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Chinese Protocol for Communication Between Chargers and Electric Vehicles
GB/T 27930 is the Chinese standard for electric vehicle battery charging. Other charging systems include the Combined Charging System (CCS) favored by European and American manufacturers, the CHAdeMO charging standard developed by a Japanese industrial consortium and Tesla’s Supercharger.
The GB/T 27930 charging standard for cable and conductive charging developed in China is suitable for both electric vehicles (EV) and hybrid electric vehicles (HEV) alike. The GB standard (Guobiao, or “national standard” in Chinese) was published by the China Electricity Council (CEC). A separate specification for inductive or wireless charging was published by the CEC as GB/T 38775.
Cable charging standard GB/T 27930 is based on the SAE J1939 network protocol and uses the CAN bus with a point-to-point connection between the charger and the battery management system (BMS).
- Uses the CAN bus
- J1939-based protocol
- Primary CAN baud rate of 250 kbit/s with reduction down to 50 kbit/s possible
- Only two participants at a time – a charger and a BMS in the vehicle – with fixed addresses:
- 86 (56h) for the charger
- 244 (F4h) for the BMS
- No direct connections to other CAN systems in the vehicle, such as the power train CAN.
- Diagnostic options: Six diagnostic messages – DM1 through DM6 – are defined (not compatible with SAE J1939).
GB/T 27930 – Based on SAE J1939
The current version of the standard is GB/T 27930-2015 from 2015, which replaced version GB/T 27930-2011. GB/T 27930 is based on SAE J1939 and uses a CAN bus accordingly, but this is just a point-to-point connection between the charger and the BMS. There are no direct connections to other CAN systems in the vehicle, such as the power train CAN.
|Based on SAE J1939|
|CAN ID||Consisting of the priority, PGN, SA and DA.|
|Transport Protocol||DA-specific data transfer only also known as RTS/CTS or CMDT (see SAE J1939-21).|
|Network Management||Nodes are identified by their addresses: |
- Charger: 86 (56h)
- BMS: 244 (F4h)
|Baud Rate||Default transfer rate: 250 kbit/s.|
|Diagnostic Messages||Names of the diagnostic messages: DM1 through DM6 .|
|DTC||Consisting of the SPN, FMI and OC.|
GB/T 27930 and SAE J1939 – Differences at a Glance
Despite being heavily based on SAE J1939, a few significant differences have to be taken into account, such as there being no address arbitration with GB/T 27930 according to SAE J1939-81. As a result, parameter groups for address claiming, commanded address and name management are not defined. This is logical and consistent, as the charger and vehicle are always the only participants involved when it comes to charging communication. The specification clearly defines their addresses: 86 (56h) for the charger and 244 (F4h) for the BMS. As the Request mechanism of SAE J1939-21 is used solely for diagnostics, neither the ACKN (PGN E800h) nor Request2 (PGN C900h) nor Transfer (PGN CA00h) parameter group is present.
We recommend using caution when it comes to diagnostic messages – GB/T 27930 uses the designations DM1 through DM6 and packs the information on arising problems into DTC (diagnostic trouble code) blocks as described in SAE J1939-73, but this is where the similarities end. Unlike names, parameter group numbers (PGNs) are defined differently from J1939 and the DTCs do not start with byte 3, but rather byte 1.
|Difference from SAE J1939|
|CAN ID||No variations for priority, source address (SA) or destination address (DA).|
|DLC||Messages with message lengths (DLCs) shorter than eight are allowed.|
|Transport Protocol||No BAM.|
Dynamic address changing is not possible, and no AC, NM or CA is defined.
If the line quality is poor or external interference fields are influencing communication, a reduction from 250 kbit/s to 50 kbit/s is permissible.
