High Voltage Direct Current (HVDC) is a growing technology due to the necessities of electric connection between islands, offshore wind farms, oil platforms, the electrification of transports and other future applications in the electric sector. This work presents a methodology that is used to design the control of the multi-terminal HVDC grids interconnecting offshore wind farms with the main onshore electrical grid. The methodology is detailed in this Thesis also including relevant information about converters and HVDC is presented. First, two simple models are analyzed to illustrate the studied control system, the first one is the Voltage Source Converter (VSC) operating in power control mode and the second one is the VSC grid converter operating in DC voltage control mode. Moreover, the control design methodology is applied in a case of a multi-terminal HVDC grid formed by four terminals. The main objective is to analyze the best range of values of the DC primary voltage regulator considering the limitations for each electrical magnitude during both the transient response and the steady state. To perform this analysis, several scenarios have been evaluated through simulation models using the software Matlab-Simulink®. Note: The schemes, the code and the graphs that have been performed in Matlab-Simulink® are shown and explained in the Annexes document. The files created in Matlab-Simulink® to perform this Thesis has been uploaded to the online repository GitHub. The files are available at https://github.com/silos94/TFM-Victor-Silos-Sanchez. Nevertheless, for space limitations, the files extracted from simulations, which they are composed by figures and data, could not be uploaded to GitHub. Please, feel free to contact the author about any issue.