Charging of Electric Vehicles

EV 101

One of the critical success factors for electric vehicle deployment is establishment of a well-designed charging infrastructure. Over time there has been developments taking place in this area in terms of charging protocols, standards, and safety precautions. The present article is an attempt to discuss in detail the types of EV charging methods, the various classification of chargers and standards.

Types of Charging:

There are many ways in which an electric vehicle (EV) can be charged depending upon the location and requirements. Currently, conductive charging technology, or plug-in(wired) charging, is the mainstream technology in use. There are two types of fuels that can be used to charge an EV, namely, alternating current (AC) and direct current (DC). Battery inside an EV or in any electronic devices such as smart phone, laptops etc., can store only DC, therefore, before a device can be charged, the AC supply from the grid must be converted into DC. That’s why, most electronic devices have an in-built convertor into the plug to convert the power from AC to DC.

Similarly, in case of an electric vehicle, the EV chargers are categorized depending upon the location, where the AC power gets converted, inside or outside the vehicle.

AC Charging:

In AC charging, the converter is built inside the vehicle, known as an “onboard charger”. The onboard charger converts power from AC to DC and then feeds it into the vehicle’s battery. Today, this is the most common way for charging electric vehicles.
DC Charging::

In case of DC charging, the DC charger has a converter inside the charger itself and the power conversion happens outside the vehicle. This means that the charger can feed power directly to the vehicle’s battery and doesn’t need the onboard charger.

The Relationship between power conversion mechanism and rate of charging

The power conversion mechanism has a direct relationship with the rate of EV charging. It is important to note that the onboard charger of an electric vehicle has its own power rating. For example, In India market, the low voltage electric vehicles (below 120V) such as electric 2-wheelers and 3-wheelers have an onboard charger only up to 3kW, whereas the high voltage electric cars such as Nexon EV, MG ZS EV and Hyundai Kona have onboard chargers of 3.2kW, 7kW and 10.5kW (max).

So, when an electric vehicle is charged by an AC charger of certain power rating, the rate of charging is limited to the rating of the lowest rated component. But this is not applicable in case of DC charging, as the DC chargers bypasses all the limitations of onboard chargers and feeds DC power directly to the battery. So, the power rating of DC charger is the key determinant along with other factors like C-rate of the battery. Only the power rating of DC charger will not guarantee fast charging, as it will depend upon the C-rate of the battery. A charger would supply power up to its rated capacity only, but it is the BMS of the battery that would decide whether it would accept that much power or not.

Classification of EV Chargers:

When it comes to EVs, it is more appropriate to classify chargers based on their power rating instead of the rate of charging vis-à-vis “slow-chargers” or fast-chargers”. The definition of a slow charger and fast charger is not sufficient, as the same charger will act as a fast or slow charger depending upon the vehicle to be charged. For e.g., a 2.5kW charger will be a slow charger for an electric car but could act a fast charger for an electric two-wheeler.

Globally, the EV chargers are categorized broadly into 3 levels: 1) Level 1 AC Charging; 2) Level 2 AC Charging; and 3) DC Charging.

Level 1: Known as slow AC charging, these are simple home sockets used for AC trickle charging. The power rating of such chargers varies between 1kW to 3kW. In North America, Level 1 charging is defined at 120V, whereas in India, the home private chargers are generally used with 230V/15A single phase plug, which can deliver a maximum of up to about 2.5kW of power.
Level 2: Known as fast AC charging, the level 2 charging supports both single phase as well as 3 phase AC charging with the help of different charging connectors available globally. In North America, the level 2 charging is defined at 208-240V, and the output power varies between 3kW to 19kW AC. As far as India market is concerned, the chargers are available with the power output ranging from 3.5kW to 22 kW supporting both single phase as well as 3 phase AC charging. These types of chargers are preferred for workplaces, shopping malls, parking garages, hotels etc.
DC Charging: These are known as fast chargers, as DC chargers bypasses the need of onboard chargers inside the vehicle, thus the EVs can be charged faster. The power rating of charger varies between 10kW to 400kW globally. The charging time will depend upon many factors such as the power rating of charger, size of battery, the C-rate of the battery etc. Many vehicles available in market today can achieve 80% charge within an hour using the different DC chargers available currently. These types of chargers are preferred mainly for public places.

