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Plug-In 2010: Two Solutions for DC Fast Charging of EVs

DC fast charging is the Holy Grail for eliminating range anxiety in pure battery electric vehicles.  It has the promise of permitting you to charge 80 miles of range on the Leaf in less than 30 minutes.  So, to the extent that these beasts are accessible out on the road, you will be able to drive farther, and recover when you forget to plug-in.  Also, they open the EV market to folks who cannot charge at home or work, including the millions of urban dwellers for whom an EV could be ideal.  No matter how big the battery, there are cases where access to a DC fast charger will be valuable. 

Well, it turns out there are two incompatible standards emerging for DC fast chargers.  There were some sessions in the Plug-in 2010 conference in San Jose this week that added clarity to these two alternatives.

One standard is the called CHAdeMO, which comes out of Japan.  CHAdeMO receptacles will be included or optional on the Nissan Leaf and Mitsubishi iMiEV.  All of the Japanese vehicle OEMs are members of the CHAdeMO Association.  Many CHAdeMO chargers have been deployed in Japan, and one has been deployed in the United States.  The upcoming EVProject deployment that is supported by $115M in federal subsidy will include 310 DC fast chargers.  Since only CHAdeMO chargers are available today, and since the Leaf is part of the project, all of the 310 units will probably be CHAdeMO type.

The other standard is an enhancement under study to the existing AC charging standard, SAE J1772-2009.  Now that the this existing AC standard is widely accepted for all vehicles targeted for the United States, the SAE has shifted focus toward modifying it to also accommodate DC charging .  This DC enhancement is still emerging, and therefore has not been implemented on any vehicles or charges yet.

At Plug-In 2010, SAE publicly proposed the “Combo Charging Connector” concept.  It defines the outline geometry for the AC core and also for the DC extension.  The AC core in North America and Japan would be based on the existing J1772-2009 layout for AC.  The AC core in Europe would use the layout based on a connector design from Mennekes.  The inclusion of the DC extension is optional, and if included, will be universal across all regions.  It is interesting that the chair of SAE is Mr. Gery Kissel of GM.  Also, there was a separate presentation by Daimler that supported Mr. Kissel’s position.  Finally, Mark Duvall of the Electric Power Research Institute appeared to also support Mr. Kissel.

Mr. Kissel stated that a key advantage of the J1772 combo connector proposal is that a single connector can support both AC and DC, and this reduces confusion for the driver.  Also, the combo connector requires less space on the vehicle.  The combo connector camp emphasized backward compatibility with the current AC standards in that a vehicle equipped with a combo connector receptacle may be AC charged from a J1772-2009 EVSE that does not have the DC extension.

Tokyo Electric Power Company (TEPCO) is an executive member of the CHAdeMO Association.  In a presentation by Mr. Takafumi Anegawa of TEPCO the point was made that CHAdeMO is not only finalized, but that many CHAdeMO compliant vehicles and chargers have been built and deployed.  Usage data based on these chargers has been gathered and analyzed to the benefit of the EV community.  Mr. Anegawa stated that keeping the AC and DC receptacles separate has the advantage of permitting the vehicle OEM to place each receptacle in a location optimum for each charging scenario.  For example, the DC receptacle may be located as close as possible to the battery to reduce the length of heavy and expensive cabling needed to support the high currents of a fast charger.  But the AC receptacle might be better located elsewhere for easy in-garage charging.  Of course a vehicle equipped with a CHAdeMO receptacle may also contain a separate J1772-2009 receptacle, and so may be AC charged from a J1772-2009 EVSE.

David Patterson of Mitsubishi emerged from the audience during one of the sessions to reiterate that CHAdeMO chargers and vehicles have been in use in Japan already and so there is no reason to propose another standard.  He said that one of the key learnings from the early deployment is that use of CHAdeMO can improve battery cycle life compared to typical Level 2 AC charging.  He asserted this because typically Level 2 AC charging is performed to 100% of the battery capacity, whereas CHAdeMO is performed to 80% of the capacity to reduce heat stress on the battery.

Developments in the next 12 months will determine which standard becomes dominant in the United States.  If sufficient Leaf and CHAdeMO charger deployments occur, then CHAdeMO can become a de facto standard.  On the other hand, if SAE finalizes the combo connector quickly, and if a major OEM such as GM or Ford rolls out vehicles with the combo connector soon, then it might displace CHAdeMO.  Ironically, GM is leading the standardization effort for this combo connector, but their upcoming Volt does not have (or critically need) a DC fast charging port because GM included a gas engine for extending range.  So, Ford’s early support of the combo connector is probably key if SAE is to have its way.

The development of two competing standards is actually good for the EV industry in that it proves that OEMs have raised the stakes because they realize market penetration of EVs will be significant.  Indeed it will be fascinating to track DC fast charging over the next 12 months.

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