Ahmadreza Momeni

A Class of Bounded Distributed Control Strategies for Connectivity Preservation in Multi-Agent Systems

This technical note proposes a general class of distributed potential-based control laws with the connectivity preserving property for single-integrator agents. The potential functions are designed in such a way that when an edge in the information flow graph is about to lose connectivity, the gradient of the potential function lies in the direction of that edge, aiming to shrink it. The results are developed for a static information flow graph first, and then are extended to the case of dynamic edge addition. Connectivity preservation for problems involving static leaders is covered as well. The potential functions are chosen to be smooth, resulting in bounded control inputs. Other constraints may also be imposed on the potential functions to satisfy various design criteria such as consensus, containment, and formation convergence. The effectiveness of the proposed control strategy is illustrated by simulation for examples of consensus and containment.

A Model Predictive Decentralized Control Scheme With Reduced Communication Requirement for Spacecraft Formation

This brief investigates the control problem for a number of cooperative spacecraft with communication constraints. It is assumed that a set of cooperative local controllers corresponding to the individual spacecraft is given which satisfies the desired objectives of the formation. It is to be noted that due to the information exchange between the local controllers, the overall control structure can be considered centralized in general. However, communication in flight formation is expensive. Thus, it is desired to have some form of decentralization in control structure, which has a lower communication requirement. This decentralized controller consists of local estimators inherently, so that each local controller estimates the state of the whole formation. Necessary and sufficient conditions for the stability of the formation under the proposed decentralized controller are obtained. It is shown that the decentralized control system, if stable, behaves almost the same as its centralized counterpart. Moreover, robustness of the decentralized controller is studied and compared to that of the corresponding centralized controller. It is finally shown that the proposed decentralized controller comprises most of the features of its centralized counterpart. The efficacy of the proposed method is demonstrated through simulations.

Technical communique: Sufficient conditions for the convergence of a class of nonlinear distributed consensus algorithms

This paper is concerned with the convergence of a class of continuous-time nonlinear consensus algorithms for single integrator agents. In the consensus algorithms studied here, the control input of each agent is assumed to be a state-dependent combination of the relative positions of its neighbors in the information flow graph. Using a novel approach based on the smallest order of the nonzero derivative, it is shown that under some mild conditions the convex hull of the agents has a contracting property. A set-valued LaSalle-like approach is subsequently employed to show the convergence of the agents to a common point. The results are shown to be more general than the ones reported in the literature in some cases. An illustrative example demonstrates how the proposed convergence conditions can be verified.

An Efficient Target Monitoring Scheme With Controlled Node Mobility for Sensor Networks

This paper is concerned with target monitoring using a network of collaborative mobile sensors. The objective is to compute (online) the desired sensing and communication radii of sensors as well as their location at each time instant, such that a set of prescribed specifications are met. These specifications include end-to-end connectivity preservation from the target to a fixed destination, while durability of sensors is maximized and the overall energy consumption is minimized. The problem is formulated as a constrained optimization, and a procedure is presented to solve it. Simulation results demonstrate the effectiveness of the proposed techniques.

Battery modeling approaches and management techniques for Plug-in Hybrid Electric Vehicles

Batteries play a critical role in Hybrid Electric Vehicles (HEV) and Plug-In HEV (PHEV) as one of the main energy sources because of their high energy density. Therefore, for designing purposes suitable battery models are necessary. Batteries have very nonlinear behavior and are dependent on many factors such as chemistry, temperature, load profile, charge/discharge algorithm, age, etc. Modeling the behaviors of the batteries can be achieved using different approaches and techniques. The more accurate battery model is, the more reliable results are obtained using simulation softwares. However, increasing the accuracy of the model increases the complexity of the whole system model and also the time of the simulations. In the case of vehicular applications batteries are used as packs of hundreds of cells which adds to the complexity of the model, since some behaviors are exaggerated. Besides, some effects such as the difference in state-of-charge of different cells which leads to the age reductions of the whole battery pack, or for example the temperature difference of the cells in different places of the pack cannot be ignored. For optimal designing purposes there should be a kind of tradeoff between accuracy and complexity. There are various battery models based on various approaches and techniques in the literature which may cause confusion. This paper tries to summarize and categorize different battery models with main focus on vehicular applications.

