Battery Modeling Solver Coupling

In Simcenter STAR-CCM+ Batteries, the battery modeling process involves running the electrical and thermal solvers sequentially for each thermal time-step, starting with the electrical solver.

The thermal time-step is determined through a user-defined number of inner iterations. To increment the time variable, the thermal solver needs to complete this number of inner iterations. From this point forward, we refer to the thermal time-step as simply time-step.

At each time-step, the coupled solver process is:

  • Map the stack temperature distribution from the previous time-step to the electrical mesh. If the current time-step is the first, then start from the default initial state.
  • Solve the electrical solution using the electrical solution from the previous time-step as the initial condition. For the first time-step, the solver starts from a default initial state. The first time-step may take substantially longer than subsequent time-steps as the electrical solver iterates as many times as necessary to guarantee convergence.
  • Map the heat generation field from the electrical mesh to the thermal mesh.
  • Solve for the thermal solution by using the number of inner iterations that you define.
  • Check the solution stopping criteria and either stop or proceed to the next time-step.

You control the convergence behavior of the thermal solver by setting the time-step parameters. For the electrical solver, because the equations are solved at smaller, adaptive time increments, Simcenter STAR-CCM+ Batteries handles the solution convergence automatically.

To set an appropriate time-step, you should consider the rate of change of the electrical load. The time-step must be small enough so that the loading function gets resolved correctly, meaning that if the electrical load changes too abruptly between time-steps the electrical solver may fail to converge. Furthermore, if the electrical load is specified using a program file and its time-step is much finer than that defined for the thermal solver, the heat generation output from the electrical solver to the thermal solver might not be correctly captured. This occurs if the electrical load changes significantly several times within one time-step.