Sanad Al-Areqi

Event-based networked control and scheduling codesign with guaranteed performance

Besides a fair distribution of limited resources among competing plants in a networked embedded control system (NECS) an efficient utilization of such scarce resources is crucial. Therefore, a novel event-based codesign concept for NECSs with limited communication bandwidth and computation capacity is presented in this paper. The codesign concept involves a joint design of an event-based controller and scheduler (EBCS) for improving the control performance provided that the limited resources are used efficiently. The NECS with a set of interacting continuous-time LTI plants is modeled as a discrete-time switched linear system. The EBCS codesign problem is then formulated as a linear matrix inequality (LMI) optimization problem minimizing an associated quadratic cost function. The EBCS strategy is then evaluated and compared with existing codesign strategies in literature for a simulation study involving a simultaneous stabilization of two mechanically coupled inverted pendulums. It should be remarked finally that the proposed EBCS strategy is generally applicable to discrete-time switched linear systems.

Event-Based Control and Scheduling Codesign: Stochastic and Robust Approaches

With the advent of networked embedded control systems (NECSs) new opportunities and challenges have arisen. Among others, the challenges result mostly from variable communication delays, access constraints, and resource constraints. An event-based control and scheduling (EBCS) codesign strategy for NECSs involving a set of continuous-time LTI plants is proposed in this paper addressing all aforementioned challenges. A novel representation of the network-induced delay as an uncertain variable belonging to a finite set of different bounded intervals is further proposed. The transition from one bounded interval to another can be arbitrary or according to a stochastic process. Regarding the type of the transition and the resulting discrete-time switched polytopic system of the NECS, two versions of the EBCS problem are introduced: A robust EBCS problem under arbitrary transition and a stochastic EBCS problem under stochastic transition. Global uniform practical stability with guaranteed performance (measured by a quadratic cost function) is guaranteed for both versions after formulating them as LMI optimization problems. The effectiveness of the proposed EBCS strategy is illustrated along with a comparison between its versions for a set of mobile robots. Notably, the EBCS strategy is generally applicable to discrete-time switched polytopic systems.

Event-based control and scheduling codesign of networked embedded control systems

For networked embedded control systems (NECSs) besides control performance an efficient usage of computation and communication resources is crucial. This paper presents a novel event-based codesign concept for NECSs. The codesign concept involves a joint design of a control law, a scheduler, and an event generator. The control law serves for improving control performance, the scheduler and the event generator for an efficient usage of the limited resources. The codesign problem is formulated as a linear matrix inequality (LMI) problem which can be solved efficiently. The developed theory is evaluated through a simulation for networked embedded control of a set of inverted pendulums. Noteworthy, the codesign concept is generally applicable to discrete-time switched linear systems.

Robust control and scheduling codesign for networked embedded control systems

Robust control and scheduling for networked embedded control systems (NECS) with uncertain but interval-bounded time-varying computation and transmission delay is addressed in this paper. The NECS is described by a set of continuous-time plant models and associated quadratic cost functions. Since the uncertainty of the computation and transmission delay affects the discretized plant models and cost functions in a nonlinear manner, a polytopic overapproximation of the uncertainty utilizing a Taylor series expansion is considered. For the resulting discrete-time switched system model with polytopic uncertainty, a periodic control and online scheduling (PCSon) strategy is proposed to guarantee stability and performance of the resulting controlled system. The design is based on a periodic parameter-dependent Lyapunov function and exhaustive search. Furthermore, a method for reducing the online complexity of the PCSon strategy is presented. The effectiveness of modeling and design is evaluated for networked embedded control of a set of inverted pendulums.

Stochastic event-based control and scheduling of large-scale networked control systems

Using a multi-purpose communication network in large-scale control systems raises new opportunities and challenges. Among others, the challenges result mostly from variable communication delays, medium access constraints, and resource constraints. A design strategy which considers all of these challenges in one framework is of special importance. For this purpose, an event-based control and scheduling (EBCS) codesign strategy for large-scale networked control systems with all aforementioned challenges is proposed in this paper. The communication delay is represented as an uncertain variable belonging to a finite set of different bounded intervals where the transition between them is according to a stochastic process. The proposed EBCS strategy is formulated as an LMI optimization problem and evaluated for a simultaneous guidance of three mobile robots.

