1.State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources (North China Electric Power University), Beijing 102206, China;2.State Key Laboratory of Power Transmission Equipment Technology (Chongqing University), Chongqing 400044, China

Modular multilevel converter with supercapacitor energy storage system (MMC-SESS) combines the advantages of MMC and supercapacitor energy storage system, and can be used in the large-scale transmission field of renewable energy. However, due to the submodule (SM) structure of MMC-SESS are more complex and the operation modes are more various, an electromagnetic transient equivalent model for MMC-SESS is proposed to increase the simulation efficiency under multiple types of transient and steady-state operation conditions, including steady-state, blocked start-up, DC fault blocking, etc. Firstly, the topology and operation modes of SMs in MMC-SESS are analyzed, and the adjoint circuits of a single submodule are obtained by using the two-value resistance and the trapezoidal integral discretization method. Afterwards, the Thevenin equivalent process adapted to the solution logic of EMTDC simulation platform is proposed to realize the equivalent simplification of SMs and bridge arms, and the overall equivalent circuit is obtained. In addition, the operation modes under blocked operation conditions are analyzed, and the blocked equivalent circuit is constructed and merged into the obtained overall equivalent model. Finally, the electromagnetic transient equivalent model of MMC-SESS is obtained under multiple operation conditions. It is verified by simulation in PSCAD/EMTDC that the proposed model has good simulation accuracy and efficiency.