Date Conversion in BPA and PSS/E Based on China Southern Power Grid

This paper undertakes transference of BPA date of the China Southern Power Grid into PSS/E data, covering a comparison between DC data and calculated results of power flow which excluded DC data, testing the accuracy of transference of power flow data, and demonstrating the transference program in data conversion is applicative. The results show that the two results fundamentally resemble each other, which indicates the transferred data is correct.


Introduction
PSS/E software with its powerful function of the simulation calculation has been more and more popular among domestic research institutions. In the past, to complete the BPA and PSS/E data transformation, manually change conversion method is usually used or write the corresponding data conversion program for a particular grid data [1,2]. This paper takes the southern power grid in 2015 high flow operation mode as an example, carrying on the conversion between BPA and PSS/E with the data conversion software, and compares the results of pure AC and hybrid AC/DC system.

The Data Description of the Southern Power Grid
Southern power grid is a typical large capacity, long distance, multi-area and interconnected power grid, composed of the five provinces of Guangdong, Guangxi, Hainan, Guizhou, Yunnan, power grid and the company directly under it, and connect the power grid of Hong Kong and Macao by the Guangdong power grid [3][4][5].
In the BPA data of Southern power grid 2015 High flow operation mode, the generators adopt sub-transient model, considering the role of excitation system, the prime motor, governor and power system stabilizer(PSS), the load adopt static ZIP mode [7][8][9]. The data contain EA, EK, EC, FK/FZ, FJ/FZ, FQ/F+, and FV/F+ seven excita-tion system models, GS+TA, GS+TB, GG, GH four prime motor and governor models, and SS, SG, SP, SI/SI+ four PSS models, DC circuit adopt steady-state model.
For such a giant and complex network, the cost of manpower and material resources in the writing of BPA data is enormous. This paper converts it to PSS/E data with the help of BPA TO PSS/E data conversion software, greatly reducing the difficulty of manually filling original data and its stability data, saving a lot of manpower and resources, and reduces the risk of input errors.

The Flow Calculation Comparison of Pure AC Network
Correct flow data conversion is the premise and basis for transient stability analysis, this paper makes flow calculation of Southern power grid DC circuit using BPA and PSS/E separately to compare the correctness of the flow data conversion in the case of pure AC network. Due to space limitations, these paper only randomly select ten nodes as shown in Table 1(a), the largest node voltage amplitude difference is 0.0006, and the maximum phase difference is 0.06°. The result shows that the converted PSS/E flow data is very accurate and reliable. As shown in Table 1(b), the flow calculation results of BPA and PSS/E are consistent, which proves the BPA TO PSS/E data conversion software can convert the flow data of pure AC system.

The Comparison of Flow Calculation in
Hybrid AC/DC System then convert the flow data of BPA to PSS/E, with the DC circuit of the hybrid AC/DC system retained, The error of node voltage amplitude and phase angle in pure AC and hybrid AC/DC system calculated by BPA and PSS/E is shown in Table 3. From the statistical results can be seen that the node voltage amplitude and phase angle difference calculated by hybrid AC/DC system is significantly larger than the pure AC system.
The comparison of active power and reactive power in DC system is shown in Table 4. From Table 4(a) can see the active power loss in PSS/E is less than that in BPA, This is because PSS/E ignores the power loss of the inverter, just considering the active loss of the converter transformer and DC circuit, and BPA calculates the active loss of the DC inverter.
The reactive loss of the rectifier station is shown in Table 4(b), it tells the results calculated by BPA and PSS/E is a little different, but the difference of reactive  loss of inverter station is large, it has some reasons as followed: 1) in the calculation process of PSS/E, the inverter station is given the γ angle control, but BPA adopts the given voltage control; 2) BPA equivalently calculates each level of the bridge converter transformer. It is because there is difference between BPA and PSS/E in calculation method and DC system model, which leads to the calculation difference about reactive loss in inverter station between both of the software.

Conclusions
This paper introduces data conversion software for BPA TO PSS/E, and makes conversion of BPA date of the China Southern Power Grid into PSS/E data, through the test of the data between pure AC system and hybrid AC/DC system, presenting the BPA TO PSS/E software is feasible. The most important is that it reduces the difficulty of manually filling original data and its stability data, saving a lot of manpower and resources, and reduces the risk of input errors.