An Improved Equivalent Circuit Model of MMC and Influence Analysis of Simulation Time Step

What is it about?

In this paper, an improved equivalent circuit model is developed for the purpose of large-scale system simulation as well as MMC station design acceleration. The proposed equivalent circuit can model the MMCs based on various SM circuits under different operating conditions (e.g., precharge, normal, and fault) for the electromagnetic transient (EMT) simulation. It can also generate bipolar arm voltage and simulate static compensator (STATCOM) operating condition during a dc fault. Based on the proposed equivalent circuit model, the influences of simulation time step on accuracy and efficiency are comprehensively investigated by considering the industrial controller including sample period (control period) and voltage balancing strategies.

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Why is it important?

Modeling and simulation of a high voltage-level modular multilevel converter (MMC) is challenging due to large amount of semiconductor switches, various MMC configurations and submodule (SM) circuits, and different operating conditions. Several equivalent models of the MMC have been proposed for efficient modeling and simulation in system level. However, there is a lack of considering a practical industrial or digital controller. To accelerate MMC station design, a highly efficient model is needed with considering detailed control parameters/strategies and accurate dynamics of voltage/current.