Protocol selection criteria: Layering + Data Rate + Distance (Source: SunLith); Golden Rule: CAN2.0B + MODBUS (Source: T/CPSS 1005); Core: Modbus (Universal) (Source: PJMotion); Note: Multi-layer protocol combinations (Source: SunLith).
I.
Layered Architecture
Cell Level: CAN Bus, SMBus (Source: SunLith); BMS Level: Modbus RTU, RS-485 (Source: SunLith); PCS Level: Modbus TCP, PROFINET (Source: SunLith); EMS Level: OPC UA, MQTT (Source: SunLith); Grid Level: IEC 61850, DNP3 (Source: SunLith)—Layers: Cell + BMS + Grid (Three-tier structure).
II. CAN vs. RS-485
Data Rate: CAN 1 Mbps (Source: dé);
Distance: RS-485 1,200 meters (Source: dé); Multi-master: CAN supports multi-master communication (Source: dé); Master-Slave: RS-485 uses master-slave architecture (Source: dé); Interference Immunity: CAN offers strong interference immunity (Source: EBYTE)—Comparison: 1 Mbps + 1,200 m + Multi-master capability (Three key differences).
III. Modbus General
RTU: Modbus RTU serial (Source: PJMotion); TCP: Modbus TCP Ethernet (Source: PJMotion); Free: Open-source, free, and universal (Source: PJMotion); Baud Rate: Stable at 19200/38400 (Source: vexenergy); Distance: Max 1200 meters for RTU (Source: vexenergy)—Modbus: RTU + TCP + Universal (three characteristics).
IV.
Industry Standards
CAN2.0B: BMS-to-PCS communication (Source: T/CPSS 1005); MODBUS: Serial communication protocol (Source: T/CPSS 1005); Physical Layer: CAN, RS-485, dry contact (Source: T/CPSS 1005); Byte: Least significant byte first (Source: T/CPSS 1005); 250k: Selectable 250/500 kbps (Source: DALY)—Standards: CAN2.0B + MODBUS + Physical Layer (three requirements).
V.
High-Speed Evolution
CAN FD: 5 Mbps data segment (Source: EBYTE); 64 Bytes: 64 bytes per frame (Source: EBYTE); EtherCAT: 100 Mbps, supports tens of thousands of nodes (Source: CSDN); Nanosecond: Nanosecond-level synchronization (Source: CSDN); Backbone: Inter-cluster backbone network (Source: CSDN)—Evolution: CAN FD + EtherCAT + Backbone (three directions).
VI. Scenario Selection
Long-distance: Choose RS485 for distances >40m (Source: insumenergy); Real-time: Choose CAN for sub-second SOC updates (Source: insumenergy); Noise: Choose CAN for environments with electrical noise (Source: insumenergy); Energy Storage: RS485 is commonly used for ESS (Source: Large Battery); Cloud Platform: MQTT for real-time data (Source: ElectricalTrader)—Scenario: Long-distance + Real-time + Cloud (three criteria).
VII.
Procurement Recommendations
First, determine the hierarchy (BMS/PCS/EMS); second, select the bus (CAN/RS485); third, align with standards (T/CPSS 1005); fourth, check the gateway (CAN-to-Ethernet);
fifth, verify safety (local encapsulation)—Protocol: Hierarchy + Bus + Standards (three core elements).
