Control Input Rate Research Articles

Relaxed nonquadratic H∞ robust constrained event-triggered fuzzy controller design for discrete-time nonlinear systems

This paper introduces an [Formula: see text] robust constrained event-triggered fuzzy controller for discrete-time nonlinear systems in the presence of system parameter uncertainties, the parameter uncertainties of the output matrices and the disturbances, simultaneously. To reduce the communication resources and improve the robust performance, the event-triggered mechanism is incorporated with the [Formula: see text] robust fuzzy controller design. Moreover, by employing the fuzzy modeling of the actuator saturation and a nonquadratic Lyapunov function (NQLF), the ultimate bounded stability (UBS) of the closed-loop system is guaranteed subject to the amplitude limitations of the control signal. This means, a new linear matrix inequality (LMI) problem is derived to ensure the robustness and constraints in an offline scheme based on the event-triggered strategy. Besides, to meet the practical problem to further improve the controlled system performance, the control input rate constraint is also considered and a new LMI condition is provided with no online computational burden. Therefore, the computational burden of the proposed controller is greatly reduced with less conservatism. Two simulation examples including a numerical dynamic system and a truck–trailer system are employed to illustrate the less conservatism and computational complexity of the proposed method compared with the existing approaches.

A pitch trimmer can cause a catastrophic structural failure in an aeroplane, but this is avoidable

ABSTRACTThis paper investigates the potential of a lever-type pitch trimmer to cause an overstress in light and microlight aeroplanes. It concludes that this potential exists and could potentially cause a catastrophic structural failure – with the evidence from one reported fatal accident suggesting that this may have already happened. However, it is shown that this need not be the case, with restricted nose-up control authority, high manoeuvre stability and the use of a trim wheel (as opposed to a lever) with a restrictive rate of control input shown as three methods, most likely in combination, by which this potential can be removed. Suggestions are made for airworthiness standard wording which might be used to ensure adequate safety of future aircraft designs.

Velocity control for improving flow through a bottleneck

A bottleneck can largely deteriorate the flow, such as a traffic light or an on-ramp at a road. To alleviate bottleneck situations, one of the important strategies is to control input rate to suit the state of the road. In this study, we propose an effective velocity control of traveling particles, in which the particle velocity depends on the state of a bottleneck. To analyze our method, we modify the totally asymmetric simple exclusion process (TASEP) and introduce a slow-to-start rule, which we refer to as controlled TASEP in the present paper. Flow improvement is verified in numerical simulations and theoretical analyses by using controlled TASEP.

High-Performance Consensus Control in Networked Systems With Limited Bandwidth Communication and Time-Varying Directed Topologies.

Communication data rates and energy constraints are two important factors that have to be considered in the coordination control of multiagent networks. Although some encoder-decoder-based consensus protocols are available, there still exists a fundamental theoretical problem: how can we further reduce the update rate of control input for each agent without the changing consensus performance? In this paper, we consider the problem of average consensus over directed and time-varying digital networks of discrete-time first-order multiagent systems with limited communication data transmission rates. Each agent has a real-valued state but can only exchange binary symbolic sequence with its neighbors due to bandwidth constraints. A class of novel event-triggered dynamic encoding and decoding algorithms is proposed, based on which a kind of consensus protocol is presented. Moreover, we develop a scheme to select the numbers of time-varying quantization levels for each connected communication channel in the time-varying directed topologies at each time step. The analytical relation among system and network parameters is characterized explicitly. It is shown that the asymptotic convergence rate is related to the scale of the network, the number of quantization levels, the system parameter, and the network structure. It is also found that under the designed event-triggered protocol, for a directed and time-varying digital network, which uniformly contains a spanning tree over a time interval, the average consensus can be achieved with an exponential convergence rate based on merely 1-b information exchange between each pair of adjacent agents at each time step.

