IEEE: PEV DC Fast Charging: Part 2

By Dave Tuttle and Ross Baldick


We discussed in the first article of our two-part series, that electric vehicles had the advantage of a much wider variety of locations that can provide refueling than even conventional vehicles.   Home, work, and public locations provide a far greater number of potential fueling (re-charging) points than the 168,000 gas stations (1) in the U.S.  While the vast majority of charging is presently performed at home overnight with low or modest rate AC charging, much higher charge rate fast charging like “AC-Fast Charging” (ACFC) or “DC-Fast Charging” (DCFC) may enable more high-utility applications.  This report specifically discusses DCFC which has the unique attribute of a direct connection to the DC leads of the vehicle battery for fast-rate charging.

Of the two types of plug-in electric vehicles (PEVs), DCFC is typically more associated with battery electric vehicles (BEVs) than plug-in hybrid electric vehicles (PHEVs) that incorporate a gasoline engine for range extension.  DCFC is typically thought to be most useful for BEVs in intercity travel, BEVs that drive a particularly large number of around-town miles every day (e.g. electric Taxis), or to support any kind of electric vehicle that may not be able to charge at home at night (e.g. multi-family housing residents or those who park on the street).  DCFC is associated with far faster charging rates than available in a home’s AC Level-1 or AC Level-2 in the attempt to approach the very rapid Mega-Watt equivalent energy transfer rate of gasoline/diesel refueling.  DCFC charge rates of 50 to 135kW+ require grid connections that are only typically available in commercial or industrial sites and not available in the typical home.

In Part 1 (2) of this 2 part series, the background of DCFC was explored.  In this article we will explore other considerations and the future of DCFC.

In the first section, we will describe the different charging rates and objectives presently associated with DCFC.  In the subsequent sections, some key DCFC considerations and the future DCFC directions will be explored.  Further in the article some key business model and grid implications will be described.

Different Charging Rates & Objectives: Bifurcation today

Today, there are fundamental differences in the service objectives between the highest rate ACFC and DCFC (e.g BYD & Tesla Superchargers (3)) and middle-rate DCFC (e.g.  CHAdeMO(4) or SAE Combo/CCS (5)).  BYD and Tesla are dedicated to BEV-only electric vehicle architectures without the gasoline engine backup incorporated in PHEVs to eliminate range anxiety.  Therefore, BYD and Tesla have used very large batteries (the BYD e6 Taxi battery is 60 kWh up to 537 kWh for the 60-foot Articulated Electric buses) and the highest charging-rate network to demonstrate the ability for their long-range vehicles to support 200 mile intercity and/or 24 hour inner-city daily travel  (such as an eTaxi would experience).  The high sales prices of Tesla vehicles in the premium market segment (and its luxury performance car competitors Mercedes, BMW, Audi, and Porsche) are better able to support the expensive large batteries needed for very long range, highest performance, and fastest DCFC rates.

Driving for more than 3 hours on the interstate and then recharging for 20-30 minutes at the very highest DCFC rates is conceptually on par with normal inter-city driving patterns when one considers the likely duration of a conventional vehicle interstate refueling stop taking into account time spent for stretching one’s legs, purchasing refreshments, or visiting the bathroom.

BEV manufacturers such as Nissan incorporated more modest sized (but still considerable) batteries to contain costs given they were targeting their vehicles at the more affordable mainstream vehicle market.  These present-day modest-range BEVs (80-100 mile range) are typically considered around-town commuters whose drivers should depend upon some other means of transportation for long trips between cities.  Understandably, this led companies like Nissan to focus their DCFC thrusts to support Intra-city charging for street-parkers or range extension of their BEVs beyond their 80-100 miles of range.  These smaller (~25kWh) batteries need only ~50kW to charge in about 30 minutes.

Given the different objectives, two dominant charge rates have become popular at this time.  BYD and Tesla Superchargers supporting up to 150 kW and the CHAdeMO or SAE Combo/CCS implementations of 50kW today.  Note that both CHAdeMO and SAE Combo/CCS standards have a 100kW maximum defined.  As battery prices decline, 200 mile range $30,000 BEVs will become “market viable” with such vehicles as the 2015 BYD e6-400, 2016 QIN-EV, 2017 Chevy Bolt or Tesla Model 3.  These larger batteries not only enable longer range but also faster charge rates and more flexibility in where or when to charge.  We see efforts by the different groups like BYD who are achieving maximum charge rates up to 200kW (with specifications up to 280kW, 480 VAC @ 600 Amp) to support charging a very large 85 kWh – 100 kWh battery to 80% State of Charge (SOC) in 30 minutes or less.

