Battery hybridization in hydropower plants is a hydropower flexibility enhancement technology innovation that can potentially expand hydropower's contributions to the grid

but its fundamental characteristics and influencing mechanisms are still unclear. In this paper

primary frequency regulation (PFR) performance and the mechanism of this new technology are studied. A battery hybridized hydropower plant (BH-HPP) model

based on a field-measured-data-based hydropower plant (HPP) model and a verified battery simplified model

is established. Analysis of system stability and dynamics is undertaken for three different battery control strategies by root locus and participation factor methods. Compared to conventional HPPs

analysis results theoretically reveal BH-HPP can not only accelerate system regulation rapidity but also effectively enlarge HPP stability region during PFR process. Time domain simulation verifies the results and further shows synthetic control has better performance among introduced strategies. Besides

initial design ranges of control parameters considering battery capacity and a renewable energy source scenario case are also discussed. This work could provide theoretical support for flexibility enhancement solutions for hydropower systems.