Fuzzy Logic Based Rate Control Scheme for ODMRP in Mobile Ad hoc Networks

On Demand Multicast Routing Protocol (ODMRP) is a popular solution designed for ad hoc networks with mobile hosts. Its efficiency, simplicity, and robustness to mobility render it one of the most widely used multicast routing protocols in Mobile Ad hoc NETworks (MANET). In ODMRP, there is no input rate control for upper layer traffic. So, it's possible that high dense traffic flow causes congestion in networks. In this work, an enhancement to ODMRP is proposed referred to as fuzzy logic based Rate Control ODMRP (FRC-ODMRP). FRC-ODMRP attempts to adapt the arrival rate from upper layers to the state in the network by using feedback information from receivers of the multicast group. Accordingly, source comes up with a decision whether to increase or decrease its transmission rate based on information collected from the receivers. In this research, delay and packet delivery ratio reconsidered as indicators of congestion in addition to number of received packets. Simulation results demonstrate that FRC-ODMRP achieves significant performance improvements in comparison to conventional ODMRP and QoS-ODMRP. Indeed, it efficiently handles simultaneous traffic flows such that no one could dominate available bandwidth of networks.

A Simulated Annealing-Based Overload Control Algorithm to Application Servers in Next Generation Electric Communication Networks

We study the overload control problem of application server in the next generation electric communication network in this paper. We introduce an energy efficiency overload control algorithm based on simulated annealing. Firstly, by considering the overload control and energy efficiency, we construct the relations function between the input rate control and energy efficiency using rate allocation. Then, we construct the optimal overload control model of energy efficiency by regarding this relation function as objective function and overload control as constraint conditions. Thirdly, we use simulated annealing algorithm to solve this model, and then obtain the optimal solution during the iterative process. The simulation results show that our algorithm is feasible and effective.

Multiple Sliding Modes with Override Logic: Limit Management in Aircraft Engine Controls

G AS turbine engines are subjected to several operational constraints, both at steady state and in the transient regime. These constraints correspond to mechanical limits such as speed and acceleration; limits in thermodynamic variables such as pressures and temperatures; and limits preventing engine components from undergoing dynamic instabilities, mainly surge, stall and flame blowout. Engine control systems incorporate measures to protect the engine from crossing these limits at all times. Achieving limit protection while ensuring fast transient response represents a design challenge, which was summarized by Spang and Brown in their 1999 paper [1]: “. . .much of the complexity of the control comes from the need to operate the engine as close as possible to its limits.” This paper presents a novel and very effective way to achieve such maximal exploitation of the available limits to enable fast responses in thrust or other relevant variables. The proposed technique is based on thewidely usedmultiregulator architecture with max–min limit protection logic [1,2], which uses linear compensators in its original form. As shown in Fig. 1, this architecture uses a single control input (fuel flow) to drive the desired output (typically fan speed or engine pressure ratio) to a setpoint through a control loop with integral action and a linear compensator. Additional compensators are set up to control limited variables to their permissible values, still using fuel flow as the control input. A max–min selection logic stage decides whether the main output regulation task or any of the limit protection tasks should be made active at anygiven time. Integral action is used to achieve type 1 loops for offset-free regulation. The regulators, thus, provide control input rates. Define two index sets as L f1; 2; . . . lg and H fl 1; l 2; . . . hg, where L contains the indices of the regulators associated with the min selector, while the elements of H are the indices of the regulators associatedwith themax selector. No index is defined for the output of the min selector. As shown in Fig. 1, the control rate applied to the integrator is selected according to the formula

Stability and Distributed Power Control in MANETs with Per Hop Retransmissions

In the current work the effects of hop-by-hop packet loss and retransmissions via ARQ protocols are investigated within a Mobile Ad-hoc NET-work (MANET). Errors occur due to outages and a success probability function is related to each link, which can be controlled by power and rate allocation. We first derive the expression for the network's capacity region, where the success function plays a critical role. Properties of the latter as well as the related maximum goodput function are presented and proved. A Network Utility Maximization problem (NUM) with stability constraints is further formulated which decomposes into (a) the input rate control problem and (b) the scheduling problem. Under certain assumptions problem (b) is relaxed to a weighted sum maximization problem with number of summants equal to the number of nodes. This further allows the formulation of a non-cooperative game where each node decides independently over its transmitting power through a chosen link. Use of supermodular game theory suggests a price based algorithm that converges to a power allocation satisfying the necessary optimality conditions of (b). Implementation issues are considered so that minimum information exchange between interfering nodes is required. Simulations illustrate that the suggested algorithm brings near optimal results.

