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This article introduces a unified Hamiltonian formulation for controlling grid-connected direct current microgrid via interconnection and damping assignment–passivity-based control. The direct current microgrid includes hydro–solar–wind hybrid renewable energy systems and battery/supercapacitor hybrid energy storage system. Hybrid renewable energy systems are integrated as a disturbed direct current source, while hybrid energy storage system is integrated via semi-active topology, where the battery is connected to the direct current bus through a bidirectional dc-to-dc converter. The proposed Hamiltonian approach allows us to design a control strategy for the bidirectional dc-to-dc converter and the grid-connected three-phase inverter to (1) reject power disturbances in the direct current bus via the supercapacitor and ensure smooth current in the battery as well as in the grid and (2) assign the system to a desired equilibrium after sharp changes. In the studied article, the stability of the system under the interconnection and damping assignment–passivity-based control controller is investigated. The interconnection and damping assignment–passivity-based control controller is compared with two conventional proportional–integral–based controllers through simulations under the MATLAB/Simulink environment. The main contributions in this article are the unified hybrid modelling for dc-to-dc power converter and grid-connected inverter using port-Hamiltonian approach, external disturbance rejection in the multi-source power system using interconnection and damping assignment–passivity-based control, and the assurance of global asymptotic stability of the closed-loop system.

IF=3.8; International audience; This article focuses on the problem of leaderfollowing consensus of second-order Multi-Agent Systems (MAS) with switching topology and partial aperiodic sampled data. MAS are subject to various constraints related to information exchange among the agents. It is considered that each agent in the network is able to measure its position only and cannot measure either its velocity or acceleration (input). Moreover, the position information is sent to the neighbors at aperiodic and asynchronous sampling rates. At last, a switching communication topology among the agents is considered. An observer-based control protocol is proposed to achieve leader-following consensus for MAS with above mentioned constraints. Using an Average Dwell Time (ADT) approach, sufficient conditions are derived through Lyapunov-based stability analysis to ensure the leader-following consensus. Numerical examples are also included to show the effectiveness of the proposed scheme.

International audience; Inspired by the echolocation behaviors of the bats and the swarm intelligence optimization, bat searching algorithm (BA) was developed to solve unconstrained optimization problems efficiently. However, due to the lack of the gradient term, the accuracy of the BA is not superior, and the enhancement of the algorithm is still of vital importance. The sign gradient descent method (SGD) is a first-order optimization method involving only the sign of the gradient of the function to minimize. Most importantly, the convergence and optimality issues of the SGD have been rigorously studied, which guarantees the competitive performance of SGD method. Therefore, in this paper, a combination of the BA and SGD method is proposed by integrating the SGD term into the update equation of the bats during the searching process. With the social behavior among the bats and the sign gradient descent method, the proposed algorithm shows significant improvement comparing with the original algorithm. Moreover, the convergence issue of the proposed algorithm is studied from system dynamics perspective. The numerical evaluations are provided to demonstrate the improvement of the proposed sign gradient descent method based bat searching algorithm. In the end, the economic load dispatch problem for the power system is studied as an application of the proposed BA algorithms. Based on the numerical results, the proposed BA shows superior performance.

International audience; This paper deals with the problem of time-varying formation tracking for second-order multi-agent systems under directed topology, where the follower states form a desired formation while tracking the state of the leader. It is considered that each agent, including the leader, has second-order dynamics and can only transmit its position to its neighbors. The velocities and inputs are not exchanged between neighboring agents. In this work, it should be mentioned that contrary to many existing schemes, asynchronous and aperiodic sampling is considered. For each agent, an observer is proposed to estimate its state and the state of its neighbors from the available local asynchronous and aperiodic sampled position data. Using these estimates, a time-varying formation tracking protocol is developed. The stability of the closed-loop system which combines the continuous-discrete time observer and the formation tracking controller is analysed using an appropriate Lyapunov function. The effectiveness of the proposed output-feedback controller is illustrated for various formations through simulation results.

International audience; The aim of this paper is to study the second-order practical consensus of homogeneous sampled-data multiagent systems (MASs). To do this, a new nonlinear emulation strategy based on homogeneity is developed. It is then applied to MASs under synchronously variable sampling. Finally, a comparison with the classical linear strategy is provided in the case of MASs under synchronously periodic sampling.

