<p>Grid-forming voltage-source converters (VSCs) tend to suffer from sideband oscillations in stiff grids. Conventional state-space eigenvalue analysis or impedance-based stability analysis based on generalized Nyquist stability criterion can only analyze how specific control parameters affect the overall system stability, which ends up with less insight into a controller design-oriented analysis. To tackle this challenge, this article starts with the impedance modeling and stability analysis of grid-forming VSCs in stiff grids. Then, an impedance decomposition approach to characterizing the impacts of multiple control loops is proposed, which benefits in a controller design-oriented analysis for stability enhancement. Finally, simulation and experimental results are provided to validate the approach.</p>

To avoid potential privacy threats and associated cyber-security issues in microgrids, this letter presents a distributed active power sharing and frequency regulation method with <i>preserved privacy</i> of local information. In the proposed approach, the transmitted data including the active power outputs and capacities are protected by adding noises to the original ones. Theoretical analysis and verification studies are performed to illustrate the advantages of the proposed method.

The harmonic state-space, the dynamic phasor, and the generalized <i>dq</i> modeling are three methods developed for linearization of ac power electronic systems. This paper reveals explicitly mathematical relationships between the three modeling methods in both time and frequency domain. Representations of linearized models in different reference frames and from time domain to frequency domain, as well as their transformations are elaborated step by step. Case studies on a three-phase voltage-source converter that is connected to an unbalanced grid verify the theoretical findings.<br>

The <i>dq</i>-frame admittance of closed-loop controlled three-phase converters is a linearized model that is dependent on the operating points of the system. Yet, it is impractical to measure the converter admittance at all operating points. This paper, thus, proposes an approach to estimating the <i>dq</i>-frame admittance of three-phase converters at a wide range of operating points. The method applies multidimensional interpolation to a given set of admittance data, which is measured from the pre-defined operating points. The accuracy of interpolation is then evaluated by using the posterior error estimation method. The number of pre-defined operating points is next adjusted to find a good compromise between the accuracy and efficiency of the approach. Simulations and experimental results verify the effectiveness of the approach.<div><br></div>

The harmonic state-space, the dynamic phasor, and the generalized <i>dq</i> modeling are three methods developed for linearization of ac power electronic systems. This paper reveals explicitly mathematical relationships between the three modeling methods in both time and frequency domain. Representations of linearized models in different reference frames and from time domain to frequency domain, as well as their transformations are elaborated step by step. Case studies on a three-phase voltage-source converter that is connected to an unbalanced grid verify the theoretical findings.<br>

The harmonic state-space, the dynamic phasor, and the generalized <i>dq</i> modeling are three methods developed for linearization of ac power electronic systems. This paper reveals explicitly mathematical relationships between the three modeling methods in both time and frequency domain. Representations of linearized models in different reference frames and from time domain to frequency domain, as well as their transformations are elaborated step by step. Case studies on a three-phase voltage-source converter that is connected to an unbalanced grid verify the theoretical findings.<br>

<p>Grid-forming voltage-source converters (VSCs) tend to suffer from sideband oscillations in stiff grids. Conventional state-space eigenvalue analysis or impedance-based stability analysis based on generalized Nyquist stability criterion can only analyze how specific control parameters affect the overall system stability, which ends up with less insight into a controller design-oriented analysis. To tackle this challenge, this article starts with the impedance modeling and stability analysis of grid-forming VSCs in stiff grids. Then, an impedance decomposition approach to characterizing the impacts of multiple control loops is proposed, which benefits in a controller design-oriented analysis for stability enhancement. Finally, simulation and experimental results are provided to validate the approach.</p>

To avoid potential privacy threats and associated cyber-security issues in microgrids, this letter presents a distributed active power sharing and frequency regulation method with <i>preserved privacy</i> of local information. In the proposed approach, the transmitted data including the active power outputs and capacities are protected by adding noises to the original ones. Theoretical analysis and verification studies are performed to illustrate the advantages of the proposed method.