Impedance shaping of three-phase grid-parallel voltage-source converters

This paper presents techniques to shape the output impedance of three-phase voltage-source converters (VSC) used as inverters for grid integration of renewable energy and energy storage devices. The objective is to avoid harmonic resonance and other unintended interactions between the inverter and the grid impedance. For this purpose, the inverter is modeled by a positive-sequence and a negative-sequence output impedance. Shaping of the inverter output impedance is achieved through changes to various inverter control functions, including grid synchronization and current control. The trade-off between grid compatibility and inverter control performance is also discussed. Experimental results from a multi-converter system test-bed are presented to validate the analyses.