A Study on Short-Circuit-Ratio for an Inverter-Based Resource with Power-Voltage Curves

The paper examines a minimum short-circuit-ratio (SCR) for a single-inverter infinite-bus system using powervoltage curves. It derives a steady-state equation between the apparent power and terminal voltage of a current-control type inverter. By normalizing the apparent power with short-circuitcapacity and voltage with that of the infinite bus, the equation proves to be determined with a single parameter, which is calculated with the R/X ratio of the looking-back impedance and the power factor of an inverter. The obtained equation gives a theoretical background on SCR as a metric to assess voltage stability. The minimum SCR is then evaluated for the nose of the power-voltage curves while considering constraints on the inverter terminal voltage. The results reveal that the SCR for an inverter with a constant power factor control has to be greater than about 2. If the reactive power of an inverter is controlled in accordance with its output power, the SCR has to be greater than about 1.