Impedance Modeling and Stability Analysis of Dual-Active Bridge Converter Interfacing DC Grids

As a key enabling component, high-power three-phase dual-active bridge (DAB3) converters are widely used to interface sources and loads to dc grids. However, with different control objectives and converter design parameters, the interconnected DAB3 converters could induce interactions that degrade the system stability. To address this issue, this paper presents a comprehensive impedance-based stability analysis method for DAB3 converter interfacing dc grids. The small-signal model of the DAB3 converter is firstly developed whereby the digital controllers for the voltage-controlled and current-controlled DAB3 converters are designed. Thereby, the output impedances of DAB3 converters are calculated, and a sensitivity analysis is performed to understand the influences of the controller bandwidth and the dc filter capacitance. With the obtained impedances, three different impedance-based stability criteria are investigated to analyze a dc system with two interconnected DAB3 converters. The unified stability criterion can determine the system stability accurately, while the gain margin and phase margin criterion can not only identify the low-frequency resonance intuitively, but also assist the design of control parameters and the filter capacitance. Time-domain simulation results are presented to validate the effectiveness and accuracy of the modeling and analysis method.