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Energy Storage Science Popularization (2)—”3S System”

The so-called “3S System” refers to the core components of an energy storage system: the Power Conversion System (PCS), Battery Management System (BMS), and Energy Management System (EMS).
The operational logic of the “3S System” is as follows: The battery pack feeds back status information to the BMS, which then shares it with the EMS and PCS. The EMS issues control commands to the PCS and BMS based on optimization and scheduling decisions, directing the energy storage battery to complete charging, discharging, and other tasks. The “3S System” works in close collaboration to ensure the safe, stable, and efficient operation of the energy storage system.
1.PCS (Power Conversion System)
The PCS, or Power Conversion System, is the core component that enables bidirectional power flow between the energy storage system and the grid. It controls the battery’s charging and discharging processes and performs AC/DC conversion.
Usually PCS products include:
Residential hybrid series: 3-12kW (battery system voltage 48V)
Residential hybrid series: 6-30kW (battery system voltage <1000V)
Commercial & industrial series: 100-125kW (battery system voltage <1000V)
Utility-scale series: 200-215kW (battery system voltage <1500V)
Advantages of Alicosolar 125kW PCS:

  • ① Fast response capability: Rated power switching time ≤100ms (actual test ≤50ms).
  • ② Multiple operation modes: Supports constant current, constant voltage, and constant power charging/discharging modes.
  • ③ High efficiency: Under self-powered mode within the operating temperature range, the charging/discharging efficiency at rated power is ≥98.0% (actual test ≥98.6%).
  • ④ Overload capacity: Capable of continuous operation at 110% rated current during both rectification and inversion processes.

2.BMS (Battery Management System)
The Battery Management System (BMS) primarily measures basic battery parameters such as voltage, current, and temperature to extend battery life. It also calculates and analyzes the battery’s State of Charge (SOC) and State of Health (SOH), manages charging/discharging to prevent overcharging/overdischarging, and reports abnormal conditions.
BMS typically has two structural types: two-tier topology and three-tier topology.
Three-tier structure breakdown:

  • | Bottom layer: Slave controller BMU (Battery Module Unit) manages individual battery cells. The BMU, consisting of battery monitoring chips and associated circuits, collects cell-level data, calculates SOC/SOH, performs active cell balancing, and reports anomalies to the master controller.
  • | Middle layer: Master controller BCU (Battery Control Unit) manages battery packs. Based on BMU data, the BCU executes control strategies, regulating charging/discharging processes (e.g., adjusting current/voltage, setting discharge cut-off voltage) and managing pack balancing.
  • | Top layer: Master controller BAU (Battery Array Unit) oversees the entire battery system. Integrating BMU and BCU functions, it performs advanced tasks like fault diagnosis, system state evaluation, and external communication with EMS/PCS to coordinate system operation.

3. EMS (Energy Management System)
The Energy Management System (EMS) is a hardware-software solution for monitoring, controlling, analyzing, and optimizing energy systems. It collects data from PCS, BMS, meters, fire protection systems, HVAC, etc., and manages energy dispatch to ensure orderly and stable operation.
EMS System Components
Typically divided into four layers:

  1. Device layer: Includes energy data acquisition (PCS, BMS).
  2. Communication layer: Covers links, protocols, and transmission.
  3. Information layer: Comprises caching middleware, databases, and servers.
  4. Application layer: Provides user interfaces (e.g., APP, WEB) for visualization and control.

General EMS Design Requirements

  • (1) Full connectivity: EMS must integrate diverse devices (BMS, PCS, HVAC, fire alarms, sensors, etc.) using multiple protocols to enable data-driven decision-making.
  • (2) Cloud-edge synergy: Ensures real-time, lossless data flow between on-site systems and cloud platforms for secure, bidirectional command transmission.
  • (3) Scalability: As commercial/industrial storage scales from 100kWh to tens of MWh, EMS must flexibly adapt to varying numbers of storage cabinets and PCS units for rapid deployment.
  • (4) Intelligent strategies: Supports peak shaving, load shifting, demand control, anti-reverse power flow, and dynamic capacity expansion, with customizable configurations for multi-transformer scenarios.

Summary
In energy storage systems:
BMS acts as the “sensory” layer, monitoring and protecting batteries.
PCS serves as the “executive” layer, managing power conversion.
EMS functions as the “decision-making” layer, orchestrating energy dispatch.
The three are indispensable and work synergistic-ally.