• Energy Research

Abstract This work analyses the use of a Three-Level Neutral Point Clamped (3LNPC) converter to control the power flow of a Hybrid Energy Storage System (HESS) and at the same time interconnect it with the common AC bus of a microgrid. Nowadays there is not any storage technology capable of offering a high energy storage capacity, a high power capacity and a fast response at the same time. Therefore, the necessity of hybridising more than one storage technology is a widely accepted idea in order to satisfy the mentioned requirements. This work shows how the operational limits of the 3LNPC converter can be calculated and integrated in a control structure to facilitate an optimal use of the HESS according to the rules fixed by the user.

The aim of this paper is to present a linear quadratic Gaussian (LQG) controller designed with two main objectives: to allow the contribution of wind turbines (WTs) to the primary frequency regulation of an island power system, and to reduce the WTs drive-train mechanical stresses. The designed LQG1_CPC_Track controller is compared, in terms of the mentioned objectives, to a more classical controller containing two uncoupled control loops. The comparison is carried out in a simulation model of the Guadeloupian island power system taken as a case study. The model is implemented in Eurostag software. Simulation results show that the contribution of both controllers to the primary frequency regulation is satisfactory, and that the LQG1_CPC_Track allows reducing drive-train mechanical stresses significantly. Thus, thanks to the LQG1_Track, on top of allowing the integration of more wind energy in the grid with the contribution to primary frequency regulation, WTs would have less maintenance costs and could be manufactured with cheaper material.

Senegal is one of the less developed countries in the world (position 158 in a list of 174 countries). 85% of its rural population does not have access to electricity and there's no doubt that this is an important barrier for socio-economic development. In this context, the project Microgrids aims at contributing to solve this problem. This project is part of the Intelligent Energy - Europe Programme supported by the European Commission. Its objective is the promotion and dissemination of the use of micro-grids with high content of Renewable Energy Sources (RES) for the electrification of villages far away from the grid in Senegal. One of the results of the project was the analysis of rural electrification needs, which is described in another paper [Camblong H, Sarr J, Niang AT, Curea O, Alzola JA, Sylla EH, Santos M. Microgrids project, part 1: analysis of rural electrification with high content of renewable energy sources in Senegal. Renewable Energy, submitted for publication.]. This paper presents the design of an electrification kit based on the information provided by that analysis [Analyse des besoins locaux pour l'electrification de zones rurales au Senegal. Technical report of Microgrids project; 2007. Available from: http://www.microgrids-eie.com.]. After identifying necessary previous conditions for the sustainability of any electrification project, a methodology is proposed for the design of the electrification kit. This methodology is applied to a typical village and results are extended to differently sized villages in the areas of Thies, Fatick and Kaolack. Economic considerations are also included to establish the relationship between electrification costs and paying capability of the communities. Now the Microgrids' consortium hopes to set-up a new project to apply the designed kit on some rural non-electrified villages.

In this paper, the operation of three-phase, four-wire voltage source inverter (VSI) under unbalanced voltage conditions is investigated. The inverter is particularly interesting for the simultaneous supply of three-phase and single-phase loads in transformerless hybrid power system (HPS) application. A control strategy for the VSI based on the decomposition of the supply voltages and currents into instantaneous positive, negative and homopolar sequence components is described. The three sequences are controlled using two different rotating reference frame systems, so that the disturbance of the output voltage due to the load unbalances is eliminated. Simulation results are presented to verify the validity of the control strategy

In self-consumption (SC) configurations, energy management systems (EMSs) are increasingly being implemented to maximise the self-consumption ratio (SCR). Recent studies have demonstrated that prediction-based EMSs significantly enhance decision-making capabilities compared to non-predictive EMSs. This paper presents the design, implementation, and testing on a real system of two machine learning (ML)-type predictive models capable of forecasting the electricity consumption of an individual building using a small dataset. A nonlinear autoregressive with exogenous input (NARX) neural network model and a support vector regression (SVR) model were designed and compared. These models predict day-ahead hourly electricity consumption using forecasted meteorological data from Meteo Galicia (MG) and building occupancy data, both automatically obtained and pre-processed. In order to compensate for the lack of recurrence of the SVR model, the effect of introducing an additional input, a time vector, was analysed. It is proved that both ML models trained with a small dataset are able to predict the next day’s average hourly power with a mean MAPE below 13.96% and a determination coefficient (R2) greater than 0.78. The model that most accurately predicts the hourly average power of a week is the SVR, which achieves a mean MAPE and R2 of 10.73% and 0.85, respectively.

RESUMEN: El objetivo de este trabajo ha sido diseñar un controlador digital robusto para controlar la tensión de un sistema de energía híbrido aislado. La única carga del sistema es resistiva y variable, y está alimentada mediante un inversor asociado a un filtro LCL. Después de plantear el problema, se explica cómo se obtiene el modelo de la planta. A continuación se analiza su comportamiento dinámico oscilante y la dependencia de ese comportamiento con respecto a la carga resistiva. Se describe después la estructura y el diseño del controlador global que contiene dos lazos de control en cascada, el primero de corriente y el segundo de tensión. Se diseñan los controladores de los dos lazos haciendo hincapié en su robustez y su capacidad de amortiguar el sistema en lazo cerrado. Para acabar, se realizan simulaciones en las que se estudia el comportamiento dinámico de los dos lazos en regulación y seguimiento en distintos puntos de funcionamiento. Los resultados demuestran la calidad del control en términos de robustez, amortiguamiento y rapidez de la respuesta. Palabras Clave: Sistema de Energía Híbrido, Control Robusto, Asignación de Polos, Control Digital, Sistema no Estacionario, Inversores

This paper is focused on a series hybrid electric bus (SHEB). A rule-based energy management strategy is proposed by controlling the state of charge (SOC) of the battery (BT) and a variable output control for the auxiliary power unit (APU). Furthermore, a power splitter control is developed to split the power among BT and supercapacitor (SC). The optimization to obtain the values for the control levels is carried out with multi-objective genetic algorithm (GA). The aim of the optimization is to minimize the daily operating cost of the bus. The objective functions are the costs related to fuel and energy (BT and SC degradation by cycling cost, recharge from the grid cost) consumption. The results are given in a Pareto front with a set of optimal solutions, the optimal one will depend of an analysis on which objective has priority to be minimized and what are the consequences of this decision on the other one.

Abstract Nowadays, the importance of electrical generation based on renewable energies is increasing, due to its low emissions of greenhouse gases. At the same time, Distributed Generation and Microgrids (MG) are becoming an important research line because of their peculiar characteristics. MGs are composed of small power sources which can be renewable, placed near customer sites. Moreover, they have the inherent property of islanding: the disconnection of either the MG from the main grid or a portion of a MG from the rest of the MG. There are two kinds of islanding: intentional or planned (for maintenance purposes), and unintentional or unplanned. The latter is mainly due to disturbances and it is used to avoid damages in sources and loads. It is the most critical case because it must be detected as soon as possible to activate all the control systems which allow continuing the energy production and distribution despite the disconnection. In islanding, it is crucial to ensure the power and the electrical signal quality. In grid-connected mode, the inverters use the electrical signal of the main grid as reference. Once in islanding, the main grid reference is lost and new control techniques for the inverters are needed in order to obtain the correct values of voltage magnitude and frequency in the MG. The main objective of this paper is to make a survey on MGs focussed on two important features: unplanned islanding and control of inverters in that scenario. The idea is to present the basic architectures and regulation techniques of MGs and to study the islanding behaviour, mainly the different detection techniques and the inverters’ control once islanded.