A Grid-Connected Multilevel Converter for Interfacing PV Arrays and Energy Storage Devices

This paper presents a design procedure and a \ud control strategy for a grid-connected single-phase multilevel \ud converter. The proposed system uses two series connected H-bridge modules, one fed by photovoltaic panels, the other by \ud energy storage devices. The former switches at line frequency, \ud while the latter operates in PWM. The system is designed to \ud minimize the voltage stress on the switches, while the control \ud strategy is such that a constant active power is delivered to the \ud grid with high power factor, even if the energy produced by the \ud photovoltaic panels is variable. The paper illustrates the power \ud converter design procedure, the hybrid PWM method and the \ud small signal modeling used to design the controllers of each \ud inverter. In addition, the performance of the multilevel converter \ud is verified by means of simulation and experimental results, \ud which show the system ability to operate as expectedFAPES

Performance improvement of a diesel generating set with fuzzy control for stand-alone and grid-connected operations.

This paper proposes a management strategy for\ud a diesel generating set (GS) covering the mechanical part of\ud the system which includes speed and active power control,\ud the electrical part of the system which includes voltage\ud and reactive power control, and the synchronism with the\ud grid. The management is based on a fuzzy PD+I controller\ud structure which uses a fixed controller surface for all fuzzy\ud controllers (FCs). Simulations results for both stand-alone and\ud grid-connected operations using fuzzy controllers were superior\ud when compared to commercial methods (CM).FAPESP-2011/02170-

Nitrogen efficiency in marandupalisadegrass pastures under increasing nitrogen levels

ABSTRACT: The use of nitrogen (N) in pastoral ecosystems leads to increased productivity, as it allows the plant to elongate its leaves and, therefore, grazing herbivores harvest the green leaves. However, there are very volatile N sources, which can be replaced by ammonium nitrate, which is less volatile and less dependent on the application in rainy days. The treatments are compound of Marandu palisade grass pastures managed under continuous stocking at a canopy height of 25 cm, with different levels of N fertilizer: 0, 75, and 150 kg ha-1year-1, as ammonium nitrate (32% of N), with four replicates (pastures) in a completely randomized design. Nitrogen uptake (54.9, 96.5, 113.8 kg N ha-1) and N nutrition index (0.67, 0.98, 1.15) were different between N level, respectively, 0, 75 and 150 kg ha-1 year-1. The N recovery (58.3, 40.9 %) differed between 75 and 150 kg ha-1 year-1, respectively. The dose of 75 kg N kg ha-1 year-1 results in better N utilization, while the dose of 150 kg N ha-1 year-1 enables greater stocking rate; therefore, requiring less grazing area

Controle por DSP conversores de potencia para acionamento de gerador de indução conectado a rede monofasica

Orientador: Jose Antenor PomilioDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de ComputaçãoResumo: O uso de máquina de indução trifásica como gerador apresenta inúmeros atrativos, especialmente por sua robustez e baixos custos de aquisição e operacional. No entanto a má regulação de tensão e de freqüência são restrições importantes em aplicações em que a boa qualidade da energia suprida deva ser garantida. O uso adequado de conversores eletrônicos de potência associados ao gerador de indução permitem obter os desempenhos desejados e, adicionalmente, podem operar em um sistema sem controle da velocidade mecânica do gerador, o que simplifica expressivamente a instalação de microcentrais hidrelétricas, com aplicação típica no meio rural. Em tais situações é comum a existência de redes monofásicas. Este trabalho estuda métodos de conexão do sistema de geração a uma rede monofásica, a qual serve como supridora de um excesso de demanda local, ou como receptora do excedente da energia gerada. O comando dos conversores eletrônicos empregados é feito por meio de um DSP, o qual controla o fluxo de potência e as formas de onda sintetizadas pelos conversores. São apresentadas e discutidas características e limitações de diferentes tipos de conversores com relação à capacidade de garantir a qualidade da energia gerada e, ao mesmo tempo, fazer o balanço de potência entre gerador e rede. Resultados experimentais verificam as análises e simulações, comprovando as expectativasAbstract: The use of three-phase induction generator presents many advantages mainly due to its robustness and low cost. However, the low performance in terms of voltage and frequency stabilization are important drawbacks if it is necessary to guarantee the power quality. The use of power electronic converters associated with the induction generator allows to improve the operation characteristics ofthe system, stabilizing both, voltage and fi-equency. Additionally it is not necessary to control the speed of the generator, drastically simplifying the installation of such a system in micro rural hydro power plants. It is common in the Brazilian rural areas to have access only to a single-phase grid. This work studies methods to connect the local three-phase generator to the single-phase grid. The grid works supplying the additional power consumed by the local load or absorbing the exceeding generated power. The power electronic converters are controlled by a DSP that determines the power flow and the current waveforms. The characteristics and limitations of each different approach are presented and discussed, considering power quality aspects. The analysis and simulation results are confirmed by experimental resultesMestradoMestre em Engenharia Elétric

Model, design and implementation of LCC converter for power generation and distributed generation.

This paper proposes to model, design and implement a LCC (Line Commuted Converter) for power generation purpose, using alternative sources such as photovoltaic panel (PV), fuel cell and permanent magnet synchronous machine as the main power source. The converter is built with a full bridge twelve-pulse thyristor topology and connected to the alternative source through a line reactor. In order to extract maximum power from the sources, a classical maximum power point tracking algorithm (MPPT P&O) is applied. To validate the theoretical and simulated analysis, a 600 W experimental setup was built and controlled in closed loop. For the experimental results, the alternative source was represented by a variable DC power source in series with a resistor, making it possible to create controlled power steps and power events. During the operation, the grid current is analyzed in terms of power quality and an islanding event was created to analyze the converter?s behavior under critical conditions. All the experimental results show perfect conformity with the theory and simulation, proving the effectiveness of this converter topology for this purpose

Application of fuzzy systems in the control of a shunt active power filter with four-leg topology

This paper presents the application of fuzzy\ud controllers to act in the current control loop of a shunt active\ud power filter (SAPF). The SAPF consists of a three-phase\ud inverter with four-leg topology, and it has been used to reduce\ud the harmonic content produced by nonlinear loads, as well as, in\ud the reactive power compensation. The generation of the\ud reference currents is based on the synchronous reference frame\ud (SRF), which requires the use of a PLL (Phase Locked Loop)\ud synchronization algorithm with the grid. The classic PI control\ud is here replaced by a fuzzy controller that has features that\ud allows fast convergence and robustness when there are\ud parametric variations in the physical system. Results obtained\ud from simulations are presented to validate the approach and to\ud demonstrate the performance of the filter in the suppression of\ud harmonic currents and reactive power.FAPESP - Proc 11/17610-