Unleashing the Flexibility of Renewable-Dominated Distribution Grids via Soft Open Point Planning

With an increasing integration of intermittent distributed energy resources (DERs), the consequent voltage excursion and thermal overloading issues limit the self-sufficiency of distribution networks (DNs). The concept of soft open point (SOP) has been proposed as a promising solution to improve the hosting capacity of DNs. In this paper, we propose an optimal planning framework for SOPs and DERs while considering building-to-grid (BtG) capability. The optimal planning model is aimed at minimizing the investment and operation costs while respecting various constraints, including the self-sufficiency requirement of the DN, SOP and DER operation, etc. A steady-state SOP model is formulated and linearized to be incorporated into the planning framework. To make full use of the BtG flexibility provided by ubiquitous buildings, a differential equation model for building thermal dynamics is formulated. IEEE 33-bus feeder is adopted to validate the effectiveness of the proposed framework and method. Case studies show that SOP / BtG can effectively improve the hosting capacity and self-sufficiency of distribution networks.