Dynamic Ancillary Services: From Grid Codes to Transfer Function-Based Converter Control

TL;DR

This paper introduces a transfer function-based method for implementing dynamic ancillary services in converter-based systems, translating grid-code specifications into practical control strategies that outperform traditional droop and virtual inertia schemes.

Contribution

It presents a systematic approach to convert piece-wise linear time-domain grid-code requirements into a rational transfer function for practical implementation in converters.

Findings

Transfer function approach ensures grid-code compliance.

Method outperforms classical droop and virtual inertia schemes.

Easy integration with standard converter control architectures.

Abstract

Conventional grid-code specifications for dynamic ancillary services provision such as fast frequency and voltage regulation are typically defined by means of piece-wise linear step-response capability curves in the time domain. However, although the specification of such time-domain curves is straightforward, their practical implementation in a converter-based generation system is not immediate, and no customary methods have been developed yet. In this paper, we thus propose a systematic approach for the practical implementation of piece-wise linear time-domain curves to provide dynamic ancillary services by converter-based generation systems, while ensuring grid-code and device-level requirements to be reliably satisfied. Namely, we translate the piece-wise linear time-domain curves for active and reactive power provision in response to a frequency and voltage step change into a desired rational parametric transfer function in the frequency domain, which defines a dynamic response behavior to be realized by the converter. The obtained transfer function can be easily implemented e.g. via a PI-based matching control in the power loop of standard converter control architectures. We demonstrate the performance of our method in numerical grid-code compliance tests, and reveal its superiority over classical droop and virtual inertia schemes which may not satisfy the grid codes due to their structural limitations.