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.

The growing adoption of electric vehicles has recently attracted increasing attention of scientists and brought about pioneering research studies from various fields. Safety concerns particularly those regarding ground faults detection and protection, have extensively been addressed. Ground faults occur quite frequently in electric vehicles and they may be due to severe operation conditions, such as vibrations, twists or even crashes. Generally, the first ground fault is not dangerous, since the powertrain systems, namely, the DC bus where the batteries are connected, the power inverter and one or more AC machines, are generally ungrounded. The second ground fault, however, can produce malfunction in some systems, power loss or even serious damages. Locating the fault has often proved hard and time-consuming. For this reason, the present study focuses on developing a ground-fault detection method for electric vehicles capable of determining on which side, the DC or the AC, the ground fault is located. The method is based on the analysis of the voltage in a grounding resistor connected between the midpoint of the battery pack and ground. Based on the polarity and harmonics, it is possible to locate the ground fault. This method has been verified excellent results have been achieved using computer simulations and experimental tests in a 140-kW electronic power inverter fed by a 480 Vdc battery.

One of the key parameters to properly and accurately assess an energy storage system is the energy efficiency, which has a direct impact in the system performance and an indirect impact in its cost. In this paper, a methodology for comparing Double-Layer Capacitors (EDLC) and Kinetic Energy Storage Systems (KESS) in terms of energy efficiency is proposed. This methodology, based in accurate loss models, takes real operating cycles into account, so a realistic result is obtained for each particular case. An accurate study of the losses of both technologies is accomplished during the paper, getting a complete model for EDLCs and KESSs, and obtaining Efficiency Maps for the whole range of operation points. Some conclusions about the convenience to use one or the other alternative and the best way to operate them are presented. In addition, a specific study case related to a wave energy power generation plant has been carried out in the paper, defining a methodology to select the energy storage requirements, calculating the round-trip efficiency and getting some recommendations related to the most appropriate operation strategy to take the most advantage of the energy storage system.

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.

The paper analyses the alternatives for the power supply of a Hyperloop type railway transport. The particular case of the technology of the Spanish company ZELEROS was studied. Based on previous technical specifications related to both the first prototype and a commercial system, different options were analyzed. We selected the use of a linear motor driven by a single power electronic converter, a distribution scheme comprising different sections along the acceleration area of the track, and an energy storage system based on supercapacitors for the energy supply. The power/energy ratio and the cycle capability are the reasons to become a feasible and competitive solution. A preliminary design methodology for the energy storage requirements is presented in the paper. Once the type of linear motor was selected, the power supply scheme was presented, based on a motor-side power electronic converter and a DC/DC converter which connects to the energy storage devices. An additional low power grid-tie converter for the recharge of the energy storage system was also used. Different track sections were defined, connected to the power electronic converter through corresponding switches, being supplied sequentially when the capsule presence is detected along the track. The particular characteristics of this application, with relatively short traction track area, as well as the high energy recuperation ratio due to the low losses, make more suitable the use of energy storage systems as the source of power supply than the direct connection to the grid.

One of the main issues of wave energy nowadays is the oscillation of the generated power, which is due to the oscillating nature of the waves. These power fluctuations may have an important undesired impact on the electrical grid. This paper proposes a system that compensates power oscillations in wave energy applications by means of a supercapacitor-based energy storage system. A laboratory test bench is used to emulate wave power oscillations and to partially suppress them. The paper describes the control strategy implemented in the test bench and includes experimental results for regular waves.