Changing Rules of Multi-infeed Short Circuit Ratio of AC/DC Power System against Multiple Factors

MSCR (Multi-infeed Short Circuit Ratio) is an important indicator to evaluate the strength of the AC power system with multi-infeed DC circuits, which can effectively represent the interactions among the multiple DC circuits falling on the same AC power network. In this paper, an ac power system with double-infeed DC circuits is chosen as example, the equations of MSCR and the gradients of MSCR to the self and mutual impedance are derived, respectively. The changing rules of MSCR against the self-impedance, the mutual impedance and the DC power are analyzed with the corresponding spatial surfaces of MSCR, respectively. The similar modelling and analysis are also carried out by another indicator of MESCR (Multi-infeed Effective Short Circuit Ratio), which takes the reactive power compensation at the inverter bus into consideration. Furthermore, another typical structure of two single-infeed AC/DC power systems interconnected by one intertie is also selected for analysis. Two kinds of deviations from SCR to MSCR and from ESCR to MESCR in this scenario are modeled and evaluated theoretically, respectively. The resulting conclusions can provide reference for the planning, operation and engineering practice of AC/DC power systems.