A novel modulation scheme and voltage balancing algorithm for modular multilevel converter

This paper presents a low cost, less computational pulse width modulation scheme for a modular multilevel converter (MMC). In the present control approach, the reference output voltage is generated by averaging the two nearest voltage levels. The switching states corresponding to the two nearest voltage levels and their duty cycles are obtained from the instantaneous value of reference output voltage. The proposed modulation scheme is easily extended to any number of submodules per arm without any modifications. In addition, a voltage balancing algorithm is proposed for the balancing of submodule capacitors voltage. The performance of the proposed modulation scheme and voltage balancing algorithm is evaluated on the 2MVA/6kV MMC system with three-level flying capacitor submodules. Also, the proposed modulation scheme is compared with the conventional phase-shifted carrier pulse width modulation (PSC-PWM) scheme and the results are presented.