Exergetic Port-Hamiltonian Systems: Modeling Basics.

Port-Hamiltonian systems theory provides a structured approach to modeling, optimization and potential-based control of multiphysical systems. Yet, it often seems to be unclear how the port-Hamiltonian structure relates to thermodynamics. One reason is that the Hamiltonian of a dissipative system is traditionally referred to as an energy function, although it is an exergy function. Clarity on this aspect leads benefits: 1. Links to the GENERIC structure of systems with local equilibrium are identified making it relatively easy to borrow ideas from a widely-accepted and actively-developed approach to nonequilibrium thermodynamics. 2. The port-Hamiltonian structure combined with a suitable bond-graph syntax is expected to become a main ingredient in thermodynamic optimization methods akin to exergy analysis and beyond. The intuitive nature of exergy and diagrammatic language facilitates interdisciplinary communication that is necessary for implementing sustainable energy systems and processes. Port-Hamiltonian systems are cyclo-passive, meaning that a power-balance equation immediately follows from their definition. For exergetic port-Hamiltonian systems, cyclo-passivity is synonymous with degradation of energy and follows from the first and the second law of thermodynamics being encoded as structural properties.