Electric Vehicle and EV charging fundamentals

The different types of electric vehicles

In 2020, the electrical vehicle market is today shared equally between two main technologies: Battery electric vehicles (BEVs) and Plug-in hybrid electric vehicles (PHEVs). Both technologies are expected to grow fast in the coming years, with the growth of BEVs expected to increase its share up to 60% of total EV production in 2025, and around 40% for PHEVs.

Battery Electric Vehicles (BEV)

Battery Electric Vehicles are electric vehicles propelled by an electric motor drawing current from an on-board battery energy storage system. BEVs are also called "100% pure electric vehicles" or "all-electric vehicles", because they are powered by electrical energy storage only. They do not have an internal combustion engine (ICE) as a back-up in case the battery is fully discharged.

The BEV’s driving distance per charge is on average between 150 and 400km, with the trend to extend even further, as battery technologies continue to improve.

Fig. EV7 – Battery Electric Vehicle: electrical vehicle powered only by a rechargeable battery

Examples of BEVs include: Tesla Model 3 Mini Electric MG ZS EV Nissan Leaf Renault Zoe Hyundai Kona Electric Kia e-Niro Jaguar I-Pace Audi e-tron 55 quattro

Battery Electric Vehicles do not produce any on-road emissions, as they are powered exclusively by electricity. They have longer electric driving ranges compared to other electric vehicle technologies.

Plug-in hybrid electric vehicles (PHEV)

A plug-in hybrid electric vehicle is an electrical vehicle that can be powered by two energy sources: a battery that can be recharged by plugging into an external source of electric power, and a diesel or petrol engine.

The battery capacity of a plug-in hybrid EV is significantly smaller than that of a 100% electric vehicle. A PHEV can, using its battery power, cover on average between 30 to 50km. After this, the petrol / diesel engine takes over.

When powered by battery, the PHEV does not produce emissions. When powered by its diesel / petrol engine, the PHEV pollutes the environment.

PHEVs are considered a “transitional” technology. Indeed, with the development of fast charging electrical infrastructures, the increase of on-board battery capacity, and government regulation requirements, BEV (100% electric) technology is expected to grow faster.

Fig. EV8 – Plug-in Hybrid Electric Vehicle: electric vehicle equipped with both diesel / petrol engine and electric motor with battery

Examples of PHEVs include: Mitsubishi Outlander Volvo XC60 Twin Engine BMW 225xe Volkswagen Golf GTE Toyota Prius PHV Mercedes-Benz E350 e SE Chevrolet Volt family

Other low carbon vehicles and technologies

Hybrid Electric Vehicles (HEV)

Hybrid electric vehicles are internal combustion engine vehicles equipped with a small battery that can be recharged by braking energy recovery, but not by plugging into an external electricity source. These vehicles are not zero nor low emission, but provide an additional CO2 reduction compared to conventional internal combustion engine vehicles.

Fig. EV9 – Hybrid Electric Vehicle: internal combustion engine vehicle equipped with small battery used for energy recuperation, with no capacity to recharge from an external source

Examples of HEVs include: Toyota Corolla Hybrid Toyota Yaris Hybrid Lexus RX450h Ford Mondeo Hybrid Honda NSX

Fuel Cell Electric Vehicle (FCEV)

A fuel cell vehicle is an electric vehicle powered by electricity produced by a fuel cell instead of electricity stored in an electrical battery. The fuel cell produces electricity using oxygen and hydrogen as primary sources.

The FCEV does not yet have the maturity of other electric vehicle technologies, such as BEV and PHEV, and currently has only a small share (<1%) in terms of EV production.

FCEV manufacturers:

• Volkswagen
• Honda
• Hyundai

Regenerative braking

Regenerative braking is an energy recovery mechanism, in which the electric motor acts as a generator during the braking, and the generated energy is used to charge the battery. This technology can be used in electrical vehicles, such as HEVs, BEVs, and PHEVs.

Integrating photovoltaic cells onto the car rooftop

Some car manufacturers offer electrical vehicle models with integrated solar PV cells on the vehicle roof. The on-board produced energy is not sufficient to charge the electrical battery but can be used to supply some accessory loads.

How do electric vehicles work?

