With the increasing demand for renewable energy power transmission

DC collection and delivery has become one of the most efficient methods. In high- proportion renewable energy and power-electronics-dominated (i.e.‘dual-high’) power systems

small-signal stability is a critical factor constraining stable power transmission. However

the stable power transmission capability of DC collection and delivery systems remains unclear. This paper first establishes the basic topology and small-signal model of a renewable energy power station’s DC collection and delivery system. Using modal analysis

it examines the characteristics of major sub/super-synchronous oscillation modes in the system. Considering the volatility of renewable power generation at the collection terminals under different integration scenarios and the impact of power regulation at the collection station on system stability

the study investigates how different power variations at the stations affect power transmission through various oscillation modes. Subsequently

by analyzing the stability under different power levels at the collection terminals

the stable power transmission range of the DC collection system is determined. The study reveals the small-signal stability constraints at different operating points and the multi-modal cross-coupling instability mechanism when the aggregated power fluctuates. Finally

propose a parameter optimization method based on the distance to the small-signal stability boundary

which can expand the stable power transmission range of the DC collection and delivery system. The effectiveness of the parameter optimization scheme in enhancing power transmission capability is verified through simulations in PSCAD/EMTDC.