An adaptive piecewise linearized weighted directed graph for the modeling and operational optimization of integrated energy systems

Operational optimization plays a vital role in ensuring the economy, security, and environmental friendliness of integrated energy systems (IES), while the nonlinear operating characteristics of energy converters have brought significant challenges to the accurate modeling and solution. Considering the nonlinear energy conversion processes, a novel adaptive piecewise linearized weighted directed graph model of IES is proposed in this paper. To accurately construct the complex energy flow relationship in IES, a weighted directed graph is first presented to describe the energy generation, conversion, storage, consumption, and demand response, thus realizing the automatic modeling of IES. On this basis, for the diverse partial-load performance of energy converters, an adaptive piecewise linearization strategy is developed to approximate the nonlinear operating characteristics of various energy converters adaptively. By taking the system operating cost, calculation time, energy mismatch, and optimization model complexity as evaluation indicators, the effectiveness of the proposed method is verified by the numerical simulations of a typical small-scale combined cooling, heating, and power (CCHP) system and a large-scale IES in a realistic industrial park. Compared with the constant efficiency method and the equispaced piecewise linearization method, the computational efficiency and accuracy are remarkably improved by the proposed method.