A multi-stage MINLP-based model for sub-transmission system expansion planning considering the placement of DG units

This paper presents a new multi-stage model, based on the mixed integer nonlinear programming (MINLP) approach, to determine the optimal sub-transmission system expansion planning (SSEP). This model considers the placement of distributed generation (DG) units in distribution networks over the planning periods. The SSEP determines the facilities which should be installed and/or reinforced so that the system serves the forecasted demand at the lowest cost while satisfying the operational constraints. These constraints include the maximum allowable voltage drop, and the operation capacity of substations, MV feeders, and DG units. Meanwhile, the proposed model presents the optimal planning of existing and new sub-transmission substations, as well as the routes of medium voltage (MV) feeders. Moreover, the allocation and operation planning of DG units over the planning period is considered, as well. On the other hand, the expanding limitations of existing and candidate sub-transmission substations and DG units are considered as the expansion constraints in the SSEP problem. The effectiveness of proposed MINLP-based model is demonstrated using several case studies.