Effect of the Dynamics of the MTDC Power System on DC Voltage Oscillation Stability

Ignoring parts of the dynamics of a multiterminal DC (MTDC) power system can simplify its stability analysis but may miss some instability risks in the analyzed results. This study analyzed the stability of DC voltage oscillation by considering comprehensive dynamics of an MTDC system in a DC voltage time scale to reveal the stability mechanism of the DC voltage oscillation accurately. It demonstrated that a DC voltage oscillation loop is first formed by the DC voltage control of the voltage source converter (VSC). Subsequently, it is affected by the dynamics of the remaining DC system (RDCS) through two paths: (1) the equivalent conductance of the RDCS is equal to an additional damping added to the DC voltage oscillation loop, and (2) the equivalent susceptance forms a mirrored subsystem and results in an open-loop modal resonance, which always induces negative effects on DC voltage oscillation stability. These conclusions are also correct in parts of the MTDC system using DC voltage droop control. Moreover, a method was proposed to quickly determine the stable operating region of the RDCS. Finally, accuracy of the stability mechanism of the DC voltage oscillation and effectiveness of the proposed method are verified based on the SIMULINK platform.