Electric Vehicle Charging Technologies

EV Charging Technology Roadmap

• 2EVCT - Electric Vehicle Charging Technology

This is a Level 2 roadmap. Level 1 would be the technologies enabling zero-emission transport while Level 3 and 4 would include technologies enabling the charging of electric vehicles.

Roadmap Overview

Our chosen technology is that of charging energy storage devices using power from the grid. With the current technology, electric vehicles can be charged using a standard 120V outlet or a 240V industrial outlet. An electric vehicle usually has an onboard charger unit (OBC) which converts AC power into DC to store it in the high voltage battery. The vehicle accepts charge via a charge port where the user can insert the charging plug. The charging plug is a part of a wall-mounted (off-board) unit which is connected to the grid and supplies AC power to the vehicle when the vehicle is ready to accept charge. The user is usually responsible for initiating charging by connecting the vehicle to the off-board unit (EVSE) and optionally keying in a unique id to “unlock” the unit to provide charge. Recent advances in charging technologies have enabled DC fast charging which has resulted in faster charge rates and reduced charging times.

*image-source - https://www.verdemobility.com/charge.html

With today’s technology long-range EVs (200+ mile range) could take as high as 12+ hours to fully charge the battery pack using a regular home outlet. Fast charging technologies have also been developed which can bring the charge time down to a few hours (~2 hours), but these times are still significantly higher than the time needed to fill a fuel tank in a gasoline/ diesel vehicle and also warrant better cooling technologies to keep optimal battery thermal performance. With the battery cost ($ per KWh or $ per mile) decreasing, we could see a trend of bigger batteries / higher range vehicles being deployed, which would further increase the charging time. Hence, we feel the current technology would have to be advanced to be able to charge as fast as possible, thus reducing range anxiety.

Technology Hierarchy Tree

The following hierarchy shows the breakdown from L1 Technologies (Vehicle Electrification in general) to L2 - Technologies that need to be developed to achieve vehicle electrification. Further, The 2EVCT decomposes into different technologies that are developed to facilitate electric vehicle charging. L4 technologies are the technologies needed to develop the formal entities of products that enable electric vehicle charging.

DSM Allocation

The matrix below shows the allocation of technologies at various levels to enable vehicle electrification. The selected technology 2EVCT is shown as a part of the bigger 1VE technology DSM

Roadmap Model using OPM

We provide an Object-Process-Diagram (OPD) of the 2EVCT roadmap in the figure below. This diagram captures the main product, Its decomposition, and shows the process flow of achieving the desired function (in this case charging the battery pack).

In the charging technology, the EVSE (Electric Vehicle Service Equipment, a.k.a charging station) receives AC power from the grid and transports it to the vehicle's on-board charger. This onboard charger is responsible for converting AC power into DC power and storing it in the high voltage battery. The EVSE can be decomposed into the main charging station, the power lines from the charging station to the vehicle, and the plug that connects to the vehicle's charge port. The onboard charger comprises electronics to correct the power factor and to convert AC power into DC and stores it in a battery pack. It has an associated cooling system to maintain the thermal performance of the unit and mechanical housing to house all the electronics. The high voltage battery comprises of the battery management system, cells, sensors (voltage, current, temperature) along with the associated cooling assembly and mechanical housing to hold everything together. Below is an OPD representation of the system and the associated OPL.

2EVCT Figure of Merits

The table below shows a list of FOMs by which charging of electric vehicles can be quantified and compared

Figure of Merit	Units	Description
Charge Rate	[KW/hr]	Total energy/ power added to the battery per unit time
Charge Time	[Hrs]	Total time taken to fully charge the battery pack of known KWh capacity
Charge Efficiency	[%]	Percent of grid power that is stored in the battery
Cost to charge	[$]	Total electricity cost for a full charge cycle at a certain time of the day
Charge Power	[KW]	Power rating of the charger (This will determine the magnitude of DC current that the pack will be charged at)
Charge Level	[dimensionless]	L1 (120V AC), L2 (240V AC), L3 (Direct Current charging)
Charging Stations	[per mile]	Number of charging stations per mile
Pack Temperature Rise (normalized to pack size)	[degC/ KWhr]	Rise in temperature of the battery pack after charging is complete
Coolant Flow Rate	[gals/hr]	Flow rate required to keep maintain the rise in temperature below a predefined threshold
Power Factor	[%]	Ratio between real and reactive power consumption from the grid
Pack capacity degradation	[Ah per year]	Reduction in the capacity of the pack after a known number of years due to frequent fast charging