Impact of the Differences in VSC Average Model Parameters on the DC Voltage Critical Stability of an MTDC Power System

Voltage source converters (VSCs) are generally assumed to be identical when studying the DC voltage critical stability of a multi-terminal DC (MTDC) system, which in reality is not the case and can lead to erroneous results. In this study, the differences in VSC average model parameters, such as VSC control loops and operating states, were considered, and the mechanism of how these differences affect the DC voltage critical stability of an MTDC power system was clarified. In an MTDC power system with DC voltage droop control, it was found that these differences can be considered as two types of added dynamic impedances, which affect DC voltage critical stability by changing the construction of the DC network. Moreover, a method was developed to numerically determine the effects of these differences on DC voltage critical stability. It was verified that these effects are related to not only the dynamic characteristics of the added dynamic impedances but also the parameters and constructions of the DC network. By considering these differences, accuracy of DC voltage critical stability can be improved. Finally, an experimental platform of a four-terminal DC power system was established to validate the findings.