowable Delay Research Articles

Using Delay for Control

This article reviews two techniques that use delay for control: time-delay approaches to control problems (which initially may be free of delays) and the intentional insertion of delays into the feedback. We begin with a now widely used time-delay approach to sampled-data control. In networked control systems with communication constraints, this is the only method that accommodates transmission delays larger than the sampling intervals. We present a predictor-based design that enlarges the maximum allowable delay, which is important for practical implementations. We then discuss methods that use artificial delays via simple Lyapunov functionals that lead to feasible linear matrix inequalities for small delays and simple sampled-data implementations. Finally, we briefly present a new time-delay approach—this time to averaging. Unlike previous results, this approach provides the first quantitative bounds on the small parameter, making averaging-based control (including vibrational and extremum-seeking control) reliable.

Strength development and durability requirement in recycled aggregate concrete: effect of drying and post curing

Present research critically investigates drying sensitivity and cement hydration resumption in recycled aggregate concrete (RAC). To determine minimum post-curing time for optimum strength resumption in RAC, a curing ratio (δ) is introduced. Curing ratio is defined as the ratio between post-curing duration and delay time before curing. Drying sensitivity of RAC is observed significantly lower than NAC. The maximum strength loss under drying conditions is 25.9% in RAC (OPC) and 23.2% in RAC (PPC). Strength criteria determine the curing ratios of RAC (OPC) and RAC (PPC) as 2.22 and 0.30. The maximum delay time for RAC (OPC) and RAC (PPC) is determined at 8 days and 21 days with a minimum post-curing for 17.76 and 6.63 days. The longest allowable delay produces ion penetration less than 1000 Coulombs, resistivity greater than 208 ohm-m, superior structural integrity and internal compactness, and sorptivity comparable to RACs cured after a shorter delay.

Distributed periodic event-triggered secondary control for islanded microgrids with switching topologies and communication delays

With the application of distributed generators (DGs), microgrids (MGs) have gained much attention. Combined with the distributed communication of networked systems, we investigates the secondary restoration problem in islanded microgrids. The periodic event-triggered (PET) controllers are designed for voltage restoration and frequency restoration with accurate active power allocation, which can naturally avoid Zeno behavior. By means of a common Lyapunov function, a PET protocol is designed that requires only the information of neighbors for event detection. Both event-checking sampling period and event trigger parameter are taken into account to reduce computation and communication redundancy by choosing appropriate parameters. Furthermore, considering the effect of communication delay, sufficient conditions are given to accomplish the secondary control objectives with allowable delays. Switching topologies are considered in an extra discussion. Finally, the effectiveness of the proposed PET control strategies is verified by several MATLAB simulations.

Receive wireless sensor data through IoT gateway using web client based on border gateway protocol

One of the significant topics in the field of the Internet of Things (IoT) pertains to the interaction and information sharing among people. The utilization of the Border Gateway Protocol (BGP) stack enhances the integration of web protocols and sensor networks, leading to greater accessibility. However, the BGP protocol stack introduces substantial overhead to messages transmitted at each layer, resulting in increased data overhead and energy consumption in networks by several orders of magnitude. This paper proposes a method to reduce the overhead on small and medium-sized packets. In multi-temporal networks utilizing BGP, scheduling and aggregating BGP packets at sensor nodes help achieve specific objectives. Various research methodologies and measures are employed to facilitate this, including request classification, BGP response prioritization within the network, determination of maximum acceptable delay, and overall network management. Synchronization and temporal integration of received messages at sensor nodes are performed, considering the maximum allowable delay for each message and the availability of the destination to process the accumulated messages. The evaluation results of the proposed method demonstrate a significant reduction in energy consumption and network traffic, particularly in monitoring applications within multi-stage networks. The protocol stack used is derived from the BGP standard.

The final part of the CRESS trilogy- how to evaluate the quality of stability studies.