On observer design for a class of impulsive switched systems

In this work, the problem of state observation for a class of impulsive switched systems is addressed. Corresponding to each subsystem, an identity Luenberger observer is employed and a switching observer is constructed accordingly. The asymptotic stability property of the proposed switching observer is discussed and LMI-based algorithms are given which provide sufficient conditions for asymptotic stability of the switching observer for switching signals with an average dwell time greater than a specific value. Since switched systems without impulse are a special case of impulsive switched systems, the results of this work can be used to design observers for switched systems without impulse as well. Numerical examples are given to show the effectiveness of the proposed algorithms.

High-Performance Decentralized Control for Formation Flying with Leader-Follower Structure

In this paper, an incrementally linear decentralized control law is proposed for the formation of cooperative vehicles with leader-follower topology. It is assumed that each vehicle knows the modeling parameters of other vehicles with uncertainty as well as the expected values of their initial states. A decentralized control law is proposed, which aims to perform as close as possible to a centralized LQR controller. The behavior of the proposed decentralized strategy and its closeness to that of the LQR controller depends on the accuracy of the corresponding a priori information. Since this information is not accurate in practice, a method is presented to evaluate the deviation of the performance of the decentralized system from that of its centralized counterpart. Furthermore, the necessary and sufficient conditions for the stability of the overall closed-loop system in presence of parameter perturbations are given through a series of simple tests. It is shown that stability of the overall system is independent of the magnitude of the expected value of the initial states. One of the advantages of the proposed decentralized strategy over its centralized counterpart is that it is in general more robust to the uncertainties in the system model. Simulation results demonstrate the effectiveness of the proposed controller in terms of feasibility and performance

Decentralized fixed modes for LTI time-delay systems

This paper investigates the stabilization problem for a linear time-invariant (LTI) time-delay system by means of a decentralized finite-dimensional LTI output feedback controller. Both commensurate and incommensurate delays are considered. It is assumed that delay can appear in the state, inputs, and outputs of the system. In this case, using the definition of μ-decentralized fixed modes (μ-DFM) introduced in a recent work necessary and sufficient conditions for the decentralized stabilizability of LTI time-delay systems is obtained. Some algebraic conditions are also provided to determine if a mode of a time-delay system is a μ-DFM. A numerical algorithm is proposed to obtain the set of μ-DFMs of the system, and the notion of μ-approximate decentralized fixed modes (μ-ADFM) is also presented. Finally, three numerical examples are given to illustrate various applications of the results.

Optimal target tracking strategy with controlled node mobility in mobile sensor networks

This paper is concerned with target tracking using a network of collaborative sensors. The objective is to compute (online) the desired sensing and communication radii of sensors as well as their location at each time instant, such that a set of prescribed specifications are achieved. These specifications include end-to-end connectivity preservation from the target to a fixed destination, while durability of sensors is maximized and the overall energy consumption is minimized. The problem is formulated as a constrained optimization, and a procedure is presented to solve it. Simulation results demonstrate the effectiveness of the proposed techniques.

Convergence analysis for a class of nonlinear consensus algorithms

In this paper, sufficient conditions for the convergence of a class of continuous-time nonlinear consensus algorithms for single integrator agents are proposed. More precisely, in the consensus algorithms studied here, the control input of each agent is assumed to be a state-dependent combination of the relative positions of its neighbors in the information flow graph. It is shown that under some mild assumptions, the contraction of the convex hull of the agents can be guaranteed. A set-valued Lasalle-like approach is then employed to derive the convergence from the contracting property. The proposed convergence criteria are verified for two different consensus algorithms via simulations.