Voltage control of common capacitor and self-faults analysis of DC current flow controllers for meshed multi-terminal HVDC grids

In this paper, the control methodology of the common capacitor voltage and the DC current flow controller (DC CFC) under self-fault conditions are investigated with the following two contributions. (1) A selection method of the common capacitor voltage based on various specific control requirements with explicit control margins of the DC line currents is proposed with analytic derivations of two-line/three-line DC CFCs in the meshed three-terminal/four-terminal high-voltage direct current grids (HVDC), respectively. (2) The impact of different self-faults of the DC CFC on the control performance of the DC line currents is analyzed with a simplified topology with unidirectional current flow presented. Case studies are conducted in the time-domain simulation environment PSCAD/EMTDC and the results justify the effectiveness of the theoretical analysis. The proposed common capacitor voltage control method and self-fault analysis would be useful for practical applications of the DC CFC under both steady and transient states. (C) 2021 The Author(s). Published by Elsevier Ltd.