A Study of Nonlinear Control Schemes for A Boiler-Turbine Unit

Advanced control is crucial for safe and efficient operations of power plants, especially in the presence of fast and large load changes. This paper studies the load change control problem for a 160MW boiler-turbine unit. Two schemes are proposed to effectively control the boilerturbine unit that has various constraints on the system states, outputs, control input and control rate. By taking advantage of the nonlinearities of the boiler-turbine unit, we design a nonlinear state feedback controller. With a careful selection of the controller gains, the states and control inputs can be guaranteed to be within the required physical constraints. Practically, lower and upper bounds on the system outputs are also imposed to prevent the critical variables, such as drum water level, moving beyond the physical limits. To further incorporate the constraints on the system outputs as well as control-input rates into feedback design, we utilize the moving horizon control strategy. The simulations of two control methods demonstrate the well-controlled performances of the boiler-turbine unit under large and fast load changes.

Feedforward Controller With Inverse Rate-Dependent Model for Piezoelectric Actuators in Trajectory-Tracking Applications

Effective employment of piezoelectric actuators in microscale dynamic trajectory-tracking applications is limited by two factors: 1) the intrinsic hysteretic behavior of piezoelectric ceramic and 2) structural vibration as a result of the actuator's own mass, stiffness, and damping properties. While hysteresis is rate-independent, structural vibration increases as the piezoelectric actuator is driven closer to its resonant frequency. Instead of separately modeling the two interacting dynamic effects, this work treats their combined effect phenomenologically and proposes a rate-dependent modified Prandtl-Ishlinskii operator to account for the hysteretic nonlinearity of a piezoelectric actuator at varying actuation frequency. It is shown experimentally that the relationship between the slope of the hysteretic loading curve and the rate of control input can be modeled by a linear function up to a driving frequency of 40 Hz

Policing and traffic shaping at the user-network-interface (UNI)

A network's decision to accommodate a new ATM connection is based in part on sustained and peak cell rate and peak duration declared by the user in the connection request. As these traffic descriptors are onlyprojections of the traffic, connection admission control must be supplemented by input rate control in order to monitor and regulate theactual traffic. None of the proposed input rate control schemes enforces multiple traffic parameters. Additionally, traffic shaping at the UNI based on regulating average and peak rates may enhance statistical multiplexing performance. This paper presents a performance analysis of the two-stage entry monitor combining a sticky bufferpolicer with aspacer. To the best of our knowledge,no analysis of tandem policers has appeared before this paper. The first stage enforces the sustained rateR/T negotiated in the connection request; the spacer shapes the traffic and controls burstiness by further ensuring that cells enter the network at leastS slots apart. We derive the probability generating function for the combined queue length distribution and evaluate numerically (i) the manner in whichS and burstiness affect the cell-loss probability, and (ii) the performance penalty caused by enforcing two rates. The principal contribution of this paper is the calculation of the buffer size required to police two parameters subject to a specified cell-loss ratio. Our principal conclusion is that the increase in buffer size needed to police the peak sustained rate in addition to the sustained rate is minimal. We will also demonstrate that the leaky bucket and the single-stage sticky buffer have comparable performance, enabling us to conclude that a two-stage sticky buffer can police both peak and sustained rates for almost the same cost as a leaky bucket.

