Jay Senthil Senior Staff Software Engineer jayapalan.senthil@siemens.com	Martin M. Glynn Senior Staff Software Engineer martin.glynn@siemens.com

Abstract

This article discusses changes in the way PSS^®E handles user-written models starting with version 31.

General

PSS^®E has a vast library of time-tested dynamic models. PSS^®E also provides the capability of creating "user-written" models, an extremely powerful technique employed by numerous PSS^®E users over the years to create highly sophisticated models. PSS^®E user-written dynamic models, like PSS^®E standard models, are analytically initialized based on the power flow results. The initialization is accurate, and the dynamics simulation can be started without any movement from initial time (t=0). In addition, users can create any type of model of any desired complexity. In fact, many of the PSS^®E-standard models in the PSS^®E library were initially implemented as user-written models, and then later transformed to PSS^®E standard library models.

In view of the widespread use of user-written models, Siemens PTI has a long-standing commitment to making the use of user-written models as easy and intuitive as possible. In order to achieve this goal, PSS^®E-31 introduces a major shift in the way user-written models are handled.

Connection Routines

The connection between PSS^®E and the user-written models is established via calls to the user-written models which, in the pre-31 releases of PSS^®E, was required to be in one of the connection routines.

In the PSS^®E-30 release, there were eight different connection routines: USRXXX, USRLOD, USRREL, USRAUX, USRDCL, USRFCT (collectively called USRzzz routines), CONEC and CONET. Subroutines USRzzz and CONEC are normally in the file conec.flx (called conec file), while subroutine CONET is in the file conet.flx (called conet file).

Depending on the model type, user-written model calls were generated in one of the USRzzz routines, the subroutine CONEC, or in the subroutine CONET. For example, user-written plant-related models were called in subroutine USRXXX, user-written load-related models in USRLOD, user-written line-relay models in USRREL, user-written auxiliary signal models in USRAUX, user-written dc line models in USRDCL, and user-written FACTS device models in USRFCT. All other model types were called in subroutine CONEC and/or subroutine CONET.

In order to include user-written models in a PSS^®E dynamic simulation, users were required to create the dynamics user library (called "dsusr.dll"). Typically this entails compiling their connection routines and user-written models and then linking the dynamics user library. Previously compiled objects of model programs can be managed at the link step.

Since there were no changes to the structure of the conet file between releases of PSS^®E-30 and PSS^®E-31, models called in subroutine CONET will not be discussed further in this article.

At PSS^®E-30, the default (or skeleton) conec file with no user-written model calls consisted of the following code:

If the dynamic simulation case has the following user-written models: CONEC-called model MYMDLA, plant-related model AVR1, load-related model LOD1, line-relay model REL1, auxiliary signal model AUX1, dc line model DCL1, and FACTS device model FCT1, then the PSS^®E-30 conec file consisted of the following code:

The conec file, for PSS^®E-31, with the same set of user-written models in the dynamics case consists of the following code:

Some of the key differences between PSS^®E-31 and earlier releases are:

• PSS^®E-31 conec file has neither the USRzzz subroutines nor the user-written model calls that were required in the previous version. Since PSS^®E can identify the user-written model names and the arguments to them, these model calls can be generated by PSS^®E like any other PSS^®E standard model.
• With no user-written model calls in any of the USRzzz routines, there is no need to “cut & paste” following addition of dynamics data (DYRE,ADD) containing user-written models.
• The structure of conec and conet files generated by PSS^®E is consistent for use either as FLECS or FORTRAN files.
• As of PSS^®E-31, the model calls in subroutines CONEC and CONET still remain. Our goal is to remove these as well. We are fully committed to doing this, to be implemented in a future PSS^®E release.
• As of PSS^®E-31, conec and conet files are not mandatory. If there are user-written models whose model calls are not generated in subroutine CONEC and/or CONET, then there is no need to generate the conec and conet files.
• If there are no model calls in conec and conet files, there is no need for conec and conet files at all, and hence there would be no need to compile them.

Although we plan to remove the need for conec and conet files, we intend to retain the CONEC and CONET subroutines as a feature. Reasons include allowing for backward compatibility and allowing for users' adjustment to the new procedures at a time of their own choosing. In addition, the CONEC and CONET subroutines are a quick and an easy place to implement in-line codes.

