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In this article, an axial modular variable flux reluctance starter generator (AMVFRSG) with dc field excitation is proposed, which can achieve physical isolation between field windings and armature windings comparing with conventional structure. The axial modular design theory is demonstrated via three-dimensional finite-element method, and the AMVFRSG is optimized to simultaneously achieve both starting and generating performance. Fault-tolerant capabilities including elimination of coupling, suppression of short-circuit current, and fault-tolerant operation are investigated and compared with conventional structures. Additionally, the influence of rotor poles on AMVFRSG performance is analyzed. Finally, a prototype is manufactured and tested, including no-load, starting performance, generating performance, fault and fault-tolerant operation tests to validate both the theoretical and finite-element analyses.

More electric aircraft have high-reliability requirements, and the dc-field excited modular variable flux reluctance machine (MVFRM) is its key component. The MVFRM has both armature and field windings in which alternating currents and direct currents are supplied. Hence, the traditional fault diagnosis is not applicable for MVFRM. In this article, the diagnostic methodology for open-circuit faults in both windings is proposed by utilizing armature currents and field currents. Based on the internal relationship between the armature currents with the αβ-axis currents and the field currents, the characteristics and diagnosis mechanisms of armature winding and field winding open-circuit faults are analyzed. The per-unit threshold setting method is adopted to improve the rapidity of the algorithm without reducing robustness. The rapidity and effectiveness of the fault diagnosis algorithm are verified by different types of open-circuit fault diagnosis experiments. Furthermore, the robustness of the fault diagnosis algorithm is verified by the variable speed and different loads of open-circuit fault diagnosis experiments.