Unified Small-Signal Impedance Modeling and Analysis of Multi-Pulse Rectifier Units for More Electric Aircraft

Moving toward the more electric aircraft (MEA) technology, the power converters, which present as constant power loads (CPL), are increasingly used in the aircraft power system. The CPLs exhibit negative impedance, which may impair the system stability. Since the multipulse rectifier units (MPRUs) are the major secondary power supplies of the MEA variable-frequency ac power system (VFAC-PS), a unified small-signal impedance model of the MPRUs in the d-q frame is established. On this basis, the terminal characteristics of the MPRUs are analyzed. Then, a case study of a MPRU connected with a motor drive system is carried out to demonstrate the effects of variable-frequency of the ac voltage therein and the MDS' controller parameters on the system stability. Finally, the accuracy of the unified impedance model and the correctness of the theoretical analysis are verified by the experiments from the hardware-in-the-loop platform of the MEA VFAC-PS.