This paper presents the analysis, design, and experimentation results of a photovoltaic energy management system with battery backup. The proposed system is capable of both grid-connected and islanded operation. The main advantage of the proposed system is that in grid-connected mode the inverter works as a current source in phase with the grid voltage, injecting power to the grid and controlling the DC-link voltage. The DC/DC converter manages the battery charge. In island-mode, the inverter control is reconfigured to work as a voltage source using droop schemes. The DC/DC converter controls the DC-link voltage to enable the maximum power point tracking reference to be followed. An operation protocol is proposed to ensure the quality of the energy supply and minimize energy loss. A battery bank is connected to the DC-link as energy storage for islanded operation mode. The aim of the paper is to show that the proposed system performs correctly, without dangerous transients for the inverter or the loads. Simulation and experimental results on a 3 kW prototype show the feasibility of the proposed control strategy.

Reconfigurable control scheme for a PV microinverter working in both grid connected and island modes.Abstract-In this paper a photovoltaic microinverter capable of operating in both island mode and grid connected mode by means of a reconfigurable control scheme is proposed. The main advantage of control reconfiguration is that in grid connected mode the microinverter works as a current source in phase with the grid voltage, injecting power to the grid. This is the operation mode of most commercial grid connected PV microinverters. The idea is to provide those microinverters with the additional functionality of working in island mode without changing their control algorithms for grid connected mode, which were developed and refined over time. It is proposed that in island mode the microinverter control is reconfigured to work as a voltage source using droop schemes. These schemes consist in implementing P/Q strategies in the inverters, in order to properly share the power delivered to the loads. The aim of the paper is to show that the proposed control reconfiguration is possible without dangerous transients for the microinverter or the loads. Simulation and experimental results on an 180W photovoltaic microinverter are provided to show the feasibility of the proposed control strategy.

Light, being the fundamental energy source to sustain life on Earth, is the external factor with the strongest impact on photosynthetic microorganisms. Moreover, when considering biotechnological applications such as the production of energy carriers and commodities in photobioreactors, light supply within the reactor volume is one of the main limiting factors for an efficient system. Thus, the prediction of light availability and its spectral distribution is of fundamental importance for the productivity of photo-biological processes. The light field model here presented is able to predict the intensity and spectral distribution of light throughout the reactor volume based on the incident light and the spectral characteristics of the photosynthetic microorganism. It takes into account the scattering and absorption behaviour of the micro-algae, as well the adaptation of the biological system to different light intensities. Although in the form exposed here the model is optimized for photosynthetic microorganism cultures inside flattype photobioreactors, the theoretical framework is easily extensible to other geometries. Our calculation scheme has been applied to model the light field inside Synechocystis sp. PCC 6803 wild-type and Olive antenna mutant cultures at different cell-density concentrations exposed to white, blue, green and red LED lamps, delivering results with reasonable accuracy, despite the data uncertainties. To achieve this, Synechocystis experimental attenuation profiles for different light sources were estimated by means of the Beer-Lambert law, whereby the corresponding 1 downward irradiance attenuation coefficients K d (λ) were obtained through inherent optical properties of each organism at any wavelength within the photosynthetically active radiation band. The input data for the algorithm are chlorophyll-specific absorption and scattering spectra at different mean acclimatisation irradiance values for a given organism, the depth of the photobioreactor, the cell-density and also the intensity and emission spectrum of the light source. In summary, the model is a general tool to predict light availability inside photosynthetic microorganism cultures and to optimize light supply, in respect to both intensity and spectral distribution, in technological applications. This knowledge is crucial for industrial-scale optimisation of light distribution within photobioreactors and is also a fundamental parameter for unravelling the nature of many photosynthetic processes.

The reconstruction of genome-scale metabolic models and their applications represent a great advantage of systems biology. Through their use as metabolic flux simulation models, production of industrially-interesting metabolites can be predicted. Due to the growing number of studies of metabolic models driven by the increasing genomic sequencing projects, it is important to conceptualize steps of reconstruction and analysis. We have focused our work in the cyanobacterium Synechococcus elongatus PCC7942, for which several analyses and insights are unveiled. A comprehensive approach has been used, which can be of interest to lead the process of manual curation and genome-scale metabolic analysis. The final model, iSyf715 includes 851 reactions and 838 metabolites. A biomass equation, which encompasses elementary building blocks to allow cell growth, is also included. The applicability of the model is finally demonstrated by simulating autotrophic growth conditions of Synechococcus elongatus PCC7942.

No abstract