Output-based control and scheduling codesign for control systems sharing a limited resource

This paper addresses the output-based control and scheduling codesign problem for control systems sharing a limited resource, especially embedded control systems (ECSs). The joint design (codesign) of a controller and a scheduler is for the purpose of improving the resulting control performance. ECSs with a set of independent linear time-invariant plants and considerable computation time delays are modeled as discrete-time switched linear systems. Based on the resulting model, the codesign problem is introduced and decomposed into a state-based control and scheduling codesign subproblem and an observer design subproblem using the separation principle. Both subproblems are eventually formulated as LMI subproblems which can be solved efficiently. Two types of observers are introduced to cope with the lack of all states: Prediction observer and current-state observer. The effectiveness of the proposed output-based codesign method is illustrated for simultaneous stabilization of three inverted pendulums.

Event-based distributed control of dynamically coupled and constrained linear systems

In this paper, a novel event-based distributed control strategy for a set of dynamically coupled discrete-time LTI plants is proposed. To avoid unnecessary communication among the distributed control system, each plant with its local controller is equipped with an event generator deciding locally whether new state measurements must be sent or not. Via a tuning parameter and a codesign of event generator and controller, the designer can adjust an eligible trade-off between control performance and communication utilization. Further state and input constraints as well as constraints on the communication topology can be included into the codesign. With a quadratic event-triggering law and the socalled S-procedure the codesign can be formulated as an LMI optimization problem which guarantees asymptotical stability of the closed-loop system and compliance with the constraints. The effectiveness of the approach is evaluated for distributed control of a set of mechanically coupled inverted pendulums.

Robust Event-Based Control and Scheduling of Networked Embedded Control Systems

Abstract Control and/or scheduling design for systems characterized by limited resources, e.g. networked embedded control systems (NECSs) with limited communication and computation resources, entails an efficient utilization of such scarce resources. Efficient utilization is in the sense of fairly distributing and occupying the resources only if a necessity exists from stability or performance perspective. For this purpose, a robust event-based control and scheduling (RoEBCS) codesign strategy is proposed for NECSs with uncertain but interval-bounded time-varying communication and computation delays. The considered system is modeled as a discrete-time switched polytopic system with an additive norm-bounded uncertainty. The RoEBCS problem is then formulated as a linear matrix inequality feasibility problem for which many efficient solvers are available. The effectiveness of the RoEBCS strategy is illustrated for networked embedded control of a set of mechanically coupled inverted pendulums. Notably, the proposed codesign strategy is generally applicable to discrete-time switched polytopic systems with additive norm-bounded uncertainty.

Stability analysis and PI control synthesis under event-triggered communication

Although setpoint tracking problems are common in practice, they are still widely unexplored in the event-triggered control framework. Therefore, an event-triggered PI control design strategy with guaranteed performance for networked control systems is proposed in this paper. The integral state of the proposed PI controller is updated at every sampling instant. The update is done by the proposed event generator and sent with new measurements to the PI controller when necessary. Based on a discretized system model and a quadratic cost function, the event-triggered PI control design problem is introduced and formulated as an LMI optimization problem. The effectiveness of the proposed strategy is then experimentally evaluated and compared with other existing strategies in the literature for a case study.

Receding-horizon control and scheduling of systems with uncertain computation and communication delays

This paper addresses robust control and scheduling codesign for networked embedded control systems (NECS) with uncertain but interval-bounded time-varying computation and communication delays. The NECS is modeled as a discrete-time switched linear system with polytopic uncertainty. A robust receding-horizon control and scheduling problem with a quadratic performance criterion is introduced and solved based on the concept of (relaxed) dynamic programming. Closed-loop stability is guaranteed a priori by imposing stability constraints formulated as linear matrix inequalities. The effectiveness of the proposed modeling and synthesis methods is evaluated for networked embedded control of a set of pendulums. Notably, the proposed strategy is generally applicable to discrete-time switched linear systems with polytopic uncertainty.