1,721,105 research outputs found
Performance analysis and optimization of power systems with spatially correlated noise
Get PDFBased on stochastic differential equations (SDEs), we analyse the overall performance of heterogeneous power systems network, subject to spatially distributed and correlated noises with random initial conditions. We determine bounds on the H2 norm of the heterogeneous system based on a closedform of the norm of the homogeneous power system. Then, we formulate possible scenarios for performance optimization and link these to applications for network design and control problems in power systems. Our results are corroborated by numerical simulations from Kundur’s four-machine two-areanetwork after adaption to our setup
Robust noncooperative attitude tracking control for rigid bodies on rotation matrices subject to input saturation constraint
Get PDFThis paper addresses the noncooperative attitude tracking control problem for rigid bodies whose dynamics evolves on the rotation matrix (Formula presented.). First, based on the relative attitude measurement, a saturated angular velocity input is designed by a proposed saturated nonlinear function. Thereafter, the attitude tracking control torque for rigid body's dynamics with input saturation constraint and active disturbance rejection is developed by a modified dynamic surface control approach which can avoid large torque in practice. Furthermore, by using only relative attitude measurements, two types of velocity-free attitude control laws are considered, respectively. In contrast to those control schemes that require that the desired angular velocity is available to the rigid body, the proposed scheme is able to solve the attitude control in noncooperative scenarios, where the desired angular velocity and acceleration are not accessible. Since the attitude described by rotation matrix (Formula presented.) enables the controller to use local measurements in the body-fixed frame rather than global measurements in an inertial frame, the proposed robust noncooperative control schemes with input saturation constraint are easier to implement in practice. Finally, numerical simulations and SimMechanics experiments are provided to illustrate the effectiveness of the proposed theoretical results
Tuning and Analysis of Geometric Tracking Controllers on SO(3)
No full textThis paper concerns the robustness of attitude controllers for dynamics configured on the SO(3) manifold and poses a set of bilinear matrix inequalities to find an optimal controller tuning with respect to (i) the ultimate bound of the error-state trajectories when perturbed by naturally arising disturbances, and (ii) the worst-case decay rate of the tracking errors. The presented optimization problem can be solved both to generate a robust tuning for experimental applications, and also to facilitate qualitative comparisons of different attitude controllers present in the literature. To solve the tuning problem, we propose an algorithm based on alternating semidefinite programming, with local linearizations of an upper bound of the associated cost function. The soundness of this approach is illustrated by comparison to an interior-point method. The algorithm is subsequently used to provide insights for the tuning of the considered controllers, and finally demonstrated by a closed-loop simulation example
Mobile Formation Coordination and Tracking Control for Multiple Nonholonomic Vehicles
No full textThis article addresses forward motion control for trajectory tracking and mobile formation coordination for a group of nonholonomic vehicles on SE(2). First, by constructing an intermediate attitude variable which involves vehicles' position information and desired attitude, the translational and rotational control inputs are designed in two stages to solve the trajectory tracking problem. Second, the coordination relationships of relative positions and headings are explored thoroughly for a group of nonholonomic vehicles to maintain a mobile formation with rigid-body motion constraints. We prove that, except for the cases of parallel formation and translational straight line formation, a mobile formation with strict rigid-body motion can be achieved if and only if the ratios of linear speed to angular speed for each individual vehicle are constants. Motion properties for mobile formation with weak rigid-body motion are also demonstrated. Thereafter, based on the proposed trajectory tracking approach, a distributed mobile formation control law is designed under a directed tree graph. The performance of the proposed controllers is validated by both numerical simulations and experiments
Distributed Computation of Graph Matching in Multi-Agent Networks
Get PDFThis work considers the distributed computation of the one-to-one vertex correspondences between two undirected and connected graphs, which is called \textit{graph matching}, over multi-agent networks. Given two \textit{isomorphic} and \textit{asymmetric} graphs, there is a unique permutation matrix that maps the vertices in one graph to the vertices in the other. Based on a convex relaxation of graph matching in Aflalo et al. (2015), we propose a distributed computation of graph matching as a distributed convex optimization problem subject to equality constraints and a global set constraint, using a network of multiple agents whose interaction graph is connected. Each agent in the network only knows one column of each of the adjacency matrices of the two graphs, and all agents collaboratively learn the graph matching by exchanging information with their neighbors. The proposed algorithm employs a projected primal-dual gradient method to handle equality constraints and a set constraint. Under the proposed algorithm, the agents' estimates of the permutation matrix converge to the optimal permutation globally and exponentially fast. Finally, simulation results are given to illustrate the effectiveness of the method
Collaborative Target-Tracking Control Using Multiple Fixed-Wing Unmanned Aerial Vehicles with Constant Speeds