An electric vehicle (electric car) is a vehicle propelled by an electric motor, using energy stored in rechargeable batteries. Electric vehicles are equipped with a charging inlet(s), and an on-board charger that converts AC power into DC so that it can be stored in the battery. An on-board controller ensures the performance of the electric vehicle.

1. electric motor,
2. battery,
3. on-board charger,
4. charging inlet (AC),
5. charging inlet (DC fast charging)

Fig. EV10 – Main components of an electric car

Electric vehicle motor

An electric vehicle is propelled by an electric motor. Typical power range for an electric vehicle motor is between 15kW and 500kW.

Electric-vehicle battery

Electric cars are usually equipped with a lithium-ion battery energy storage system. The battery typically has a power range of 5 to 100 kWh and operates at voltage levels from 300 to 800 V.

The battery determines the autonomy of the electric car. As a rough estimation, 1kWh of energy storage is equivalent to 5km driving distance.

The battery lifespan depends on the use of the car and the type of charging. Usually, the battery set lasts more than 10 years. However, if DC fast charging is used frequently (more than 3 times / month), the battery capacity, performance and life time are reduced.

Onboard charger

Electric vehicles include an on-board charger, which converts the power from AC to DC to charge the battery. The charging capacity of the onboard charger is limited to 22kW AC. In case of fast DC charging (see charging mode 4), the onboard charger is bypassed, and the DC electricity is supplied directly to the battery.

Charging inlet

The charging inlet port is used to plug the car to a power supply, in order to recharge the battery.

An electrical vehicle has at least one AC charging inlet port. Electrical cars can have a second DC charging inlet for fast charging (mode 4). The DC charging inlet may or may not be an option, depending on car models or countries. Also, some models offer a single port for both AC and DC charging.

Electric vehicle connectors

There are different types of connectors to plug the charging cable to the vehicle inlet.

AC connectors are defined by IEC 62196-2, DC connectors are defined by IEC 62196-3.

Type 1 connector (SAE J1772)

Type 1 connector is used with AC charging station.

The J1772 connector is easily identifiable by three large pins – similar to the power outlet layout at home – and two smaller pin for the car connection. The three broad pins are for Phase, Neutral and Ground while the two small pins are used for communication between the charger and the electric car (Pilot Interface).

It can deliver between 3 and 7.4 kW and supports only single phase with a maximum current of 32 A. It includes an extra protection to lock the connector while charging, in order to avoid disconnection by a third party.

It’s mainly used in USA and Japan, but is also accepted in Europe.

Type 2 connector (IEC 62196-2)

Type 2 connector is used with AC charging station.

This type of connector is approved as the European standard. The connector stands out with a unique design, rounded but with a flat edge on the top. Its pins distribution is similar to type 1, but includes two more pins, corresponding to the two extra phases needed for three-phase charging.

It allows a recharge between 3 and 43 kW and can support single phase up to 16 A and three phases up to 63 A.

An evolution of this connector is the T2-S which includes additional lock to the connector. In France, connector version T2-S is mandatory.

Type 3

This type of connector is abandoned in favor of type 2 connector.

CHAdeMO

CHAdeMO connector is used with DC charging station.

CHAdeMO is the contraction of "Charge Move". But the acronym is also present in the Japanese sentence: "O cha demo ikaga desuka" which translates as "You will have tea while the car is charging". This sentence represents the will of the association composed by Toyota, Mitsubishi and Nissan, among others: fast charging with direct current. It can therefore be installed as a second socket by vehicle manufacturers next to an alternating current charging socket.

It can deliver up to 62.5 kW and can reach 125 A, yet the revised CHAdeMO 2.0 specification allows for up to 400 kW.

Combined Charging System (CCS) Combo 1

CCS Combo 1 is based on the J1772 Type 1 connector by adding two additional pins. The Combined Charging System is made for DC Fast Charging. The connector can do both AC and DC charging up to 350 kW.

Combined Charging System (CCS) Combo 2 (IEC 62196-3)

CCS Combo 2 is based on Type 2 connector by adding two additional pins. The Combined Charging System is made for DC Fast Charging. The connector can do both AC and DC charging up to 350 kW.

