Papers by Eduardo Mojica-Nava
In proceedings of the 2013 European Control Conference
Motivated by the increasing interest in networked multi-agent systems and the wide number of appl... more Motivated by the increasing interest in networked multi-agent systems and the wide number of applications in decentralized distributed control of smart grids, we address the problem of synchronization when each node (e.g., a microgrid, a distributed generator) is modeled as a linear-time continuous system whose output measurements are sent through communication links. However, the inclusion of a communication infrastructure adds new challenges to control strategies and some problems may arise such as time delays, packet losses, sampling period, just to name a few. In this work, we consider that data is sampled with homogeneous sampling periods. Then, using the novel concept of average passivity, we define the conditions for synchronizability when all nodes are identical and unstable dynamics are present. Additionally, results are extended to the case of non-uniform agents, and some simulations of synchronization in smart grids are introduced.
n proceeding of the American Control Conference 2014, 2014
The Kuramoto oscillator has been widely studied because it can model biological, social, chemical... more The Kuramoto oscillator has been widely studied because it can model biological, social, chemical, and engineering problems. Conditions for frequency synchronization of a network of Kuramoto oscillators have
been well established, but it depends on the connectivity of the network and on the natural frequencies. However, some applications requires that oscillators oscillate to a desired frequency even when the network topology is
disconnected. In this work we propose a consensus-based control strategy that forces the network to follow a virtual agent with constant frequency. Besides, we consider that the control input is constrained and we establish the limits of the set of inputs that assure frequency tracking. The results are extended to the smart grid case, where the nodes of a power network are modeled as Kuramoto oscillators that synchronize to a desired frequency using the injection/absorbsion of power according to a consensus based control. We show that our results are feasible when isolated group of nodes are taken into account, and they can be connected or disconnected to the main grid. Finally, the effects of time-varying sampling are analyzed and sampling period independence is demonstrated.
Accepted to the 53th Conference on Decision and Control, 2014
The consensus algorithm can represent many problems in cooperative behavior, and has been widely ... more The consensus algorithm can represent many problems in cooperative behavior, and has been widely used in engineering and social sciences. In this work, we prove that the consensus model where the information that each agent receives from its neighbors has time-varying asynchronous delays and sampling, converges to an agreement independent of these communication constraints. This independence is useful in the context of ``data minimization,'' which is one of the principles for privacy. As a practical example, we show how this independence can be used for microgrids with a consensus-based secondary control scheme where participants have incentives to share their states to ensure frequency synchronization, while at the same time minimizing the amount of data shared to preserve their privacy. We then propose two data sharing algorithms: 1) periodic sampling, and 2) discretionary sampling, and study their privacy as well as their performance. We show that even when a discretionary sampling scheme ``lies'' to their neighbors in order to preserve their privacy, the consensus algorithm performs almost as well as with periodic sampling.
2007 46th IEEE Conference on Decision and Control, 2007
... 2004. [7] E. Mojica, A. Gauthier, and C. Collazos, Control Automático de un Bioreactor de Cr... more ... 2004. [7] E. Mojica, A. Gauthier, and C. Collazos, Control Automático de un Bioreactor de Crecimiento Celular, In Proc. 2nd IEEE Colombian Workshop on Robotics and Automation, 2006. [8] M. Rewienski and J. White, A Trajectory Piecewise-Linear Approach to Model Order ...
In proceeding of the Conference on Decision and Control (CDC 2013), 2013
Motivated by the increasing interest in networked multi-agent systems and the wide number of appl... more Motivated by the increasing interest in networked multi-agent systems and the wide number of applications in distributed control of smart grids, we address the problem of synchronization of microgrids. Two topologies are considered: the physical topology that relates the interconnection of distributed generators and loads, and the communication topology, which describes the information flow of the power system measurements. We propose a control strategy based on the information flow and we show that there exists a strong relationship between both topologies in order to achieve synchronization. As a matter of fact, we show that our results can be extended when isolated group of nodes are taken into account, and they can be connected or disconnected to the main grid. Finally, the effects of time-varying sampling are analyzed using some average passivity conditions, and sampling-time independence is demonstrated with the proposed controller.
IEEE Security & Privacy Magazine, 2014
Most of the government, industry, and academic efforts for protecting the power grid against comp... more Most of the government, industry, and academic efforts for protecting the power grid against computer attacks have focused on information security mechanisms for preventing and detecting attacks. In this article we give a short introduction to control problems in the power grid and show that in addition to information security mechanisms, we can use control engineering to help improve our analysis and design of an attack-resilient power grid.
International Journal of Electrical Power & Energy Systems, 2014
There exists an increasing interest in networked systems due to the wide number of applications i... more There exists an increasing interest in networked systems due to the wide number of applications in distributed and decentralized control of large scale systems, such as smart grids. We address the problem of distributed frequency synchronization of several isolated microgrids, each one described by a linear-time continuous system, composed by different types of generators, whose outputs are measured and sent through a communication infrastructure. We assume that each microgrid possesses renewable resources with storage capabilities that helps to improve stability of the network when small damping ratio is considered. Thus, using the smart grid communication infrastructure and the data flow through the network, we propose a cooperative control strategy based on the consensus algorithm that simultaneously manages the turbine governor input and the amount of energy that the storage devices have to absorb/inject from/into the grid. Nevertheless, physical constraints need to be included, which can be modeled using saturation non-linearities, and conditions to assure synchronization even with saturation are obtained based on multi-agent systems. Additionally, we consider that sensor measurements are sampled and we extend the results of frequency synchronization with saturation to the case of control discretization and sampling-period independence is demonstrated using passivity concepts.
