Abstract: Method and apparatus for simulating a MMC system in an electronic simulator uses a computing unit and a connected input/output interface. The electronic simulator comprises a simulation model of a modular multilevel converter (MMC) system including at least one MMC valve, each MMC valve including a plurality of connected converter-submodules (SMs), each SM preferably comprising at least two controlled switches, a capacitor and auxiliary switches. The inventive approach replaces each MMC valve by an equivalent circuit whereby each SM in the valves may be solved separately. Multiple computing units are used to simulate those SMs in parallel, thus achieving fast or real-time simulation speed. The computing unit may comprise multiple computing means using CPU cores, FPGA or GPU cores and combinations thereof. The present inventive method keeps the model-detail including its precision, and enables a real time simulator to achieve fast or real-time speed for very large MMC system-simulations.