Reduced-Order Small-Signal Model of Microgrid Systems

The objective of this study was to develop a reduce-dorder small-signal model of a microgrid system capable of operating in both the grid-tied and the islanded conditions. The nonlinear equations of the proposed system were derived in the dq reference frame and then linearized around stable operating points to construct a small-signal model. The high-order state matrix was then reduced using the singular perturbation technique. The dynamic equations were divided into two groups based on the small-signal model parameters ε. The “slow” states, which dominated the system´s dynamics, were preserved, whereas the “fast” states were eliminated. Step responses of the model were compared to the experimental results from a hardware test to assess their accuracy and similarity to the full-order system. The proposed reduced-order model was applied to a modified IEEE-37 bus grid-tied microgrid system to evaluate system´s dynamic response in grid-tied mode, islanded mode, and transition from grid-tied to islanded mode.