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BMW, Daimler and VW Propose Global e-mobility Standardization on Vehicle2Grid Communication, Harmonization of Chargers

26 September 2009

BMW, Daimler and VW are proposing a global OSI-Layer based standardization of smart charge communication. This diagram shows requirements and technologies mapped against the OSI 7-layer reference model for interoperability. Source: Oestreicher/Preuschoff/Bogenberger. Click to enlarge.

In a joint presentation at the California Air Resource Board ZEV Technology Symposium last week, BMW, Daimler and Volkswagen proposed global standardization for the e-mobility charging infrastructure, including one worldwide standard for smart charge communication, as well as a proposed pathway for harmonizing the two main standards for AC chargers and infrastructure.

Vehicle communications. Currently, there are two primary and parallel standardization efforts for vehicle to grid communications: a joint ISO/IEC working group and an EPRI/SAE effort. These could result, said Werner Preuschoff from Daimler, in two sets of standards, one ISO/IEC standard, and one SAE standard. “So which to implement, both of them? That’s a lot of effort.

Standards provide the basis for global harmonization. Source: Oestreicher/Preuschoff/Bogenberger. Click to enlarge.

Since the use cases are the same, there should be one common set of standards based on the ISO OSI seven-layer reference model for interoperability, the companies are suggesting. Basic needs are:

  • Optimized charging. This includes rid and energy mix optimized charging; improving battery life through intelligent charging; reliability (i.e., plug and charge not plug and pray); and customer defined end of charge to maximize vehicle availability.

  • Automatic payment and billing. This should entail a system oriented on well known mobile phone functionality, with a simple contract with an electricity supplier. It should support automatic billing and roaming.

  • Value added services. This should include safe and private payment through public/private key security; mobile access to important vehicle parameters (state of charge range, charging profile); and online tracking of contract/payment information.

Given existing APIs (application programing interfaces) between the different layers in the stack, Preuschoff said, one of the important things to be worked out is defining the application layer protocols specific to e-mobility. Separate implementations of different solutions, requiring action by both the auto OEMs and the utility companies, “will be a nightmare”, Preuschoff said.

What you need here is a worldwide standard defining down to bit and byte level what needs to be implemented on both sides. Hooking up the car to some kind of charge spot, exchanging information, specifying all the detail, making sure everybody’s implementation is correct and the same.

—Werner Preuschoff

Preuschoff noted that the first joint meeting between the ISO/IEC and the SAE groups was taking place last week, and that another meeting between the two major efforts was taking place this coming week.

Failure to establish worldwide standards might keep electric mobility from becoming mainstream, Preuschoff warned. If different technologies to be installed on vehicles to support regional standards, it increases the cost for achieving similar goals while delivering no added value for customers or the grid. Incompatible solutions highly limit an available low-cost charging infrastructure, and thus impose high market introduction hurdles for electric vehicles, he said.

If I want to have cheap charging spots, I want to have one single implementation.

—Werner Preuschoff

Chargers and infrastructure. Unlike the situation with vehicle to grid communications component of e-mobility infrastructure, there are already two primary AC charger standards emerging, said Ralf Oestreicher, also from Daimler: IEC 62-196-2 Type I (the Japanese/SAE J1772 proposal) and the IEC 62-196-2 Type II proposal (Europe).

Although there are fundamental differences between the two, there still is a potential pathway for harmonization, Oestreicher said.

Two Connector Standards
IEC 62-196-2 Type I
IEC 62-196-2 Type II
Maximum voltage 240V 480V
Maximum current 32A (80A in US) 63A (70A single phase)
Phases 1 1 to 3
Maximum power 7.2 kW (19.2 kW US) 49.9 kW
Interlock Mechanical latch on connector Electromechanical latch on socket
Control Pilot PWM signal PWM signal
Proximity Resistor in connector (also used to detect latch status) Resistor (also used to detect latch status)
Digital communication PLC PLC
Intended use Vehicle Vehicle/infrastructure

The European automakers and power companies started working on a charging strategy about 1.5 years ago, Oestreicher said. Based on their analysis, the came up with five primary customer requirements:

  • High density infrastructure for consumer confidence and more daily range given battery size. In other words, a more comprehensive network of charge points that could more quickly charge vehicle batteries could not only increase consumer confidence, but also reduce the requirements for “very, very big batteries” in electric vehicles.

  • High power to allow fast charging in critical situations.

  • High convenience to improve consumer acceptance and battery lifetime.

  • High reliability and safety.

  • Long-term viability.

Based on those requirements, they concluded that using on-board vehicle AC chargers capable of up to 43 kW for high power and high density was the best option. DC charging for them was only for a range-extension use-case, likely on highways. They opted for three phase power for charging beyond 7-10 kW to reduce cost, volume, and the weight of the charger and cable.

From physics, we felt that above a power level of about 7-10 kW, we should change from single phase to three phase. It’s just physics. You have a higher voltage, you have a constant power flow and you are increasing the power level of the charge with only a small penalty in cost or weight.

—Ralf Oestreicher

The same connector geometry supports both 1 and 3 phase charging, and all current levels. (Most of Southern Europe is single phase at home, Oestreicher noted.)

The Europeans are also opting for a loose Mode 3 cable to improve reliability and safety, given that maintenance, vandalism and theft could be problems for public charge points with attached cables.

The US and Japan are pursuing a solution optimized for single phase charging with permanently attached cables. However, Oestreicher noted, despite different geometries, both types of connectors can be used in the same system, as the signals to control the charging process have been harmonized.

