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User Defined Controllers (UDCs) and User Defined Topologies (UDTs).

All equipment and controllers modeled into conventional power system stability programs were built-in. The constant need to include new models to face the continuous development and design of new power system control equipment made it desirable to develop User Defined Controllers (UDCs) capabilities into modern software.

The User Defined Controllers models are built by interconnecting elementary control blocks, which enable the engineer to reproduce in the simulation program datafile the block diagram of the controller being modeled. A large set of these elementary blocks must be implemented in a simulation program. These blocks include arithmetic blocks, exponential or rational polynomial blocks, limiters, relay blocks among others and allow the construction of UDCs of any desired topology.

User Defined Controllers can be used to model excitation systems, speed governors, additional stabilizing signals, FACTS devices, non-linear dynamic loads and any other desired power system controller.

A natural evolution of the UDC technology is the User Defined Topology (UDT). A User Defined Topology, as the name suggests, is the topology of a User Defined Controller. A User Defined Controller is then built by a User Defined Topology plus its Associated Parameter Set (APS). Fig. 6 shows, schematically, the relationships among UDCs, UDTs and APSs. The UDC#1 is defined by the association of the UDT#1 with the APS#1. Note that the UDC#4 uses the same topology of UDC#1 (UDT#1), but uses a different parameter set (APS#3). An UDC can be defined without an associated UDT (this is the case of UDC#3).

This scheme allows the user to build a Power System Controller Library, which includes the various UDTs. New controller topologies may be easily included into the library by an experienced user. A less experienced user may then only provide the controller parameter values through a Parameter Set, once the controller topology is modeled in the topologies' library (see the picture below).

Relationship among UDCs, UDTs and APSs.

The UDT/APS scheme allows to easily implement into a simulation program the ability to read controller data in various input datafile formats. The user only needs to know the controller block diagram to model the controller topology (UDT) and include it in the library. The simulation program must have input routines for reading the parameter values from various program formats.

The system initialization is done in a completely automatic way, no matter the topological complexity of the various UDCs, by using the Newton-Raphson method.

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