No full textThis paper considers a collaborative tracking control problem using a group of fixed-wing unmanned aerial vehicles (UAVs) with constant and nonidentical speeds. The dynamics of fixed-wing UAVs are modeled by unicycletype equations with nonholonomic constraints, assuming that UAVs fly at constant altitudes in the nominal operation mode. The controller is designed such that all fixed-wing UAVs as a group can collaboratively track a desired target’s position and velocity. This paper first presents conditions on the relative speeds of tracking UAVs and the target to ensure that the tracking objective can be achieved when UAVs are subject to constant-speed constraints. A reference velocity is constructed that includes both the target’s velocity and position as feedback, which is to be tracked by the group centroid. In this way, all vehicles’ headings are controlled such that the group centroid follows a reference trajectory that successfully tracks the target’s trajectory. A spacing controller is further devised to ensure that all vehicles stay close to the group centroid trajectory. Tradeoffs in the controller design and performance limitations of the target tracking control due to the constant-speed constraint are also discussed in detail. Experimental results with three fixed-wing UAVs tracking a target rotorcraft are provided
Frequency synchronization of a high-order multi-converter system
Get PDFWe investigate the stability properties of a multi-converter power system model, defined on a high-order manifold. For this, we identify its symmetry (i.e., rotational invariance) generated by a static angle shift and rotation of AC signals. We characterize the steady state set, primarily determined by the steady state angles and DC power input. Based on eigenvalue conditions of its Jacobian matrix, we show asymptotic stability of the multi-converter system in a neighborhood of the synchronous steady state set by applying the center manifold theory. We guarantee the eigenvalue conditions via an explicit approach. Finally, we demonstrate our results based on a numerical example involving a network of identical DC/AC converter systems
A Unified Approach for Finite-Time Global Stabilization of Affine, Rigid and Translational Formation
Get PDFThis paper studies the multi-agent control problem for affine, rigid, and translational formation, with the aim of developing a unified distributed control strategy for global and finite-time convergence. Global stabilization of rigid formation in arbitrary dimensional spaces still remains open and challenging. This paper provides a general solution to it based on the sliding mode control idea. The control law design consists of two parts: the main control force regulates the trajectories of all agents to reach a sliding surface defined by an affine formation space in finite time and remain in it thereafter; the extra control force governs certain chosen leader agents towards the desired formation in the sliding surface. The paper then presents in detail two approaches for designing the extra control force, one based on distance constraints and the other based on relative position constraints. For the first time, the proposed sliding mode formation control laws solve the open problem of (almost) global and finite-time stabilization of affine, rigid and translational formations in any dimensional space
Grid-forming lambda-omega virtual oscillator control in converter-based power systems
Get PDFInspired by the kinetics of wave phenomena in reaction-diffusion models of biological systems, we propose a novel grid-forming control strategy for control of three-phase DC/AC converters in power systems. The () virtual oscillator control or (lambda-omega) VOC is a natural increment on ideas from virtual oscillator dynamics rotating at a fixed nominal frequency to adaptive, angle-based frequency function. We study a network of identical three-phase DC/AC converters interconnected via transmission lines. For this, we prove almost global asymptotic stability for a reduced (time-scale separated) version of the model, associated to a well-defined set of controller gains and system parameters. Additionally, we link the (\lambda-\omega) VOC to well-studied controllers in the literature, e.g. droop control. Finally, we validate our results on an example three DC/AC converter network
A unified control method for consensus with various quantizers
Get PDFThis paper studies the distributed consensus problem for networked general linear systems in the presence of different quantizers. The distinct features of this work are three-fold. First, both uniform and logarithmic quantization effects are analyzed. A unified control method (involving a distributed controller, a distributed event-detector, time-varying gains and constant parameters) is developed based on the relative quantized state information, which is applicable to practical scenarios where uniform and logarithmic quantization phenomena appear separately or alternately. Second, the updates of the relative information involved in the controller and the communication between adjacent agents are executed only at certain discrete event instants, significantly reducing the information update burden and data transmission load. Moreover, an internal variable, which is adjustable in accordance with the update law, is introduced in the event-detector to enhance the dynamic characteristics of the triggering performance with a lower triggering frequency. Simultaneously, the undesired Zeno behavior can be ruled out. Third, time-varying coupling gain (regulated by an adaptive rule) and triggering gain (relevant to the coupling gain) instead of constant ones are designed for the controller and the event-detector, respectively. Besides, other constant parameters can be easily tuned. These settings enable the developed control method to feature more flexibility and to be implemented in a fully distributed manner, requiring no global information. Finally, simulation examples are presented to illustrate the applicability of the theoretical results
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