There is still a need to compile user-written models, and there is still a need to communicate to PSS^®E where to find them. This will be addressed in the sections below.

Compilation and Creating the Dynamics User Library

In the pre-31 releases of PSS^®E the following methods were provided to compile the conec and conet files and any user-written models: (1) use the PSS^®E generated batch file "compile.bat" (to compile FLECS files only), (2) use the PSS^®E supplied batch file "cmdlusr.bat" (which could be used to compile FORTRAN as well as FLECS files), (3) employ a user-modified version of one of the batch files. After compilation the only method provided to create the dynamics user library was to run the PSS^®E batch file "cload4.bat".

"cload4.bat" always created a file named "dsusr.dll". Although it is possible to modify "cload4.bat" to create a dll with a different name, the changes required in "cload4.bat" to do this were not very obvious and, more importantly, there was no API routine prior to PSS^®E-31 to load a dll by name. "dsusr.dll" is loaded automatically, and always was.

At PSS^®E-31, a GUI method for compiling and creating the dynamics user library is provided. This method, called “create usrdll”, is supplied with PSS^®E and combines the functions of "compile.bat", "cmdlsur.bat", and "cload4.bat" procedures of PSS^®E dynamic simulation.

Users can use either "cload4.bat" or the "create usrdll" facility to create the dynamics user library. "cload4.bat", as before, will always create the file named "dsusr.dll". With the "create usrdll" facility users can create a dll of any name. By default the name "dsusr.dll" will be presented in the "create usrdll" GUI. However the user has the liberty to change the name "dsusr.dll" to any name (for example "abc.dll"). When PSS^®E is started up, by default it will attempt to load "dsusr.dll". If it finds "dsusr.dll", it will load it. However, if PSS^®E does not find it, there will be no error. In previous versions of PSS^®E "dsusr.dll" was required; this is no longer the case. In contrast, "abc.dll" will not get loaded automatically because PSS^®E does not know this name. The user can load "abc.dll" using the ADDMODELLIBRARY API routine.

The natural approach for an experienced PSS^®E dynamics user to take when using the new "create usrdll" process is to specify the sources to be used to build the library – i.e., conec and conet, if used, and user-written models, if used – and create "dsusr.dll". When used in this way the change from the preceding methodology is minimal. The GUI process is simpler and more intuitive.

Of greater benefit to the user is the ability to create a customized dll. For example, users can maintain all their models in one dll, and that dll does not need to have the CONEC and CONET subroutines. In fact, it would be better if "abc.dll" does not have any references to CONEC and CONET. As explained earlier, CONEC and CONET have hard coded numbers in model calls and are, therefore, user-specific, and perhaps even case-specific. Each user or study can have unique CONEC and CONET routines in "dsusr.dll", if needed. If the models themselves are all in "abc.dll", then only that dll needs to be recreated if the source to one of the models changes.

The same "abc.dll" can be used for more than one study. It would not need to be rebuilt by every user. It can be maintained by one person (the contact person) and distributed to all users who need it or referenced from a common network drive. If the user model types do not generate any model calls in conec.flx and conet.flx, then the user does not have to compile and generate "dsusr.dll". In such situations, although there are user models in the case, if users employ "abc.dll", they do not have to compile or link (i.e., there is no need for a compiler). All they have to do is get "abc.dll" from the contact person, start PSS^®E, load "abc.dll", and they are ready to run PSS^®E.

With the current PSS^®E release (version 31.0.1), the user will need to enter the ADDMODELLIBRARY call for every execution of PSS^®E that needs access to a dynamics user library named other than "dsusr.dll". Enhancements to retain additional library names from one execution to the next, and then provide GUI access to this list, are in development.

Conclusions

Siemens PTI is committed to making the handling of user-written models as easy and intuitive as possible. The overall goal is to remove the need for user dependence on conec and conet files, and to limit the need for compilers to only those users who write or modify user-written models. Our first step was to simplify the connection routines and allow the creation of user named model libraries. In the immediate future we’ll be enhancing the tools to manage these user named model libraries. In a future PSS^®E release there will be no need for the conec and conet files at all. At that time only the user-written models themselves will need to be maintained by the user community, and only developers of those models will need to compile programs or link libraries in order to use those models in PSS^®E dynamics studies.

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