PadeDelay block with small time delay results in unreliable simulation and wrong Bode plot

[modelica-trac-importer]

Reported by otter on 5 Jan 2015 20:59 UTC
Simulating Blocks.Nonlinear.PadeDelay with delayTime=0.001 and n=4 is practically halting the simulation (no progress in simulation time). Linearizing this model give a completely wrong linear model (number of zeros/poles are wrong).

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Migrated-From: https://trac.modelica.org/Modelica/ticket/1637

[modelica-trac-importer]

Comment by otter on 5 Jan 2015 21:09 UTC
Fixed in 187f8b3 (in trunk) by a more reliable numerical implementation and adding 2 test models in ModelicaTest:

A new parameter balance=false/true introduced. The default balance=false results in the previous implementation of MSL 3.2.1 (for backwards compatibility). For balance=true, the state space representation is balanced, resulting in a much smaller norm of the system matrix. Simulation of the critical system does now pose not any problems. Also higher order, say n=10, can now be simulated without problems. Furthermore, linearization results in the correct linear system.

In r7840 the Bode plot computation in Modelica_LinearSystems2 was improved to handle systems with large positive zeros in a numerically reliable way. With this change, the Bode plot of the critical system, also with higher n, is now also correct.

[modelica-trac-importer]

Changelog modified by otter on 5 Jan 2015 21:09 UTC
PadeDelay block: More reliable numerical implementation