Does integrating battery storage significantly improve voltage stability in residential micro grids?

Abstract

This paper explores the battery energy storage systems (BESS) usage to achieve substantial voltage stability in residential micro grids with high photovoltaic (PV) penetration. It is motivated by the growing need to use inverter-based resources, which, in contrast to synchronous generators, offers less inertia and reactive support, which results in such issues as voltage sag, swells, and poor regulation during disturbances. A dynamic model of a residential micro grid comprising of five nodes was modeled in equation-based MATLAB, expressed as a differential-algebraic system to be solved by means of the Newton-Raphson iteration and backward integration with the Euler method. Load steps, PV generation ramps, short-circuit faults and grid islanding were all considered disturbance scenarios. Three types of inverter control schemes, namely grid-following PQ mode, droop-based support, and emulation of a virtual synchronous generator (VSG) were tested. The simulated cases with and without BESS were done in several replicates to provide statistical reliability. The outputs of primary data were bus voltages, active and reactive flows of power, and state-of-charge (SoC). Measures of stability were established as the index of voltage deviation, the percentage of time below the +-5% statutory band, minimum bus voltage and a Jacobian singular value proxy of margin evaluation. The findings also indicate that consistent implementation of BESS decreases the variability of the peak voltage and decreases the range of variability of all disturbances. As an example, BESS minimized mean deviation by almost 40 per cent under PV ramp conditions and by almost 50 per cent during load step events. Control grid strategies (droop, VSG) were better at giving transient stability than PQonly operation, VSG being smoother to recover than droop (because of virtual inertia). Sensitivity tests indicated that BESS and state-of-charge flexibility have a significant impact on performance, and the reduction in returns with increasing BESS capacity is steep: beyond approximately 30 per cent of peak load rating. These results reaffirm that BESS on residential scale, even small-scale, can significantly enhance stability of voltage, which is of benefit to engineering design and policy projects aimed at resilient PV-heavy microgrids. The article offers a clear and reproducible simulation model and indicates further developments with hardware-in-theloop testing, unbalanced three-phase modeling, and technoeconomic optimization.