Sara Ghaemi, Director Technical Development, Avnet Abacus
We are all familiar with the phrase work smarter, not harder. Well, the EV charging infrastructure needs to be hardworking and intelligent to meet the needs of vehicle users and the communities impacted by them. The hard work is associated with distributing enormous quantities of energy, as the number of EVs on the roads increases massively over the next few years. On the other hand, managing that energy and ensuring the right quantities are available in the right places at the right times is no simple task. Also, safety, accurate billing, and security are critical must-haves.
Smart infrastructure is essential to support the accessible and convenient mobility to which we have become accustomed while safeguarding the grid's stability and achieving everything – as far as possible – using energy from renewable sources. These, by their nature, are transitory and provide limited electricity that must be captured when available and accumulated, then released over time in a controlled fashion.
This process relies on appropriate interactions between the various parties and items of equipment in the process: the vehicle owner or charging-account holder, the charging point or EV service equipment (EVSE), the vehicle itself charging through the on-board charger (OBC) or direct DC charging, the charging-point operator, and the grid operator.
Account Holder to Charge-Point Operator
When a vehicle arrives at a public charge point needing charging, the charging account holder must provide credentials to begin charging. A practical and convenient channel is a contactless near-field communication (NFC) connection using a smartphone and app or tokens like a smartcard or smart key fob. The EVSE can then contact the charge-point operator to verify the customer’s credentials, typically using a standard wired Internet connection. At this point, the EVSE can check necessary information like the account status and available credit on the operator’s database before authorising charging.
The charge-point operator also needs information from the grid operator about the current status of the grid and the availability of energy for charging. Tariffs and maximum allowable charging rates will change during the day as demand changes continuously and the available solar and wind energy levels fluctuate. There may also be problems in the grid system, such as equipment failures that may be localised or may affect a large area.
If there are problems with generators or demand is high relative to supply when the session is requested to start, the charge-point operator may restrict the maximum charging rate. In addition, they need to communicate any restrictions to the customer, such as the maximum charging rate in kW. Alternatively, the charge-point operator may calculate an expected end time for the charging session.
EV to EVSE
The EV and EVSE must communicate to confirm the correct connection and start, manage, and terminate the charging session when the vehicle is connected. The EVSE needs to identify the vehicle’s charging parameters, including the maximum charging rate and battery state of charge. The EVSE and vehicle charging system need to agree on the charging rate, which may be up to the maximum allowed by the battery/charging-management system, subject to any supply-related restrictions.
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A secure and correct connection can be verified using information shared through essential communication such as coding resistors. However, more sophisticated communication is needed to manage the charging session. Typical standards for the EV-to-EVSE connection include SAE J2847 (US) and ISO 15118 (Europe). The interface contains power connections for AC and DC charging, as well as a proximity signal and control pilot signal. For the control pilot, which carries the main digital communication between the EV and EVSE to initiate, manage, and terminate charging, the SAE and ISO standards have each adopted Power-Line Communication (PLC) as defined in the HomePlug Green PHY specification.
The battery charging may stop when fully charged, or the session terminated early if the user decides or the account credit becomes depleted.
Connections to individual EVSE are needed, from the charging-point operator’s point of view, to manage the EVSE fleet and authenticate and maintain the subscriber’s account. The process helps identify when maintenance or repairs are needed and accumulates information such as popular charging locations. This, in turn, helps plan future infrastructure expansion: where to add extra charging points, which ones to upgrade, e.g. to a higher power output, and to help identify potentially profitable new sites.
Charge-Point Operator to Grid Operator
The grid operator needs regularly updated information from charge-point operators to control the supply of electricity to charging points, and balance energy flows throughout the grid to maintain stability as the effective installed generating capacity varies throughout the day. From the grid operator’s standpoint, the EV charging-point operators are one party among many others - both residential and industrial - constantly demanding energy. They have different demand intensity, usage patterns, and priorities.
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The grid operator works to satisfy all demands to the greatest extent possible. A smart and green grid presents a far more complex management challenge than a grid supplied by conventional generators powered by fossil fuels such as gas or oil. Green grids do not have the same ability to generate extra electricity at peak demand and must rely on battery energy storage systems (BESS) to satisfy demand when generating capacity is low.
As the number of EVs in regular use increases, a grid that would allow large numbers of vehicles to take power from the grid in an uncontrolled manner risks instability and blackouts.
On the other hand, controlling the flow of power from vehicles to the grid enables EVs to provide a stabilising resource by returning unused energy when not in use, acting as grid-connected battery energy storage.
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This process creates the case for implementing V2G communication, which allows vehicles to supply energy from their batteries to the grid when connected but not in use. A prime example is when the vehicle is connected to charge in the evening after the owner returns from work. Most likely, the vehicle will not be used until the following morning to repeat the commute to the owner’s workplace.
A smart grid that knows the owner’s typical usage pattern can automatically delay charging the vehicle if there is an elevated demand until demand has reduced. Charging can then commence without risking instability in the grid. If any significant charge remains in the battery when it is connected, this, too, can be communicated to the charge-point operator and grid operator. They can then utilise this energy if needed to keep the grid stable and reward the EV owner for the service provided. The smart, informed grid can automatically ensure that the EV is charged and ready for the next time the owner needs to travel.
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The various parties in the charging session have certain expectations. The owner, charge-point operator, and grid operator have their own needs and interests. The end-user only wants to charge the vehicle as quickly and efficiently as possible. The charge-point operator seeks to ensure the network's success by delivering value for customers and safeguarding profitable operation. The grid operator must meet agreed environmental targets by maintaining a safe and stable energy supply.
It is critical to meet all needs as fully as possible through the end-to-end exchange of appropriate information. This process encompasses essential functional communication between the vehicle and the EVSE using short-range mobile communications such as NFC between the customer and EVSE and any combination of long-range, cellular, and WAN connections between the EVSE, charge-point operator, and grid operator.