Inside a BESS system, Lithium-ion batteries store energy, but what determines their safety, longevity, and performance is a sophisticated electronic system: Battery Management System (BMS).
Often referred to as the “brain of the battery system”, the role of the BMS can also be imagined as a silent “bodyguard”, working non-stop 24/7. The BMS does not directly generate energy, but without it, the most expensive asset in the BESS system will quickly lose performance and face serious safety risks.
So, what does this bodyguard do? Let’s explore the four vital functions of a modern BMS.
1. Protection – The First Line of Defense
This is the most important task of the BMS. It acts as a smart circuit breaker, constantly monitoring and intervening to keep the battery cells operating within the Safe Operating Area (SOA). The BMS will proactively disconnect the battery from the system if it detects any of the following dangerous situations:
- Over Voltage Protection: Prevent overcharging the battery, which can lead to damage and heat loss.
- Under Voltage Protection: Prevent over-discharging the battery, which can cause irreversible damage to the battery's chemical structure.
- Over Current Protection: Protects the battery from excessive charging or discharging current, which may cause overheating and damage.
- Over Temperature Protection: Monitoring the temperature of battery cells and disconnecting them if they exceed safe thresholds is a core line of defense against thermal runaway.
2. Monitoring – Real-Time Data Collection
To provide effective protection, the BMS must continuously “measure the health” of the battery system. It uses sensors to monitor and record key parameters at the individual cell, module, and entire battery string levels, including:
- Voltage: Of each individual battery cell.
- Temperature: At various points in the battery modules.
- Current: Charging and discharging current of the entire system.
This data not only serves the protection function but also serves as an important input for more advanced functions.
3. Diagnosis & Estimation
From the raw data collected, BMS uses complex algorithms to calculate and estimate important battery states, providing a deeper insight into the “health” of the system:
- State of Charge (SoC): Estimates the percentage of energy remaining in the battery, similar to an electronic fuel tank.
- State of Health (SoH): Assesses the “aging” status of the battery, indicating its current maximum storage capacity compared to when it was new.
- Available Capacity (State of Power – SoP): Estimates the maximum charge/discharge capacity the battery can safely supply at the current time.
These parameters are extremely important for higher level Energy Management Systems (EMS) to make optimal operational decisions.
4. Communication
BMS does not operate alone. It is part of a larger ecosystem. The communication functionality allows BMS to:
- Data reporting: Send all important parameters and alarms to the central control system (EMS).
- Receive command: Receive control commands from the EMS, e.g. enable or disable the charger/inverter.
- Battery cell balancing: Controls the voltage balancing process between battery cells (will be explored further in another article).
A BESS without a BMS is like a car without brakes, a dashboard, or a radiator. The four core functions – Protection, Monitoring, Diagnosis, and Communication – of the BMS work together to form a secure and intelligent management network, ensuring that your valuable battery assets are operated in the safest, most efficient, and most durable way possible.
