Research on Efficient Electromagnetic Transient Simulation Method of Modular Multilevel Converter

The large number of sub-modules for modular multilevel converters (MMCs) results in low simulation efficiency, which is not suitable for full electromagnetic transient simulation analysis of large power systems. This article optimized the MMC model equivalent method and the ranking algorithm in three aspects: 1) Used a flexible switching algorithm to discretely simulate the MMC model, while maintaining high-precision simulations to avoid numerical oscillations, ensured the accuracy of the model, further reduced the number of internal nodes, and accelerated model calculation; 2) Studied the nearest level control of MMC to reduce unnecessary sequencing, and proposed "an incomplete sub-module capacitor voltage sequencing algorithm for bidirectional heap sequencing", to speed up model calculation; 3) The virtual diode was used to achieve accurate simulation when the MMC was locked, which improve the simulation accuracy of the MMC in the case of the lock. Finally, combined with typical examples of Matlab and PSCAD to test, it verified the accuracy and efficiency of the improved electromagnetic transient simulation method. © 2020 Chin. Soc. for Elec. Eng.