Kelly Caroline Mingorancia de Carvalho

Stable oscillations of a predator-prey probabilistic cellular automaton : a mean-field approach

We analyze a probabilistic cellular automaton describing the dynamics of coexistence of a predator–prey system. The individuals of each species are localized over the sites of a lattice and the local stochastic updating rules are inspired by the processes of the Lotka–Volterra model. Two levels of mean-field approximations are set up. The simple approximation is equivalent to an extended patch model, a simple metapopulation model with patches colonized by prey, patches colonized by predators and empty patches. This approximation is capable of describing the limited available space for species occupancy. The pair approximation is moreover able to describe two types of coexistence of prey and predators: one where population densities are constant in time and another displaying self-sustained time oscillations of the population densities. The oscillations are associated with limit cycles and arise through a Hopf bifurcation. They are stable against changes in the initial conditions and, in this sense, they differ from the Lotka–Volterra cycles which depend on initial conditions. In this respect, the present model is biologically more realistic than the Lotka–Volterra model.

Leakage current minimization techniques for single-phase transformerless grid-connected PV inverters — An overview

This paper presents an overview about techniques employed to minimize the leakage current in single-phase transformerless grid-connected PV inverters, using topologies derived from the full-bridge voltage source inverter (VSI). Some representative topologies and common mode (CM) filter implementations are presented. Among the analyzed solutions, a CM filter integrated to the harmonics filter, applied to a conventional full-bridge converter with unipolar output voltage, represents a promising solution, confirmed by simulation and experimental results. Additionally, discussions about safety standards and analysis of leakage current production mechanism are presented.

PROBABILISTIC CELLULAR AUTOMATA DESCRIBING A BIOLOGICAL TWO-SPECIES SYSTEM

We consider two probabilistic cellular automata to analyze the stochastic dynamics of a biological two-species system. We focus our attention on the characterization of the dynamic patterns exhibited by both models. Performing Monte Carlo simulations, we observe a time oscillating behavior that occurs at a local level.

Integrated common and differential mode filter applied to a single-phase transformerless PV microinverter with low leakage current

This paper proposes an integrated common and differential mode filter with passive damping for single-phase grid-connected transformerless photovoltaic (PV) microinverters, employing the full-bridge voltage source inverter (VSI) topology with continuous unipolar modulation. This strategy achieves low current distortion, low leakage current and high efficiency. A design procedure for the proposed filter is presented including the passive damping components. The effectiveness of the proposed solution is confirmed by simulation and experimental results. Additionally, discussions about safety standards, analysis of leakage current production mechanism and some common mode (CM) filter implementations found in the literature are presented.

Anisotropic probabilistic cellular automaton for a predator-prey system

We consider a probabilistic cellular automaton to analyze the stochastic dynamics of a predator-prey system. The local rules are Markovian and are based in the Lotka-Volterra model. The individuals of each species reside on the sites of a lattice and interact with an unsymmetrical neighborhood. We look for the effect of the space anisotropy in the characterization of the oscillations of the species population densities. Our study of the probabilistic cellular automaton is based on simple and pair mean-field approximations and explicitly takes into account spatial anisotropy.

Robust control design for the voltage tracking loop of a DVR

The Dynamic Voltage Restorer (DVR) is a solution for protection of sensitive loads from voltage sags and swells. Its basic function is to inject voltages in the grid line in order to mitigate voltage sags and/or swells. Typically the controller structure for a DVR is composed by an inner current loop and an outer voltage loop. Usually a proportional or proportional integral controller is used for the current loop and a resonant controller is used for the voltage loop. This paper presents the design of a robust controller for the voltage tracking loop of a DVR that guaranties the robust stability against load parameters variation, and assures the tracking of a sinusoidal voltage waveform and the rejection of the non linear load current influence with a pre specified error. The voltage controller design is based on H8 parameter specification approach. All the performance and robustness requirements are specified and analyzed based on the frequency response plot of closed loop transfer function. The proposed controller performance is validated by using PSIM software simulation and by experiments carried out on a DVR.

Optimized tuning method of stationary frame Proportional Resonant current controllers

This paper presents an optimized tuning method of Proportional Resonant (PR) current controllers implemented in the stationary frame. The approach consists of defining three operation regions based on behavior of the closed loop poles, and of determining simplified tracking and disturbance transfer functions for each of these regions. Charts of proportional and resonant normalized gains versus settling time and overshoot are then built, allowing the designer to easily visualize the influence of these gains on the transient response. It is shown that the disturbance response performance is more significant than the tracking one, and that minimum settling time and overshoot for this case are obtained if the resonant gain is set equal to the controller resonant frequency, providing a simple and efficient rule-of-thumb for the designer. Simulation and experimental results are presented to validate the method.

Disturbance calculation based on space vector dot product: Applications to compensators

The ability to individually extract the many disturbances of the AC line currents or voltages is desirable for reference signal calculation algorithms employed in power conditioners, allowing improved utilization of the power converter. This paper proposes a novel algorithm based on the dot product of three dimensional space vectors in the abc coordinate system, for real time calculation of the instantaneous positive, negative and zero sequence components for each individual harmonic. It is presented the functionalities for compensating fundamental reactive power, selected current harmonics and current unbalances. This method is computationally simple and requires no coordinate transformation. The proposed algorithms are validated by simulation and experiments.