On the use of information quality in stochastic networked control systems

ABSTRACTIn practical networked control systems (NCS), such as smart grids, cooperative robotics, and sensor networks, often multiple control applications share a communication infrastructure, requiring a smart and efficient scheduling mechanism to coordinate the access to the capacity-limited communication medium. In this article we consider the problem of event-based scheduling design for NCSs consisting of multiple control loops over a shared communication medium. We extend the notion of Try-Once-Discard (TOD), which is one of the basic deterministic event-based scheduling protocols for resource constrained NCSs, to the case of multiple stochastic control systems coupled via a shared communication medium subject to capacity limitation and stochastic packet delivery failure. Showing that the overall network-induced error is a homogeneous Markov chain in our stochastic set-up, we first study stability properties of such networked systems under the TOD scheduling scheme employing the concepts of stochastic stability. Then, we derive sufficient stability conditions under the TOD rule assuming that the communication channel is not ideal, i.e. a scheduled data packet for transmission might be lost in the communication channel with a non-zero probability. Furthermore, we derive analytic performance bounds by finding uniform upper-bounds for an average quadratic cost function. The numerical simulations are performed for variety of system parameters and NCS set-ups to strengthen our stability claim as well as illustrating performance bounds. Additionally, we show that the TOD scheduling rule outperforms the conventional time-triggered, and uniform and non-uniform random channel access arbitration mechanisms, in terms of efficient coordination of channel access in stochastic NCSs.

Periodic event-triggered control for networked control systems based on non-monotonic Lyapunov functions

Event-triggered [formula omitted] stabilization for networked stochastic systems with multiplicative noise and network-induced delays

Based on the controlled process that is linear time-invariant system, the network-induced long time delay is viewed as time-varying parameter uncertainties. The uncertainty parameters model of networked control systems with long time delay is set up. The existing conditions of asymptotic stability for networked control system with long time delay are presented by Lyapunov method and robust control theory. The design method of stabilization controller for networked control system is proposed in terms of linear matrix inequalities. In the end the simulation based on the networked control unstable system is studied. The simulation results show the proposed controller is feasible and effective.

Networked Control Systems (NCS) form a key element of Cyber-Physical Systems (CPS) where sensors, actuators (plants) and controller functions are spatially distributed and interconnected by communication networks. In this contribution models are developed where significant properties of communication networks such as stochastic delays, error control protocols and shared-network influences are embedded in a closed-loop control system. The resulting integrated systems are analyzed by methods of classical system-theoretic and discrete-time state analysis methods as well as by computer simulations. Fundamental insights in the properties of NCSs can already be gained through system-theoretic studies on basic architectures which provide closed-form expressions which are verified and extended by more detailed studies based on tool-supported discrete-time system state analysis and simulation-tool results. The approach allows for a more detailed detection of network protocol impacts on, e.g., the real-time behavior of NCSs when certain Service Level Agreements (SLA) have to be guaranteed as prescribed percentiles of control reaction times.

Markovian jumping systems have arisen naturally in the mathematical modeling of phenomena spanning disciplines in the social sciences, natural sciences, and engineering. This kind of stochastic dynamical systems can be employed to model the dynamics when parameters are subject to random abrupt changes due to sudden environment changes, subsystem switching, system noises, executor faults, and so forth. Much attention has been given to modeling, optimization, and real applications of such stochastic dynamical systems in the literature in recent years. As the advanced control and optimization will provide a basis for the design and application of such stochastic systems, these advanced techniques would result in substantial and sustainable benefits. The accepted papers in this special issue include stochastic stability, stabilization, stochastic control optimization, system modeling and identification methods, predictive control, signal processing, robust filtering, multiagent systems, networked control systems, time-delayed systems, neural networks, the Takagi-Sugeno fuzzy systems, simulated annealing, and fault detection methods.

In this paper, a robust H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> filter for networked control system is designed. A continuous model of networked control system is investigated and it is denoted by the one that is similar to time-delay system, through some assumption and transformation. Because only limited information can be transported in the network, time-invariant logarithmic quantization is considered in the output of system. The filtering error system designed in this paper is robustly asymptotically stable and fulfils the given H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> performance level. Based on a linear matrix inequality approach, a solving method of the filter is provided. A numerical example is given to show the effectiveness of the method.

