In active distribution system planning problem in addition to the line and substation reinforcement, installation of DGs are allowed. I want to decompose a multi-year active distribution planning problem into a sequence of single-year problems. To this end, I used backward pull-out approach in which, firstly the planning problem is solved for the last year (year Y) considering the demand in the same year and the network configuration at the beginning of the planning period. Then, the elements determined in year Y are considered as expansion options in year Y-1 and the planning problem is solved for year Y-1. The procedure continues until the optimal plan is determined for the year 1.
I employed the backward pull-out approach on a test distribution system and observed that this method works properly for the planning of the test system in which network reinforcement and DG installation are considered concurrently.
However, somebody said to me that "back-ward algorithm was suitable for passive distribution networks, i.e. networks without DGs, and not for active ones. The overall load in year Y seen by a supply substation, can be lower than the load in year Y-1 due to the installation of new DGs in the area of the considered substation. Hence, the network expansions in year Y may not be sufficient to serve the loads in year Y-1 in which the DGs are not yet built".
My argument is that in backward approach, the elements determined in year Y are as expansion "candidates" and elements determined in year Y should exist in the same year and it is not necessary to install them in year Y. in other words, the purpose of backward approach is to determine the installation year of required elements for the last year of planning horizon considering load growth in each year.
But, I am not quietly sure about my argument.