Control of MMC-HVDC transmission system operating with local variables

The search for new energy sources has lead to the installation of renewable energy plants located far away from the centers of consumption. In this scenario, the transmission of electrical energy over long distances has become a key issue and high voltage DC (HVDC) transmission systems have demonstrated to be the best cost effective solution. Among the different HVDC technologies, modular multilevel converters (MMC) provide the highest power quality, modularity, reliability and availability. In this paper, the control of two HVDC stations based on MMC is proposed. A set of power and voltage limits are defined for each station and the control scheme is designed to work inside these limits. Due to this operation mode, the controller in one station does not require information from the other station. The different operating modes of the MMC-HVDC transmission system are analized and simulation results are obtained, in order to validate the proposed control strategy.