Technology and Challenges

DC Fast Charging Stations TECHNOLOGY AND CHALLENGES SFO TECHNOLOGIES R&D SOLUTIONS Dr. Pratheesh K, S. S. Ghosh, N. Mangal, R. Poulose & R. Narayanan CONTENTS Introduction....................................................................................................................... 3 Types of Electric Vehicles.............................................................................................. 3 The Global EV Outlook.................................................................................................. 4 The Electric Vehicle Charging Infrastructure ........................................................ 4 Standards for EV Charging ......................................................................................... 5 EV Chargers: Classication........................................................................................... 6 Charger Connector Types............................................................................................. 7 Charging Network Protocols....................................................................................... 8 Converters for DC Fast-Charging Stations.............................................................. 8 Topologies for PFC Stage.............................................................................................. 9 Topologies for DC-DC Stage........................................................................................ 10 Technical Challenges..................................................................................................... 12 Technical Specications................................................................................................ 12 The Modular Architecture........................................................................................... 12 A 50kW DC fast-charging station developed by SFO Technologies ............ 13 Eciency Considerations............................................................................................ 13 Communication System and Controllers.............................................................. 14 Environmental and Thermal Management.......................................................... 14 Conclusion....................................................................................................................... 16 References........................................................................................................................ 16 WWW.SFOTECHNOLOGIES.NET 2 INTRODUCTION The energy demand has increased exponentially over the past decades, due to industrializa- tion and globalization. It is predicted that world energy consumption will increase beyond 50% by 2030. At present, the world relies heavily on fossil fuels which provide almost 80% of the global energy demands. The increase in retail prices of fossil fuels and the side eects on the environment have been a motivation to look for cheaper, environment-friendly, and ecient alternative options. The major contributor to these energy-related issues is the automotive industry. As such, there is an increased focus on alternative energy sources to drive the vehicles. While this focus has been there for the last few years in other countries, in India, this is on the way to becoming an important focus area in present times. The most common and successful form of alternate source of energy is electricity that has been utilized in electric and hybrid vehicles due to the recent enhancements in battery and its charging technology. However, the fear of becoming stranded with a discharged battery and long charging times caused reluctance in the adoption of electric vehicle (EV) technologies. To overcome these issues, EV manufacturers have come up with larger and improved battery technologies. Parallelly, the charging solution providers have moved to DC fast-charging stations (DCFCS). The DC fast-charging is necessary since the ever-increasing battery in the vehicles needs to be charged over a very short time for public convenience. This whitepaper is primarily focused on the DC fast-charging technology and its challenges. Dierent types of EV chargers, charging requirements and standards, power converters for DCFCS, technology enhancements for eciency improvement, and environmental aspects will be discussed in the rest of this paper. Types of Electric Vehicles Hybrid Electric Vehicles (HEV): These vehicles are powered mainly by an internal combustion engine or other propulsion sources that can run on conventional or alternative fuel and an electric motor that uses the stored energy in the battery. The primary purpose is to combine the benets of high fuel economy and low emissions with the power and range of EVs. A HEV uses both regenerative braking and an internal combustion engine to recharge the batteries since it cannot be plugged into o-board chargers. HEVs can be further classied into mild/micro and full hybrid vehicles. Mild/micro hybrids use a smaller battery and electric motor, which can power the vehicle at rest. This allows the engine to shut o and save fuel. Mild hybrid vehicles cannot drive using electricity alone. Full hybrids vehicles have more powerful electric motors and larger batteries that can drive for short distances at low speeds. Plug-in Hybrid Electric Vehicles (PHEV): These vehicles can charge their batteries from an o-board charger. PHEVs have larger battery packs than HEVs, which enables them to drive moderate distances using electricity only (referred to as all-electric range). The internal combustion engine usually powers the engine when the battery is mostly depleted, during accel- eration or when intensive air-conditioning is required. All Electric Vehicles: These are also called battery electric vehicles (BEVs), which use only the stored energy in the battery to power the vehicle. BEVs have large batteries to support running with electricity only. These batteries are charged by an external electrical power source, the nature of which can determine its charging time. Because BEVs use only electricity, there is no associated pollution. WWW.SFOTECHNOLOGIES.NET 3 The Global EV Outlook In 2020, despite the Covid-19 pandemic, the global electric car stock has hit the 10 million mark, a 43% increase over 2019. BEVs contributed to two-thirds of new electric car registra- tions and two-thirds of stock in 2020. One particular reason is the availability of a wide range of BEV models with a higher range in the market as in Fig. 1 (a). The charging infrastructure goes hand-in-hand with the electric vehicle market. Publicly available chargers reached 1.3 million units in 2020, of which 30% are fast chargers. Publicly available fast chargers facilitate longer journeys, while the increase in their deployment will enable longer trips and faster adoption of EVs. Even then, the ratio of public chargers per EV is remarkably less for the majority of the countries as shown in Fig. 1(b). Figure 1: (a) EV stock available (b) Public chargers available per EV; Source: Global EV outlook 2021 by IEA As evident from the above discussions, there is certainly a need for more fast-charging infrastructure to enable the growth of EV adoption. Charging levels above 22kW are normally classied as fast-chargers. DC fast-chargers use high power DC (>22kW) to charge the EV battery directly up to 80% in 20-40 minutes. DC fast-chargers are usually rated at 50kW which are mainly targeted for city use. Highway DC fast-chargers are rated as high as 150kW. For supercars, trucks, and buses, 350kW DC fast-chargers are used. THE ELECTRIC VEHICLE CHARGING INFRASTRUCTURE Delivering the electrical energy from an electrical source to the electric vehicle requires EV supply equipment (EVSE) often called EV chargers. They will have cables, connectors, and inter- faces between the utility power and the electric vehicle. This entire system contributes to EV charging infrastructure. Countrywise, specications and congurations of the EVSE could be dierent. The most important part of the charging infrastructure is its conguration, which is well dened through various international standards. The Society of Automotive Engineers (SAE) and the International Electrotechnical Commission (IEC) are two popular associations that deal with various standards for EV and EV charging. WWW.SFOTECHNOLOGIES.NET 4 Standards for EV Charging Although there are several guidelines followed in various countries/ regions, IEC covers all of them in its dierent series of standards. These are dened for connectors, EVSE, EV, and communication interface between EV and EVSE. Table 1 shows the IEC standards related to EV charging infrastructure. Other notable standards SAE J1772: This covers general physical, electrical, communication protocol, and performance requirements for the EV conductive charge system and coupler. In SAE terminology, dierent charging solutions are dened in levels, which are reviewed in consecutive sections. DIN SPEC 70121: Denes digital communication between a dc charging station and an EV for control of dc charging in the combined charging system (CCS). Table 1 Applicable Standards in EV Charging Infrastructure No. Standards Scope 1 IEC 61851 Conductive charging systems (a) IEC 61851-1 Defines cables and plug setup (b) IEC 61851-21 EV requirements for conductive connection to an AC/DC supply (c) IEC 61851-22 AC electric vehicle charging station requirements (d) IEC 61851-23 Electrical safety, harmonics, grid connection and communication architecture for DCFCS (e) IEC 61851-24 Digital communication

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