Modelling a fixed-speed pumped hydro storage system for reactive power management in power grids with high penetration of inverter-based resources: A case study of Aotearoa New Zealand

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Abstract
The increasing penetration of inverter-based renewable energy resources (IBRs) presents significant challenges to power system voltage stability and reactive power management due to the declining contribution of conventional synchronous generation. This study investigates the reactive power support capability of a fixed-speed pumped hydro storage (FS-PHS). A dynamic FS-PHS model was developed in MATLAB/Simulink based on a validated Sandia National Laboratories model and adapted to Aotearoa New Zealand operating conditions. The validated model was integrated into a modified IEEE 9-bus system operating at 220 kV transmission voltage. Load flow and electromagnetic transient studies showed that the FS-PHS unit provided effective voltage support and dynamic reactive power compensation under varying reactive loading conditions. The system successfully responded to changing network requirements while maintaining stable operation and acceptable bus voltage profiles. The findings demonstrate that FS-PHS can provide valuable ancillary services beyond energy storage, including voltage regulation and reactive power support. The technology represents a promising option for strengthening weak renewable-rich regions, such as Aotearoa New Zealand, where future system strength and voltage stability are expected to become increasingly important.