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With the increase of power offtake requirements, it is proposed that the more electric engine (MEE) draws electrical power from a generator mounted directly on the gas turbine shaft-line without the use of a gearbox. It is expected that this arrangement will improve the power density and reliability of the whole system. The challenges include limited available space, high temperature, affordability, high power density and an exceedingly high reliability requirement. The segmented rotor flux switching machine is one of the promising topologies that are suitable for this application. The objective of this article is to investigate quantitatively the influence of several design parameters on the electromagnetic performance. The design parameters include, the excitation type, stator split ratio, segmented rotor length and load advance angle. Back EMF, cogging torque, average torque, torque ripple and magnetic force are considered to be the key evaluation criteria and are used to guide the search for the optimized design. The material discussed in this paper may be helpful to provide insight in the selection of key design parameters in the direct shaft-line gas turbine generators.

The Flux Switching Machine is one of the novel topologies within the hybrid machine class. It has many advantages such as flux focusing effect, compatibility with simple power converters, high fault tolerance with independent concentrated armature windings, mechanical robustness due to its simple salient pole rotor and high power density. With such attributes the machine is a promising candidate for high speed, high power density applications. It includes toothed rotor with permanent magnet excitation and segmented rotor with field coil excitation. This article reports on comparative studies into the mechanical stress, magnetic flux, back EMF, D axis, Q axis inductance and saliency ratio, loss distribution, efficiency and power density for these topologies via finite element analysis under open circuit and various load conditions. Quantitative simulation results reveal that the segmented rotor with field coil excitation topologies exhibit better electromagnetic performance, among which the 12/7 combination of stator pole and rotor segments exhibits superior EM performances than those of other combinations. Parametric analysis with respect to the aspect ratio and rotor segment arc angle are also performed on 12/7 topology to investigate their relationship with the torque, efficiency and power density.

The concept of a More Electric Aircraft (MEA) demands a highly optimized airframe power system which is achieved by replacing pneumatic and hydraulic systems with energy efficient electrical systems. With increasing power offtake requirements, the More Electric Engine (MEE) could play a key role in future MEA, where more electrical power will be drawn from gas turbine shaft using the conventional gear driven electrical machine, which is known to present inefficiencies and reliability issues. Embedding an electrical machine directly at the engine shaft would help eliminate the need for the accessory gearbox along with potentially improving the reliability and efficiency of the whole system. However embedding the electrical machine presents significant design challenges to meet the key requirements. Some of these include: the necessity of the electrical machine to operate in high temperatures and high vibration environments, the mechanical constraints such as space limitations, and the need to operate at high speeds. Other requirements include the need for high power density, high torque density, high efficiency and maintenance-free operation of the electrical machines. At present, different electrical machine topologies have been developed for a number of challenging industrial and automotive applications where some of the requirements and criteria have been partially met. In this paper the detailed investigation and the trade study carried out of the various electrical machine topologies to understand their advantages, constraints and drawbacks is presented to provide a preliminary evaluation of their suitability for meeting the stringent requirements of embedded machines in aerospace applications.

Traditional methods of AC synchronous generator short-circuit fault analysis such as symmetrical component method, coordinate transformation method can not consider eddy current, while multi-loop method can only use air-gap magnetic conductivity concept to calculate inductances, which roughly considers the saturation of ferromagnetic materials. Finite Element Method (FEM) can solve the above problems, but it has disadvantage of considering single coil type in one model. Therefore Uniform Field and Circuit Coupled FEM (UFCCFEM) is proposed in this article. It adds additional variable loop-current into external circuit equations to form systematic coupled equations, which can fully consider solid coil eddy current influence and stranded coil current linear distribution influence. This method has less simulation time than pure eddy FEM model and more accurate short-circuit current transient characteristic than pure transient FEM. Perform this method on a certain aeronautic AC power synchronous generator, eddy current and electric potential transient waveforms are obtained and compare with experimental values to verify the correctness of the method. Spatial flux linkage transient distribution plot also show that UFCCFEM can conveniently consider transient armature reactance towards magnetic field. This method has been successfully applied on synchronous generator short-circuit fault analysis of constant speed and frequency aeronautic AC power.