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Choosing Between Simulation Snapshot and Operating Point from Specifications

You can find steady-state operating points (or trim conditions) from specifications or at specific simulation times (or simulation snapshots).

Choosing which approach to use for computing your operating point depends on what you know about the operating point.

Use optimization-based steady-state operating point search when you know some of the operating point states and model input or output signal levels. Successful operating point search finds an operating point very close to a true steady-state solution.

Optimization-based search produces poor results when you specify:

  • Initial guesses for steady-state operating point values that are far away from the desired steady-state operating point.

  • Incompatible input, output, or state constraints at equilibrium.

    This is equivalent to overconstraining the optimization search.

Use the simulation-based approach when the simulation time is sufficiently short for the model to reach steady state. The algorithms extracts operating point values when the simulation reaches steady state. You must also specify the initial conditions that drive the model to steady state.

Simulation-based computations produce poor operating point results when you specify:

  • Simulation time that is insufficiently long to drive the model to steady state.

  • Initial conditions do not cause the model to reach true equilibrium.

    Note:   If your Simulink® model has internal states, do not linearize this model at the operating point you compute from a simulation snapshot. Instead, try linearizing the model using a simulation snapshot or at an operating point from optimization-based search.

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