DCFC considerations

The vehicle manufacturers could not agree on a single DCFC standard in the U.S. so the industry presently has multiple cord types: CHAdeMO, SAE Combo/CCS, EU’s GB and Tesla’s.  The preferred solution for DCFC appears to have settled on “multi-standard” (Figure 1) and incorporate both the CCS and CHAdeMO standards (with possibly all three of the charge cord types in the future).  DCFC EVSE manufacturers have already announced multi-standard products that incorporate CHAdeMO and Combo/CCS.  Multi-standard DCFC manufacturers include ABB, IES, Fuji, Efacec, BTC Power, Eaton, Delta, and AV (6).  In addition, Tesla has announced a CHAdeMO to Tesla adapter.

Figure 1: Multi-Standard DC (and one AC) Fast Charging EVSE (6)

Additional charge cords on a single EVSE are not likely to be a large incremental cost as a percentage of the overall DCFC infrastructure investment.  The concept of multiple cords/pump handles is not new, nor specific to PEVs. Gasoline pumps many times have two to four pump handles (gasoline + diesel, or three grades of gasoline + diesel) attached to the same pump.  The significant cost for the fueling station is not the pump handle (or the charging cord + coupler), it is the cost related to the overall land and equipment purchase and installation, the transformer equipment required for high power transfer levels, and ongoing O&M costs.  Separate cord handles to support the three different standards is a relatively minor additional expense.

With the concept of Multi-standard DCFC electric vehicle supply equipment (EVSE) settled, the most important issues are less about the particular coupler standard, and far more related to finding attractive locations, more DCFC-enabled PEVs on U.S. roads, increasing the true maximum charge rate for most vehicles, and creating sustainable business models for DCFC charging stations.  Tesla provides some instructive examples with many of their inter-city Supercharger stations attractively located near popular bakeries, restaurants, coffee shops, and outlet shopping centers where drivers may easily find interesting activities to occupy their attention while their vehicle is charged for 30 minutes.

Standards Future directions

All three DCFC standards are relatively young.  Adopted by Nissan, Mitsubishi, Subaru, and Toyota, CHAdeMO is the most mature with the most DCFC enabled vehicles on the U.S.  highways (offered presently on the Nissan LEAF and Mitsubishi iMiev) and DCFC installations at this time.  Vehicles that have CHAdeMO ports for DCFC typically also have a SAE J1772 for AC Level-1 and Level-2 charging.  SAE J1772 Combo/CCS was more recently developed to create an upward compatible coupler from AC Level-2 to DCFC so only one charge port would be required on a vehicle.  Advocates claim a single vehicle charge port reduces cost, complexity, and the size of the door that covers the charge port.  A smaller charge port door also can increase flexibility of placement of the port on the vehicle.  The SAE Combo/CCS standard is supported by Audi, BMW, Daimler, Ford, GM, Porsche, and Volkswagen.

The Tesla standard introduced with the 2012 Model S is the newest and arguably the most refined.  Tesla participated in the SAE committee and leveraged insights from prior efforts.  The Tesla coupler is a sleek single design that supports AC Level-1, AC Level-2, as well as DCFC and deploys a communications protocol similar to the SAE J1772/IEC standard.  This protocol similarity enables a simple plastic adapter from SAE J1772 AC Level-2 (or Level-1) to a Tesla Model S for AC charging.   The BYD ACFC coupler is the China and European GB-connecter standard.

The support for developing and installing DCFC infrastructure are not equal across all vehicle manufacturers.  An important aspect to consider is the degree of commitment and the strategy of the various manufacturers to vehicle electrification.  The degree spans from Tesla and BYD who are solely dedicated to building electric vehicles to a few vehicle manufacturers who offer only “compliance car” PEVs to meet regulatory mandates in such states as California.

DCFC is mostly associated with BEVs.  PHEVs with a gasoline engine for long trips are typically believed to eliminate the need for DCFC.  Vehicle manufacturers who believe PHEVs are the most viable architecture will clearly have a different view of the priority of DCFC compared to, say, BYD and Tesla with their commitments to long range BEVs.  To the degree that PHEV architectures become dominant, DCFC may not be an infrastructure priority.  Over the past few years, some utilities aggressively installing charging infrastructure have purposely focused on AC Level-1 and AC Level-2 and avoided installing meaningful numbers of DCFC stations until there was better clarity in the DCFC standards and a greater number of PEVs that would use DCFC sold.  Where government agencies have influence, many have now begun requiring multi-standard DCFC equipment that supports both CHAdeMO and SAE Combo/CCS.