High quality laboratory results are critical for patient management. However, poor sample quality can impact these results and patient safety. To ensure reliable and accurate results laboratories must be aware of each analyte's stability under various storage conditions and matrices to guarantee correct and dependable outcomes. This knowledge allows laboratories to define the allowable delay between sample collection and centrifugation/analysis for all analytes to guarantee appropriate results quality and interpretation. The EFLM Working Group for the Preanalytical Phase (WG-PRE) therefore established a 4-step plan to tackle this issue, aiming to standardize and harmonize stability studies for improved comparison andmeta-analysis. The plan included the development of checklists and how-to guides for performing and reporting stability studies as well as a central resource of stability data. This manuscript deals with the issue of evaluating publications and incorporating them into a central resource. To evaluate stability studies, the CRESS checklist was used to structure 20 sections used to judge the quality of studies. Each section has 4 levels of quality, with scores converted to numerical values and weighted based on expert opinion. Based on this, a final score ranging from A to D was determined. The procedure was then tested on six manuscripts and checked for agreement between expert judgements. The results demonstrated that the proposed evaluation process is a useful tool to distinguish between best in class manuscripts and those of lower quality. The EFLM WG-PRE strongly believes that the provided recommendations and checklists will help improving stability studies both in quality and standardisation.

Anti-delay Kalman filter fusion algorithm for inter-vehicle sensor network with finite-step convergence

Intelligent vehicle applications in autonomous driving and obstacle avoidance commonly require the precise relative state of vehicles. Accordingly, this study focuses on the coordinate fusion of vehicle state problem experienced by an inter-vehicle sensor network with time-varying transmission delays. Using the ingeniously designed low-complexity integration with a consensus strategy and buffer technology, an anti-delay distributed Kalman filter (DKF) with finite-step convergence is proposed. By introducing an appropriate weight matrix to assess local estimates, the optimal fusion state result is available as a linear minimum variance. In addition, to accommodate practical engineering in intelligent vehicles, the communication weight coefficient and directed topology with unidirectional transmission are considered. From a theoretical perspective, the proof of error covariances’ upper bounds with different communication topologies with delays are presented. Furthermore, the maximum allowable delays of inter-vehicle sensor network are derived backwards. Simulations verify that while considering the various non-ideal factors presented above, the proposed DFK algorithm produces more accurate and robust fusion estimation state results than those of the existing algorithms, making it more valuable in practical applications. Moreover, a mobile car trajectory tracking experiment is conducted, which further verifies the feasibility of the proposed algorithm.

Stability analysis of discrete-time delayed systems via matrix-injection-based transformation method for bivariate quadratic functions

In this paper, the stability analysis of discrete-time systems with a time-varying delay is studied. First, a selectable matrix-injection-based transformation lemma is proposed to guarantee the negative (or positive) definiteness of bivariate quadratic function. This lemma allows a selection of conditions that combine different delay sets, which is more relaxed than that in most previous studies. Then, an improved Lyapunov–Krasovskii functional (LKF) with delay-squared-product summation is given, which introduces extra cross-terms about delay-variation square for stability analysis. Considering the role of injection matrices in the proposed lemma, together with two types of allowable delay sets, four stability criteria are established. Finally, the less conservatism of the proposed criteria is verified by two numerical examples, which demonstrate the superiority of the presented methods.

Stability analysis of linear delayed systems based on an allowable delay set partitioning approach

This note is concerned with the stability analysis of linear systems with a time-varying delay, where the delay is assumed to be a periodically varying bounded function with restricted derivatives. Combining the allowable delay set (ADS) definition and the region partitioning technique, an ADS partitioning approach is proposed, and then by with aid of this approach, a novel Lyapunov–Krasovskii functional (LKF), namely delay-set-partition-based (DSPB) LKF, is developed. Compared with the previous LKF method, the main advantage of the DSPB LKF lies in allowing the considered system to construct its own LKF in each sub-ADS. By utilizing the proposed LKF, less conservative stability criteria are derived. Finally, two simulation examples are provided to verify the effectiveness and superiority of the proposed method.

