Robust Energy Management Systems for Isolated Microgrids Under Uncertainty

Abstract

Microgrids are small and local clusters of generation and load operated in a coordinated manner. These systems are being enhanced with Smart Grid technologies in order to better integrate more Renewable Energy (RE) sources and thus reduce dependency on fossil fuels. This thesis focuses on isolated microgrids, which are characterized by low inertia Distributed Energy Resources (DERs), limited availability of resources, and high correlation of RE sources of the same type, where, variability and uncertainty become significant issues. In order to enhance the operation of microgrids, a mathematical formulation and archi- tecture of a robust Energy Management System (EMS) for isolated microgrids is proposed in this thesis. The developed algorithm is able to manage the uncertainty of RE sources and hedge the system against uncertainty in RE forecast. The proposed strategy addresses uncertainty using Receding Horizon Control (RHC), combined with a two-stage decision- making process with recourse. The first-stage decisions are the Unit Commitment (UC) variables, determined using a Robust Optimization (RO)-based formulation, and solved using a primal cutting-planes algorithm. Also a method based on the historical perfor- mance of the forecasting system is presented for the selection of the uncertainty policy, which represents the decision maker’s risk preference. The second stage refines the dis- patch commands using an Optimal Power Flow (OPF) calculation with a rather detailed model of the microgrid considering relevant system dynamic constraints. The proposed architecture is based on di↵erent look-ahead windows to better account for uncertainty, and obtain a feasible dispatch solution within reasonable computational times. The EMS is tested on a modified CIGRE test system for di↵erent configurations, com- paring the results with respect to deterministic and Stochastic Optimization (SO)-based formulations. The results reflect the e↵ectiveness of the proposed EMS to hedge the sys- tem against uncertainties, improving the system’s level of reserves, and dispatching Energy Storage Systems (ESSs) appropriately, so that the operational costs are reduced. The im- provements are achieved without requiring probabilistic information from the forecasting system, and based on an appropriate definition of the uncertainty set. The results show that the developed architecture and algorithm are compatible with real-time applications.