By using Type II sockets instead of fixed cables on the charge spot, he suggested, loose mode 3 cables could be used to connect both Type I (Japan and US) and Type II (Europe) vehicles. The Type I vehicles could still use the J1772 connector on the vehicle, just with a loose cable. This could maintain the option to use three phase in the future.

Oestreicher also suggested that if all new single phase chargers were designed to be compatible with 277V phase to neutral instead of 240V, that would preserve the option to implement three phase in the future.

September 26, 2009 in Electric (Battery), Infrastructure, Smart charging | Permalink | Comments (9) | TrackBack (0)


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I know exactly how this will play out: SAE for North America and ISO for the rest of the World.

The mentioned Type II 480 V is limited to 49.9 kW to make the needed cable manageable. It will be too heavy and rigid if they went further with a 480 V charger. Still 49.9 kW can only charge about 100 miles or 25kWh in 30 minutes. This is no good when you need to visit family or go to your secondary residence both of which may be over 100 miles away or longer than the range of most of the EV vehicles that are coming to market soon.

One way to overcome this problem of limited charging power is to make a charging system that accommodates multiple simultaneous changing connections. Plug-in three of those 49.9 kW chargers and it will only take 10 minutes to charge 25 kWh or about 100 miles in a medium sized vehicle. Even better, use two 600 V chargers that deliver 75kW each. Such a charger could also be used for heavy duty vehicles that may need to connect up to 10 of these simultaneously to charge a very large battery. This is one charger that fits all vehicle types and therefore will be inexpensive to produce.

The idea about using a loose cable that you bring yourselves in the car is horrible. Such a cable will cost about 1000 dollars each and they will be stolen as soon as you leave your vehicle at a public service station. They also force you to connect two plugs one in each end for each cable you need to connect and you need to carry them in and out of your trunk. Hopeless.

Hopefully they make a scalable standard from the start by allowing for multiple 75kW, 600 V connections.


Even in America 95% of all trips are 40 miles or less. Those +100 miles trips your so worried about will happen less than 5% of the time so I'd say anyone planning to make a trip to grandma's house should start by actually doing some PLANNING and rent a trailer with a generator in it.

I think they should make the plugs compatible at the vehicle. And have the vehicle detect what voltage it is offered and charge accordingly.

The vehicle would default to a rather slow charge. If the owner wants a faster charge allow them to select it manually.

Henrik. Tesla owners report significant power lost to heat during charging. I have to believe that very fast charging is going to make that worse.

And I think it will be very bad for the batteries, at least those of today.

So I doubt that multiple charging cables into one vehicle is the way to go.

To all those EV advocates it is finally sinking in that the devil is in the details.

Those 5 to 30 trips that most people need to drive during the year and that are over 100 miles these are the trips that make them not want to buy an EV with a 100 miles range that can’t charge in less than ten minutes or swap the battery. It is irrelevant whether they only represent 5% of the annual miles driven.

If you can afford it you can solve the problem by getting an EV with over 200 miles range like the Model S or the BYD e6. Alternatively go for a PHEV such as the Volt that is almost zero emission with 230 mpg.

Going from a 100 miles EV to a 200 miles EV will add about 10000 USD to the price of the car. It should be less costly to add real 10 minutes fast charge to a 100 miles EV. The 100 mile fast charge battery will be more expensive because it needs, 1) fast charging C6 cells, 2) stronger power electronics, 3) a stronger cooling system to remove heat during charging and 4) thicker wiring. It will also be more complex and time consuming to test that such a fast charging system is durable enough for its purpose.

I think the only reason we have not yet seen an EV with real fast charge capability is that most vehicle producers prioritize to get their EVs to the market ASAP while it is still newsworthy to do so and then the more sophisticated features will have to wait for the second generation models. However, the standards for the charging infrastructure is decided today and they should accommodate the needs of tomorrow and this is why we need 600 V, 75kW chargers that scale by allowing for multiple simultaneous connections.

I think Henrik has pointed out clearly that EVs are not good for long range mobility (at present).

The solution is to have 2 cars - an EV and an ICE.

These could be combined into 1 car ( as in a PHEV ) or just 2 separate cars. (If you have 2 houses, you may as well have 2 cars).

Or you could have a rental / swap deal that comes with the EV.
[ You drive your EV to a station on the ring road and swap it for an ICE ]. You could be allowed N of these swaps / year (say 4-12) or M days of car swap.

Having 2 standards (one for the US, the other for Europe) would not be too bad - few people move their cars across the Atlantic (but loads of people cross borders within Europe).

It strikes me that the ability to charge from a 240V 8 KW domestic supply would be a very high priority (for night time charging).

Night time charging is what makes EVs a winner - if you can charge at night, you can level the daily electricity demand load. If you encourage people to charge at work (or during the day), you are making the electricity supply problem worse.

So the 240V domestic plug is KEY. (I see no reason why you cannot have both a high power and a domestic charger).

Henrik may have the best approach for large battery pack quick charges. Splitting a large battery pack into 3 or 6 modules could make 3-phase 600 volts quick charging practical and could tranfer 50+ Kwh in a few minutes, at specialized public charge stations.

Most, if not all, domestic slow charging stations could operate from single phase 220/240 VAC @ 50/60 Hz. Installing an electric dryer type outlet + a 20 to 40 Amps electronic timer in your garage is not a major challenge.

For very long trips, a PHEV may be the best/proper solution, at least until such times as BEVs and batteries have evolved enough to allow very quick charges.

I would still like to see modular upgrades in PHEVs and EVs. You buy a PHEV with maybe 10 miles of all electric range and you can upgrade in 10 mile increments later if needed. It is not a one size fits all approach when it comes to individual needs. I realize using packs of varying ages can cause problems, but if that can be worked out it might make the vehicle more attractive and create some after market business.

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