Fast frequency response services, designed to quickly balance the electrical grid within seconds, have a critical importance for managing sudden anomalies in low-inertia power systems. Battery systems often serve as versatile prosumers on the demand side to facilitate fast frequency response services. However, the nature of the fast frequency response services leads to a highly fluctuating power profile for batteries, which can shorten their lifetime. In contrast, distributed air-source heat pumps in residential areas have a substantial untapped potential to support fast frequency response services. This paper seeks to integrate them into the existing services through a controller upgrade. We analyze the influence of air-source heat pumps' inherent complex thermal dynamics on fast frequency response services, revealing control challenges posed by unpredictable operating condition changes. Such a challenge is tackled with a decentralized control strategy based on H∞ and inverse-droop control, guaranteeing practical and stable operations within the permitted operating condition range. Finally, the proposed fast frequency response service scheme is tested through multiphysics simulations on a small-size low-inertia residential microgrid. The obtained results strongly supported the proposed new service.

Paper submitted to PSCC 2024. In this paper, we present a standard power-hardware-in-the-loop testing platform that can real-time simulate detailed air-source heat pump dynamics based on well-established modeling knowledge. Distributed air-source heat pumps can be potentially used for fast frequency response. However, using air-source heat pumps for rapid modulation cannot be based on the current assumptions of linear speed-power transient characteristic, which was developed for low-speed temperature control applications. Customized setups with experimental validation options are needed to design the new fast frequency response compatible heat pump controllers. Most power system laboratories struggle in building a customized air-source heat pump, which hinders the research progress. The proposed platform is relatively universal, can fit to different heat pumps with minor modifications and be implemented on standard PHIL emulators in power system laboratories. Emulation results, real-time implementation details and model complexity metrics are presented, to assist transference of the setup to other laboratoriesÂ

The heat pump system is complicated to model dynamically because of the phase changing in both evaporator and condenser. The  moving boundary model tackles this problem by dividing the evaporator and condenser into variable-length zones, and their lengths  vary with the thermal state of the refrigerant. This document explains the full derivation process of the moving boundary model of an air source heat pump system.