Recording of Model Frequency Responses and Describing Functions in Modelica

An assistant Modelica package is introduced which supports the determination of model frequency responses or describing functions of Modelica models, as the case may be. The result is frequency response data which can be used for further analysis such as stability properties of the system in closed loop control or the derivation of linear time invariant (LTI) model approximations. The paper addresses inter alia proper scheduling of excitation frequency and amplitude, a brief theory of describing functions (harmonic linearization), the Modelica classes implemented in the package, and some application examples.