International audience; This paper deals with the leader-following consensus problem of multi-agent systems with the consideration that each agent can only transmit its position state to the neighbors at irregular discrete sampling times. In the proposed algorithm, a continuous-discrete time observer is designed for the continuous estimation of both position and velocity from the discrete position information of the neighbors. These estimated states are then used for designing a continuous control law which solves the leader-following consensus problem. Moreover, the dynamics of the leader is not fixed and can be controlled through an external input. The stability analysis has been carried out by employing the Lyapunov approach which provides sufficient conditions to tune the parameters according to the maximum allowable sampling period. The developed algorithm has been simulated and then tested on an actual multi-robot system consisting of three differential drive wheeled robots. Both simulation and hardware results validate the effectiveness of the control algorithm.

International audience; The article deals with the stability of discontinuous homogeneous nonlinear systems with aperiodic sampled-data inputs. We first extend results about robustness of homogeneous nonlinear systems to the discontinuous case. Then, we prove that this framework is well suited for studying the stability of discontinuous homogeneous nonlinear sampled-data systems. The results are illustrated on the double integrator.

International audience; The second-order practical consensus tracking of multi-agent systems with a fixed topology and a varying leader's velocity is obtained by using a linear control strategy and the input-to-state stability framework. Then, a new control protocol is proposed where the leader, called a perceptive leader, receives information from its followers. Finally, a study is provided in simulation and on a fleet of mobile robots showing the effectiveness of non perceptive and perceptive strategies in terms of speed of convergence, precision and connectivity maintenance.

Open access; International audience

International audience; A novel distributed consensus protocol, where only sampled position information is exchanged between neighboring agents, is designed for second-order multi-agent systems under a directed communication topology. This protocol allows to reach the consensus for asynchronous and aperiodic sampling periods, which means that every agent can send its measurements independently from its neighbors. Furthermore, the upper bound on the sampling periods can be chosen arbitrarily long by adapting the tuning parameters. This result is obtained by using a continuous-discrete time observer which allows to reconstruct the system state in real time from only discrete-time measurements. The feedback control gain is set according to the observer gain which is itself set according to the maximum sampling period.

The purpose of this paper is to apply filter banks to the control problem involving the rejection of multi-sinusoidal disturbance from output of slowly time-varying stable systems. The use of filter banks allows to distribute the control effort in many independent adaptive controllers, each of them taking care of a sinusoidal component of the disturbance. By varying the filter banks specifications, the method handles the trade-off between a time-behavior controller, with interesting settling time and a tonal-behavior controller showing the properties of simplified control, reduced computational time and on-line system identification with the system output noise via the feedback loop. Numerical examples are presented to illustrate this trade-off.

International audience; The main goal of this article is to study the robustness of continuous homogeneous systems with sampled-data inputs subject to external disturbances. We characterize how the perturbations affect the system and we show that global asymptotic set stability is achieved.

This paper is concerned with the leader-following consensus problem for a class of Lipschitz nonlinear multi-agent systems with uncertain dynamics, where each agent only transmits its noisy output, at discrete instants and independently from its neighbors. The proposed consensus protocol is based on a continuous-discrete time observer, which provides a continuous time estimation of the state of the neighbors from their discrete-time output measurements, together with a continuous control law. The stability of the multi-agent system is analyzed with a Lyapunov approach and the exponential practical convergence is ensured provided that the tuning parameters and the maximum allowable sampling period satisfy some inequalities. The proposed protocol is simulated on a multi-agent system whose dynamics are ruled by a Chua’s oscillator.

International audience; This technical note deals with the study of uplink (from the mobile phone to the base station) transmitted power control in Long Term Evolution (LTE). It provides a nonlinear Potential Feedback Control (PFC) for scalar discrete-time systems with input delays and disturbances by using the Lyapunov theory and the Artstein transform. It is an original approach in which a stabilization problem of a linear scalar system with a constraint on the state space is transformed into a problem of nonlinear stabilization. We use this strategy of stabilization for the uplink transmission power control in LTE.

International audience; The aim of this study is to develop a new feedback stabilisation strategy involving a non-linear potential feedback control (PFC) for scalar discrete-time systems with disturbances by using Lyapunov functions. The main interest of the PFC is to achieve the stabilisation with a constraint on the state space. The authors apply this strategy for the uplink power control in a real wireless sensor network and compare with the adaptive transmission power control (ATPC) usually used in telecommunications. A study of the energy saving is also provided.