Leonidas Dritsas

Guidance and Control Design for a Class of Spin-Stabilized Fin-Controlled Projectiles

This article presents a complete design concerning the guidance and autopilot modules for a class of spin-stabilized fin-controlled projectiles. The proposed concept is composed of two sections: the rapidly spinning aft part contains the charge, whereas the front part, which is roll decoupled from the aft, includes all the necessary electronic equipment and actuator devices needed for guidance and control. As far as the front section is concerned, a skid-to-turn control configuration is adopted, employing two pairs of movable trajectory correction aerodynamic surfaces, whereas a coaxial motor is added for nose roll angle positioning. The main advantage of the overall setup is that, on the one hand, it maintains the inherent dynamic stability properties of a rapidly spinning body due to the aft part, while at the same time, the front part, containing the guidance fuse, remains easy to be fit to any unguided projectile, hence transforming it into a guided one. The design of the guidance and control modules ...

Robust stability analysis of networked systems with varying delays

Robust stability conditions for Networked Controlled Systems (NCS) with uncertain, varying, bounded transmission delays and discrete-time static control laws are derived in this article. The delay uncertainty is shown to give rise to a discrete-time uncertain NCS model. The robust stability analysis is carried out via a linear matrix inequality approach which, when combined with a directed parameter search, yields an estimate of robust stability bounds on the maximum allowable delay (constrained within one sampling period) that the closed-loop system can tolerate. The presented simulation results show a drastic reduction of conservatism when compared with other techniques relying on the singular values of the perturbed NCS-model.

Constrained Optimal Control over Networks with Uncertain Delays

In this article a constrained finite time optimal controller (CFTOC) for networked controlled systems (NCS) is presented for the case where: a) the induced network delays are uncertain and bounded, and b) there are constraints in the magnitude of the control action and the outputs/states of the system. Based on the assumption that the round-trip latency time varies within known bounds, the uncertain network-induced delays are embedded in the system model resulting in a polytopic uncertain system. A polytopic uncertain system model is developed for the cases where: a) the uncertain delay is smaller than the sampling period, and b) the delay is longer than one sampling period but can be decomposed into a fixed known part (integer multiple of the sampling period) and an uncertain part bounded by one sampling period. When the constraints on the input and the output/state are added, the control objectives can be cast in a CFTOC formulation, and the resulting affine control law guarantees both the robust stability and the robust performance of the closed loop system, while satisfying the constraints. Simulation results are presented that prove the efficacy of the proposed control scheme

Modeling Approaches and Robust Stability Conditions for Networked Controlled Systems with Uncertain Delays

Abstract In this article two modeling approaches for Networked Controlled Systems (NCS) with different types of uncertainly varying bounded transmission delays and static discrete– time control laws are presented. Different models are offered for each case, all linked to the objective of designing robust discrete-time controllers. It is analytically shown how the careful mixing of asynchronous (event–driven) and synchronized (clocked) signals can lead to discrete time uncertain (possibly switched) systems, where results form robust control analysis and synthesis can be applied. After showing the implications of these modelling results for control synthesis purposes, sufficient conditions for the robust stability are given for each approach and a comparison of the conservatism of results is discussed.

On the modeling of networked controlled systems

In this article modeling approaches for networked controlled systems (NCS) with different types of varying communication latency times are presented. The embedded delays are unknown, bounded and depending on their size relative to the sampling period, four different models are offered. There is distinct treatment for delays longer than one sampling period, since these are decomposed to a term which is integer multiple of the sampling period and a residual which can be time-varying. The careful mixing of asynchronous (event-driven) and synchronized (sampled) signals can lead to discrete time uncertain and possibly switched systems, where classical control approaches could be applied.

Adaptive Constrained Control of Uncertain ARMA-Systems based on Set Membership Identification

In this article an adaptive constrained finite time optimal (CFTO) controller design is presented for unknown, discrete-time linear systems, whose dynamics are identified via set-membership identification (SMI) algorithms. The controller consists of two modules: a) the set membership(SM)-identifier that identifies the systems dynamics through the extended recursive least squares (eRLS) while providing the vertices of an orthotope that contains the nominal identification parameter vector, and b) the CFTO-controller; the tuning of the controller is based on a batch tuning procedure. The controllers feasible operating region remains unchanged for: a) all SM-orthotopes that are subsets of the last orthotope for which the controllers tuning was based, and b) the calculated CFTO-controller remains constant for a large period of time. In the opposite case the control partition of the controller is re-calculated (batch process) based on the current vertices of the identified SM-orthotope. Simulation results are presented that prove the efficacy and the validity of the suggested control scheme

Constrained Finite Time Control of Networked Systems with Uncertain Delays

In this article a constrained finite time optimal controller (CFTOC) for networked controlled systems (NCS) is presented for the case where: a) the induced network delays are uncertain and bounded, and b) there are constraints in the magnitude of the control action and the outputs/states of the system. Based on the assumption that the roundtrip latency time varies within known bounds, the uncertain network-induced delays are embedded in the system model resulting in a polytopic uncertain system. When the constraints on the input and the output/state are added, a CFTOC formulation of the control objectives yields an affine control law which guarantees both the stability and the performance of the closed loop, while satisfying the constraints. Simulation results are presented that prove the efficacy of the proposed control scheme

Adversary control strategies for discrete-time systems

This paper addresses the concept of adversary control for a single-input dynamical system. The system evolves in the discrete-time domain and is subject to both state and input hard constraints. A control law guarantees positive invariance and contractivity of a bounded, convex, polyhedral set with respect to the system as well as asymptotic stability of the origin with maximum convergence rate. Periodically, an adversary controller succeeds in gaining control of the system and sends false control commands attempting to drive the state vector outside of the polyhedral set at the maximum admissible rate. An enhanced adversary policy which takes measurement errors into account is also developed. Simulation studies highlight the results of this sequential, non-cooperative control game.

Combined networked switching output feedback control with D-region stability for performance improvement

In this article, a combined networked switching output feedback control scheme, with a -region stability performance improvement module is presented. The network induced time delays, that are considered to be time varying and integer multiples of the sampling period, are being embedded in the system model, by state augmentation. The resulting model of the overall networked closed-loop system is switching, with the current measured round-trip time delay acting as the switching rule. Based on this modelling approach, a Linear Matrix Inequality (LMI) tuned switching output feedback controller is designed. The proposed approach establishes robustness against time delays and is able to guarantee the overall stability of the switching closed-loop system. Integrated in the controlled synthesis phase, an LMI tuned performance improvement module is being introduced, based on -region stability. Multiple simulation results are being presented that prove the efficacy of the proposed scheme.

Feedback stabilization of Networked Control Systems

In this paper the stability analysis and control synthesis problems for Networked Control Systems (NCS) with bounded transmission delays (constant and unknown or time-varying) are investigated. First, stability conditions for NCS described by ARMA models are established and a method for the determination of admissible delay range is developed. Then, a linear programming method for the design of linear state-feedback controllers guaranteeing the stability of the system for any delay belonging to a prespecified range is developed. Contrary to the usual approaches based on the use of quadratic Lyapunov functions, a polyhedral Lyapunov approach is adopted for both analysis and synthesis. A control synthesis numerical example is given to illustrate the reduction of conservatism of the tolerable delay range when compared to former results.