Communication Protocols

Innovative solutions are becoming increasingly available to make electric mobility mass-market-capable. An important part of this is the charging technology. In this context, the term smart charging is used for charging systems of electric or hybrid vehicles according to standards like ISO 15118 and DIN SPEC 70121.

In this know-how section essential knowledge about communication protocols is presented.

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In order to achieve interoperability between the vehicle and the infrastructure, the standards IEC 61851, ISO 15118, DIN 70121 and VDV 261 exist. They specify the charging communication and ensure correct data exchange before and during the actual charging process.

Low-Level Communication

Pulse Width Modulation (PWM)

The PWM is used for low-level communication between the electric vehicle (EV) and the electric vehicle supply equipment (EVSE) . The signal voltages alternates between two defined levels.

+12 V State A No EV connected to the EVSE
+9 V State B EV connected to the EVSE, but not ready for charging
+6 V State C Connected and ready for charging, ventilation is not required
+3 V State D Connected, ready for charging and ventilation is required
+0 V State E Electrical short to earth on the controller of the EVSE, no power supply
-12 V State F EVSE is unavailable


The EVSE specifies the maximum charging current for the EV via the duty cycle. The PWM signal is applied to the circuit of control pilot. The standard IEC 61851-1 is defining the meaning of the applicable duty cycle values.

Duty cycle < 3 %  No charging allowed
3 % ≤ duty cycle ≤ 7 % Force high-level communication protocol according to ISO 15118 or DIN 70121
7 % < duty cycle< 8 % No charging allowed
8 % ≤ duty cycle< 10 % Max. current consumption for AC charging is 6 A
10 % ≤ duty cycle ≤ 85 % Available current = duty cycle * 0.6 A
85 % < duty cycle ≤ 96 % Available current = (duty cycle - 64) * 2.5 A
96 % < duty cycle ≤ 97 % Max. current consumption for AC charging is 80 A
Duty cycle > 97 % No charging allowed

High-Level Communication

Power Line Communication (PLC)

For the EVSE and EV communication IP-based protocols are used. PLC technology with a dedicated physical connection (CP, PE) is used for this purpose. In this system, the data stream is modulated onto the PWM signal. It is more familiar under the names Homeplug AV and IP-overpowerline in the consumer products field. In the vehicle’s charge control module, a Transmission Control Protocol / Internet Protocol (TCP/IP) stack is used for communication. 

  • PLC is used for high-level communication in CCS


Signal Level Attenuation Characterization (SLAC)

The SLAC mechanism of HomePlug Green PHY works according to the request/response method and it is compliant to ISO 15118-3 and DIN SPEC 70121.

First, the vehicle sends a broadcast message and any EVSE that received this message (cross-talk) computes the signal strength and sends it back to vehicle. Then SLAC ensures that the vehicle and EVSE are physically connected by measuring the attenuation: the EVSE with the highest received signal strength is defined as the correct EVSE. The vehicle and charging station agree on a unique identification feature that must be contained in all subsequent messages of the same SLAC session. The SLAC protocol is supported by AUTOSAR basic software components.


Controller Area Network (CAN)

CAN is a message-oriented multi-master protocol for quick serial data exchange between electronic control units in automotive engineering and factory automation.

  • CAN is used for high-level communication in DC GB/T and DC CHAdeMO

Value Added Services (VAS)

ISO 15118-2 does not define but leaves room for so-called Value-Added-Services. VAS comprise a transparent http connection, e.g. for remotely controlling a vehicle from the infrastructure during charging. The VAS is used by passenger cars and commercial EVs but there is no official specification. VDV 261 is a VAS defined for preheating and precooling public transportation buses.

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More Know-How

Electric Vehicle Charging Communication Know-How Chart in DIN A1 format, folded to DIN A4

Order the Vector Electric Vehicle Chart. The clearly structured Poster in DIN A1 format gives you important technical details on Charging Communication. Among other things, the unique poster illustrates the following topics:

  • Electric Charging Use Cases
  • Charging Methods
  • Charging Interfaces
  • Standards and Protocols
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