The sticky buffer flow control for the ATM

Data from different applications — voice, video, file transfer, interactive — will be multiplexed in the future over broadband integrated services digital networks (BISDN). Data are segmented into 48-byte blocks prefixed by a 5-byte header and transported over the network using the asynchronous transfer mode (ATM). An ATM connection-request is a contract between the user and the network; the user specifies a rate requirement, delay constraints, a bound on the cell-loss probability and other quality of service parameters. If the network can meet these requirements, a connection is made. Bursty traffic producing peak traffic rates in excess of the projected average rate could result in congestion and lead to performance degradation. As a result, the network might no longer be able to deliver the negotiated quality of service to existing connections. To lessen the chance of congestion, input rate control must be implemented. This paper contains a performance analysis of the sticky buffer (SB), a moving window input rate control scheme intended to limit the rate at which input traffic may enter a network. Policing is achieved by buffering and hence delaying the entry of ATM-cells into the network. The scheme is determined by parameters ( R, T) which specify that no more than R ATM-cells are permitted to enter the network in every window of size T cells. We present an exact analysis, deriving the probability generating function of the queue length distribution. A comparison with the leaky bucket is given. Our numerical examples show the required buffer size is comparable to that required by the leaky bucket.

Congestion control in asynchronous, high-speed wormhole routing networks

High-speed networks use lightweight protocols and a simple switch architecture for achieving higher speeds. A lightweight switching technique for local area and campus environments is wormhole routing, in which the head of a packet (worm), upon arriving at an intermediate switch, is immediately forwarded to the next switch on the path. Thus, the packet, like a worm, may stretch across several intermediate switches and links. Wormhole routing networks provide low latency. However, they are particularly prone to congestion, thus requiring careful flow control. The authors consider high-speed, asynchronous, unslotted wormhole routing networks. For such networks, two different flow control mechanisms are compared and contrasted, namely, backpressure flow control and deflection routing (with local input rate control). With backpressure, in order to maintain deadlock-free routing, either up/down routing or shortest path routing with virtual channels is assumed. With deflection routing, to avoid livelocks, worm alignment (delayed deflection) is performed at the switches. It is shown via simulation that the throughput performance of the two schemes is comparable (except for up/down routing). The authors also discuss the tradeoffs with respect to the complexity of hardware, routing protocols and buffer requirements. The authors further examine the role of input rate control at the hosts to overcome unbounded delays typical of deflection routing, and show it is possible to achieve lower average number of hops and transit delays by employing suitable input rate control policies.

Input rate constrained, continuous-time, indirect, adaptive control

Stability analysis of continuous-time, indirect, pole placement, adaptive control with input rate constraint is presented in this paper. It is shown that with an appropriate controller design, the closed-loop system is robustly stable for a class of stable minimum-phase plants in the sense that all the signals in the loop remain bounded in the presence of modelling uncertainties and bounded disturbances. It is also shown that if the plant is free from modelling uncertainties and disturbances, and if the control input rate remains unsaturated for a finite period of time, then the closed-loop system will asymptotically be characterized by the desired closed-loop poles within this time period

Input rate flow control for high-speed communication networks: Blocking and delay at the access points

Abstract We present queueing models to study the system performance at the access points of a high-speed communication network. An input rate control mechanism, using a Leaky Bucket type scheme (also identified as a Credit Manager Algorithm), is applied to regulate traffic from end-user stations to the network. For the performance analysis, we select a sub-network topology which consists of a network switch (such as a fast packet or cell switch in high-speed metropolitan or wide area networks) and a number of regulated source stations. To reduce packet or cell loss probabilities at the access switch, each user station implements locally a replica of the input regulation scheme. The output traffic streams from the source stations feed into the switch, which is modeled as a multiple-server queueing system. An efficient recursive method is introduced to characterize the output traffic streams from the source stations as Markov Modulated Processes. We demonstrate the ensuing tradeoffs between message delays incurred at source stations due to the input rate control mechanism and the message delays incurred at the switch as affected by the statistical multiplexing of the input message streams. Performance curves are presented to illustrate the statistical behavior of the queue-size and message delays. Using our results, the system designer can properly select the parameters of the flow control scheme to guarantee acceptable limits of queue sizes and message delays at the source stations and at the network switches.

