An Objective-Oriented Aggregate Modeling Approach of Distributed Energy Resources

With the increasing integration of distributed energy resources (DERs) into the distribution system, an accurate aggregate model (AGM) that can describe the outer characteristics of the DER cluster is critical for unlocking their flexibility potential. Because the exact solution of the AGM is an NP-hard problem, existing research usually tries to seek an inner approximation by maximizing the feasible region of a prescribed parametric AGM. Although an AGM with the largest feasible region can be obtained by this method, it is usually not optimal for the distribution system because some parts of the feasible region of the AGM contribute little to the operational flexibility of the distribution system, i.e., the ineffective feasible region. In short, maximizing the feasible region is not consistent with maximizing operational flexibility. Considering this, we propose a novel objective-oriented aggregate model (OOAM) for the DERs that integrates the operational objective of the distribution system into the computation of the AGM to maximize the effective feasible region. First, we introduce the concept of the OOAM and formulate the mathematical model. Second, we propose a duality theory based solution method for the OOAM model. Particularly, the OOAM approach features a bi-level coordination framework: 1) At the distribution system level, the system operator uses a multi-scenario stochastic programming model to optimize its scheduling decisions and quantify its preference for the feasible region of the AGM; 2) At the DER level, the aggregator optimizes the parameters of the AGM based on the preference of the distribution system. Finally, case studies based on the IEEE 33-bus and IEEE 123-bus systems verify the effectiveness and superiority of the proposed approach.