Evaluation of the use of short-circuit ratio as a system strength indicator in converter-dominated power systems

Abstract

This paper investigates the applicability of short-circuit ratio (SCR) as a system strength indicator in power systems with a high penetration of voltage source converters (VSCs). In power systems dominated by synchronous generators, the SCR has been widely used to estimate the system strength by using short-circuit level information obtained at the relevant bus. However, the emerging converter technology such as VSCs has different short-circuit characteristics from synchronous generators, in the sense that the short-circuit currents are typically lower in magnitude and more controllable. Moreover, SCR calculations are based on the static analysis of the power system, neglecting the dynamic and control aspects of VSCs. These aspects raise the question whether the SCR can still be used to evaluate system strength of converter-dominated systems. To this end, in this paper, the fundamental definition of the SCR is revisited, and factors influencing its applicability in converter-dominated power systems are listed. A case study is provided to demonstrate the limitation of the SCR in converter-dominated systems, and the impact of the control strategy on the dynamic performance of the system is also discussed.