Concrete ablation depth analysis of OPR1000 NPP during top flooding ex-vessel cooling

This study assesses the integrity of OPR1000 nuclear power plant (NPP) containment during top flooding ex-vessel cooling in the event of a postulated severe accident. Maintaining containment integrity during ex-vessel cooling is critical for preventing substantial release of radioactive materials to the environment. To analyze the feasibility of top flooding ex-vessel cooling of the OPR1000 NPP, the spread of molten corium in the dry reactor cavity is first calculated, followed by calculating the concrete ablation depth according to the reactor cavity flooding delay time. It is judged whether the leak-tightness integrity of the containment during ex-vessel cooling is maintained based on whether the containment liner plate (CLP) is damaged or not. In the first step analysis, the spread of molten corium in the dry reactor cavity is calculated using computational fluid dynamics (CFD) methodology for various cases, and results indicate a uniform deposition of approximately 143 tonnes of molten corium, with a thickness of about 33 cm, meaning that the thermal load is distributed uniformly in the reactor cavity. In the second step analysis, concrete ablation depths are calculated base on the delay time for flooding the reactor cavity. For the postulated severe accident, injecting coolant into the reactor cavity one hour after breach of the reactor vessel results in a concrete ablation depth of about 0.74 m, indicating no damage to the CLP and ensuring containment integrity. The maximum allowable delay time for flooding the reactor cavity for the postulated severe accident is evaluated to be 2.24 hours maintaining the leak-tightness integrity of the OPR1000 NPP containment. The research methodology and findings presented in this study are expected to aid in assessing the feasibility of top flooding ex-vessel cooling and establishing appropriate accident management strategies for nuclear power plants like the OPR1000 NPP.

Type-Dependent Average Dwell Time Method and Its Application to Delayed Neural Networks With Large Delays.

This article investigates the stability of delayed neural networks with large delays. Unlike previous studies, the original large delay is separated into several parts. Then, the delayed neural network is viewed as the switched system with one stable and multiple unstable subsystems. To effectively guarantee the stability of the considered system, the type-dependent average dwell time (ADT) is proposed to handle switches between any two sequences. Besides, multiple Lyapunov functions (MLFs) are employed to establish stability conditions. Adding more delayed state vectors increases the allowable maximum delay bound (AMDB), reducing the conservatism of stability criteria. A general form of the global exponential stability condition is put forward. Finally, a numerical example illustrates the effectiveness, and superiority of our method over the existing one.

A two-warehouse inventory model with credit policy and inflation effect

This study investigates a non-instantaneous deteriorating two-warehouse inventory problem with allowable delay payments under inflation. The objective is to maximize the total profit per unit of time by determining the optimal order quantity, the product’s selling price, and the business cycle length. We developed a mathematical model to address this inventory optimization problem. Built on top of the available literature, we comprehensively considered credit policy, inflation, price- and time-dependent demand, and partial backlogged shortage in this study. By changing some parameters, we demonstrated that our model is a generalized version of several specific inventory models presented in the literature. We performed numerical examples to validate our model. Additionally, we carried out a sensitivity analysis to examine the impact of several parameters on the optimal solutions. The results highlight that if the fixed part of the demand decreases, the product’s selling price and the total profit decrease. In addition, if the setup cost decreases, the total profit increases, and vice versa. The results also demonstrate that the unit purchase cost and inflation significantly affect the average profit. To conclude, our study can potentially help firms (i) reduce the total inventory system’s setup cost, (ii) optimize unit purchase cost, and (ii) understand the influence of inflation.

Delay-variation-dependent summation inequality and its application to stability analysis of discrete-time systems with time-varying delay

This work tends to research the stability of the discrete-time systems with a time-varying delay based on the Lyapunov-Krasovskii functional (LKF) method. In order to acquire a less conservative stability criterion, some techniques in this work are refined and taken into use. Firstly, to reduce the conservatism generated when estimating the forward difference of the LKF, a newly delay-variation-dependent summation inequality is constructed, which includes the existing free-matrix-based and Bessel function-based summation inequalities, using delay-variation-product relaxed matrices to provide more freedom for the estimation results. Secondly, to further show the influence of the introduced variation information in the time-varying delay, we give another selection of the allowable delay set for the delayed discrete-time systems. Thirdly, by taking advantages of the above method and by constructing a delay-product-type LKF, using extended free-weighting-matrices zero equations, and considering different allowable delay sets, two improved linear matrix inequality (LMI)-based delay-variation-dependent criteria for delayed discrete-time systems are formulated. Some classical numerical instances are presented to explain the effectiveness of these proposed stability criteria.

