Influence of inverter coupling transformer magnetizing curve on Fault Ride Through operation in a grid tied application

This paper presents the topic of grid connected power converter operation during power transformer recovery inrush current. The phenomenon is as a consequence of temporary voltage dip occurrence. Based on the measurements results and multiple simulations the authors show the relevance of this phenomenon to the typical Fault Ride-Through (FRT) studies. In this study multiple simulations have been run in order to verify the error that can be potentially obtained by not accounting for transformer saturation. This error is expressed by prolonged FRT operation phase due to additional voltage sag occurring after fault clearing. In the idealized case which was also studied, it has been found that the relevance of power transformer magnetizing curve implementation on the FRT study outcome is clearly visible. However, the model with no saturation in the studied configuration is not critical, due to the fact that the additional post fault dip magnitude is small and short in duration. Therefore, the typical FRT algorithm can handle such distortion without exceeding the specified limits. Nonetheless one should keep in mind that the idealized scenario where no saturation is included may vary from the actual output of the real inverter.