Selective Frequency Support Approach for MTDC Systems Integrating Wind Generation

This paper introduces a new control approach for Voltage Source Converter (VSC) stations in a multi-terminal dc (MTDC) grid to provide mutual frequency support among asynchronous ac networks. The developed coordinated control strategy modifies the active power references of each droop-controlled converter considering its adjacent ac system's operational condition to enable the desired frequency support. Specifically, the proposed controller accurately achieves operator pre-specified frequency deviation ratios between the disturbed ac systems and other areas, thereby providing frequency support to affected grids during the whole frequency event. Therefore, an extra degree of freedom can be achieved in determining the extent of mutual frequency support. The performance of the proposed strategy is tested considering grids with significantly different frequency regulation characteristics. The stability analysis and time-domain validation of the proposed strategy are conducted in Matlab/Simulink.