A baud rate of 500 kbit/s is not defined.
|Message Definition||Defined differently than in the J1939 Digital Annex.|
|Diagnostic Messages||IDM1 through DM6 are defined differently than in J1939-73. DTCs do not start with byte 3 as described in J1939-73, but with byte 1 instead.|
|DTC||SPN and FMI are defined differently than in J1939-73 and the J1939 Digital Annex.|
GB/T 27930 – Comparison of Versions 2011 and 2015
The current version of the standard is GB/T 27930-2015 from 2015, which replaced version GB/T 27930-2011. In addition to editorial changes, GB/T 27930-2015 differs from the preceding version in terms of the following technical modifications:
|GB/T 27930-2011||GB/T 27930-2015|
|New Message Type||—||CHM, BHM|
|J1939 Priority||Priority 6 for:|
RM, BCP, BCS, BMV, BMT and BSP
Priority 7 for:
BRM, BCP, BCS, BMV, BMT and BSP
|Message Period||1 s for|
BMV, BMT and BSP
|10 s for|
BMV, BMT and BSP
|– BRM Length||41 Byte||49 Byte|
|– BCP: SPN2822||Total voltage||Current voltage|
|– BST: SPN3511||3 suspending reasons||4 suspending reasons.|
- “charger actively suspends”
|– BST: SPN3512||6 suspending reasons|
8 suspending reasons.
|– CRM: SPN2561||Length: 1 Byte||Length: 4 Byte|
|– CRM: SPN2562||Length: 6 Byte, optional||Length: 3 Byte, mandatory|
|– CCS Length||6 Byte||8 Byte|
|– CCS: SPN3929||Not defined||Mandatory|
|– CSD Length||5 Byte||8 Byte|
|– CSD: SPN3613||1 Byte||4 Byte|
|– CML Length||6 Byte||8 Byte|
|– CML: SPN2827||Not defined||Mandatory|
|– BCL||100 ms||1 s|
|– BCS||—||5 s|
|– CCS||100 ms||1 s|
Charging communication primarily involves both the battery management system and the charger agreeing on the power requirements of the vehicle and both the amperages and voltages used during charging, as well as monitoring the charging process. With the GB/T-27930 protocol, communication is divided into the following phases during the charging process:
1) Handshake Initiation
The first phase of communication is started once the charger and vehicle are connected with the charging cable. The charging process has not yet begun at this point, i.e. current is not flowing. The connection is checked, and the vehicle informs the charger of the maximum permissible charging voltage.
2) Handshake Recognition
In the handshake recognition phase, the charger connection check is completed and general information such as the protocol version and vehicle information (battery type, vehicle identification number etc.) is exchanged.
3) Parameter Configuration
In the parameter configuration phase, the parameters of the charging process are negotiated. The vehicle informs the charger of the permissible amperage and voltage. The charger informs the vehicle of the available amperage and charging voltage.
If the requirements of the vehicle can be met by the charger, the charging process is started in the charging phase and the battery is charged. During the charging process, the vehicle informs the charger of the current charge status of the battery at regular intervals.
5) Suspension of Charging
In the suspension of charging phase, either side can terminate the charging process. Reasons for this can include the battery being fully charged or a fault occurring during the charging process.
6) End of Charging
In the end of charging phase, the charging process is terminated and the charger stops outputting power.
In each phase of charging communication, the charging process can be terminated in case of a fault. The charger then has the option of restarting the charging process.
Phases 1 Through 4:
Messages and Status Transitions
Phases 1, 2, 3, 5 and 6 work according to the same principle. Participant 1 begins by sending a data record, e.g. a CHM (charger handshake message). Participant 2 then receives the CHM and carries out the corresponding action, e.g. by checking the connection. To signal that it has successfully carried out the action, participant 2 begins sending a BHM (BMS handshake message) to participant 1. As soon as participant 1 has received the BHM, it starts the corresponding action on its part and checks compatibility, for example. Once the task is complete, it begins sending another message. The procedure is like a soccer game in that two players reach the opponent’s goal or target by continually passing the ball back and forth to one another (Figure 3).
Phases 4 Through 6:
Messages During the Power Transfer
In phase 4, the actual charging process, communication is considerably clearer, as status transitions no longer occur. BMS and Charger send their messages to each other cyclically and independently.
