Although the concept of a multiphase drive system dates back to the middle of the 20th century, the initial pace of development was rather slow, as witnessed by the first two surveys of the area published in the beginning of this century. However, considerably new developments have resulted in the last decade of the 20th century and the beginning of this century, leading to an authoritative survey of the asymmetrical six-phase drive control and subsequently of the review of the complete area. This also initiated the organization and subsequent publication of the first IEEE Transactions on Industrial Electronics "Special Section on Multiphase Machines and Drives" in May 2008, which commenced with another survey paper, and that contained 12 original research papers. Since the publication of this Special Section in May 2008, the level of interest and pace of developments in the area have further accelerated and substantial new knowledge has been generatedwith an ever-increasing number of published research papers and reported new industrial applications. Such a trend has been emphasized in a recent paper. It therefore seemed appropriate to revisit the area and organize this Special Section as a sequel to the first one. The call for the Special Section papers resulted in 51 submissions, almost twice as many as the total back in 2008, thus confirming a substantial growth of the area. Indeed, the amount of new knowledge acquired since the publication of the first Special Section in 2008 has meant that it was not possible to provide a complete and thorough survey of the field in a single review paper.

/pdf/multiphase-machines-and-drives-revisited-2kmbx8a5nm.pdf

Multiphase machines and drives - Revisited

Aircraft electrification is currently the best alternative to address the rising demand for more air transportation and deal with anticipated economic and environmental impacts. Although the all-electric-aircraft (AEA) concept is not yet a feasible solution, the more-electric aircraft (MEA) is gaining significant attention. Electrical systems either partially or entirely replace the large and inefficient hydraulic, pneumatic, and mechanical conventional aircraft actuating systems. The upgrade could also encompass the propulsion system, as in hybrid- and turbo-electric aircraft. This upgrade reduces the aircraft weight, reduces the usage of pollutant fluids, increases fuel efficiency, reduces carbon emissions, and increases aircraft controllability and reliability. This article reviews various application areas of electric machines in electrified aircraft, such as actuation, taxiing, propulsion, and generation. Moreover, it reviews the main types of currently/to be utilized electric machines and the critically required specifications. Finally, a comparison between the different considered machines and potential future research is discussed.

Review of Electric Machines in More-/Hybrid-/Turbo-Electric Aircraft

The author’s object in this book is to describe, by means of theory and example, the method of “squares” for the solution of boundary-value problems in twodimensional partial differential equations. This method has been developed and applied by Professor Thom .and his colleagues (including, more recently, Dr Apelt) during the last thirty years. For example, we are indebted to Professor Thorn’s valuable work for much of our knowledge of steady viscous flow past bluff bodies in the range of Reynolds number below that at which a periodic wake develops. The method of squares differs from the “relaxation” method in that the former is a straightforward iterative method, whereas in relaxation the individual worker uses his experience and skill to determine the precise step to take at a given stage of computation. For this reason the authors emphasize that the method of squares is far more suitable than the relaxation method for use with a digital computer. This is certainly an important factor in a comparison of the two methods, but it should be borne in mind that much of the work described in the book was done with a desk machine. After two useful chapters on finite differences, several chapters of the book are devoted to the solution of Laplace’s equation for various boundary conditions. Following are chapters on the solution of Poisson’s equation, fourth-order linear equations, the Navier-Stokes equations of viscous flow, and the equations of compressible fluid flow. The book is liberally illustrated and has many examples, mostly taken from the fields of fluid motion and elasticity theory. It is recommended to those interested in the numerical solution of partial differential equations.

Field Computations in Engineering and Physics. By A. Thom and C. J. Apelt. Pp. 165. 30s. 1961. (Van Nostrand, New York)

More electric aircraft (MEA) architectures consist of several subsystems, which must all comply with the settled safety requirements of aerospace applications. Thus, achieving reliability and fault-tolerance represents the main cornerstone when classifying different solutions. Hybrid electric aircraft (HEA) extends the MEA concept by electrifying the propulsive power as well as the auxiliary power, and thereby pushing the limits of electrification. This paper gives an overview of the high-power electrical machine families and their associated power electronic converter (PEC) interfaces that are currently competing for aircraft power conversion systems. Various functionalities and starter-generator (S/G) solutions are also covered. In order to highlight the latest advancements, the efficiency of the world’s most powerful aerospace generator (Mark 1) developed within the E-Fan X HEA project is graphically represented and assessed against other rivaling solutions. Motivated by the strict requirements on efficiency, power density, trustworthiness, as well as starting functionalities, supplementary considerations on the system-level design are paramount. In order to highlight the MEA goals and take advantage of all potential benefits, all subsystems must be treated as a whole. It is then shown that the combination of PECs, aircraft grid and electrical machines can be better adapted to benefit the overall system. This survey outlines the influence of these concerns and offers a view of the future technology outlook, as well as covering the present challenges and opportunities.

