A modified per-unit STATCOM model and analysis of open loop response time

The per-unit system has brought much advantage for the analysis and calculation of traditional AC systems, so it is a natural idea to make a per-unit mathematical model for static synchronous compensators (STATCOMs). However, due to the lack of a set of properly selected base values, such a model is still unavailable till now. The present quasi-per-unit model of STATCOM has resulted in the misunderstanding of physical meaning for DC side voltage and a severe mistake in determining the rating of DC capacitor. Based on the theoretical research and engineering experience derived from developing three different rating STATCOMs, the authors proposed a per-unit STATCOM mathematical model in this paper. This new model provides a systematic foundation for performance analysis and controller parameter determination. As an illustration of application, the relationship between the open loop response time constant and the main circuit parameters is discussed with the per-unit model