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BESS Energy Storage System — Structure & Composition

BESS (Battery Energy Storage System) consists of battery system, power conversion system, control system, and auxiliary system (BOS).

1. Battery Core System

·         Cell: Basic energy storage unit (usually LFP lithium iron phosphate).

·         Battery Module: Multiple cells connected in series/parallel with casing.

·         Battery Rack/Cabinet: Multiple modules assembled into a cabinet.

·         Battery Cluster: Multiple racks connected in series to form high-voltage DC.

2. BMS (Battery Management System)

·         BMU (Battery Module Unit): Monitors cell voltage and temperature.

·         BCU (Battery Cluster Unit): Manages a single battery cluster.

·         BMS Main Control: Coordinates all clusters, communicates with EMS/PCS.

·         Functions: Overcharge/overdischarge protection, thermal management, SOC/SOH estimation, cell balancing.

3. PCS (Power Conversion System)

·         Bidirectional AC/DC converter.

·         Charging: Converts grid AC to DC for batteries.

·         Discharging: Converts battery DC to AC for grid/loads.

·         Supports grid connection, off-grid operation, frequency and voltage regulation.

4. EMS (Energy Management System)

The “brain” of the system:

·         Controls charge/discharge strategy and power distribution.

·         Communicates with grid dispatch, BMS, PCS, and monitoring platform.

·         Real-time status monitoring, fault alarm, remote control.

5. BOS (Balance of System) Auxiliary Systems

·         Thermal Management: Air cooling or liquid cooling to maintain optimal temperature.

·         Fire Protection: Smoke detection, temperature sensing, clean agent fire suppression.

·         Power Distribution: AC switchgear, DC combiner cabinet, breakers, fuses, lightning protection.

·         Communication & Monitoring: Ethernet, Modbus, IEC 60870-5-104, sensors, cameras.

6. Typical Energy Flow

Charging Mode

Grid / PV / Wind → Transformer → Switchgear → PCS (AC→DC) → DC Combiner → Battery Clusters

Discharging Mode

Battery Clusters → DC Combiner → PCS (DC→AC) → Transformer → Grid / Load

7. Containerized BESS Layout

·         Battery Compartment: Battery clusters, BMU, BCU, cooling pipelines.

·         Electrical Compartment: PCS, DC/AC cabinets, transformer.

Auxiliary Compartment: Cooling unit, fire system, EMS host, UPS.