Energy Systems Integration in Smart Districts: Robust Optimisation of Multi-Energy Flows in Integrated Electricity, Heat and Gas Networks

Smart districts can provide flexibility from emerging distributed multi-energy technologies, thus bringing benefits to the district and the wider energy system. However, due to nonlinearity and modelling complexity, constraints associated with the internal energy network (e.g., electricity, heat and gas) and operational uncertainties (for example in energy demand) are often overlooked. For this purpose, a robust operational optimisation framework for smart districts with multi-energy devices and integrated energy networks is proposed. The framework is based on two-stage iterative modelling that involves Mixed Integer Linear Programming (MILP) and linear approximations of the nonlinear network equations. In the MILP optimisation stage, the time-ahead set points of all controllable devices (e.g., electrical and thermal storage) are optimised considering uncertainty and a linear approximation of the integrated electricity, heat and gas networks. The accuracy of the linear model is then improved at a second stage by using a detailed nonlinear integrated network model, and through iterations between the models in the two stages. To efficiently model uncertainty and improve computational efficiency, multi-dimensional linked lists are also used. The proposed approach is illustrated with a real UK district; the results demonstrate the model’s ability to capture network limits and uncertainty, which is critical to assess flexibility under stressed conditions.