**Morris Brenna 1, Michela Longo 1,\* and Wahiba Yaïci <sup>2</sup>**


Academic Editor: Sergio Saponara Received: 26 June 2017; Accepted: 10 August 2017; Published: 25 August 2017

**Abstract:** The aim of this investigation is the analysis of the opportunity introduced by the use of railway infrastructures for the power supply of fast charging stations located in highways. Actually, long highways are often located far from urban areas and electrical infrastructure, therefore the installations of high power charging areas can be difficult. Specifically, the aim of this investigation is the analysis of the opportunity introduced by the use of railway infrastructures for the power supply of fast charging stations located in highways. Specifically, this work concentrates on fast-charging electric cars in motorway service areas by using high-speed lines for supplying the required power. Economic, security, safety and environmental pressures are motivating and pushing countries around the globe to electrify transportation, which currently accounts for a significant amount, above 70 percent of total oil demand. Electric cars require fast-charging station networks to allowing owners to rapidly charge their batteries when they drive relatively long routes. In other words, this means about the infrastructure towards building charging stations in motorway service areas and addressing the problem of finding solutions for suitable electric power sources. A possible and promising solution is proposed in the study that involves using the high-speed railway line, because it allows not only powering a high load but also it can be located relatively near the motorway itself. This paper presents a detailed investigation on the modelling and simulation of a 2 × 25 kV system to feed the railway. A model has been developed and implemented using the SimPower systems tool in MATLAB/Simulink to simulate the railway itself. Then, the model has been applied to simulate the battery charger and the system as a whole in two successive steps. The results showed that the concept could work in a real situation. Nonetheless if more than twenty 100 kW charging bays are required in each direction or if the line topology is changed for whatever reason, it cannot be guaranteed that the railway system will be able to deliver the additional power that is necessary.

**Keywords:** electric vehicles; fast-charging stations; simulation; railway system

### **1. Introduction**

In order to meet future mobility needs, decrease greenhouse gas and toxic emissions, and eliminate dependence on fossil fuels, nowadays automotive technologies require to be substituted by further effective, efficient and clean environmentally alternative energy sources. On the evolution to a sustainable society, proficient mobility technologies are mainly desirable worldwide. Electric vehicles have been recognised as being such a technology. In parallel, some nations, like Denmark, Germany and Sweden have agreed to replace electricity production from fossil fuel to renewable energy sources, hence further advancing sustainability and viability of electric vehicles when compared with internal combustion engine vehicles.

People realised in the 1950s and 1960s that trains could compete with commercial flights if travelling time by train was shorter than by plane. Two things have to be remembered when comparing trains and planes: the location of the airports and train stations; and the boarding procedures. Most airports are on the outskirts of the city and an additional trip by public transport or taxi is required to get to the city centre, while railway stations typically are located in the city centre [1]. Boarding procedures are also very different between trains and planes. Usually the boarding procedure for trains requires getting to the station in time to catch the train and proceeding through passport control, while flying requires getting to the airport at least one hour before the flight departure for national flights (two hours when flying internationally) to dropping off luggage and passing extensive security checks in addition to passport control [2]. Flying requires time after landing as well, especially for the luggage claim, which is not needed for train travel. This means train travelling can be much faster than flying for short distance travel. An example of this is the Tokaido Shinkansen line between Tokyo and Osaka. Built in 1964, today it carries, on a daily basis, more than 400,000 passengers on average, with 330,000 available seats on limited stop trains compared to 30,000 seats of airlines capacity. This is also due to the fact trains can carry far more passengers than any airliner, making trains more energy efficient. This led other developed countries to establish their own high-speed train services and to build a high-speed network. Because of the high-power demands of high-speed trains, it became clear that traditional electrification schemes were not very good at delivering that much power, so the 2 × 25 kV autotransformer system was used for new lines and new electrifications [3,4]. This system allows for having a relatively low number of substations while delivering a lot of power to the trains, with the advantage of minimising energy losses and voltage drops [5].

The issue of climate change and greenhouse effects led governments and regulating agencies to enforce stricter emission limits on traditional internal combustion engines [6]. This led to the rediscovery of the electric car. Invented in 1830, the electric car became a research topic when it was clear that internal combustion engines were the best solution available. Recent developments in battery technology, especially the lithium ion batteries, and in electronics led to the modern electric car, which is comparable with traditional cars in terms of performance. Despite the technological developments, the long charging times mean that electric vehicles are mostly used in cities and towns [6].

The increase in popularity of electric vehicles requires the construction of a suitable fast-charging infrastructure to allow driving longer distances. Usually high-speed lines are built (or designed to be built) near existing motorways [7–9]. Since the best place to install fast-charging facilities are motorways service areas because the necessary services are already there, it is interesting to study the possibility of connecting these charging facilities to the neighbouring high-speed line rather than the high-voltage transmission grid [10].

