This thesis presents a new dynamic phasor model of a modular multilevel converter (MMC), which can be used for electromagnetic transient (EMT) simulation studies. The model is extendable to capture and replicate any given number of harmonics of the output waveforms and also it produces the most dominant frequency components of internal capacitor voltages and arm currents waveforms. The internal dynamics of the MMC are modeled using the conventional dynamic phasor (CDP) principles in form of a linear state equation system. Solution of the state equations, which is obtained via numerical integration, is then used to build the dynamics of output voltage waveforms of the MMC by applying a new concept referred to as base-frequency dynamic phasors (BFDP). Validation results illustrate that the new MMC model is much more computationally efficient than other two models and is also capable of maintaining a high level of accuracy.