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.

An MVDC Based Meshed Hybrid Microgrid Enabled Using Smart Transformers

Decentralized integration of distributed generation (DG) units and loads are increasing in the modern distribution grid. Maintaining the power flow and power quality within their accepted limits is a challenging task. The formation of meshed hybrid microgrids is an effective method to improve the power system. The smart transformer (ST) is a promising solution to establish meshed hybrid microgrids in the distribution system. This paper analyzes the performance of an ST based meshed hybrid microgrid interconnected to the main grid feeder through medium voltage (MV) dc link of a second ST. The coordinated operation of interconnected ST system is proposed to explore the features of the configuration. During normal operation, the MVDC bus voltage is controlled by one ST, and this reduces the complexity of the overall control. The main grid and microgrid MVAC source failure and converter fault conditions are explored to analyze the reliability of the proposed microgrid structure. Moreover, the reactive power support capability and active power losses for the proposed system are compared with the existing solutions. Simulation and experimental results are presented to show the operation of the proposed system

Grid filter design for a multi-megawatt medium-voltage voltage source inverter

This paper describes the design procedure and performance of an LCL grid filter for a medium-voltage neutral point clamped (NPC) converter to be adopted for a multimegawatt wind turbine. The unique filter design challenges in this application are driven by a combination of the medium voltage converter, a limited allowable switching frequency, component physical size and weight concerns, and the stringent limits for allowable injected current harmonics. Traditional design procedures of grid filters for lower power and higher switching frequency converters are not valid for a multi-megawatt filter connecting a medium-voltage converter switching at low frequency to the electric grid. This paper demonstrates a frequency domain model based approach to determine the optimum filter parameters that provide the necessary performance under all operating conditions given the necessary design constraints. To achieve this goal, new concepts such as virtual harmonic content and virtual filter losses are introduced. Moreover, a new passive damping technique that provides the necessary damping with low losses and very little degradation of the high-frequency attenuation is proposed.Postprint (author’s final draft

Reinforcement Learning Based Modulation for Balancing Capacitor Voltage and Thermal Stress to Enhance Current Capability of MMCs

Balancing DC capacitor voltage of many submodules (SMs) is one of the important issues in modular multilevel converter (MMC) systems. In addition, the balance of thermal stress between SMs should be considered to equalize the lifetime expectation of semiconductors and to enhance the current capability of MMC systems. However, it is complicated to balance all the various factors satisfactorily at the same time. Recent machine learning (ML) techniques can achieve optimal results through learning using numerous data acquired in complex environments. Therefore, this paper proposes a new modulation based on reinforcement learning (RL), which is a subclass of ML methods, to optimally balance the capacitor voltage and thermal stress of SMs. A deep Q-network (DQN) agent, which is one of the RL algorithms, is applied in accordance with a nearest-level modulation (NLM), and main features of the DQN agent are described in this paper. The effectiveness of the proposed modulation based on RL is verified by simulations results

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

A Reduced Power Switches Count Multilevel Converter-Based Photovoltaic System with Integrated Energy Storage

A multilevel topology for photovoltaic (PV) systems with integrated energy storage (ES) is presented in this article. Both PV and ES power cells are connected in series to form a dc link, which is then connected to an H-bridge to convert the dc voltage to an ac one. The main advantage of the proposed converter compared to the cascaded-H-bridge (CHB) converter, as well as compared to the available multilevel topologies, is that fewer semiconductor devices are needed here. As the output voltage levels increase, more switches are saved, which results in a more efficient, cheaper, and smaller converter. So far, there is still no modulation strategy that is designed particularly for PV-fed multilevel converters with built-in ES. The standard modulations are impractical for such an application since they suffer from deficiencies, such as polluted output signals - thus, requiring larger output filter - and overmodulation. A modified modulation strategy for PV+ES multilevel inverters is, therefore, introduced in this article. The proposal has been simulated and experimentally validated to evaluate its effectiveness, where it has been shown that the proposed topology is not exclusively feasible, but also suffers from less conduction and switching loss, achieving higher efficiency with respect to its counterpart CHB. </p