Cristina Morel

A novel global MPPT based on genetic algorithms for photovoltaic systems under the influence of partial shading

This paper presents a novel maximum power point tracking (MPPT) algorithm, based on genetic algorithms (GA). This algorithm is used for searching the global maximum power point (GMPP) for photovoltaic systems affected by partial shading. The “Perturb and Observe” (P&O) algorithm is embedded into the GA function for improving the optimisation process. By adding this functionality to the algorithm, the number of iterations and the population size is low, thus finding the MPP in a short time. Description of this algorithm and its performances will be detailed in this article, verified through simulation and experimental results.

A learning real-time routing system for emergency vehicles

This paper describes a learning routing system designed to ease the movement of emergency vehicles through a network of congested streets. Real-time capabilities of the routing system are given by the use of GPS equipment installed aboard of every emergency vehicle. The same type of equipment is used to control the state of traffic lights and to collect real-time data on the current traffic volume. The actual routing algorithm is part of the A* class and reaches decisions with the help of a neural network that estimates the expected time of arrival of every feasible route the emergency vehicles might follow. Real-time traffic data is used to train the neural network and to help the routing algorithm work faster. This not only reduces the response time but it also increases the safety of the emergency vehicles.

Anticontrol of Chaos Reduces Spectral Emissions

Switch-mode power supplies usually emit electromagnetic interferences at the switching frequency and its harmonics. Inducing chaos in these systems has recently been suggested as a means of reducing these spectral emissions, yet at the expense of aggravating the overall magnitude of the ripple in the output voltage. We propose here a new nonlinear feedback, which induces chaos and which is able at the same time to achieve a low spectral emission and to maintain a small ripple in the output. The design of this new and simple controller is based on the propriety that chaotified nonlinear systems present many independent chaotic attractors of small dimensions.

Modeling and simulation of a peak current controlled PFC converter in chaotic regime

This paper reports the modeling and simulation aspects of a peak current controlled power-factor-correction converter (PFC), which is widely used in switch-mode power supply applications. The main objective is to show the real behavior of this converter operating under specific conditions [1]. Firstly, a numerical simulation based on a discrete model is used. Analysis of this model shows that chaos and bifurcations may occur along with the changing values of some system parameters. Secondly, a Power System Blockset (PSB) model using Simulink/Matlab is designed and simulation results are compared to those obtained from numerical simulation.

A novel global MPPT algorithm for distributed MPPT systems

This paper is focused on the implementation of an original algorithm for global maximum power point tracking (GMPPT) in photovoltaic systems. The algorithm detects when partial shading occurs, thus eliminating unwanted voltage sweeping. The paper gives a detailed analysis on how the algorithm succeeds in finding the global maximum power point (GMPP) in a short time and all its highlights. The system is controlled by a DSP which implements a voltage and a current loop for a better response of the system in case of a luminosity step change. Simulation and experimental results are finally provided to verify the performance of the system.

Generating chaotic attractors on a surface

Abstract: The present paper introduces a new method to generate several independent periodic attractors, based on a switching piecewise-constant controller. We demonstrate here that the state space equidistant repartition of these attractors is on an arbitrarily precise zone of a paraboloid or plane. We determine the state space domains where the attractors are generated from different initial conditions. A mathematical formula giving their maximal number in function of the controller piecewise-constant values is then deduced.

Nonlinear modeling of power-factor-correction converter

Recently, power factor correction (PFC) boost converters have been reported as exhibiting a wide range of bifurcations and chaos under specific conditions [1]. In this paper, we derived a nonlinear model from one point of observation to the next. Analysis of this model shows that chaos and bifurcations may occur along with the changing values of some system parameters. A current-mode controlled PFC boost converter in chaotic behavior is chosen as an application example. A numerical simulation using MATLAB confirms the predicted bifurcations. Finally, a blockset model using Simulink/Matlab is designed to conclude the validity of the numerical simulation.

Synchronization of chaotic attractors with different equilibrium points

This paper investigates the synchronization of coupled chaotic systems with many equilibrium points. By addition of an external switching piecewise-constant controller, the system changes to a new one with several independent chaotic attractors in the state space. Then, by addition of a nonlinear state feedback control, the chaos synchronization is presented. This method can be used in many couples of chaotic systems characterized by the same equilibrium point or by two different equilibrium points, even they are the same systems (Lorenz, Jerk, Van der Pol) or two chaotic systems with different structures (Lorenz modified).

Generalization of the Filippov method for systems with a large periodic input

Using the Filippov method, the stability of a nominal cyclic steady state of a nonlinear dynamic system (a buck dc–dc converter) is investigated. A common approach to this study is based upon a complete clock period, and assumes that the input is from a regulated dc power supply. In reality, this is usually not the case: converters are mostly fed from a rectified and filtered source. This dc voltage will then contain ripples (i.e. the peak-to-peak input voltage is not zero). Therefore, we consider the input as a sinusoidal voltage. Its frequency is chosen as a submultiple T of the converter’s clock and our objective is to analyze, clarify and predict some of the nonlinear behaviors that these circuits may exhibit, when the input voltage frequency changes in time. This input frequency’s parameter T determines the number of the switching instants over a whole clock cycle, obtained as Newton–Raphson solutions. Then, for the considered buck converter, we develop a mathematical model in a compact form of the Jacobian matrix with a variable dimension proportional to the input voltage harmonics. Finally, the Floquet multipliers of the monodromy matrix are used to predict the system stability. Numerical examples illustrate how these multipliers cross the unit cycle causing various bifurcations.

Reduction of EMI using anticontrol of chaos

DC-DC converters are employed in various electrical devices, thus forming main sources of electromagnetic interference (EMI). By making the DC-DC converter operating in chaos, using a new nonlinear feedback controller, the simulation results illustrate that a reduction of spectral peak and consequent spreading of the spectrum can be shown. This simple strategy not only improves the electromagnetic compatibility of the converter, but also reduces the output voltage ripple. A Power System Blockset (PSB) model using Simulink/Matlab is designed and results are compared to those obtained with the classical anticontrol method.