Since high power energy transmission is required for a grid-level energy storage system

a high-power energy storage system based on modular multilevel converter (MMC) is very promising at present. However

in order to produce desired high power

an MMC-based energy storage system needs to be constructed by cascading a large number of energy storage units

which will make it difficult to balance state of charge (SOC) of these units. To solve SOC unbalancing of these units

special modeling and control methods are employed and an SOC balancing controller is designed. First

a high-power energy storage system is modeled as a multi-agent model. Then

an event-trigger control method is used to control information transmission and operation period of the energy storage agent

which further reduces the amount of communication and computation. Moreover

observers are designed to estimate battery current

which can reduce in half the amount of status information that needs to be collected. Finally

the simulation platform of the MMC-based storage system is established with MATLAB

the proposed SOC balancing control method is simulated and its validity is verified.