Research

Hybrid control of switched systems

The switched systems as the converters constitute an important class of systems, which concentrates the interest of the control community. A new formulation of the problem is developed in the context of hybrid dynamical systems, which represents an adequate way for handling the requirements of  converters, while guaranteeing theoretically and practically all specifications in terms of stability and performance. In this sense, the proposed approach encompasses several methods considered in the literature.


Sensor node activity using hybrid dynamical system approach

A hybrid control algorithm for energy management in a Wireless Sensor Network (WSN) is proposed. The energy in the sensor nodes is modeled using a hybrid dynamical system representation, where solutions may continuously flow according to some differential equations and may discontinuously jump according to some rules.. The WSN has to provide a given functionality (named “mission”), while taking into account the possibility for nodes to fall in a faulty  condition. The goal of the proposed control strategy is to improve the scalability issues while the network lifespan is reduced.


Hybrid control of agent network

Management problem for a cluster of servers treating external requests. A    deterministic hybrid dynamical model of the overall system is built (differently, from probabilistic approaches like Markov chains are used). Then, inspired by consensus theory, it is proposed a centralized control law distributing the computational load among the agents and deciding when to turn on or off each agent, for energy efficiency, while ensuring that the queues of each agent asymptotically converge to a desirable level. it is  formally proved the properties of the proposed law and highlight some interesting peculiarities in terms of non-uniform convergence. In summary, a distributed activity management of the agents to adjust the number of them to the total demanded load appears as an innovative and relevant solution.

 


Control for power efficient DVFS management

A joint controller is designed to jointly manage voltage and current frequency in Dynamic Voltage-Frequency Scaling (DVFS) mechanism. It is implemented to control a Vdd-Hopping driver and a FLL clock generator. The internal controller of each driver, among other characteristics, rejects perturbations and provide outputs without signal overshoots. From these properties, it has been designed an external joint controller that in order to reduce the power consumption. This joint controller  has been validated through Matlab simulations. It has been shown, that the power consumption can be reduced by 40.5% in the evaluated test-case.


Generation of oscillations by Energy Shaping

Definition of a dynamical system such that a closed curve (e.g. an ellipse) is its limit set. This can be reached by adopting a function V(G) as a Hamiltonian function, where G is the closed curve function. Using LaSalle invariance principle it can be seen that for all initial conditions except the origin the trajectories of the system tend to the curve G= 0.

 


Adaptive controller & global stability analysis by singular perturbation approach

Design of one or more observers for dealing with variations and/or uncertainties in parameters. The proof of the system global stability is based on time-scale separation, by using singular perturbation form.


Estimation of the attraction domain for systems with constraints

Estimation of the attraction domain for polynomial non-linear systems with saturation-like constraints and other some constraints due to system properties, based on the optimization techninique of Sum of Squares descomposition for multivariate polynomials.