Average-Value Modeling of Multi-Phase Machine-Converter Systems with Asymmetric Internal Faults

Multi-phase machine-converter systems are being utilized in many advanced energy conversion systems, e.g., aircraft, marine and vehicular power systems, and renewable energy generation. Accurate and efficient models are essential for simulation, analysis and design of such systems. Recently, a parametric-average-value modeling (PAVM) technique has been presented for 12-pulse rectifiers connected to six-phase machines including several dominant harmonics (i.e. 5
^th
, 7
^th
, etc.). Although the presented PAVM allows fast simulations, it assumes symmetrical operation of the rectifier, which limits its application only to normal operation. In this paper, the PAVM methodology is extended to consider asymmetrical operation of the 12-pulse rectifiers that may occur due to internal faults of some of the switches. This is achieved by formulating the characteristic as well as non-characteristic (i.e. 2
^nd
, 3
^rd
, etc.) harmonics in both positive and negatives sequences in addition to the dc components appearing in ac voltages and currents. Using a case-study system consisting of a six-phase generator connected to a 12-pulse ac–dc rectifier, it is demonstrated that the proposed extended PAVM can accurately reconstruct the waveforms of the detailed switching model of 12-pulse rectifier in faulty conditions while allowing much faster simulations.