Investigation of inverter-based sources in terms of voltage stability in active distribution networks

This thesis investigates the effects of inverter-based renewable energy sources (photovoltaic (PV) and wind turbine generators (WTGs)) as well as battery energy storage systems (BESS) on voltage stability in active distribution networks. The main objective is to quantitatively evaluate the impact of these sources on the voltage profile of the distribution grid and to assess their contribution to voltage stability margins. A real-world electrical distribution network was analysed, comprising 9 buses, 466 connection points, 312 distribution lines, 157 transformers, and 155 loads. Voltage stability limits were determined by generating P-V (power-voltage) curves using DIgSILENT PowerFactory software. In this context, several scenarios were created by integrating PV, WTG, and BESS individually and in combination into the critical bus. Furthermore, quasi-dynamic simulations (QDS) were performed using a power-controlled BESS model. Time-dependent generation and load characteristics were included to analyse the charge-discharge response of the battery system. Simulation results demonstrate that the integration of PV and WTG systems increases the loadability of the critical bus by approximately 30% by enabling higher active power transfer at the 0.95 p.u. voltage level. These findings suggest that the combined use of inverter-based renewable sources with battery storage offers an effective approach to enhance voltage stability in active distribution networks.