Study on modeling and time step in real time digital simulation of voltage sourced converter

The power system simulator is convenient for understanding the system characteristics, foreseeing the difficulty and conducting countermeasures, but the conventional analog type model is not flexible to evaluate the progressing apparatus, such as FACTS (Flexible AC Transmission System), DESS (Dispersed Energy Storage System), etc. This paper develops the real time digital simulation model of the voltage sourced converter, which is sufficiently flexible to evaluate the power electronics apparatus. This paper also discusses about the relation between the accuracy of the output of the model and the calculation time-step, which become restriction in real time calculation. The evaluation of the accuracy is performed not only by the waveform itself but also by the frequency characteristics of the harmonics generated from the converter model. Moreover, this paper proposed to use Wavelet-transform to evaluate the accuracy of the output of the proposed model in the time-frequency domain. The obtained results show that the proposed real time digital simulation model can give appropriate output with high accuracy to the objective frequency area.