Second order effect of binary sources on characteristics of queue and loss rate

A wideband source in high speed networks is typically represented by a binary random process. In this paper we characterize the second-order properties of each binary source by a multi-state Markov modulated Poisson process (MMPP). A comprehensive numerical study is carried out to identify the individual effect of the source second-order dynamics on the queue length and loss rate. The results can be used to verify the validity of the two-state Markov chain binary source assumption which is commonly made within the framework of input rate control and bandwidth allocation in high speed networks. The concept of input power spectrum is then developed as a unified source characterization for multimedia traffic queueing analyses.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Input rate flow control for high speed communications networks using burst level feedback control

AbstractWe propose a new input rate flow control scheme wherein the credit increment rate is updated periodically as the loading status varies. Based upon the observed status of each station's burst‐level activity, the network access node distributes feedback control signaling messages to the stations. These signaling messages allow the stations to adapt their credit increment rates in accordance with system burst‐loading conditions. The Generic Flow Control (GFC) field of the ATM cell header can be used to carry information characterizing the burst‐level loading activity at the switch used in the proposed scheme. We also present queueing models to study the system performance at the network access points. For this purpose, we select a sub‐network topology which involves a network switch (such as a fast packet switch in high‐speed metropolitan or wide area networks) and a number of regulated source stations which drive the network switch. To avoid packet retransmissions due to cell losses at the access switch, each user station (or CPN) implements locally a replica of the input regulation scheme. The output traffic streams from the source stations, as regulated by the local input rate control mechanism (and adapted by the status messages), load a packet switch which is modeled as a multiple‐server queueing system. Performance curves are presented to illustrate the statistical queue‐size behavior and message delays at both the source stations and the network switch.

A simulation study of bursty data traffic with hybrid source smoothing in an ATM node

In this paper, we study the mean delay and maximum buffer requirements at different levels of burstiness for highly bursty data traffic in an ATM node. This performance study is done via an event-driven simulation program which considers both real-time and data traffic. We assume that data traffic is loss-sensitive. A large buffer (fat bucket) is allocated to data traffic to accommodate sudden long burst of cells. Real-time traffic is delay-sensitive. We impose input traffic shaping on real-time traffic using a leaky-bucket based input rate control method. Channel capacity is allocated based on the average arrival rate of each input source to maximize the utilization of channel capacity. Simulation results show that both the maximum buffer requirements and mean node delay for data traffic are directly proportional to the burstiness of its input traffic. Results for mean node delay and cell loss probability of real-time traffic are also analyzed. The simulation program is written in C++ and has been verified using the zero mean statistics concept by comparing simulation results to known theoretical or observed results.

Stability of rate constrained robust pole placement adaptive control systems

This paper presents stability analysis for discrete time pole placement adaptive control systems with input rate saturation constraints. It is shown that with appropriate design, the robust adaptive control system is stable for a class of stable minimum phase plants in the sense that all the signals in the loop remain bounded in the presence of modelling uncertainties and disturbances. If the plant is free from modelling uncertainties and disturbances and the control input rate remains unsaturated for a period of time, then the closed loop adaptive control system will asymptotically be characterized by the desired closed loop poles within this period.

Nuclear Reactor Control Using Walsh Function Variational Synthesis

The optimal control problem of nuclear reactor systems is solved by using the Walsh function variational synthesis technique. In this technique, the control input rate is expanded in a Walsh series with coefficients to be selected such that a general criterion functional covering all practical situations is optimized. The nuclear reactor system is assumed to be in its integral equation form, and the nonlinearity due to the product of the reactivity input and the power level output is overcome by using in the criterion functional power-times-reactivity penalty terms rather than pure reactivity ones. A numerical example is presented to illustrate the feasibility of the approach. The results are first derived for point reactors and are then extended to space-dependent ones.