While both CHAdeMO and SAE groups have welcomed adoption by other parties that have previously advocated a different standard, there is no apparent move for CHAdeMO supporters such as Nissan or GB-ACFC supporters such as BYD to migrate to SAE Combo/CCS.  The SAE Combo/CCS supporters effectively rejected CHAdeMO and the GB standard before embarking on the creation of the upward compatible SAE Combo/CCS standard.  In addition, no vehicle manufacturer appears willing to abandon their existing standard to adopt the BYD or Tesla standards.  The vehicle manufacturers appear to have made their decisions on the standard they prefer for DCFC, equipment makers have created “Multi-standard” DCFC EVSEs with both CHAdeMO and SAE Combo/CCS cords for a modest incremental cost, and BYD and Tesla have created their own Supercharger networks exclusively for their customers as well as adapters to use other types of EVSEs.

There will likely be substantial regional variations across the world so the vehicle manufacturers will need to be capable in implementing all the standards.  While the physical couplers can be different, fortunately there are substantial technical similarities in many of the communications and safety attributes of the standards.

The DCFC Business Model and Grid Implications

In order to have a sustainable DCFC infrastructure, eventually there must be enough PEVs creating DCFC demand and the potential for unsubsidized positive profit margins for the charging stations.  The major fixed costs include the location acquisition, equipment, transformer or other grid distribution system connections, trenching, and installation labor.  Once installed, the actual fuel (i.e. electricity) costs can be a small percentage of the overall fixed plus non-fuel variable costs.  Demand charges that reimburse utilities for peak fixed cost distribution equipment investments to service maximum loads are based on kilo-Watt peak consumption and can be larger expenses than the per kWh energy charges for low capacity factor loads such as EVSEs(6).

Given the installation and demand charges are fixed costs, selling more DC fast charging sessions is important to increasing asset utilization in order to improve the profitability of the charging station.  While some additional costs may be incurred for the DCFC to be included in a charging network to enable reservations or easy payment, it would seem that with broad proliferation of DCFC in the future reservations may eventually not be necessary.  In the future, it is not clear why a drivers’ credit card would not also be used for payment as they are today for gasoline stations.

Gasoline stations purportedly make most of their profits from sales of non-gasoline items such as bottled water, chips, drinks, and tobacco (7).  They usually have fairly small profit margins on the sale of gasoline itself.  In a somewhat similar circumstance, a substantial challenge will be DCFC siting in locations that have attractive and compelling complementary retail, hospitality, sports or other activities.  The flexibility of placement of DCFC chargers without concern over buried gasoline storage tanks or provision for large semi-tractor trailer tanker truck deliveries enables a much greater degree of innovation on DCFC location placement.

In the future, once the number of DCFC enabled PEVs and DCFC stations substantially increase in the U.S. there may be the potential for DCFC charging stations to be as profitable as traditional gasoline stations.  PEV control software typically does not allow the vehicle to drive away while still connected to the charging cord, reducing the potential for equipment damage.  These charging stations also do not require groundwater or tank leakage detection methods nor many of the other safeguards or maintenance of traditional gasoline stations.  In addition, DCFC do not require an attendant.  Also, the ability to share the peak demand charges across another commercial building grid utility expenses may improve the economics further (8).

As battery or ultracapacitor energy storage costs continue to decline, utility demand charges may reduced by the DCFC deploying “behind the meter storage”.  This storage may also beneficially buffer the grid from substantial changes in charging load or to store intermittent renewable generation to be later used in PEV charging (9).


DCFC technology has progressed beyond the point where defining the coupler standard is the main impediment.  In the U.S., the three standards are defined and “multi-standard” charging stations can effectively support any of the DCFC standards with their multiple charge cords in a similar fashion to gas pumps that have multiple pump handles for different grades of gasoline or Diesel fuels.  The vehicle manufacturers of PEVs have the technical capability to fit any of the standards on their vehicles.  Their selection in the future will be more determined by compatibility with existing DCFC stations installed or corporate strategy.  The most important issues are asset utilization to provide positive profit margins for unsubsidized sustainable business models for DCFC stations, increasing the maximum DCFC charging rates, and more DCFC-enabled PEVs on the road.

DCFC is needed to support inter-city travel of pure BEVs (not PHEVs) and charging of PEVs owned by those drivers who must park on streets or residents of multi-family dwellings that do not have a charging station available where they live.  Unlike gasoline/diesel refueling stations whose only competition is only from other gasoline/diesel stations, DCFC competes with a wide variety of PEV refueling options including convenient overnight charging at home or workplace charging.

