Comprehensive Modeling and Measurement of the Control Influence on Impedance at Critical LCL Frequencies for a 50 kHz SiC Converter

The impedance-based stability criterion has been established as an important tool to assess interactions of power converters with each other and the electrical grid. The converter impedance is strongly influenced by the converter control system, which can include a variety of parameters. This is especially relevant for converters connected to the grid using LCL filters. Additionally, higher switching frequencies extend the frequency range where the converter impedance is affected by the control parameter selection. Insights on how the selection of control parameters shapes the resulting impedance are therefore essential. This paper presents an impedance model of a 50 kHz LCL-connected converter that includes all relevant control parameters. The modeled influences on the converter impedance are verified with measurements of impedance curves with parameter variations. Finally, control parameters are adjusted to shape the impedance and to prevent resonances in a laboratory setup.