Zero tracking error nearest level modulation for modular multilevel converters

The nearest level modulation is the simplest and most practical method for a modular multilevel converter due to its large number of sub-modules. Traditional nearest level modulation ignores voltage fluctuation of a capacitor, when it calculates the number of inserted sub-modules. This will cause errors between the actual voltage generated by sub-modules and its reference. These errors will lead to the fluctuation of circulating currents and additional losses. This paper proposes a zero tracking error nearest level modulation, which can eliminate the errors. This method is validated by 71 voltage-level modular multilevel converter simulation results.