Three-phase T-type qZ source inverter with control current associated to a vectorial modulator for photovoltaic applications

This paper presents a fast and robust control system for a three-phase quasi-Z-source inverter (qZSI) connected to the grid. The topology combines two quasi-Z-source networks with a T-type inverter allowing to obtain AC voltages with multilevel characteristics and properties of the referred networks. To control this system a closed-loop current controller for the AC currents is proposed. The controller is based on a vectorial modulator associated to the shoot-through states. The DC-link voltage is maintained stable at the reference value by adjusting the shoot-through duty cycle. The controller is characterized by fast transient response and robustness to parameter and load variations. In order to confirm the desired characteristics and performance of the converter and control system several simulation tests were performed.info:eu-repo/semantics/publishedVersio

Metabolic effects of elevated temperature on organic acid degradation in ripening <em>Vitis vinifera</em> fruit

First published online: September 1, 2014Berries of the cultivated grapevine Vitis vinifera are notably responsive to temperature, which can influence fruit quality and hence the future compatibility of varieties with their current growing regions. Organic acids represent a key component of fruit organoleptic quality and their content is significantly influenced by temperature. The objectives of this study were to (i) manipulate thermal regimes to realistically capture warming-driven reduction of malate content in Shiraz berries, and (ii) investigate the mechanisms behind temperature-sensitive malate loss and the potential downstream effects on berry metabolism. In the field we compared untreated controls at ambient temperature with longer and milder warming (2-4 °C differential for three weeks; Experiment 1) or shorter and more severe warming (4-6 °C differential for 11 days; Experiment 2). We complemented field trials with control (25/15 °C) and elevated (35/20 °C) day/night temperature controlled-environment trials using potted vines (Experiment 3). Elevating maximum temperatures (4-10 °C above controls) during pre-véraison stages led to higher malate content, particularly with warmer nights. Heating at véraison and ripening stages reduced malate content, consistent with effects typically seen in warm vintages. However, when minimum temperatures were also raised by 4-6 °C, malate content was not reduced, suggesting that the regulation of malate metabolism differs during the day and night. Increased NAD-dependent malic enzyme activity and decreased phosphoenolpyruvate carboxylase and pyruvate kinase activities, as well as the accumulation of various amino acids and γ-aminobutyric acid, suggest enhanced anaplerotic capacity of the TCA cycle and a need for coping with decreased cytosolic pH in heated fruit.C. Sweetman, V. O. Sadras, R. D. Hancock, K. L. Soole and C. M. For

BacHBerry: BACterial Hosts for production of Bioactive phenolics from bERRY fruits

BACterial Hosts for production of Bioactive phenolics from bERRY fruits (BacHBerry) was a 3-year project funded by the Seventh Framework Programme (FP7) of the European Union that ran between November 2013 and October 2016. The overall aim of the project was to establish a sustainable and economically-feasible strategy for the production of novel high-value phenolic compounds isolated from berry fruits using bacterial platforms. The project aimed at covering all stages of the discovery and pre-commercialization process, including berry collection, screening and characterization of their bioactive components, identification and functional characterization of the corresponding biosynthetic pathways, and construction of Gram-positive bacterial cell factories producing phenolic compounds. Further activities included optimization of polyphenol extraction methods from bacterial cultures, scale-up of production by fermentation up to pilot scale, as well as societal and economic analyses of the processes. This review article summarizes some of the key findings obtained throughout the duration of the project

Bidirectional boost/buck quadratic converter for distributed generation systems with electrochemical storage systems

The increasing number of distributed generation systems using renewable and non-conventional energy sources show the trend of future generation systems. Most of these systems require power electronic converters as an interface between the DC voltage buses and electrochemical storage systems. Such storage systems, like batteries or supercapacitors, usually need bidirectional DC-DC converters to allow their charge or discharge according with necessary operation conditions. In this paper, a non-isolated bidirectional Buck-Boost converter with high voltage gain for electrochemical storage devices used in distributed generation systems is presented. To achieve high voltage gain ratios, the proposed topology presents quadratic characteristics in both step-down (Buck) and step-up (Boost) operation modes. In addition to the wide conversion range, it presents continuous input and output current, reduced charging/discharging ripple and simple control circuitry. All these features allow the energy exchange smoothly and continuously resulting in a longer durability of storage devices. The principle of the operation of the proposed converter in both operation modes, as well as their theoretical analysis will be discussed. The performance of this bidirectional power converter is confirmed through simulation and experimental results.info:eu-repo/semantics/publishedVersio

A Multilevel Voltage Source Inverter for Two-Phase AC Motor Drive Systems

This paper presents and studies a multilevel converter with two DC voltage sources and three H Bridges. The inverter modulates two independent single-phase voltages using a four wires output. The design of the inverter allows five levels to the modulated voltages that feed an asymmetrical two windings phase induction motor. The classical SPWM technique was used to modulate the multilevel power inverter switches; the frequency of the carrier (a triangular wave) was varied and total harmonic distortion (THD) of voltages and currents were compared. The simulation results were obtained using the Matlab/Simulink (R)/SimPowerSystems software

Three-phase multilevel inverter for grid-connected distributed photovoltaic systems based in three three-phase two-level inverters

A multilevel three-phase voltage source inverter (VSI) for distributed grid-connected photovoltaic system is proposed in this paper. This multilevel inverter is based on a new topology using three three-phase two-level VSIs ((TVSI)-V-3) with isolation transformer. The photovoltaic panels are connected at the DC side of each three-phase VSI. The three-phase VSIs AC sides are connected to the three-phase isolation transformer with primary open-end windings, ensuring multilevel operation. The (TVSI)-V-3 can be modulated using existing multilevel Pulse Width Modulation (PWM) schemes. A control system designed to ensure the transfer of the energy generated by the PV generators to the grid is also presented, together with a Phase Disposition PWM (PDPWM) adapted for the multilevel (TVSI)-V-3. Tests of the grid-connected PV multilevel (TVSI)-V-3 will be shown through simulation and experimental results. Several results obtained from experiments confirm the expected characteristics of the multilevel (TVSI)-V-3 photovoltaic system.info:eu-repo/semantics/publishedVersio