Small-Signal Impedance Modeling and Analysis of Variable-Frequency AC Three-Stage Generator for More Electric Aircraft

With the penetration of power electronics in more electric aircraft (MEA) power systems, the number of constant power loads continues increasing and the characteristics of negative resistance of their terminal impedances tend to impair the system stability. The variable-frequency ac (VFAC) three-stage generator (TSG) is the main power supply of the MEA VFAC power system, and it is essential to establish its small-signal impedance model for analyzing the system stability. In this article, an accurate small<italic>-</italic>signal impedance model of the VFAC-TSG is established under the synchronous <italic>d-q</italic> frame. On this basis, the terminal characteristics of the VFAC-TSG in open<italic>-</italic>loop and closed<italic>-</italic>loop modes are analyzed in detail. Furthermore, the impacts of the rotation speed and digital control delay on the terminal characteristics are demonstrated. Finally, the experimental results from a hardware<italic>-</italic>in<italic>-</italic>the<italic>-</italic>loop platform are provided to verify the accuracy of the proposed impedance model and the correctness of the theoretical analysis.