Research on Three-Stage Pre-Charging Control of Cascaded Energy Storage Converters Considering Battery Characteristics

To address the issues of battery overcharge damage caused by voltage imbalance and excessive grid-connected inrush current when high-rate charge-discharge energy storage batteries are connected to the DC side of cascaded energy storage converters, this paper proposes a three-stage pre-charging control strategy considering battery characteristics. This strategy achieves rapid charging and voltage balancing control of energy storage modules through the orderly connection of three stages: “uncontrolled rectification - sorting and voltage balancing - balancing maintenance”. In the first stage, an uncontrolled rectification method with series soft-start resistors is adopted to reduce the inrush current at power-on. In the second stage, based on the FPGA parallel full-comparison sorting algorithm, the DC-side voltage of each sub-module is quickly balanced by switching sub-modules. In the third stage, the number of fixed sub-modules to be cut off is maintained to continuously optimize the state of charge (SOC) balance of energy storage modules until the grid-connection conditions are met. To verify the effectiveness of the strategy, a three-phase 7-module star-connected cascaded energy storage simulation system is built on the Simulink platform. The simulation results show that the control strategy can stabilize the DC-side voltage of sub-modules to 44V and 53V sequentially within 1.2s, significantly attenuate the AC-side inrush current, and finally realize the non-impact grid-connection of the energy storage system. The research results provide technical support for the safe and stable operation of cascaded energy storage grid-connected systems, and improve the charging efficiency and reliability of the system.