Standards and Connector types for EV charging around the world:

Generally, whenever a new technology is introduced in the market, the initial phase always remains challenging and full of competing standards. Each manufacturer uses and develops his own standards and processes. Only time can determine which one will sustain. The world witnessed the same in case of charging connectors for mobile phones. Today, the same is happening with the connectors on charging cables for electric vehicles. The details below explore the different charging connectors used by OEMs across geographies and models.

J 1772 (Type1) connector – North America

North America was the first continent to come up with the specifications of EV charging, in the form of J 1772 (Type1) connector. The connector was defined by the Society of Automotive Engineers (SAE). This connector only supports single phase AC charging and can be found in North America and Japan. This connector has total 5 pins (3 main pins for carrying the current and 2 smaller pins for communication between the EV and the charging equipment). Out of the 2 smaller communication pins, one pin is known as the Proximity Pilot (PP), which tells the charging equipment about the type of cable connected to the socket, as different cable thicknesses can deal with different amounts of electrical current. The other pin is known as the Control Pilot (CP), which provides the bi-directional communication between the EV and the charging equipment and keep checks on the maximum amount of current that an EV can take at any point of time.
Mennekes (Type 2) EV Connector – EU & Rest of Market (except China)
Similarly, like North America, Europe has also defined its own connector, i.e., Mennekes - type2 based on IEC standard 62196. This has been the official charging plug within the Europe since 2013. This connector can support both single phase as well as the 3 phase AC charging. This connector has total 7 pins (5 main pins for carrying the current and 2 smaller pins for communication between the EV and the charging equipment).
CHAdeMO:

Japan made the first attempt to come up with its own connector, known as “CHAdeMO” for DC charging. This connector is now used as the official standard in Japan for all DC fast chargers. This connector has 2 pins to carry the DC current and the data signals are conveyed on the CAN protocol.
CCS1 & CCS2 EV Connector:

Combined Charging System (CCS) covers Combo 1 (CCS1) and Combo 2 (CCS2) chargers. This connector is based on Type 1 and Type 2 connector with 2 additional pins to support the DC charging. CCS1 is widely used in North America whereas CCS2 is used in EU and rest of the markets except China.
Guobiao (GB/T):

Like other regions, China has also created its own standard known as “GB/T” for AC as well as the DC charging. The connector used for AC charging is effectively inverse of the Mennekes Type 2 charger. This connector supports only single-phase AC charging, and it is based on GB/T 20234.2 standard. This connector has also 7 pins like type 2 connector, but it uses only 3 pins to carry the current and 2 pins for the communication. The remaining two pins are simply unused.
TESLA Connector: (AC and DC Combined):

TESLA has created its own proprietary plug in North America for charging of their electric vehicles. Unlike other manufacturers, TESLA doesn’t have a separate connector design for AC and DC charging. Instead, they use the same connector for both type of charging. In Europe, TESLA has launched electric cars compatible with the CCS2 charging protocol.

India Market Standards:

In India, with respect to Level 1 AC charging, Government has notified Bharat AC-001 standard based on IEC 60309 commando connector. The connector has 3 pins, and it can support only single-phase AC charging. The connector doesn’t have any additional pins for the communication between the vehicle and the charging equipment. As far as level 2 AC charging is concerned, the Government has adopted the European Type 2 connector.

With respect to DC charging, the government has notified Bharat DC-001 standard based on GB/T standard of China for charging the vehicles at 48/72V. As far as high voltage charging is concerned, the government has adopted the Japanese “CHAdeMO” and the European “CCS 2” connectors.

Further, the Bureau of Indian Standards (BIS) in association with department of Science and Technology (DST) and other industry stakeholders under ETD-51 committee is working on new low-cost AC charging connector for EV’s. Recently, the committee notified the draft standard and by end of this year, BIS will publish the final standards.

References:

https://dhi.nic.in/writereaddata/UploadFile/Standardization%20of%20protocol.pdf

https://versinetic.com/ev-charging-connector-types-guide/

https://www.evexpert.eu/eshop1/knowledge-center/connector-types-for-ev-charging-around-the-world

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