Analysis of Dynamic Properties of VSCs Connected to Weak Grids Including the Effects of Dead Time and Time Delays

In recent years, the penetration of distributed generators (DGs) with power electronics interfaces has rapidly increased and this fact has created new challenges for the operation of power systems. In some cases, when DGs are connected via long distribution cables, an interaction between their control systems and the network may produce undesired resonant effects. This emphasizes the importance of more accurate dynamic modeling of the system to predict and prevent such events. This paper presents an integrated small-signal model of voltage source converters (VSCs) that includes the dead time and time delays implementation effects that are typically not considered in the literature. An approach based on eigenvalue and singular value decomposition is used to evaluate the impact of the network impedances on the robustness of the power system. The accuracy of the integrated small-signal model was validated by using a dedicated laboratory test network composed of 15-kVA VSCs connected to the grid via emulated distribution lines. The analysis of the implementation effects revealed their significant impact on the accuracy of the small-signal models as well as on the overall system stability. The two models that include and exclude the implementation effects are critically compared and the experimental results are provided.