Research on the dynamic energy conversion and transmission model of renewable energy DC off-grid hydrogen system

•Traditional energy hub models often focus solely on the energy perspective during the establishment process. However, in the context of wind and solar fluctuations, the conductance of subsystems in DC off-grid hydrogen systems exhibits a nonlinear changing pattern. Therefore, this model introduces a nonlinear admittance model for subsystems, enhancing its applicability to real-world conditions.•The dynamic responses among electrical, hydrogen, and thermal multi-energy flows in DC off-grid hydrogen systems demonstrate highly coupled and nonlinear characteristics. This model, building upon the working mechanisms of subsystems, establishes a nonlinear dynamic transformation characteristics matrix to describe the intricate energy transmission laws in hydrogen production systems.•Under wind and solar fluctuations, extensive calculations are performed on a DC off-grid hydrogen system comprising subsystems such as wind turbines, solar cells, FC, DC inverters, inverters, rectifiers, electrolyzers, batteries, and hydrogen storage tanks. The paper evaluates the energy transmission laws of the system under dynamic conditions, providing valuable insights into its performance. The dynamic response characteristics between the multiple energy flows of electricity-hydrogen-heat in the renewable energy DC off-grid hydrogen production system are highly coupled and nonlinear, which leads to the complexity of its energy conversion and transmission law. This study proposes a model to describe the dynamic nonlinear energy conversion and transmission laws specific to such systems. The model develops a nonlinear admittance framework and a conversion characteristic matrix for multi-heterogeneous energy flow subsystems, based on the operational characteristics of each subsystem within the DC off-grid hydrogen production system. Building upon this foundation, an energy hub model for the hydrogen production system is established, yielding the electrical, thermal, and hydrogen energy outputs along with their respective conversion efficiencies for each subsystem. By discretizing time, the energy flow at each time node within the hydrogen production system is computed, revealing the system’s dynamic energy transfer patterns. Experiments were conducted using measured wind speed and irradiance data from a specific location in eastern China. Results from selected typical days were analyzed and discussed, revealing that subsystem characteristics exhibit nonlinear variation patterns. This h