# ODM application

**Background**

On the modeling large-scale power systems on RTDS (real time digital simulator), it is needed to simplify the structure of the power grid through dynamic equivalent. BPA is the most commonly used software for modeling and dynamic equivalent of power systems in China. Taking into account the convenience that RTDS is providing a data conversion from PSSE to RTDS. Moreover, BPA and PSSE are both based on the electromechanical transient computation. Therefore, it is of great practical significance to study the data conversion from BPA to PSSE.

On the other hand, with the existing of ODM and the adapter from BPA to ODM, it is more advised to developed a data adapter from ODM to PSSE. Due to the well-defined structure of ODM, developing an adapter to a specified data format would be straight-forward.

This project is on-going, working in progress by the InterPSS developing team and a research team of School of Electrical Power at South China Univ. of Technology, under Prof. Zhang Yao and Prof. Zhigang Wu. If you are interested and want to contribute, please contact the InterPSS development team.

**Project introduction**

On the analysis of the BPA and the PSSE, the conversion methods and the related source codes are designed and implemented, which include power flow model, synchronous machine model, static load model, excitation system model, turbine-governor model and PSS model.

**power flow data conversion**

Power flow calculation is the basis of any power system analysis. By analysis of the BPA, ODM and PSSE, we conclude that the factors that contributes to the success of power flow data conversion includes:

1. Make the correct translation of bus types and their parameters between the two software packages;

2. Map correctly the branch model from BPA--ODM--PSSE;

**Bus data mapping**

To make the conversion successful, it is necessary to find out the difference of ways how this two package treating a bus. A summary about the difference and their relationship is listed below:

**Branch data mapping**- Non-transformer branches data mapping

"L" card in BPA format is relating to Non-transformer branches data in PSSE. The two types of data descriptions are matched perfectly and requires no any special workload. In other words, the conversion is very straightforward.

- Transformer data mapping

In BPA, a two-winding transformer is represented by a "T" card, and a three-winding transformer should be firstly simplified into a two-winding one, then modeled by a "T" card. So it is advised to use the two-winding transformer model in PSSE to model any transformer in BPA. However, the ways that the two packages model a two-winding transformer are not excatly the same, so it is needed to make ceratin analysis and conversion before actural implementation.

The models of a two-winding transformer in BPA and PSSE are illustrated below perspectively:

The conversion of this two model could be made by:

**Test results comparison**

In order to test the power flow data conversion, a IEEE 9 bus system is used. The data is originally in BPA format, and then use the data conversion package described above to convert the data into PSSE. Test results are showed in below:

From the table avove we can see that the load flow result is perfectly matched.

**Transient data conversion****Generator model mapping**

In BPA, there is four generatr models, sub-transient model, transient model, classical model and equivalent-loaded model. While in PSSE, there is more types of generator models. The relations between models in this two types of packages are listed below:

We can see that nearly all the models in BPA could find their related models in PSSE except the non-salient pole transient model. However, PSSE provides a full dimensional model--CGEN1, so we can use this CGEN1 to model the non-salient pole transient model in BPA format. Conversion is shown below:

**Exciter system mapping**- Currently, implemented exciter models and their corresponding models in PSSE format are list below:

By the use of ODM, it is very straightforward to implement other types of exciter system. For more information, please visit the source code.

**PSS system mapping**- Currently, implemented PSS models are listed belows:

BPA

SS

SI/SI+

PSSE

IEE2ST

PSS2A

Also, implementation of other types of PSS systems is easily accomplished.

**Turbine-governor system mapping**- Currently, implemented turbine-governor system are listed below:

BPA

GS

GH

PSSE

IEEEG1

IEEEG3

**Static load mapping**

Static load model in BPA is modeled as:

And in PSSE, it is modeled as:

These two types of models could be easily related and mapped.

**Test case**

(working in progress.)