Electric vehicle charging modes

The international standard IEC 61851-1 « Electric vehicle conductive charging system» defines four modes of charging:

• Mode 1 – Standard socket outlet - domestic installation
• Mode 2 - Standard socket outlet with an AC EV supply equipment– domestic
• Mode 3 - AC EV equipment permanently connected to an AC supply network
• Mode 4 - DC EV Supply equipment

Fig. EV11 – Four electric vehicle charging modes, as defined by IEC 61851-1

Mode 1 – Standard socket outlet - domestic installation

Fig. EV12 – EV charging mode 1: Standard socket outlet and cable for domestic installation

Mode 1 is a method for connection of an electric vehicle to a standard socket-outlet on an AC supply network, using a standard cable and plug, without any additional equipment.

The rated values for current and voltage must not exceed:

• 16 A and 250 V AC for single-phase,
• 16 A and 480 V AC for three-phase installation according to the IEC 61851-1,

Local standards may be more stringent.

Due to this power limitation, charging time takes several hours.

Mode 1 is the simplest mode, but as there is no dedicated circuit or equipment for the electric vehicle charging, it presents the following risks:

• breaker tripping: since the recharging socket used shares the same switchboard outgoing circuit as other power sockets, if the sum of power consumption exceeds the protection limit (generally 16A), the circuit breaker will trip, interrupting the vehicle charging.
• risk of fire or electric shock in case of obsolescence or non-compliance of the electrical installation

For these risks and limitations, the use of this mode is limited and even forbidden in some countries (ex. USA)

Mode 2 - Standard socket outlet with AC EV supply equipment

Fig. EV13 – EV charging mode 2: Standard socket outlet with special cable, integrating a system for power control and protection, for domestic installations

Charging mode 2 is a method for the connection of an EV to a standard socket-outlet, with a control pilot function and a system for personal protection against electric shock, integrated into the connection cable, between the standard plug and the EV.

The rated values for current and voltage must not exceed 32 A and 250 V AC in single-phase, and 32 A and 480 V AC in a three-phase installation, as defined in IEC 61851-1

This mode is limited to domestic electric installations. The connection cable is usually provided with the electric car. As with mode 1, a standard socket outlet is used, but in this case, the protection device and the socket outlet should be able to carry higher charging currents, up to 32A, which is usually not the case for standard domestic power socket circuits.

Mode 3 - AC EV equipment permanently connected to an AC supply network

Fig. EV14 – EV charging mode 3: Dedicated circuit and specific charging system (EV charger), integrating protection and control functions. Cable integrating a pilot wire.

In Mode 3, electric vehicles are charged by specific equipment, called EV charging station (or EV charger), permanently connected to an AC supply network and integrating protection and control functions.

Because Mode 3 uses a dedicated EV charger (and not a standard socket outlet), the power range is higher, from 3.7kW up to 22kW AC. This higher power range enables fast charging of electric cars, compared to Modes 1 and 2.

The addition of a pilot wire inside the charging cable enables communication between the vehicle and the charging equipment through standard protocols. It also allows the implementation of control functions, such as:

• verification that the electric vehicle is correctly connected to the EV supply equipment,
• continuous verification of the integrity of the protective conductor,
• energization and de-energization of the power supply
• transmission of information about the maximum permitted current to draw

Specifically designed for electrical vehicle charging, mode 3 is recommended for the following reasons:

• The use of a dedicated and independent electrical circuit eliminates the risk of connection to a non-compliant installation, thus guaranteeing the safety of property and people.
• The control function manages the charging period of the vehicle and optimizes electric consumption according to user needs. It ensures optimal charge of the batteries and preserves their lifespan.

Mode 4 - DC EV Supply equipment

Fig. EV15 – EV charging mode 4: Dedicated DC EV supply equipment, for fast EV charging.

In Mode 4, charging is done through DC EV supply equipment, called EV charging station (or EV charger), connected to an AC or DC supply network. The EV charging station delivers DC current directly to the battery, e.g. bypassing the on-board charger. Charging of the electric vehicle can be done much faster than in mode 1, 2 and 3, as the electrical power charging range is higher than 24kW.

In mode 4, the digital communication between the electric vehicle and the EV supply equipment is mandatory, and should comply with the requirements described in IEC 61851-24

How Long Does It Take to Charge an Electric Car?

The charging time can be roughly calculated as the ratio between the electric vehicle battery capacity and the charging power. The charging power is limited to the power that the charging station can deliver and that which the Electrical Vehicle can accept.

