Battery energy storage stations have become important measures to solve problems such as peak shaving and valley filling, new energy consumption, and peak load regulation due to their short construction period and rapid response. In order to ensure the battery safety, reliability, and cycle life of large-scale battery energy storage stations, it is necessary to conduct in-depth research on battery management system technology.
Subsystem debugging
The battery energy storage station has multiple subsystems according to different functions, including battery energy storage subsystem, relay protection and safety automatic device subsystem, clock synchronization subsystem, integrated AC/DC power supply subsystem, energy storage station auxiliary monitoring subsystem, measurement subsystem, telecontrol communication subsystem, and secondary safety protection subsystem. Among them, the battery energy storage subsystem, composed of batteries, BMS, PCS, and EMS, is the core component of the battery energy storage station.
System debugging
After the functions of various subsystems of the battery energy storage station are verified correctly and communication debugging with the dispatch main station at all levels is completed, it is still necessary to carry out the line fiber differential protection joint debugging test for the connection of the energy storage station and the access to the grid point of the substation as a safety guarantee for the system debugging of the battery energy storage station to access the power grid.
The battery management system mainly has two operating modes: automatic operation mode and maintenance mode. In automatic operation mode, based on the battery cluster status of the subordinate BCU, BAU automatically controls the closing and opening.
Detection of total voltage difference when powered on
When BAU is detected to be in place, the total voltage difference is judged. When the voltage difference between the maximum total voltage and the minimum total voltage of the battery pack is less than the allowed maximum total voltage difference for the battery pack, BMS judges that all the installed battery packs have small voltage difference and meet the closing conditions of the relay, and then closes all the main negative relays of BCU for pre-charge balance process. When BAU detects that the current total voltage difference in place exceeds the allowed value, BAU reports a large fault in total voltage difference and manual intervention is required to close the faulty battery pack or activate the maintenance mode to balance the battery pack manually.
Pre-charge control when powered on
Before each relay is closed, the capacitor in the high-voltage system connected to the battery cluster must be pre-charged. After determining that the pre-charge process is completed, the relay can be closed. Otherwise, the relay may be damaged due to contact welding caused by overheating resulting from overcurrent. When BAU performs pre-charge control, it first controls all BCU to close the pre-charge relay. When BCU detects that the pre-charge current and the voltage difference before and after pre-charge are less than a certain value and the pre-charge time is greater than a certain value, BCU reports that the pre-charge is completed. At this time, BAU detects that all the pre-charge is completed and controls the closing of the main positive relay and the disconnection of the pre-charge circuit.
By installing AGC, AVC, and other functional modules in the local monitoring device, it has the same power control function as the back-end monitoring system. The emergency communication solution for the battery energy storage station is that each energy storage unit adopts a ring network switch to form a local area ring network. When the system communication is normal, the energy storage equipment communicates with the back-end monitoring system through the normal network, and the local monitoring device stores the control commands for the entire station. Once all the energy storage units determine that the communication is interrupted, the local monitoring device with the smallest designated address number becomes the main control device and controls the continued operation of the energy storage equipment through the local area ring network.
The number and scale of power-side and grid-side energy storage stations are increasing year by year. Further research and optimization are needed in battery management, system protection, and operation control.
