Efficient model for modular multi-level converter simulation

Abstract

Detailed models of modular multi-level converters (MMCs) are cumbersome for electromagnetic transient simulation programs because of their high number of components which involve large simulation times. In this work, the modeling of an MMC is addressed with the objective of reducing the simulation time. First, the MMC structure is presented, including the modulation technique, the voltage balancing algorithm and the circulating current control used to validate the model. Next, an efficient simplified model is proposed. This is formed by just one variable voltage source, one variable capacitor and one variable resistor per arm, regardless of the number of submodules. This simplified model allows the simulation time to be reduced while keeping the dynamics of the MMC. The comparison through several PSCAD simulations with a detailed 5-level MMC model proves its validity during both steady-state and transient conditions (ac and dc short-circuits).