The Modular multilevel converter (MMC) is becoming a promising converter technology for HVDC transmission systems. Contrary to the conventional two or three level VSC-HVDC links, no capacitors are connected directly on the DC bus in an MMC-HVDC link. Therefore, in such an HVDC link the DC bus voltage may be much more volatile than in a conventional VSC-HVDC link. The intention of this paper is to propose a connection between the DC bus voltage level and the stored energy inside the MMC in order to greatly improve the dynamic behavior in case of transient. EMT simulation results illustrate this interesting property on an HVDC link study case.

Modular Multilevel Converters are becoming increasingly popular with the development of HVDC connection and, in the future, Multi Terminal DC grid. A lot of publications have been published about this topology these last years since it was first proposed. Few of them are addressing explicitly the 2 different roles that are held by this converter in a HVDC link: controlling the power or controlling the DC voltage level. Moreover, for a given function, different ways of controlling this converter may be considered. This paper proposes an overview of the different solutions for controlling the MMC and proposes a methodology to synthesize the control architecture.

Study the impact of two control variants (compensation of the average or the instantaneous AC grid power) : differential and AC grid currents, capacitor voltages ripple, losses.

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