Massive inverter-based thermostatically controlled load (ITCL) cluster has immense potential for frequency regulation. As the power system inertia continues to decrease

how to enable the inertia support and primary frequency regulation support (synthetic inertia support for short) of the ITCL cluster has become the key to practical applications. Therefore

this paper focuses on the time-scale matching between ITCL dynamic behaviors and frequency regulation requirements

establishes a reduced-order dynamic model of ITCL that meets the frequency regulation requirements

and proposes the concept of response domain to quantify the frequency regulation capability of ITCL. Then

according to different control topologies

this paper classifies the synthetic inertia support technologies into centralized

decentralized and hybrid types. Furthermore

this paper discusses the regulation framework

synthetic inertia support control strategy

and simplified frequency response model of the 3 modes

and clarifies the technical difficulties and key research issues of the synthetic inertia support of ITCL cluster.