An independently controlled energy storage to support short term frequency fluctuations in weak electrical grids

This paper proposes the use of Energy Storage (ES) to support frequency fluctuations in weak grids powered by low-power synchronous generators (SGs). Traditionally, large synchronous generators rely on high inertia and governor control to guarantee the frequency stability of the network. The scenario changes in networks with a large penetration of small distributed generators (DGs) with smaller inertia, where load variations can lead to large frequency deviations, violating the over/under frequency protection limits. The proposed energy storage control injects active power during load transients so that the frequency is constrained within predefined thresholds. The system frequency is detected by a Double Second-Order Generalised Integrator Frequency Locked Loop (DSOGI-FLL), eliminating the need for communication between energy storage and synchronous generator and providing “plug-and-play” capability. The proposed method combined with the continuous speed governing supports the frequency well within the primary frequency transient requirements. The solution has been validated using an 8kW laboratory system.