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Energy Storage System Operational States and Control Logic

 

The operational states and control logic of an energy storage system are critical to ensuring its efficient, safe, and stable operation. 

 

Taking a grid-connected energy storage system as an example, local control primarily handles system self-testing, device startup, PCS (Power Conversion System) power dispatch, alarm management, and fault protection. The workflow of the energy storage system is divided into :

7 main states:

1. Black Start

2. Power-On

3. Standby

4. Startup

5. Operation

6. Fault & Alarm

7. Shutdown

 

Black Start Phase:

- All internal equipment is in a shutdown state. 

- Control power and main power supplies are disconnected. 

 

Power-On Phase:

- The system achieves a "black start" using external power or an internal UPS (Uninterruptible Power Supply). 

- The local controller coordinates self-testing across major internal devices and waits for the main power circuit to energize. 

- Air conditioning and heating systems activate to create a suitable temperature environment for the batteries. 

- Once conditions are met, the system enters **Standby** mode, awaiting EMS (Energy Management System) or upper-level startup commands. 

Note: If using UPS power, operators must promptly connect the main power circuit to avoid UPS over-discharge or recharge the UPS via an external control power port. 

 

Standby Phase：

- The system maintains suitable internal temperatures. 

- Continuously monitors grid voltage, internal conditions, and device statuses. 

 

Startup Phase：

- The local controller receives an external startup command and sequentially: 

  - Activates battery voltage output. 

  - Establishes and verifies DC circuit voltage. 

  - Configures PCS operating modes. 

  - Initiates PCS operation. 

  - Engages transformer soft-start circuits (if applicable). 

  - Reports startup status and data to the EMS. 

 

Operation Phase：

- The local controller: 

  - Executes commands based on system operating modes. 

  - Monitors environmental conditions and system statuses. 

  - Collects, records, and uploads data. 

  - Manages human-machine interfaces. 

  - Adjusts PCS output power in real-time based on battery status and temperature. 

  - Coordinates power/current command corrections for parallel PCS groups (if applicable). 

 

Fault & Alarm Phase：

- Faults are classified into three severity levels: 

  1. Alarm: Non-critical issues (e.g., single battery cluster shutdown, PCS overtemperature, transient SPD alerts). 

     - The system continues operating but notifies operators or reduces power temporarily. 

     - Alarms may escalate to **Fault I** if unresolved within a set timeframe. 

  2. Fault I: Severe issues (e.g., widespread battery cluster failures, critical insulation faults, cooling system failures). 

     - PCS power ramps down to shutdown. 

     - DC/AC circuits disconnect. 

     - Battery outputs open at zero current. 

     - Auxiliary systems (e.g., cooling, fire protection) remain active. 

  3. Fault II: Critical emergencies (e.g., fire). 

     - Immediate full shutdown (equipment and power circuits). 

     - Maintains temporary communication to transmit temperature/pressure data. 

     - System enters **Black Start** state. 

 

Shutdown Phase:

- Two shutdown modes: 

  1. Shutdown I:

     - PCS stops grid-connected output. 

     - Batteries remain connected to the PCS DC side for rapid restart. 

  2. Shutdown II:

     - Full disconnection of PCS and batteries from AC/DC circuits. 

     - Auxiliary systems (cooling, fire protection) continue operating. 

 

Control Logic for Large-Scale Systems:

- A local controller may manage **n independent subsystems** (each with dedicated PCS and batteries). 

- Key responsibilities: 

  - Ensure total output meets EMS requirements. 

  - Allocate power between PCS units based on battery SOC (State of Charge). 

 

Notes: 

- Technical terms retained: PCS (Power Conversion System), EMS (Energy Management System), UPS (Uninterruptible Power Supply), SPD (Surge Protection Device).