MMC is a new topology that has revolutionized the VSCHVDC for electrical transmission over long distances and interconnecting asynchronous AC grids. Being a very complex and distributed plant, the modulation become more challenging. The purpose of this thesis is to analyse the existing modulation techniques and propose improved solutions that are able to: improve the capacitor voltage balancing, reduce the switching frequency and uniformly distribute the losses among power switches. A comparison of different modulation techniques has been carried out for several converter power ratings, a small scale prototype and a HVDC system, in order to compare their performance. Finally a small scale prototype has been designed and built in order to validate the simulation results.