Frequency coupling characteristics of electromagnetic oscillation in grid-connected converters

Under certain conditions, grid-connected voltage source converter (VSC) may result in electromagnetic oscillations. Many coupling components with different frequencies could be observed in converter outputs when oscillation happens. The characteristics and mechanism of frequency coupling phenomenon in oscillations of VSC are studied. The magnitude relationship between first-order components in the three-phase domain is drawn by impedance model. The two first-order components will result in higher-order components due to the non-linearity of VSC controller. There are mainly three coupling paths in a controller: phase-locked loop, DC voltage fluctuation and overmodulation. The coupling mechanism and frequency distribution characteristics are investigated in this study. Theoretical results are validated by simulations with PSCAD/EMTDC.