Electric vehicles need to have their batteries recharged to gain extra range, just as a traditional gasoline car needs to have its tank filled up at a gasoline station. There are three ways to get the batteries charged [11–13]. Battery swapping consists in swapping the depleted batteries with fully charged ones. In practice, almost no current electric car (except Tesla's) allows for it and has lost much of its appeal when a service provider went bankrupt in 2013. Wired charging brings electricity to the vehicle using cables and plugs. It is the most widely used technology. Induction charging transmits electricity through high frequency variable magnetic fields. It is still in development and it is only used in a few pilot locations [14].

The CENELEC EN 61851-1 standard on wired charging requires that the Electric Vehicle (EV) shall be connected to the EVSE (Electric Vehicle Supply Equipment) so that in normal conditions of use, the conductive energy transfer function operates safely [15,16]. In particular, the standard defines four charging modes but they are not all legal in every country. The four charging modes are: (a) Mode 1; (b) Mode 2; (c) Mode 3; and (d) Mode 4. Mode 1 charging requires connecting the EV to the Alternating Current (AC) supply network (mains) utilizing standardised socket-outlets not

exceeding 16 A and not exceeding 250 V single-phase or 480 V three-phase, at the supply side, and utilizing the power and protective earth conductors [17–19]. Mode 2 charging requires a connection of the EV to the AC supply network (mains) not exceeding 32 A and not exceeding 250 V single-phase or 480 V three-phase utilising standardised single-phase or three-phase socket-outlets. It requires also utilising the power and protective earth conductors together with a control pilot function and system of personnel protection against electric shock (RCD) between the EV and the plug or as a part of the in-cable control box. The in-line control box needs to be located within 0:3 m of the plug or the EVSE or in the plug. Mode 3 charging requires connecting the EV to the AC supply network (mains) using dedicated EVSE where the control pilot function extends to control equipment in the EVSE, permanently connected to the AC supply network (mains). Mode 4 charging needs a connection of the EV to the AC supply network (mains) utilizing an on-board charger where the control pilot function extends to equipment permanently connected to the AC supply [20,21].

It is possible to classify the four charging modes according to the charging speed: Modes 1 and 2 are generally used for slow charging from the household plug, while Mode 4 is usually used for fast DC charging at a charging station. Mode 3, on the other hand, can be used both for slow charging and for fairly quick charging depending on the capability of the car and the infrastructure. The existence and the differences between Modes 1–3 are due to different factors: the consumer representatives want something cheap and feel that the stock household plugs are acceptable for home charging, while the industry feels that a purpose-built solution would be better thanks to higher safety and reliability.

There are three connectors standardised for AC charging: the US, Japan, and other countries that have a predominantly single-phase distribution network use the type 1 (or SAE) connector. Europe has settled on the Mennekes type 2 connector, which supports both single and three-phase power supplies up to 40 kW, and China uses its own standard. DC fast charging (Mode 4) sees a different situation, because there are four standards available on the market and the question has not been fully settled yet. The available standards are: (a) Tesla's Supercharger [22,23]; (b) the Chinese GB/T [24,25]; (c) the Combined Charging System (CCS) [26]; and (d) the CHAdeMO [27].

The power quality analyses carried out are also useful to predict the aging of the power devices as substation transformers [28,29].

A limited number of research studies propose different concepts for EV charging stations powered by renewable energies, including architectures, control strategies and infrastructure planning [30–37]. Despite the above efforts, the authors did not find detailed information on the modelling and simulation of electric vehicle fast charging stations powered by high-speed railway lines in Italy [38–40]. In order to further investigate the characteristics of the concept, a model of a 2 × 25 kV system to feed the railway was proposed and simulations of the battery charger were presented in detail. It is hoped that this contribution will lead to optimisation of the system design and characterisation and to encourage its widespread improvement and applications.

Moreover, many current researchers are focused on power electronic converters and devices for automotive applications [41,42].

The aim of this work is the analysis of the opportunity introduced by the use of railway infrastructures for the power supply of fast charging stations located in highways. In fact, long highways are often located far from urban areas and electrical infrastructure; hence, the installations of high power charging areas can be problematic.

This paper is organised as follows: Section 2 presents a detailed description of the 25 kV railway electrification, dividing the section in two different parts, a focus on the configuration and design of the 2 × 25 kV systems and another focus on the mathematical model of the 2 × 25 kV system, respectively. The specifications and configuration of the charging facility used in this analysis and the simulation model of the load are given in Section 3. Section 4 provides details of the system simulation of the charging system and results. Finally, the conclusions are reported in Section 5.

#### **2. The 25 kV Railway Electrification**
