Revolution of frequency regulation in the converter-dominated power system

With the increase of converter-fed devices such as renewable energy sources, energy storage, electric vehicles, direct current transmissions and power electronic loads in the power system, the conventional synchronous generator (SG)-dominated power system has been gradually evolving toward a converter-dominated system. Power electronic interfaces (PEIs) can be controlled to emulate the frequency responses of SGs, but their inherent control mechanisms are quite different. As a result, the revolution of frequency regulation in the future converter-dominated power system is foreseeable from theory to practice. In this paper, the principle of frequency responses and the corresponding control strategies of PEIs are summarized. The major inherent differences between PEIs and SGs are clarified, and the distinctive releasable energy reserves and frequency response performances are revealed. The state-of-the-art frequency regulation strategies adopted by PEIs in different operation modes are reviewed. The multiple time-scale frequency behavior in converter-dominated power systems is presented. Some major technical challenges for future work are highlighted.