Passivity-based harmonic control through series/parallel damping of an H-bridge rectifier

Nowadays the H-bridge is one of the preferred solutions to connect DC loads or distributed sources to the single-phase grid. The control aims are: sinusoidal grid current with unity power factor and optimal DC voltage regulation capability. These objectives should be satisfied, regardless the conditions of the grid, the DC load/source and the converter nonlinearities. In this paper a passivity-based approach is thoroughly investigated proposing a damping-based solution for the error dynamics. Practical experiments with a real converter validate the analysis.

Networking Aspects based on the Talkative Power Concept for DC Microgrid Systems

The talkative power concept is a simultaneous power-line communication and energy transfer technique which integrates data modulation into a power converter. The information sequence is deterministically represented by the ripple, which superimposes the output voltage. With a few exceptions, so far emphasis has been on scenarios where only a single node is actively transmitting data in a certain time slot in simplex mode. In microgrid applications, however, multiple active power sources are of interest as well. Examples include battery management systems, smart metering, electricity trading systems, and smart grids with several power sources, energy storage devices, loads, and data receivers. In this contribution, bus networking aspects based on the talkative power concept are presented for scenarios with several active nodes and for full-duplex communication. The paper addresses potential multiple access techniques as well as duplexing schemes for connected power converters supporting bidirectional power and information flow. In numerical results, a spread spectrum scheme based on orthogonal variable spreading factor codes in conjunction with frequency shift keying (FSK) is presented for four simultaneously active buck converters with a sum data rate of 500 kbps at a switching frequency of 1 MHz. In general, with 2-ary FSK, the maximum achievable sum data rate is half of the switching frequency in a synchronous setup

Wavelet-based Islanding Detection in Grid-Connected PV Systems

Distributed Power Generation Systems (DPGS) based on inverters require reliable islanding detection algorithms (passive or active) in order to determine the electrical grid status and operate the grid connected inverter properly. These methods are based on the analysis of the DPGS voltage, current and power in time or frequency domain. This paper proposes a time-frequency detection algorithm based on monitoring the DPGS output power considering the influence of the PWM, the output LCL filter and of the employed current controller. Wavelet analysis is applied to obtain time localization of the islanding condition. Simulation and experimental results show the performance of the proposed detection algorithm also in comparison with existing methods

Simulação do sistema gastrintestinal humano para avaliação da resistência de probiótico em queijo de coalho com leite de cabra.

Resumo: Neste projeto, foram produzidos queijos com leite de cabra e probióticos para avaliação da resistência desses microrganismos à passagem pelo trato gastrintestinal simulado. Os queijos foram adicionados de Lactobacillus acidophilus e após 15 e 30 dias de estocagem refrigerada, amostras do queijo foram avaliadas para quantificação de L. acidophilus e sobrevivência dos probióticos à passagem simulada pelo sistema gastrintestinal humano. O suco gástrico com pH 2,5 foi adicionado de pepsina (3g/L). O suco entérico, com a adição de bile (3g/L), foi simulado com pH 5,6 e 7,5, de acordo com as condições do sistema intestinal humano. As contagens totais de L. acidophiluspara o queijo após 15 e 30 dias foram semelhantes, 7,03 e 7,04 logUFC/g, respectivamente. Considerando para consumo porção diária de 30g de queijo, obtémse um total de 108 células, o que atende às exigências da legislação brasileira para alimentos com alegações funcionais. Após o ensaio em condições simuladas do sistema gastrintestinal, as populações de bifidobactérias foram reduzidas a 3,79 e 4,33 logUFC/g para os queijos com 15 e 30 dias, respectivamente. Conclui-se que as contagens do probiótico após ação de suco gástrico e entérico formulados com pepsina e bile foram reduzidas em aproximadamente 3 ciclos logarítmicos, apesar da contagem inicial do queijo estar de acordo com a legislação brasileira. Abstract: In this study, goat milk cheeses with probiotic were produced and the survival of these bacteria after simulated conditions of human gastrointestinal tract was evaluated. The cheeses were added of Lactobacillus acidophilus and evaluated after 15 and 30 days of refrigerated storage. The gastric juice at pH 2.5 was added of pepsin (3g/L). The enteric juice added of bile (3g/L) was simulated with pH 5.6 and 7.5 according to the conditions of the duodenum, jejunum, ileum, and the large intestine. The counts of L. acidophilus were similar in the cheeses kept at 15 and 30 days, respectively 7,03 and 7,04 log CFU/g. These results show that the portion of 30g of cheese contains 108 cells. These data agree to the Brazilian legislation requirement related to the functional foods. After the assays simulating gastrointestinal conditions, the population of L. acidophilus were reduced to 3,79 and 4,33 log CFU/g in the cheese after 15 and 30 days of storage, respectively. It was observed that the population of probiotics after simulated conditions of gastric and enteric juices formulated with pepsin and bile, respectively, was reduced in approximately three logarithmic cycles, despite the initial counts attend to the brazilian legislation requirements

DC Multibus based on a Single-Star Bridge Cells Modular Multilevel Cascade Converter for DC smart grids

In the last years a growing interest towards DC Smart Grids has been registered due to high penetration of distributed generation systems with embedded storage. Trying to foresee the possible future scenarios of the power systems, it can be noticed that DC Smart Grids can be even preferable to AC Smart Grids in terms of flexibility and redundancy since they are compatible with the achievement of a DC Multibus working at different voltage levels. In this paper the Single-Star Bridge Cells Modular Multilevel Cascade Converter is used to create a DC Multibus. The performances of the system are analyzed considering different load configurations and coexistence of different voltage levels of the buses forming the DC Multibus. Results confirms the validity of the proposed solution and the robustness of the control system in case of load variations

Simultaneous wireless information and GaN-based power transfer exploiting a dual frequency band

A simultaneous wireless information and power transfer system employing separated frequency bands for energy and data, dubbed dual-band SWIPT, is investigated. Elementary circuit elements are optimized numerically. An experimental testbed based on a gallium nitride (GaN) full-bridge converter demonstrates data rates in excess of 450 kbps employing onoff keying in conjunction with a simple diode detector for data recovery

Reactive Power Flow Control for PV Inverters Voltage Support in LV Distribution Networks

This paper proposes a reactive power flow control pursuing the active integration of photovoltaic systems in LV distribution networks. An alternative power flow analysis is performed according to the specific characteristics of LV networks, such as high resistance/reactance ratio and radial topologies. The proposed solution gives high performances,in terms of rms- voltage regulation, by estimating the reactive power reference on each node considering the influence of the rest of the nodes in terms of active and reactive power demanded/generated by them. The local control of each photovoltaic system is based on the power converter control,interfacing these units with the grid and the loads respectively. The local control is designed on the basis of locally measured feedback variables. Photovoltaic units thus guarantee universal operation,being able to change between islanding-mode and grid-connected mode without disrupting critical loads connected to them, and allowing smooth transitions. Exhaustive results are also included and discussed in this paper