Simplified Small-Signal Modelling of Grid-Connected Voltage Source Converters for Transient Grid Studies

Distributed generation (DG) units increasingly become subject to grid codes requiring an active and reactive power control capability. Since voltage source converters (VSCs) represent a key component in many DG units, accurate but simple models are crucial for analysing transient grid phenomena and to find adequate solutions that help to maintain a high power quality. This paper presents a simplified analytical model of a grid-connected VSC, which covers the power flow from the primary energy source, over the DC link to the injected converter's output current for frequencies well below the converter's switching frequency. After modelling all relevant components of an open-loop power-controlled VSC, a model reduction is performed with special emphasis on the influence of DC link dynamics. Finally, the resulting model accuracy is validated and compared to its low-frequency approximation by means of computer simulations and Bode plots, respectively.