Internal Communication Methods in Energy Storage Systems: RS485, CAN Bus, and Ethernet

Efficient internal communication within energy storage systems (ESS) is critical for ensuring stable operation, optimal performance, and safety management. Various communication methods are utilized to facilitate seamless data exchange between different system components, including low-speed serial interfaces like RS485, CAN bus interfaces, and Ethernet communication interfaces.

### 1. Low-Speed Serial Interface (RS485)

RS485, a widely-adopted industrial communication standard, is especially popular due to its reliability, improved transmission speed, and strong resistance to interference. This interface operates primarily in a master-slave mode, allowing only one device to transmit data at any given moment while others receive signals. In energy storage systems, RS485 utilizes a polling mechanism controlled by a master device, with the bus operating in a half-duplex mode.

Design considerations are essential to mitigate interference in complex electrical environments typical in ESS. Twisted-pair shielded cables are recommended for their superior noise resistance. RS485 communication typically uses linear topology (daisy chain), significantly reducing signal reflection risks compared to star or tree topologies. For bus lengths exceeding 300 meters or to prevent reflections, termination resistors of approximately 120Ω are connected at both ends of the cable. Proper grounding and single-point shielding are also advised to protect interfaces from damage.

### 2. CAN Bus Interface

The Controller Area Network (CAN) bus is another crucial internal communication method in ESS, initially developed by BOSCH and widely applied in automotive and industrial sectors. CAN bus offers significant advantages over RS485, including multi-master capabilities, real-time performance, and robust error detection.

Unlike RS485’s master-slave structure, CAN bus facilitates simultaneous multi-point, full-duplex communication. Nodes compete using bitwise arbitration for bus access, ensuring high data integrity and reliability. CAN bus communication complies with ISO 11898 for high-speed communication (125kbit/s–1Mbit/s, max 40m) and ISO 11519 for low-speed applications (5–125kbit/s, max 10km).

For optimal reliability, CAN bus systems utilize twisted-pair shielded cables with a characteristic impedance of around 120Ω. Linear (daisy chain) topology is most common, with termination resistors installed at both ends. Tree topologies, though easier to manage, require very short branches to maintain signal integrity. Star topologies necessitate precise cable lengths or specialized CAN hubs.

### 3. Ethernet Communication Interface

Ethernet interfaces, standardized by IEC(60)603-7, are integral to modern ESS, supporting high-speed and extensive data exchange requirements. Ethernet interfaces comprise Media Access Controllers (MAC), typically integrated into CPUs, and Physical Layer Transceivers (PHY) as separate chips.

Due to Ethernet’s sensitivity to electromagnetic interference (EMI), specific cable placement guidelines outlined in GB 50311—2016 standards must be followed. Adequate distances from electrical machinery like transformers or motors are essential for data integrity.

Ethernet interfaces in ESS typically support Modbus and IEC104 protocols, enabling communication with Power Conversion Systems (PCS), internal monitoring devices, and external systems such as SCADA or grid dispatch systems.

In conclusion, understanding the specifics of RS485, CAN bus, and Ethernet communication methods helps optimize energy storage system management, ensuring efficient, safe, and reliable operation.

---