/pdf/high-power-machines-and-starter-generator-topologies-for-dl61u7qxmz.pdf

High-Power Machines and Starter-Generator Topologies for More Electric Aircraft: A Technology Outlook

Dual-active-bridge (DAB) enabled dc microgrids stabilization is investigated in this article. DAB has two control objectives: load current regulation and the dc-bus voltage stabilization. In multiobjective control applications, the conventional proportional integrator (PI)-based controllers face challenges in the control loop coordination. The saturation of the loops largely deteriorate the control performance. Moreover, the system impedance has to be measured before designing the active damping control. In this article, a moving discretized control set—model predictive control (MDCS-MPC) is proposed for DAB. The proposed MDCS-MPC is inherently a good choice for multiobjective control. It provides several advantages, such as a good tradeoff between two control objectives and adaptive performance on system impedance. The evaluation and comparison of the proposed MDCS-MPC and PI are carried out. Experiments on a 270–270V, 20 kHz, 1 kW DAB converter are conducted to verify the theoretical claims.

Predictive Control Based DC Microgrid Stabilization With the Dual Active Bridge Converter

Wound-field synchronous generators are widely used in aircraft and marine electrical systems. As the electric power requirements increase, there is renewed interest in dc power networks, but the electrical source remains a synchronous generator. The combination of a diode rectifier with a wound-field multiphase generator reduces the voltage ripple on the dc network and increases fault tolerance, compared with an equivalent three-phase system. It also increases the options in terms of the winding design and configuration. This paper uses circuit modeling, including harmonics, informed by static finite-element results, to understand the wound-field generator performance for star and polygon connections of both short- and fully-pitched coils. Experimental results are used to validate the models. A polygon connection of short-pitched coils is shown to give good generator utilization for a healthy machine. However, careful design is required to prevent circulating harmonic currents. Under winding open-circuit faults, the polygon connection requires significant derating, making the star connection the preferred option.

/pdf/winding-configurations-for-five-phase-synchronous-generators-lntujrelfe.pdf

Winding Configurations for Five-Phase Synchronous Generators With Diode Rectifiers

Increased electrical loading on aircraft power systems has led to interest in DC electrical networks for aircraft applications. This paper investigates a wound-field synchronous generator and uncontrolled diode rectifier as the DC source and analyses the power quality of the AC and DC sides of the rectifier. The paper gives expressions for voltage and current distortion for a multiphase generator as a function of the number of phases. For a star-connected machine, the power quality on the AC side is shown to deteriorate rapidly as the phase number increases, resulting in increased losses and a higher rating requirement. A delta connection provides better utilisation of the generator; however, at the expense of the fault tolerance. Mathematical models for the multiphase system are developed and the analysis is supported by simulation results; verified through laboratory testing.

/pdf/diode-rectification-of-multiphase-synchronous-generators-for-3tjnyvmwoc.pdf

Diode rectification of multiphase synchronous generators for aircraft applications

More electric is a platform being widely adopted by the current generation of aircraft. It offers significant benefits in terms of fuel savings and flexibility of airframe design but relies on the development of torque dense machines. This paper documents the development of an air-cooled transverse flux machine for use in short-haul aircraft to improve on-ground operational efficiency. If its potential is to be realized, this topology of the machine comes with a new set of manufacturing challenges. Two competing machine layouts with different approaches toward their fabrication are discussed. Experimental results and experiences gained from overcoming the challenges of building the machines are presented. A combined phase topology with soft magnetic composite core-back is shown to give a better rated torque, whereas a separate phase bent lamination concept gives better overload capability.

/pdf/comparison-of-two-transverse-flux-machines-for-an-aerospace-55lxgy6uei.pdf

Comparison of Two Transverse Flux Machines for an Aerospace Application

Electric motors are becoming increasingly utilized in aircraft, replacing traditionally mechanical or hydraulic auxiliary systems to realize improvements in mass, control and efficiency. Aerospace motor design has the unique characteristic that mass and, therefore, torque density is of critical importance. For low maintenance, non-safety critical components, which are only used for short durations of the flight cycle, efficiency also becomes less important, whilst eliminating an external cooling circuit and gearbox will further benefit mass constraints. This paper considers the design of a high torque density machine in order to meet a specification for an aerospace application with a stringent mass target. As mass is reduced, thermal capability becomes critical and detailed thermal models, along with simulation results, are presented for operational characteristics.

https://www.eprints.ncl.ac.uk/file_store/production/230227/FABD887C-E165-46B3-997E-8EC06F76702C.pdf

Design and build of a mass critical, air-cooled transverse flux machine for aerospace

AC copper losses can represent a significant proportion of the total loss in electrical machines under high frequency excitation. With the current trend being towards high speed machines for higher power density in, for example, automotive applications, a fast and accurate technique for estimating the AC loss in the early design stages is essential. This paper presents a method for estimating the AC loss in coils in the concentrated winding of an axial flux machine (AFM) using two-dimensional (2-D) finite element analysis (FEA). Effects in the dimension not modelled in the simulation, including the end region of the winding, are compensated for to increase the accuracy of the model. The results are calibrated and verified by detailed three-dimensional (3-D) FEA, and the significant simulation time improvement over conventional 3-D and hybrid approaches is demonstrated. The principles of the method may be readily applied to other machine types, including radial flux machines.

Estimation of AC copper loss in electrical machine windings with consideration of end effects

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