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Simulation

To model hybrid dynamic systems, the mathematical model has to be implemented by a model that supports the idiosyncrasies of dynamic physical systems. In physical system models, event generation tex2html_wrap_inline957 is based on continuous signals and separated from the discrete model part, tex2html_wrap_inline995 , [6]. Furthermore, event generation often is specified in terms of signal values, s, that are derived from state variables given a mode tex2html_wrap_inline767 , tex2html_wrap_inline1001 . Fig. 7 shows the implementation model. In this model mythical modes emerge from two loops

  1. tex2html_wrap_inline1003 which results in mythical modes without discontinuous changes in the state vector. Therefore, it allows sequences of mythical modes on

    picture573

    transitions.

  2. tex2html_wrap_inline1005 which results in mythical modes when discontinuous changes in the state vector occur. Given temporal evolution of state, this can only occur on

    picture565

    transitions.

   figure453
Figure 7: A general hybrid system.

The recursive relation in Eq. (6) is implemented by SEL_MODE which is presented in Algorithm 1. SEL_MODE is executed twice for each time step. First when a new mode based on continuous evolution is determined. To improve precision, tex2html_wrap_inline1007 is variable and a bisectional search is used to find the switching point within a pre-specified accuracy. Second when pinnacles are traversed, and, therefore, the tex2html_wrap_inline1007 argument of SEL_MODE in Algorithm 1 is set to 0.

  algorithm483

The DER_SIGNAL function deals with numerical effects of the derivative part of h, tex2html_wrap_inline1025 , as a special case. In case either tex2html_wrap_inline1027 (a pinnacle), or if tex2html_wrap_inline1029 (a discontinuous change), the area of the corresponding Dirac pulse is returned without including the signals that do not contain derivative effects as embodied by tex2html_wrap_inline1031 . Otherwise, no discontinuous changes occur and an Euler approximation can be used for the derivative, in which case signals as a result of tex2html_wrap_inline1031 are included.


next up previous
Next: Summary Up: Extended Abstract Previous: Simulation

Pieter J. Mosterman
Wed Aug 20 15:28:13 CDT 1997