Chance-Constrained Pre-Contingency Joint Self- Scheduling of Energy and Reserve in VPP

With the increasing penetration of primarily inertia-less distributed energy resources, allowable delay in the fast frequency reserve provision to ensure marginal stability condition can become comparable with the requisite dead-time for fast-switching in a radial power distribution system (PDS) connected to the transmission system. Consequently, the prevailing short-duration load-generation imbalance might propagate as system-wide frequency excursion in the future power system, which traditionally has not been observed. Furthermore, during the fast-switching, some of the fast-acting reserve (FAR) providing local generators remain inaccessible to the bulk power system (BPS). This work has answered the questions of requisite reserve requirements to cater to such events through efficient energy and FAR provision joint-scheduling. Stochasticity of fast-switching, with temporary faults as a use-case, requires modeling of load-generation imbalance and local resource unavailability, vis-á-vis FAR requirement problem, as a chance-constraint. Due to the limited visibility at the BPS level, PDS operators must ensure sufficient FAR availability for a given confidence level of the chance-constraint. Individual chance-constraints are used to ensure mathematical simplicity. Here, the PDS is operated as a virtual power plant (VPP), where the operator can procure resources locally or from the wholesale market with the aim of profit maximization before the contingency occurs. Results show that FAR requirements can influence the local energy schedule and raise energy costs. Furthermore, the confidence level of the chance-constraint can impact overall profitability, and FAR should be scheduled carefully. Comparative analysis with a modified benchmark IEEE 33-node radial test system and a 98-node test system shows the superior performance of the proposed approach. The impact of the limited available FAR is also demonstrated.

A non-singular terminal sliding mode controller for a communication-based hybrid microgrid

The paper proposes a robust and effective networked control for a hybrid based islanded microgrid. Renewable energy sources with energy storage systems are linked in parallel using voltage source inverters to supply the loads in a microgrid. The master-slave control strategy is implemented. CAN and the ZigBee networks are selected to share data, where the master controller transmits the reference signals to the slave controllers in the microgrid via these two networks. As the control loop incorporates a communication network and energy storage systems, the impacts of external disturbances, parametric uncertainties, and time delay executed by the devices introduce challenges in control of voltage and current. Thereby, it is crucial to use a robust and stable control approach. Using the binary iteration algorithm, stability criteria in the form of linear matrix inequalities based on the Lyapunov-Krasovskii function are employed to derive the system's maximum allowable delay boundary. As the reliability of the communication network can be affected, a nonsingular terminal sliding mode controller is employed. The proposed robust control method was implemented in MATLAB/Simulink and the True-time 2.0 simulator and its performance were evaluated under different loads, uncertainties, disturbances, and communication impairments. Simulation results show that the desired performance i.e., maintaining the microgrid's stability with accurate voltage and current control even in unallowable delay limits is met.

A hybrid framework of dynamic periodic event-triggered networked control systems subject to time-varying delays

This paper investigates the dynamic output-feedback control for networked control systems (NCSs). The data transmissions in the sensor-to-controller and the controller-to-actuator channels are generated by the dynamic periodic event-triggering mechanism. Due to the existence of time-varying delays in the two channels, the updated data is received after a time delay. To cope with this problem, a hybrid dynamical framework of the NCSs is established. With the help of Lyapunov function-based approach, a new event-triggering condition is designed and sufficient conditions on input-to-state stability are derived. By introducing an auxiliary function, the obtained sufficient conditions are transformed into linear matrix inequalities and the explicit forms of the dynamic output-feedback controller gains are provided. Moreover, the upper bounds on the maximum allowable transfer intervals and the maximum allowable delays are derived. Finally, a numerical example illustrates the feasibility of the proposed method.

Resilient control design for large‐scale networked control systems under denial‐of‐service attacks

AbstractThis paper focuses on the exponential stability and the resilient state feedback controller design for large‐scale networked control systems under denial‐of‐service attacks. The duration of each denial‐of‐service attack is captured by a logical processor embedded in the controller. The closed‐loop system of periodic sampled‐data control is modelled as an aperiodic sampled‐data control system associated with lower and upper bounds on the duration of the denial‐of‐service attack. Two formal results are demonstrated. The first result is the stability criterion for large‐scale networked control systems under denial‐of‐service attacks obtained by constructing a two‐sided mode‐dependent loop‐based Lyapunov–Krasovskii functional under the action of a prediction‐based controller. The second result presents a criterion based on linear matrix inequalities to design the controller against denial‐of‐service attacks. In particular, iterative algorithms are given for computing the allowable delay upper bound for the system. Finally, the effectiveness of the proposed method is verified by the interconnected power systems of the two areas.

