Issue with Increasing Time Step in "Two-Zone MVDC Electric Ship" Model

I am working on the "Two-Zone MVDC Electric Ship" model in Simscape Electrical. The project can be found here: Two-Zone MVDC Electric Ship.

I need to run the model simulation on the desktop for several thousand seconds and want to increase the time step to speed up the simulation and limit data logging. The default time steps are:

• TsELEC = 25e-6
• Ts = 25e-6
• TsTHERMAL = 1e-3

The solver time step is set to TsELEC, and the model uses a local solver partitioning by default.

• Increasing TsELEC to 1e-4:

Error: An error occurred while running the simulation and the simulation was terminated

Caused by:

['Two_Zone_MVDC_PSolver_R2020b/Subsystem4/Solver Configuration']: Nonfinite (Inf or NaN) states found. Use a different partition method.

Component: Simulink | Category: Block error

• Changing Partition Method to Robust Simulation:

Error: An error occurred while running the simulation and the simulation was terminated

Caused by:

['Two_Zone_MVDC_PSolver_R2020b/Subsystem4/Solver Configuration']: Nonfinite (Inf or NaN) states found. Use a different local solver or turn the local solver option off.

Component: Simulink | Category: Block error

• Switching Solver to Backward Euler:

Error: An error occurred while running the simulation and the simulation was terminated

Caused by:

['Two_Zone_MVDC_PSolver_R2020b/Subsystem4/Solver Configuration']: At time 9.067000, one or more assertions are triggered. See causes for specific information.

Argument of sqrt must be finite (not Inf or Nan). The assertion comes from:

Block path: Two_Zone_MVDC_PSolver_R2020b/Subsystem4/Gas turbine/ AVR and exciter/Terminal Voltage Measurement

Assert location: (location information is protected)

Could you please provide guidance on how to properly increase the time step without encountering these errors?

Thank you for your assistance.

Best regards,

Answer 1

[Sumukh]

Hi Ali.

The MVDC model has a default time step of 25e-6 and runs for 30 sec. So, increasing the time-step to 1e-4 throws an error, as the time step is too large to capture the dynamics of the system, and it is possible that the solution diverges over time. The local solver setting controls the time-step of the whole model, while the Solver Configuration block specifically controls the sample rate of the Simscape blocks.

The model, however, works for 1e-5 time-step, increasing the time-step by 2.5x, so the simulation speed can be iteratively checked around this value, instead of 1e-4 time-step. Increasing the time-step value affects the accuracy of the system and must be accounted for when running for longer time.

Please check out the following documentation to improve the model speed, while also accounting for model accuracy:

https://www.mathworks.com/help/releases/R2023a/simscape/ug/improving-speed-and-accuracy.html?searchHighlight=improving-speed-and-accuracy

I hope this helps in resolving the error in the model.