Energy storage systems (ESS) are becoming essential as a solution for troublesome industrial systems. This study focuses on the application of a type of ESS, a high-power technology known in the literature as supercapacitors or electric double layer capacitors (EDLC). This technology has had a huge impact during the last decade on research related to the electric traction drives, renewable sources and powergrids. Related to this aspect, this paper summarizes the most relevant scientific publications in the last five years that study the use of supercapacitor technology (SCs) in electric traction applications (drives for rail vehicles and drives for road vehicles), generation systems for renewable energy (wind, solar and wave energy), and connection systems to the electric grid (voltage and frequency regulation and microgrids). The technology based on EDLC and the practical aspects that must be taken into account in the op-eration of these systems in industrial applications are briefly described. For each of the aforementioned applications, it is described how the problems are solved by using the energy storage technology, drawing the solutions proposed by different authors. Special attention is paid to the control strategies when combining SCs with other technologies, such as batteries. As a summary, some conclusions are collected drawn from the publications analyzed, evaluating the aspects in which it is necessary to conduct further research in order to facilitate the integration of EDLC technology.
Supercapacitors, one of the most promising energy storage technologies for high power density industrial applications, exchange the energy mostly through power electronic converters, operating under high frequency components due to the commutation. The high frequency produces important effects on the performance of the supercapacitors in relation to their capacitance, inductance and internal resistance (ESR). These parameters are fundamental to evaluate the efficiency of this energy storage system. The aim of the paper is to obtain an accurate model of two supercapacitors connected in series (functional and extrapolated unit) to represent the frequency effects for a wide range of frequencies. The methodology is based on the definition of an appropriate equivalent electric circuit with voltage dependance, obtaining their parameters from experimental tests, carried out by means of electrochemical impedance spectroscopy (EIS) and the use of specific software tools such as EC-Lab ® and Statgraphics Centurion ® . The paper concludes with a model which reproduces with accuracy both the frequency response of the model BCAP3000 supercapacitors, provided by the manufacturer, and the experimental results obtained by the authors.Energies 2020, 13, 1156 2 of 18 reducing the battery stress and extending the lifespan of the system. Moreover, in applications where long-time backups are not required, SCs can totally replace the battery storage system [8][9][10]. Thirdly, SCs are used in the energy harvesting industry for their integration with non-dispatchable renewable energy sources, i.e., wind and solar energies. The intermittent nature and uncertain prediction of these energy resources results in voltage and frequency fluctuations, which can destabilise the electric grid. Hence, energy storage systems, particularly SCs, play an important role in frequency regulation and peak shaving [11][12][13].SCs modelling has become of maximum importance when designing and dimensioning SC installations since it is the way to know in advance about the behaviour and performance of the energy storage system when applied to particular operation profiles or conditions. Control strategies or operational parameters and limits can also be obtained from a model, enlarging the lifetime of the storage technology and therefore achieving a higher level of reliability and competitiveness. Numerous SC models have been published in the literature for different purposes, including capturing electrical dynamic behaviour, which is of utmost importance for the aforementioned industrial applications. The models that capture electrical behaviour of SCs can be classified in three main categories: electrochemical models, intelligent models and equivalent circuit models [2].Commonly, electrochemical models account for high accuracy and low calculation efficiency, since they capture the reactions inside the SCs by employing coupled partial differential equations (PDEs). Among the electrochemical models, the three-domain model based on the uniform formulation of e...
The increasing penetration of Electric Vehicles (EVs) in LV distribution networks can potentially cause voltage quality issues such as voltage unbalance and under-voltage conditions. According to the EV charger characteristics, some strategies can be adopted to mitigate the aforementioned effects. Smart decentralized charging controls seem to be a more practical solution than centralized controls, since there is no need for communication because they rely only on local measurements. The four most relevant decentralized charging strategies, two for single-phase and two for three-phase EV chargers, have been implemented in a typical three-phase four-wire European LV distribution network. Simulations have been carried out for scenarios with single-phase EV chargers, three-phase EV chargers, and a combination of both. Single-phase controls are aimed at under-voltage regulation, while three-phase controls are focused on mitigating voltage unbalance. Results show that the implementation of a decentralized EV charging control is an adequate solution for Distribution System Operators (DSOs) since it improves the reliability and security of the network. Moreover, even though decentralized charging control does not use any communication, the combination of three-phase and single-phase controls is able to mitigate voltage unbalance while preventing the under-voltage condition.
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