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Individual Channel Design-Based Modeling and Analysis of Three Phase Grid-Tied Inverter with Unbalanced Grid Impedance

Three-phase grid-tied inverters are usually designed to operate in symmetric grid impedance. In actual operations, due to the imbalanced loads, three-phase systems with significant single-phase loads, imbalanced power line impedance or the imbalanced short-circuit impedance of the three grid power transformer, the equivalent three-phase grid impedance is unbalanced. It is, consequently, important to develop an effective model and stability analysis method to address three-phase grid-tied inverter with unbalanced grid impedance. Traditionally, the stability of unbalanced system can be analyzed by harmonic linearization technique, however, the model derivation is complex and the controller parameters need second designing. This paper develops the system model in a multivariable frequency domain, by using the individual channel analysis and design (ICAD), simplifying the stability analysis of the unbalanced system. The detailed study on the three-phase LCL filter-based grid-tied inverter under the unbalanced grid impedance condition is presented. Simulation and experiment analysis are carried out on a 380 V/50 Hz/6 kW grid-tied inverter prototype.