A procedure for the design and tuning of two control loops of a High Voltage DC system is presented. The controlled variables are direct current on the rectifier side and direct voltage on the inverter side. The dynamics of both control loops interact with each other and are determined by the overall properties of the combined AC-DC system. Constraints on the information available for feedback in each loop require a decentralised controller structure. Genetic Algorithms are demonstrated to be an efficient tool for the design and tuning of such a decentralised control system.