Combined Cooling, Heating, and Power Systems: Modelling Optimization, and Operation
4 Energy Hub Modeling and Optimization-Based Operation Strategy for CCHP Systems
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The CCHP system is the connection between the energy input, that is, the electricity and the fuel, and the building users’ demand. From such a mapping perspective, a CCHP system can be viewed as an energy hub with multiple energy vectors at the input and output terminals. The energy hub represents an interface between different energy infrastructures and/or loads. The coupling of different energy carriers is established by the conversions among them. For instance, the PGU in the CCHP system can generate electricity and thermal energy simultaneously by combusting fuel. The electricity and thermal energy provided by the PGU will affect the purchasing of electricity from the local grid and additional fuel for the auxiliary boiler. By using the input–output mapping, the CCHP system can be modeled by a connection matrix. In , the authors model the system by introducing the concepts of dispatch factors and coupling matrix, and optimize the power flow and operation strategy using the KKT conditions. In , the authors model the system by using the concept of junctions, bifurcations, and the backtracking. However, the modeling process of the latter is not practically implementable. In this chapter, a more comprehensive and intuitive approach, that is, the matrix modeling, is proposed to describe the CCHP system. Having the matrix modeled system, the optimal operation strategy can be obtained by solving a non-convex optimization problem. SQP is adopted to solve the problem for a sold-back-disabled system; a novel algorithm is proposed to convexify and solve the problem for a sold-back-enabled system. The result of the optimization problem is the optimal power flow and operation strategy for the CCHP system.