Queries about USRMDL keyword

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In rev 33 model REGCA1 was implemented by PTI as a user defined model and the DYR-record was

IBUS, 'USRMDL', ID, 'REGCAU1', 101 , 1, 1, 14, 3, 4, ICON(M), CON(J) to CON(J+13) /

The model code was supplied with PSSE and the user didn't need to add any .dll file.

In rev 35 the model is included in the standard library and the DYR-record is

IBUS, 'REGCA1', ID, ICON(M), CON(J) to CON(J+13) /

Note, rev 35 will also read the old rev 33 .DYR file and automatically convert to REGCA1 model

Many models are implemented in this way by PTI. First an interim user defined model, and eventually a final standard model.

It is possible for a user to write his own user defined model. It is described in POM, Chapter "Model Writing". The soruce code must then be compiled and linked to a .dll file.

The important point is not the user-defined model (UDM) provided by PSS/E. Sometimes you would like to implement a function/model behavior, but unfortunately, PSS/E does not provide the model you need. Then, you can build your model by programming UDM, that is the point of significance.

For my experience, I did build the function of frequency regulation of wind turbines by UDM!!