An analytical frequency-domain modeling of a Modular Multilevel Converter

The Modular Multilevel Converter (MMC) is a new topology for multilevel converters with potential for medium voltage and high voltage applications. This paper focuses on the modeling technique in the frequency domain of an MMC. Using this frequency domain modeling it is possible to analyze and predict the harmonic content in the arm current and capacitor voltages. In MMC, a strong harmonic content exists in the arm current, although it is not reflected in the load current. This essentially controls the dynamic behavior of the converter. Moreover, explicit derivation of the equations that describe the harmonic evaluation on the floating capacitor voltage has been developed based on the switching functions concept. It can be employed for reducing the ripple voltage using harmonic components in the arm currents. The most dominant harmonics (2^nd and 4^th) in the arm current are derived analytically and compared in the paper.