How does an EVSE work?

Before discussing how electric vehicle supply equipment (EVSE) works, it’s necessary to define EVSE. According to the National Electrical Manufacturers Association (NEMA), EVSEs are: “Commonly called charging stations or charging docks; they provide electric power to the vehicle and use that to recharge the vehicle’s batteries.”

However, the electric vehicle (EV) industry considers all the systems in the electric grid that generate and deliver electricity to the chargers to be EVSEs. This FAQ looks at how EV chargers are evolving. It reviews a more expansive view of EVSEs and how they work — particularly, how they work together to support EV operation and can be integrated into the smart grid.

EVSE installations include:

Public charging stations.
Workplace charging stations.
Residential charging stations.
Fleet charging locations.
The related software and hardware infrastructure.

EV battery chargers are complex devices. Except for slow charging stations, EV chargers require communication with the vehicle to determine the battery’s state or charge and how fast it can accept additional charges. Once the initial charging rate is determined, the charger sometimes monitors the charging process and the battery pack’s temperature. Some chargers allow EV owners to use a smartphone to monitor the charging process remotely, determine charging schedules, and get notified when charging is complete.

Not all chargers are powered solely by the electric grid. They can be designed for off-grid operation or hybrid systems that can use a combination of grid or off-grid power sources.

For example, an EV battery charger can be powered by solar energy, replacing the grid power in an off-grid installation or supplementing grid power. The system can include a photovoltaic (PV) array for energy generation and a boost converter to smooth out the voltage variations that occur as the insolation of the PV array changes. It also includes a battery storage system and related charger to save solar energy between EV charging sessions and a dedicated EV charger (Figure 1).

Figure 1. An EVSE can be much more than a simple EV charger. It can also include local power generation like a PV array, an energy storage system, and associated power electronics and controls (Image: MDPI processes).

Broader EVSE infrastructure
The system described above hints at the broader EVSE infrastructure needed to support EV battery charging. The basic electric grid was not designed to support the charging of large numbers of EVs. Additional types of EVSE are required to expand the capabilities of the grid to support EV charging.

This includes distributed energy resources (DERs) like large-scale PV and wind generation installations, utility-scale battery energy storage systems (BESS), switchgear and transformers to enable and manage the flow of electricity to EV chargers, charger power distribution cabinets in large multi-charger installations, and so on (Figure 2).

Figure 2. Several different types of EVSE will be needed to enhance the capabilities of the electric grid and support the large numbers of EV chargers that will be required as EVs become commonplace (Image: Panduit).

Smart grid and EVSEs
The integration of EVSEs into the smart grid is necessary to realize the full potential of EVs. The smart grid enables large numbers of EVs to be intelligently scheduled so that not all are charged at once, but each is fully charged when needed. Instead of setting a specific charging time, EV users will tell the smart grid when they need the charging to be completed, and sophisticated software will analyze the required load patterns, compare them with the availability of electricity from primary and secondary generation sources and BESS and schedule the charging of the vehicles for maximum benefit.

Also, it won’t necessarily be just conventional energy resources charging EVs; other EVs can serve as energy sources using vehicle-to-grid (V2G) technology. With V2G technology, the utility can harness the energy storage potential of large numbers of EVs to avoid brownouts or blackouts and help make the grid more stable and resilient to the increasing integration of wind and solar power using frequency control techniques.

To the extent that EVSEs operate as DERs, they must meet the latest IEEE 1547-2018 standard that requires all DERs to be capable of frequency-watt control for over-frequency and under-frequency events.

Summary
EVSEs are more than just EV chargers. They include all the added grid infrastructure elements needed to support large-scale EV deployment. To realize the maximum long-term benefit from EVs, EVSEs must be integrated into the smart grid using V2G technology.

References
Analysis and Design of a Standalone Electric Vehicle Charging Station Supplied by Photovoltaic Energy, MDPI processes
Electric Vehicle Supply Equipment, Panduit
Electric Vehicle Supply Equipment/System, NEMA
Fast Grid Frequency Support from Distributed Energy Resources, National Renewal Energy Laboratory
Plug-in electric vehicles, GmastGrid.gov
What is EVSE?, Lectron