Abstract
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.
Highlights
The delay of the Electric vehicles (EVs) is kept constant to 1 second, and the system inertia is kept constant to 4.3 seconds
The investigation demonstrated that converter-connected resources are capable of providing fast frequency control and contribute to the frequency stability as long as certain conditions are fulfilled, primarily response time and share in the total reserve
The method was applied to the Bornholm power system and validated by using EVs with bidirectional controllability as specific type of converter-connected resources
Summary
Power systems mostly rely on controllable generation units to steer the balance between production and variable consumption. This simple, yet effective, principle is challenged by the increase of uncontrollable sources connected to the grid. Frequency provision requirements are still designed while keeping in mind the dynamic response of rotating generators. This leads to the risky assumption that a control scheme designed for rotating machines could work well for converter-driven units. The focus of this work lies on the implications of procuring fast frequency reserve with converter-connected resources and on whether set requirements are beneficial to frequency stability. The derived results are, applicable to converter-connected resources, being all of them characterized by the absence of rotating components and by power response affected by delays
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