Impedance Modeling and Stability Analysis of Grid-Interactive Converters-Slides

Abstract: Modern power systems equipped with large amount of power electronic converters may suffer from small-signal instability due to the control interactions. To deal with this topic holistically, this webinar discusses impedance-based modeling and stability analysis approaches for converter-based systems and the application of these approaches for converter control design.
First, the impedance modeling of converter systems is introduced. A unified frequency-domain modeling approach of three-phase converters in the stationary reference frame is developed for both balanced and unbalanced grid conditions. The corresponding measurement approach is developed, which verifies the analytical model by frequency scan in experiments.
Next, how to utilize the impedance models for stability analysis is introduced. For single-input single-output systems, a more general impedance-based stability analysis approach implemented on individual impedance Bode diagrams is proposed, which enables to analyze black-box systems with open-loop right-half-plane poles and facilities the impedance specification for converter systems. Then, how to extend the impedance-based stability analysis for multi-input multi-output systems is introduced.
Finally, the impedance modeling and stability analysis approaches are applied to grid-forming converters for controller design and stability enhancement. For high-frequency stability, a passivity-based controller co-design method is proposed to achieve the passivity till half of the sampling frequency, which improves the stability in various grid connected scenarios. For low-frequency stability, a control-loop decomposition method is developed to analyze the impacts of multi-loop controllers on the converter’s impedance shaping, which facilitates the controller design to improve the stability in stiff grids.