A Two-Layer Model for Microgrid Real-Time Dispatch Based on Energy Storage System Charging/Discharging Hidden Costs

Real-time dispatch in microgrid (MG) is to balance the fluctuating supply and demand resulted from load and renewable generation by dispatching the energy storage system (ESS) and controllable generators. However, it is difficult to evaluate the real-time charging and discharging costs of ESS. In this paper, two hidden costs, discharging opportunity cost and marginal charging cost, are proposed and modeled for ESS from the perspective of real-time operation, which lead to more efficient coordination between ESS and controllable generators. A two-layer model is presented for MG real-time operation. The upper layer is a look-ahead dispatch that optimally allocates power for each generator. Then, two hidden costs of ESS are analyzed and modeled according to the Lagrangian formulation of the look-ahead dispatch problem. On the basis of the two hidden costs, a practical, efficient, and time-saving corrective strategy is proposed for the lower layer real-time dispatch. Feasibility and effectiveness of the proposed method are verified on a typical MG system. Simulation results validate the correctness of the two hidden costs of ESS. Further, the proposed method has proven to outperform existing real-time dispatch methods by a comparative study.