Modeling of modular multilevel converters using extended-frequency dynamics phasors

This thesis investigates modeling of modular multilevel converters (MMCs) using an averaging method known as extended-frequency dynamic phasors. An MMC can be used as an inverter or a rectifier in high voltage direct current (HVDC) system. This research develops a dynamic phasor model for an MMC operated as an inverter. Extended-frequency dynamic phasors are used to model a system with only interested harmonics present. The developed model is capable of capturing both the low and high-frequency dynamic behavior of the converter depending on the requirements of the study to be performed. The selected MMC model has 5 submodules per arm (6-level converter), nearest level control, capacitor voltage balancing, direct control and phase-locked loop (PLL) synchronization. With the above features, the developed dynamic phasor model is validated with electromagnetic transient model is developed using PSCAD simulation software. The results are compared at transient and steady state with disturbances. The main computational advantage of this modeling is achieving less simulation time with inclusion of harmonics of interest.