For street-parkers or residents of multi-family dwellings there will likely be a combination of solutions in the future.  Some of these include:  greater numbers of apartments/condos/townhomes that have power outlets or EVSEs available for resident’s PEV charging needs, AC Level-1 cords fed from streetlamps or ground lighting that have wireless revenue grade meters incorporated, wireless charging combined with autonomous vehicle capability, or perhaps battery swapping.

As battery prices continue to decline, BEVs with very large batteries and longer range will become available at mass market-viable prices.  These larger batteries not only enable longer range, but also support faster charge rates and more flexibility on where and when to charge.  While the BYD and Tesla architecture already supports up to 150kW charge rate, the CHAdeMO and SAE Combo/CCS standards organizations may need to update their standards to support up to or beyond 150kW charge rates to better accommodate BEVs with very large batteries in the future.

Just as the gasoline stations business model generally depends upon selling other items in addition to gasoline to be make attractive profit margins, new models for the placement of DCFC near other retail, hospitality, or sports locations will need to be developed.  Over time, there will progressively be more DCFC-capable PEVs and more DCFC stations, which together will provide an increasing sales volume of DCFC sessions and asset utilization.  Increasing DCFC charging session sales are needed to support long-term sustainable unsubsidized station businesses.


(1) How many gas stations are in the U.S.
(2) Tuttle, Dave, Plug-In-Hybrid Electric Vehicles DC Fast Charging: The Future Just Got More interesting,
(3) Tesla Superchargers,
(4) CHAdeMO,
(5) SAE Combo/CCS,
(6) EPRI, Electric Vehicle Infrastructure Working Counsel (IWC), Presentations, Day Two, March 26-27, 2014. and
(7) NPR: Gas Stations Profit from More than Just Gas, (
(8) Jim Francfort, U.S. Department of Energy’s Vehicle Technologies Program, EPRI/IWC 2013 – EV Project Charging Infrastructure Usage and Other Infrastructure Activities,
(9) J. Song, A. Toliyat, D. Tuttle, and A. Kwasinski, “A Rapid Charging Station with an Ultracapacitor
Energy Storage System for Plug-In Electrical Vehicles,” in Proc. ICEMS 2010, pp. 2003-2007,
Incheon, South Korea, October 10-13, 2010.


David Tuttle received the B.S. and M.Eng. degrees in Electrical Engineering with Highest Honors from the Speed Scientific School, University of Louisville, Louisville, KY. and the M.B.A. degree with the Dean’s Award from the University of Texas at Austin. He is currently a Research Fellow and Ph.D student in the Department of Electrical and Computer Engineering at the University of Texas at Austin. His current research interests are PEVs, Smartgrid, PEV interactions and synergies with the electric grid, and renewable energy.

Dave was one of the original designers and technical team leaders of the POWER1 microprocessor which launched IBM’s UNIX/RISC systems. He then led the joint Apple/IBM/Motorola team which designed the first PowerPC microprocessor that launched the Apple PowerMac and IBM PowerPC based systems. He went on to lead multiple R&D teams responsible for high speed fiber optic based adapters & switches, the POWER2-SC microprocessor (used in the 1997 IBM Deep Blue chess playing Supercomputer which beat World Chess Champion Garry Kasparov), and other advanced processors and systems. He later formed a design team for Sun Microsystems focused on power efficient multi-core/multi-thread microprocessor development. From 2006 to 2007 he was the team manager of the University of Texas DARPA Urban Challenge autonomous vehicle team and an adviser to the UT-Austin Mechanical Engineering Department of Energy/ChallengeX hybrid vehicle development team. Today, he is one of the researchers in Austin’s Pecan Street Consortium/University of Texas Plug-In Vehicle and Smartgrid research project.


Ross Baldick (F’07) received his B.Sc. in Mathematics and Physics and B.E. in Electrical Engineering from the University of Sydney, Australia and his M.S. and Ph.D. in Electrical Engineering and Computer Sciences in 1988 and 1990, respectively, from the University of California, Berkeley.  From 1991-1992 he was a post-doctoral fellow at the Lawrence Berkeley Laboratory.  In 1992 and 1993 he was an Assistant Professor at Worcester Polytechnic Institute.  He is currently a Professor in the Department of Electrical and Computer Engineering at The University of Texas at Austin.  Dr. Baldick is an IEEE Fellow.


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