The vehicle initiates the charging process. The vehicle sends the requirements to the charger using the BCL (battery charging demand) message and informs it of its own status using the BCS (overall battery charging status) and BSM (power storage battery status information) messages. There are also three optional messages with which the vehicle can provide additional information on its internal status to the charger while charging: single power storage battery voltage (BMV), temperature of power storage battery (BMT) and reserved message of power storage battery (BSP).
The charger, on the other hand, sends the CCS (charger’s charging status) message and informs the vehicle of its status, the current being provided and the maximum voltage which can be generated.
The charging process lasts until either the battery management system or the charger initiates the end of charging. This happens either when the battery is fully charged, the specified charging duration is reached or the passengers wish to continue traveling without a fully charged battery (Figure 4).
These errors are general in nature and can occur during any phase of the process. This is why the procedure is always the same. The participant which identifies such an error stops its regular bus communication and power output (charger) or power intake (BMS). Instead, it begins cyclically sending the corresponding error message (the charger uses the CEM message, and the BMS uses the BEM message). The other participant must respond accordingly and stop its communication as well.
Faults of this type can actually only occur in the charging phase. They are reported as a regular request to terminate the charging process and are treated accordingly (Figure 4). The fault causing the message is reported in the corresponding suspending message here (CST for chargers, and BST for the BMS).
Conformity and Interoperability Tests
Test Specification GB/T 34658
Closely associated with GB/T 27930 is another standard which describes the testing of a BMS and charger: GB/T 34658. This includes definitions of a total of 85 test cases (42 for the BMS and 43 for the charger) structured according to the following scheme:
- First, the test hardware (either the BMS or the charger) is tested under optimum conditions. The testing system operates strictly according to the specifications of the GB/T 27930 standard, where all messages are sent in the correct format and with the correct cycle time, all transferred information is valid, all status transitions occur at the right time. For its part, the test hardware must change its status at the right time and send suitable messages in a correct format and with the correct cycle time. There is always a suitable test case for each status change: 14 for the BMS and 15 for the charger.
- Following this, a test is carried out to determine whether a protocol violation was correctly identified and signaled by the test hardware. Possible violations include, among other things:
- Incorrect cycle time of a specific message
- Premature or delayed status change
- Messages with inconsistent contents
To pass this test, the test hardware only needs to identify the deviation from the standard as a fault if the deviation exceeds a threshold defined in the standard. Ignoring a violation is also identified as a fault, just like switching to fault mode too quickly. There are 28 test cases for both the BMS and the charger here.
Chaoji: Harmonization of the Japanese CHAdeMO Charging Standard and the Chinese GB/T Standard
In 2018, cooperation on development of a new charging standard called ChaoJi was announced by the publishers of the two national standards: CHAdeMO by the CHAdeMO Association in Japan, and GB/T 27930 by the China Electricity Council (CEC) in China.
The goal of the new standard is secure, versatile and rapid charging technology (up to 900 kW) using a standardized charging protocol and standardized physical infrastructure.
In the first step, a new connecting plug is being developed. Using adapters, it must also be possible to charge vehicles which only support the CHAdeMO or GB/T standard at ChaoJi chargers.
The CHAdeMO and GB/T 27930 communication protocols will both continue to be supported for the time being. Version 3.0 of CHAdeMO, which contains protocol enhancements for negotiation of the charging protocol to be used (CHAdeMO or GB/T 27930) with a ChaoJi charger, has been published. A new version of the GB/T-27930 specification with modifications for ChaoJi is expected in 2021. There are plans for a new, standardized charging protocol, but it will not be implemented until later on so as to ensure backward compatibility with existing vehicles.
Charging Communication in Chinese
Developing and Testing GB/T-27930-compliant Electric Vehicles and Chargers
Electric mobility plays an important role in China in particular, as an ever-increasing number of vehicles on the streets there are electric. This requires the availability of extensive charging infrastructure. Standards like GB/T 27930 are necessary for ensuring that electric vehicles and chargers can communicate reliably with one another.