Improving Operational Flexibility of Integrated Energy Systems Through Operating Conditions Optimization of CHP Units

As a type of energy system with bright application prospects, the integrated energy system (IES) is environmentally friendly and can improve overall energy efficiency. Tight coupling between heat and electricity outputs of combined heat and power (CHP) units limits IES operational flexibility significantly. To resolve this problem, in this paper, we integrate operating mode optimization of the natural gas combined cycle CHP unit (NGCC-CHP) into dispatch of the IES to improve flexibility of the IES. First, we analyze operational modes of the CHP units from the perspectives of thermal processes and physical mechanisms, including the adjustable extraction mode, back-pressure mode, and switching mode. Next, we propose an explicit mathematical model for full-mode operation of the CHP units, in which the heat-electricity feasible region, switching constraints, and switching costs are all formulated in detail. Finally, a novel economic dispatch model is proposed for a heat and electricity IES, which uses the full-mode operation of CHP units to improve operational flexibility. The Fortuny-Amat transformation is used to convert the economic dispatch model into a mixed-integer quadratic programming model, which can then be solved using commercial solvers. Case studies demonstrate the proposed method can reduce operational costs and obviously promotes wind power utilization.