The dc communication protocol between the electric vehicle (EV) and the electric vehicle supply equipment (EVSE) occurs with the support of digital communication. This FAQ will discuss the two types of dc communication for proper EV charging.
The signal pins inside the EV charger connectors convey the necessary information when charging occurs. Such communication can be of two types:
1. Low-level communication
2. High-level communication
Both types of communication are governed by well-known standards such as IEC 61851, ISO 15118, and DIN 70121. Figure 1 shows the classification and the associated features of the communication types.
Figure 1. A control pilot circuit as per IEC 61851-1. (Image: Vector)
What is low-level communication in EV charging?
Low-level communication is the basic connectivity between the EV and the EVSE. During this communication, safety checks are carried out, such as the maximum current limit and the EV’s charging state.
As per the IEC 61851 standards, signal voltages are used as a reference to identify the different EV charging states. The various reference voltages are generated using the pulse width modulation (PWM) technique.
Any EV charging connector will have a control pilot (CP) and a proximity pilot (PP) pins for communication purposes. Figure 2 shows a CP circuit between the EV and the EVSE. Depending on the status of the switch S1 and the associated PWM of S1, the various EV charging states (A to F) are decided.
Figure 2. A control pilot circuit as per IEC 61851-1. (Image: MDPI)
- State A refers to no connection between the EV and EVSE. The voltage at the pilot contact, as seen in Figure 2, is now fixed at +12 V.
- State B is when the switch S1 is operated at a PWM duty cycle such that the pilot contact voltage is +9 V. This state represents that the EV and EVSE are connected. However, the EV is not ready for charging.
- State C refers to the EV’s readiness to charge, but ventilation is not required. The voltage at the pilot contact is +6 V.
- State D is similar to the earlier state, but ventilation is required now. The pilot contact voltage reduces to +3 V.
- State E denotes +0V at the pilot contact, signaling an electrical short to earth. During this state, no power supply is provided to the EV.
- State F is the last of the states that refer to the unavailability of EVSE. At this point, the pilot contact carries a -12 V supply.
What is high-level communication in EV charging?
High-level communication is advanced and more complex than low-level communication. Rather than merely depending on a voltage reference, this communication involves data exchange to control and optimize the charging sessions.
High-level communications can take place in three ways in an EV charging session:
1. Power Line Communication (PLC): uses a Transmission Control Protocol (TCP) or an Internet Protocol (IP) for communication within the various subsystems of an EV. This type of communication can be observed in the CCS1 and CCS2 connections.
The advantage of PLC is that the existing power lines can be used to transmit the data. Therefore, information can be passed on through the same medium as the power is transmitted. Such an arrangement helps reduce costs and reduce the overall weight of EVs.
2. Controller Area Network (CAN): has found its application in EVs from the mid-1980s when Bosch introduced it. This protocol allows communication between the microcontrollers and devices in the EV without using a dedicated computer. CAN is used mainly in the dc GB/T and dc CHAdeMO.
3. Signal Level Attenuation Characteristics (SLAC): is commonly used when multiple EVs are charging at a common charging point, such as fleet electrification and commercial parking space. The protocol works based on a request-response process and ensures no crosstalk when multiple EVs charge simultaneously.
Summary
Dc charging is more complex than it looks when connecting the EV and EVSE for vehicle charging. The communication protocols are streamlined for this purpose and should be respected. For higher levels of EV charging, such as level 3, both types of communication protocol work in tandem to successfully charge an EV. PLC continues to be the preferred way of high-level communication, but it would be interesting to see how the other two take direction.
References
- The Electrical Vehicle Simulator for Charging Station in Mode3 of IEC61851-1 Standard, MDPI
- DC Charging: A complete guide to hardware, Heliox
- Communication Protocols, Vector
- Optimization of a Power Line Communication System to Manage Electric Vehicle Charging Stations in a Smart Grid, MDPI
- CAN Protocol: Understanding the controller area network, Engineers Garage
Images
Filed Under: Charging, FAQs