Estimating the delay margin for stability of linear delay systems by the weighted matrix measure

AbstractIn this paper, the delay margin problem of a linear system with multiple delays is investigated. Estimations for allowable delay bounds of the system are provided in the form of matrix measure. By means of the weighted matrix measure and optimization technologies, the conservatism of estimated delay bounds is reduced. Numerical examples show that the weighted matrix measure has better performance in estimating the delay margin of the system than usual matrix measures.

Distributed Dynamic Event-Triggered Secon- dary Control for Islanded Microgrids With Disturbances and Communication De- lays: A Hybrid Systems Approach

This paper investigates the secondary control problem of islanded microgrid (MG) under hybrid systems framework. Owing to network-induced imperfections caused by communication and limited communication resources, we consider the event-triggered secondary control problem under time-varying delays. A hybrid dynamic event-triggering mechanism (DETM) is proposed to reduce the usage of communication resources, the event triggering interval is enforced to be lower bounded by strictly positive value. A hybrid closed-loop model is constructed, that incorporates the communication delays and event-triggering mechanism (ETM), and it facilitates stability and performance analysis. Lyapunov-based stability conditions are proposed, while the maximum allowable delay can be determined. Moreover, the proposed hybrid DETM ensures that the minimum event-triggering interval (METI) can be designable and pre-specified, even in the presence of disturbances, which is important for control implementation. Finally, the effectiveness of the proposed control strategy is illustrated by simulation examples.

Delay-Dependent Stability Analysis of Multi-Area LFC-EVs System

In this study, the delay-dependent stability of a multi-area Load Frequency Control (LFC) system with Electric Vehicle (EV) aggregators is investigated with the help of the Advanced Clustering with Frequency Sweeping (ACFS) method for incommensurate time delays. Both Integer-Order (IO) and Fractional-Order Proportional Integral (FOPI) controllers are utilized as a controller. The communication infrastructure used in LFC systems induces time delays resulting in deteriorations in the system stability. Even if the maximum allowable delay margin limits are not exceeded, these inevitable time delays could cause undesired frequency deviations and tie-line power fluctuations. The ACFS method is employed in this study to investigate impacts of time delays and to ensure better controller performance objectives taking into account the effects of time delays. Firstly, 2-dimensional (2D) stability delay maps are obtained for various LFC-EVs system parameters. The stability regions are then verified by the Quasi-Polynomial Mapping Root (QPmR) finder algorithm and MATLAB/Simulink-based time-domain simulations. The results clearly show that the participation of the EV aggregators in traditional LFC systems improves the frequency regulation and tie-line power-sharing in the system. Finally, it is concluded that the stability regions are enhanced as the fractional order of the FOPI decreases.

Distributed Secondary Control for Island Microgrids With Expected Dynamic Performance Under Communication Delays

In island microgrids, the increasing integration of inverter-interfaced distributed generators (DGs) degrades the dynamic performance of the control system. The operation voltage and frequency may appear unacceptable overshoots and fluctuations under disturbances. To achieve rapid convergence while efficiently suppressing overshoot, this paper develops a distributed control method for island microgrids with expected dynamic performance. In addition to the typical distributed consensus design, an auxiliary dynamic reshaping function is introduced into the algorithm to increase the control degree of freedom of the operation dynamics. Thus, the proposed method can realize independent and flexible configurations of the damping ratio and natural frequency of the control system, and obtain the expected state convergence and overshoot suppression performance according to the actual requirements of microgrids. Besides, different delays between DGs are also considered. Instead of simply adopting the conventional global fixed delay time, we preserve the difference of delays to the greatest extent. Such processing can effectively reduce the conservatism of control and improve the response rate. A nonlinear programming problem is also established for DGs to calculate the allowable delays under the specific performance. Finally, several case studies and an RT-Lab experiment evaluate the effectiveness of the method.