Small-Signal Analysis of a Microgrid with Secondary Control Including the Dynamics of Primary Control and Communication Delays

Microgrids (MGs) facilitate the integration of distributed energy resources (DERs) in electrical grids. To coordinate the operation of these DERs, a three-level hierarchical control is commonly used. In general, different control layers are designed with sufficient bandwidth separation between them to avoid unwanted dynamic interactions, resulting in slow outer controllers. However, the interactions between primary and secondary controllers when their bandwidths are close has not been addressed in detail in the literature. In addition, communication latency represents an important bottleneck for the controller speed, and its modelling and impact on the control are both of interest for the scientific community. In this paper, possible interactions between primary and secondary controllers in an islanded MG are studied as well as the role of communication delays. For that purpose, participation factor and eigenvalue analyses are used. Results show that primary and secondary controllers are engaged in a slight interaction linked with the weighting factors of the secondary controller. It is also shown that the sensitivity of secondary control eigenvalues to communication delays is similar for different designs of the primary control.