Modeling of Unbalanced Three-Phase Grid-Connected Converters with Decoupled Transfer Functions

The unbalanced three-phase passive filters or grid impedances lead to a multiple-input multiple-output (MIMO) dynamic model for grid-connected converters in the stationary αβ-frame. The MIMO system with the couplings between the α-axis and β-axis components complicates the stability analysis and current controller design. This paper thus presents a modeling method that decomposes the MIMO system into two single-input single-output (SISO) transfer functions, which enables to use the classical SISO system tools for the dynamic analysis and controller design. Time-domain simulations and experiments are performed and the results validate the effectiveness of the approach.