The main role of PCS (energy storage converter) in lithium battery energy storage system includes realizing bidirectional conversion of AC and DC power, controlling battery charging and discharging, and maintaining a stable connection between the power grid and the energy storage system.

Specifically, the role of PCS in lithium battery energy storage system can be subdivided into the following aspects:

‌Bidirectional power conversion‌: When charging, PCS converts the AC power of the power grid into DC power and stores it in the battery; when discharging, it converts the DC power of the battery into AC power and feeds it back to the power grid. This bidirectional conversion function enables the energy storage system to flexibly store and release power according to demand.

‌Charge and discharge control‌: By adjusting the voltage and frequency, PCS can accurately control the charge and discharge rate and capacity of the energy storage unit to ensure the safe and efficient use of the battery. In addition, PCS can also protect the battery from overcharge, over-discharge and overheating to prevent the battery from being damaged due to abnormal conditions, effectively extending the battery life.

‌Grid-connected/off-grid operation‌: PCS supports synchronous operation with the grid in grid-connected mode, and also has the ability to independently power the load when off-grid. This means that the energy storage system can interact with the grid when the grid is normal, and independently supply power when the grid fails, which improves the reliability and flexibility of the system‌.

‌System stability protection‌: PCS monitors the grid status in real time, protects against abnormal conditions such as overvoltage, undervoltage, and islanding effect, and ensures system safety‌. In addition, some high-order PCS also participate in auxiliary services such as grid frequency regulation and reactive power compensation to enhance the overall flexibility of the power system‌.

‌Power dispatch‌: PCS can flexibly adjust the output active power and reactive power according to the needs of the grid to ensure the stable operation of the grid. During peak power consumption, PCS can output the power in the energy storage battery to the grid to alleviate the pressure on power consumption; during low power consumption, it controls the battery charging to achieve "peak shaving and valley filling"‌