BMW, Daimler and VW Propose Global e-mobility Standardization on Vehicle2Grid Communication, Harmonization of Chargers
26 September 2009
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 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)|
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.
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.
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