A SOC equilibrium control strategy for MMC-SCES based on capacitor voltage balancing

Abstract

The super capacitor energy storage （SCES） system based on modular multilevel converter （MMC） is one of the key technologies for addressing issues with the grid integration of large-scale renewable energy. However， differences in supercapacitors can lead to inconsistencies in state of charge （SOC）， thereby affecting the utilization rate of energy storage capacity. In response to this issue， the paper proposes a SOC equilibrium control method for MMC-SCES based on capacitor voltage balancing. This balance is achieved by altering the energy storage power and equalizing the submodule capacitor voltage for all levels of SOC. The feasibility and effectiveness of the proposed control strategy are verified in a bipolar transmission system built in PSCAD/EMTDC. The results indicate that the proposed SOC equilibrium control strategy significantly reduces the number of controllers and simplifies the control system. The capacitor voltage balancing control strategy， which uses state sequencing and increment switching can effectively reduce the number of IGBT switch operations whilst balancing SOC， thus reducing switch loss.

Keywords

• mmc
• sces
• soc equilibrium
• bidirectional dc/dc converter
• submodule capacitor voltage balancing