The rapid integration of renewable energy generators (REGs) alongside flexibility resources into the grid introduces significant data complexities

alongside increased unpredictability and variability within the distribution network. Reasonable allocation of flexibility resources can improve the utilisation of REGs and the flexibility of the distribution network. Addressing these challenges

an innovative two-stage model for distribution network expansion planning is proposed in this paper. The model uniquely combines the construction of new substations

the extension of existing lines

the integration of soft open points (SOPs) and strategic siting and sizing of energy storage systems (ESSs). Specifically

considering that SOPs can quickly regulate node voltages

thereby proposing flexibility zones as novel metrics to gauge the adaptability of the distribution network. Furthermore

a multivariate copula function is employed to delineate the correlation between REGs outputs and loads. This approach

devoid of reliance on extensive historical datasets

leverages discrete scenario ambiguity sets alongside norm theory to enhance scenario generation. To navigate the intricacies of the proposed model

a structured solution methodology encapsulated in a three-level process is developed. Validation through numerical simulations on the modified Portugal 54-bus system underscores the robustness and practicality of the methodology and solution framework in facilitating informed decision-making.