Frequency stability with converter-connected resources delivering fast frequency control

Converter-connected resources, such as electric vehicles and stationary batteries, are being recognized by grid operators as contributors to frequency stability. Their fast-response potential makes them ideal candidates to provide fast frequency control. In this paper we discuss and present evidence on what kind of dynamics a power system experiences when using electric vehicles to provide frequency control. Initially, we present a method to assess a system balance by deriving so called system residuals, given historical frequency time series and components characteristics. The system residuals consist of the non-controllable, and not explicitly measured, part of generation and load. Afterwards, the Danish island of Bornholm, where vehicles are used on a commercial basis to provide primary frequency control, is used as the test-bed for the investigation. The analysis is supported by validating the described components and system models against real measurements from the islanded power system. The key outcome is that the overall response time needs to be within 1 second. For the considered system scenarios, the share of reserve provided by electric vehicles should be up to 30% to improve the system stability. We finally generalize the results by highlighting key factors needed to replicate the findings in other power systems.