Systems & Control Letters, 2010
A polynomial approach to deal with the stability analysis of switched non-linear systems under ar... more A polynomial approach to deal with the stability analysis of switched non-linear systems under arbitrary switching using dissipation inequalities is presented. It is shown that a representation of the original switched problem into a continuous polynomial system allows us to use dissipation inequalities for the stability analysis of polynomial systems. With this method and from a theoretical point of view, we provide an alternative way to search for a common Lyapunov function for switched non-linear systems.
International Journal of Robust and Nonlinear Control, 2013
Optimal control problems for switched nonlinear systems are investigated. We propose an alternati... more Optimal control problems for switched nonlinear systems are investigated. We propose an alternative approach for solving the optimal control problem for a nonlinear switched system based on the theory of moments. The essence of this method is the transformation of a nonlinear, nonconvex optimal control problem, that is, the switched system, into an equivalent optimal control problem with linear and convex structure, which allows us to obtain an equivalent convex formulation more appropriate to be solved by high-performance numerical computing. Consequently, we propose to convexify the control variables by means of the method of moments obtaining semidefinite programs.
2007 46th IEEE Conference on Decision and Control, 2007
... 2004. [7] E. Mojica, A. Gauthier, and C. Collazos, Control Automático de un Bioreactor de Cr... more ... 2004. [7] E. Mojica, A. Gauthier, and C. Collazos, Control Automático de un Bioreactor de Crecimiento Celular, In Proc. 2nd IEEE Colombian Workshop on Robotics and Automation, 2006. [8] M. Rewienski and J. White, A Trajectory Piecewise-Linear Approach to Model Order ...
2007 IEEE International Conference on Control Applications, 2007
... [7] E. Mojica, A. Gauthier, and C. Collazos, Control Automático de un Bioreactor de Crecimie... more ... [7] E. Mojica, A. Gauthier, and C. Collazos, Control Automático de un Bioreactor de Crecimiento Celular, In Proc. 2nd IEEE Colombian Workshop on Robotics and Automation, 2006. [8] M. Rewienski and J. White, A Trajectory Piecewise-Linear Approach to Model Order ...
IX Latin American Robotics Symposium and IEEE Colombian Conference on Automatic Control, 2011 IEEE, 2011
A Wireless Networked Control Systems review is presented. It begins with a brief history about NC... more A Wireless Networked Control Systems review is presented. It begins with a brief history about NCS (Networked Control Systems), recognizing the fundamental features, its advantages over other classical control systems, and the protocols that can be used to do control over the wireless network. Also, we deal with the different problems that can affect the network behavior; including interferences and delays that take place when the control acts. The behavior of the system in different environments is shown through simulations using TrueTime blocks, included in a Simulink/MATLAB box.
2007 IEEE International Conference on Control Applications, 2007
... [7] E. Mojica, A. Gauthier, and C. Collazos, Control Automático de un Bioreactor de Crecimie... more ... [7] E. Mojica, A. Gauthier, and C. Collazos, Control Automático de un Bioreactor de Crecimiento Celular, In Proc. 2nd IEEE Colombian Workshop on Robotics and Automation, 2006. [8] M. Rewienski and J. White, A Trajectory Piecewise-Linear Approach to Model Order ...
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Papers by Eduardo Mojica-Nava
been well established, but it depends on the connectivity of the network and on the natural frequencies. However, some applications requires that oscillators oscillate to a desired frequency even when the network topology is
disconnected. In this work we propose a consensus-based control strategy that forces the network to follow a virtual agent with constant frequency. Besides, we consider that the control input is constrained and we establish the limits of the set of inputs that assure frequency tracking. The results are extended to the smart grid case, where the nodes of a power network are modeled as Kuramoto oscillators that synchronize to a desired frequency using the injection/absorbsion of power according to a consensus based control. We show that our results are feasible when isolated group of nodes are taken into account, and they can be connected or disconnected to the main grid. Finally, the effects of time-varying sampling are analyzed and sampling period independence is demonstrated.
been well established, but it depends on the connectivity of the network and on the natural frequencies. However, some applications requires that oscillators oscillate to a desired frequency even when the network topology is
disconnected. In this work we propose a consensus-based control strategy that forces the network to follow a virtual agent with constant frequency. Besides, we consider that the control input is constrained and we establish the limits of the set of inputs that assure frequency tracking. The results are extended to the smart grid case, where the nodes of a power network are modeled as Kuramoto oscillators that synchronize to a desired frequency using the injection/absorbsion of power according to a consensus based control. We show that our results are feasible when isolated group of nodes are taken into account, and they can be connected or disconnected to the main grid. Finally, the effects of time-varying sampling are analyzed and sampling period independence is demonstrated.