Long-term voltage stability with large-scale solar-photovoltaic (PV) generation

Abstract The dynamic characteristics of power grids have substantially evolved over the last two decades due to the large-scale integration of power-electronic converter (PEC)-interfaced renewable energy sources (RESs). Therefore, the impact of PEC-interfaced RESs on power system stability must be thoroughly examined. This paper comprehensively investigates the long-term voltage stability (LTVS) phenomenon with large-scale solar-photovoltaic (PV) generation. The reactive power characteristics and control schemes of the synchronous generator (SG) and solar-PV system are carefully analysed, as these characteristics significantly affect the voltage stability. First, the LTVS phenomenon is analysed using a simple test system. Time-domain simulations and dynamic reactive power-voltage (QV) curves at critical time-domain snapshots have been used to analyse the trajectory of the system operating point. Moreover, important parameters of the solar-PV system, such as the inverter rating, current limiting strategies, and reactive power gain are also thoroughly examined to characterize their impact on LTVS. The effect of variation in solar-irradiance and ambient temperature on LTVS is also studied in the paper. Finally, the effect of the solar-PV generation on LTVS is investigated using the Nordic test system. This study has shown that solar-PV systems with improved controllers could provide enhanced dynamic reactive power response, hence improve the LTVS. However, large-scale solar-PV systems have both beneficial and adverse impact on stressed power systems, and the nature of the impact depends on the relative loading level of the replaced over excitation limiter (OEL) activated SGs.