[math]\displaystyle{ \text{Charge time (h)} = \frac{\text{EV Battery capacity (kWh)}}{\text{Charging power (kW)}} }[/math]

[math]\displaystyle{ \text{Charging power (kW)} = min\ (\text{ EV onboard charger rate ; Charging station delivery rate}\ ) }[/math]

For example, for an electric vehicle with:

• 40kWh battery set
• 6.6kW onboard charger for AC charging

The estimated full charging time is:

• 11h for home charging station of 3.7kW (40kWh / 3.7kW)
• 6h30 for AC charging station of 11kW (40kWh / 6.6kW, 6.6kW due to the limitation of the onboard charger)
• 50min for DC fast charging station of 50kW (40kWh / 50kW)
• 10min for DC ultra-fast charging station of 250kW (40kWh / 250kW)

Check also this overview of the charging time according to charging mode and charging power.

Note that this formula provides a rough estimation. The actual charging time is usually longer for the following reasons:

• the charging speed profile is not linear. Electric vehicles are not continuously charged at maximum power. In particular, DC charging (mode 4) is charging very fast until the battery reaches 80% - 90% of its capacity, and slows down significantly for the remaining 10-20%.
• the charging speed depends on the battery temperature. The optimum temperature for charging is between 20°C and 30°C. If the battery temperature is outside of this range, charging can be slower.
• Charging speed also depends on the electric vehicle model, and on the charging strategy/algorithm of the charging station.

Fig. EV16 – Example of an EV DC charging power versus time

Electric vehicle charging location

Unlike conventional internal-combustion engine (ICE) vehicles, which refuel at gas stations, electric vehicles can recharge at multiple locations: @home (residential buildings), @work (small to large office buildings ...), @destinations (public parkings, hypermarkets ...), @fleet (city buses, delivery trucks, company cars ...), @transit (highways, city stations ...). The charging time and cost for the end user, the charging mode, the number of chargers and their power range are all dependent on the charging station location.

Fig. EV17 – Electric vehicles can be charged at multiple locations

Residential EV charging stations

Home is the most common place to charge. Home charging is cost-effective and usually sufficient for daily trips. It is generally considered as more convenient than refuelling ICE vehicles at gas stations.

Residential (home) charging can be:

• single-family: low-rise individual houses with a private garage usually equipped with one or two charging points
• multi-family: residential buildings with multiple apartments (condominium), where charging points may be private (individual garage) or shared between condominium inhabitants (a number of EV charging points located in the common parking place)

Residential charging is done mainly at night, when the car is not in use and when electricity is usually cheaper. EV charging equipment is most commonly single-phase and with a power delivery rate up to a maximum of 7.4 kW. Charging is slow and may require several hours. Charging Mode 3 is recommended for its built-in safety features.

Workplace EV charging stations

Workplace EV chargers are becoming available at a growing number of companies, especially those committed to the reduction of greenhouse gas emission. It can be attractive for employees, especially if the price for charging is equivalent or lower than the price for charging at home. Workplace charging can be an opportunity to encourage electric vehicle adoption for employees that do not have charging points at home or for employees needing to charge both at home and at work for their daily usage.

Workplace charging is done mainly during the day. EV chargers in the workplace are usually 3-phase with a power range of 11kW and 22kW. Charging Mode 3 is recommended for safety reasons.

Commercial building EV charging stations

Other destinations, such as supermarkets, shopping malls, restaurants, public car parks and commercial facilities equipped with EV charging points, can provide occasional charging opportunities for their users.

Because a car is parked at these locations for a few hours only, fast charging is usually preferred, typically with 22kW-EV charging stations, using charging mode 3.

Fast in-transit EV charging stations

Fast in-transit charging stations provide efficient charging when the charging time is an important consideration. They are usually located on highways or at city hubs.

Charging is done in mode 4 (DC charging, also sometimes called DC fast charging). The power range of the EV charging station is from 50kW up to 350kW. The charging time depends on the power range – usually less than 30min.

Even though fast charging is convenient, it is to be used sparingly, as frequent usage of fast DC charging reduces the EV battery lifetime.

Charging modes - synthesis

Fig. EV18 – Charging scenarios with typical values for charging station delivery rate, time of charge and charging mode