Connecting a complex control system with various sensors, actuators, and controllers as a networked control system by a shared data network can effectively reduce complicated wiring connections. This system is also easy to install and maintain. The trend is to use networked control systems for time-sensitive applications, such as remote DC motor actuation control. The performance of a networked control system can be improved if the network can guarantee quality-of-service (QoS). Due to time-varying network traffic demands and disturbances, QoS requirements provided by a network may change. In this case, a network has to reallocate its resources and may not be able to provide QoS requirements to a networked control application as needed. Therefore, the application may have to gracefully degrade its performance and perform the task as best as possible with the provided network QoS. This paper proposes a novel approach for networked DC motor control systems using controller gain adaptation to compensate for the changes in QoS requirements. Numerical and experimental simulations, and prototyping, are presented to demonstrate the feasibility of the proposed adaptation scheme to handle network QoS variation in a control loop. The effective results show the promising future of the use of gain adaptation in networked control applications.

In this paper, the wireless networked control system defined on a connected directed graph is studied. The networked control system is defined over a strongly connected directed graph with decentralized controllers. Based on the structure of strongly connected digraph and the characteristics of wireless networked control system, the model of wireless networked control system on the connected digraph is established. The controller of the system is derived. The control law of each controller is a function of the current controller's state and other controllers' state signals.

Research on mean square exponential stability of networked control systems with multi-step delay

In this paper, finite horizon optimal control and communication co-design problem has been investigated for uncertain networked control system (NCS) with limited transmit power. Firstly, the mathematical relation between network imperfections (e.g. network-induced delays and packet dropouts) and practical wireless communication channel quality has been studied. Then, a novel networked control system model has been represented that includes both physical system dynamics and network dynamics. Next, adopting the emerging neuro dynamics programming (NDP) technique and actor-critic-identifier (ACI) architecture, a novel time-based finite horizon optimal control and communication co-design has been proposed. The proposed scheme cannot only learn the optimal co-design within fixed final time, but also relax the requirement of NCS dynamics and satisfy the practical transmit power constraint. The Lyapunov Theorem is used to validate the effectiveness of proposed scheme. With the proper NN weight update law, proposed scheme can ensure all closed-loop signals and NN weights are uniformly ultimately bounded (UUB). Moreover, simulation results are also included to demonstrate the effectiveness of the proposed scheme.

Design, Analysis and Real-time Implementation of Networked Predictive Control Systems

Networked control system has been a hotspot in the research fields of control theory and control engineering applications at home and abroad. Immune PID controller based on biological immune mechanism has simple structure and algorithms, and with the features of strong robustness and adaptability. The structure of networked control system based on immune PID controller had been designed in this paper, taking the typical one-order inertia plant with time delay and second-order inertia plant in the process of industrial production for example, the simulation model of immune PID networked control system based on TrueTime toolbox had built in the MATLAB environment, and simulation studies have shown the feasibility and effectiveness of the control scheme.

A mathematical model of networked control systems (NCS) with dynamic controllers is presented when the network-induced random time-varying delays of NCS are bounded and the upper bound of which is longer than one sampling period. This paper discretizes the model of continuous-time systems, applies augmented state-space method to the model and builds a discrete-time jump system model governed by a finite state Markov process. And the necessary and sufficient conditions guaranteeing stability of the system are discussed. This paper applies interior-point algorithm to design stabilizing controllers, presents a method to get the feasible initial solution and replaces Newton direction which is generally used in the interior-point algorithm with conjugate gradient direction for simplifying the algorithm. And this improved algorithm stated above is applied effectively to the networked control system of a cart and inverted pendulum with long delays.

This paper considers model and designing of networked vibration control with time delays for offshore platforms. According to wave theory and ocean engineering, exosystem is designed to describe irregular wave forces. The model of networked vibration control system for offshore platforms with two buffers is presented. The time delays in sensor-controller and controller-actuator channels are stochastic, bounded, and may bigger than one sampling interval. Based on the model, we design networked predictive feedforward and feedback controller. Stability of system can be guaranteed. Simulation results show that with presented controller, displacement and velocity of offshore platform gets smaller and required control force gets less too, compared with networked predictive state feedback optimal controller.