GB/T 32895-2025Communication protocols for swapping battery pack of electric vehicle (English PDF)

4.1 The battery pack communication interface adopts CAN bus (including. CAN2.0 and

CAN FD), which is compatible with the communication network of the road vehicle control system, including.

a) The CAN communication interface between the charging device and the BMS (hereinafter referred to as "charging CAN"), whose communication network is based on CAN2.0B and uses extended frame requirements;

b) The CAN communication interface between the vehicle management system and the BMS (hereinafter referred to as "monitoring CAN"), whose communication network is based on CAN bus (including. CAN2.0 and CAN FD), using standard frames or extended frames.

4.2 When the charging CAN is used for communication interaction between the battery

pack and the battery swap station, the message meets the requirements of 9.1; when the monitoring CAN is used for communication interaction between the battery pack and the battery swap station, the message meets the requirements of 9.2.

4.3 The message format and content of charging CAN and monitoring CAN shall meet the relevant provisions of Appendix A and Appendix B.

4.4 After the battery pack is physically connected in the battery swap station and the BMS auxiliary power is powered on and awakened, it shall include two states. static monitoring state and charging and discharging state. The state transition of the battery pack in the battery swap station is shown in Figure 1.

4.5 Data transmission adopts the format of sending the low bit first. The positive current value represents discharge, whilst the negative current value represents charging.

4.6 The communication model between the battery pack and the battery swap station is divided into the physical layer, the data link layer, the application layer.

4.7 The battery pack can be used in combination of one box or multiple boxes. The network topology diagram is shown in Appendix C.

5.1 General requirements

The physical layer shall comply with the provisions on the physical layer in ISO 11898- 1, ISO 11898-2, ISO 11898-5, SAE J1939-11.The communication rate of CAN2.0 shall be no less than 250 kbit/s; the control segment of CAN FD shall be no less than 250 kbit/s; the data segment shall be no less than 1 Mbit/s.

5.2 Battery pack communication architecture

5.2.1 The battery pack has two independent communication CANs. one charging CAN

and one monitoring CAN. This method is defined as communication architecture I.

After the battery pack BMS wakes up, the battery pack and the battery swap station in the communication architecture I enter the static monitoring state and send static state message information through the monitoring CAN. In the charging and discharging state, the charging and discharging state message information is sent through the charging CAN; because the two CAN channels are independent, the monitoring CAN can continue to send messages in the charging and discharging state. The schematic diagram of communication architecture I is shown in Figure 2.

5.2.2 The battery pack has charging CAN and monitoring CAN functions through an

independent communication CAN. This method is defined as communication architecture II. The battery pack and battery swap station under communication architecture II enter the static monitoring state, after the battery pack BMS wakes up;

sends the static state message information through the CAN channel. If it enters the charging and discharging state, the charging and discharging state message information is sent through the CAN channel. The schematic diagram of communication architecture II is shown in Figure 3.

6.6 Message type

Supports 5 types of messages, namely command, request, broadcast/response, confirmation, group function. The specific definition complies with the provisions of message types in GB/T 27930.

7.7 When modifying the parameter group defined in this document, the definition of

the defined bytes or bits shall not be modified; the newly added parameters shall be related to the original parameters in the parameter group; irrelevant parameters shall not be added to the defined PGN to save the number of PGNs.

7.8 The definition of fault diagnosis complies with the requirements of the CAN bus diagnostic system in 5.1 of SAE J1939-73 2006.

7.9 The single-byte parameter setting of the invalid information unit shall be 0xFF; the double-byte parameter setting shall be 0xFFFF; the four-byte parameter setting shall be 0xFFFFFFFF.

8.1 Overall state transfer

8.1.1 A brief description of the overall state transfer of the battery pack in the battery swap station is as follows.

a) After the battery pack enters the battery swap station, the battery swap station plugs in the power connector for the battery pack to make a physical connection.

After the battery pack BMS auxiliary power is powered on, the BMS is awakened in the agreed manner. The battery swap station establishes a communication connection with the battery pack BMS; the battery pack enters the static monitoring state;

b) In the static monitoring state, the battery swap station needs to communicate and interact with the battery pack, to monitor the battery pack in the station;

c) In the static monitoring state, if the battery pack needs to be charged or discharged, the charging and discharging is started according to the process; the battery pack enters the charging and discharging state;

d) After the charging and discharging is completed, the battery pack re-enters the static monitoring state when it has not been swapped out of the station;

e) Thereafter, if the battery swap station needs to swap, the dormant battery pack BMS and auxiliary power need to be powered off; the battery pack enters the swappable state.

8.1.2 The overall state flow diagram of the battery pack in the battery swap station is shown in Figure 4.The overall state flow process of the battery pack in the battery swap station, such as static, charging, battery swapping, is shown in Appendix E.

9.1 Charging CAN message

Passenger cars or commercial vehicles use the charging CAN channel for communication interaction, when the battery pack is in static monitoring or charging and discharging state. The message format and content are shown in Appendix A; the start and end conditions of message sending are shown in Appendix F.

9.2 Monitoring CAN message

Passenger cars or commercial vehicles use the monitoring CAN channel for communication interaction when the battery pack is in static monitoring or charging and discharging state. Passenger cars are based on standard frames; the message format and content are shown in B.1.Commercial vehicles are based on extended frames; the message format and content are shown in B.2.