Virtual Synchronous Machine Control for Low-Inertia Power System Considering Energy Storage Limitation

The reduced inertia due to integration of power-electronic converters brings about large frequency deviation and rate of change of frequency (ROCOF) in power system which may trigger frequency protection or increase the tears and wears of generators. The existing synthetic inertia and fast frequency response based on renewable energy resource is limited by the unidirectional power reserve, while the emerging virtual synchronous machine (VSM) control is limited by the energy storage needed on DC side. In this paper, an enhanced VSM control is proposed, considering the limitation of energy storage in response speed and energy capacity. The fast-acting energy storage system (FAESS), usually having small energy capacity, is used for emulating inertia and damping. An energy recovery control is proposed so that the energy will be automatically recovered after disturbance, thus reducing the energy capacity needed. The slow-acting energy storage system (SAESS) is controlled like governor control of synchronous machine, which adjusts power based on frequency change, thus taking advantage of its high energy capacity. DC and AC coupling of governor-like control and inertia-damping emulation is proposed, which is unanimous under the scheme of grid-forming and grid-following control. Comprehensive simulation results demonstrated the effectiveness of the proposed control strategy.