Benefit of Fast Reactive Power Response from Inverters in Weak Distribution Systems

Electric power systems worldwide tend to become inverter-dominated. We witness an increasing integration of inverter-based resources (IBRs) in both transmission and distribution systems along with a decline in the share of synchronous generators. Unlike synchronous machines, today's IBRs have relatively small contribution to system strength, which can be quantified by the reduced short circuit level in an IBR dominated grid. As a result, the short circuit ratio at a distribution substation may decrease, which may expose the distribution connected IBRs to weak grid operating conditions. This paper investigates the potential stability challenges that may occur in such conditions. A potential instability issue with the present-day inverter controls is identified and the mitigation effect of two alternative control methods is demonstrated. Fast reactive power response, which is a common feature of the two alternative methods, is discussed to be a potential performance requirement to mitigate the instability.