Disturbance Attenuation of DC Voltage Droop Control Structures in a Multi-Terminal HVDC Grid

DC voltage droop control is seen as the preferred control structure for primary voltage control of future multi-terminal HVDC systems. Different droop control structures have been proposed in literature which can be classified in eight categories. This paper contributes to an analysis of the disturbance rejection of these droop control structures. The approach is based on multi-variable frequency response analysis where both ac and dc grid dynamics are incorporated. In particular, the amplification of dc voltage oscillations due to wind power variations is analyzed using singular value analysis. Further, the impact of dc cable modeling on the results is discussed. In addition, it is shown that the maximum singular value limits, frequently used in literature for MIMO-analysis, are not sufficient to prove that the impact of certain disturbances on analyzed outputs is within a certain boundary. It is necessary to verify the results by a multiple input single output analysis of the transfer functions connecting the inputs with the highest amplified output.