Integrated Battery and Heat Pump System for Decentralized Primary Frequency Control in Low-Inertia Microgrids

Battery energy storage systems are often used as flexible prosumers to support frequency stability. However, they are still relatively expensive, which hinders their large-scale usage. On the other hand, an air-source heat pump system is potentially useful for frequency control in residential microgrids. Unfortunately, the thermal inertia in air-source heat pumps makes them slow for fast frequency support. In this paper, an integrated battery and heat pump system is proposed with the aim of ensuring an uninterrupted supply of heat and providing fast and sustainable frequency support that exceeds the original capacity of the battery. The transient response of the heat pump system is enhanced with battery dynamic boosting to meet the requirements of fast frequency support. With such a configuration, the proposed integrated system performs closely to a pure battery system in terms of dynamic power behavior but can provide frequency support much longer than a battery system alone. As the dynamics of air-source heat pump systems can be affected by the ambient air and condensing water temperatures, there is a risk of instable operation of such systems. Therefore, this paper discusses how to design the control for such integrated systems with the aim of ensuring robust stability. Finally, the performance of the integrated system are verified through co-simulation between Simulink and Dymola.