Simulink Control Design™ - MathWorks

Compute Operating Points Using Custom Constraints

and Objective Functions

Typically, when computing a steady-state operating point for a Simulink® model using an

optimization-based search, you specify known fixed values or bounds to constrain your

model states, inputs, or outputs. However, some systems or applications require

additional flexibility in defining the optimization search parameters.

For such systems, you can specify custom constraints, an additional optimization objective

function, or both. When the software computes a steady-state operating point, it applies

these custom constraints and objective function in addition to the standard state, input,

and output specifications.

You can specify custom equality and inequality constraints as algebraic combinations of

model states, inputs, and outputs. These constraints let you limit the operating point

search space by specifying known relationships between inputs, outputs, and states. For

example, you can specify that one model state is the sum of two other states.

You can also specify a custom scalar objective function as an algebraic combination of

model states, inputs, and outputs. Using the objective function you can optimize the

steady-state operating point based on your application requirements. For example,

suppose that your model has multiple potential equilibrium points. You can specify an

objective function to find the steady-state point with the minimum input energy.

For complex models, you can specify a custom mapping function that selects a subset of

the model inputs, outputs, and states to pass to the custom cost and constraint functions.

You can specify custom optimization functions when trimming your model:

• At the command line: Create an operating point specification using operspec, and
  specify the custom functions using the CustomConstrFcn, CustomCostFcn, and
  CustomMappingFcn properties of the specification.


• Using Steady State Solver: On the Specification tab, click Trim Options. In the
  Trim Options dialog box, in the Custom Optimization Functions section, specify the
  function names.


• Using the Linear Analysis Tool: On the Linear Analysis tab, in the Operating Point
  drop-down list, click Trim Model. In the Trim the model dialog box, on the Options
  tab, in the Custom Optimization Functions section, specify the function names.

1 Steady-State Operating Points