Electromagnetic analysis of a synchronous reluctance motor with single tooth windings.

This paper explores some key electromagnetic design aspects of a synchronous reluctance motor which is equipped with single tooth windings (i.e. fractional slot-concentrated windings). The analyzed machine, a 6 slot 4 pole motor, utilizes a segmented stator core structure for ease of coil winding, pre-assembly and facilitation of high slot fill factors (~60%). The impact on the motors torque producing capability and its power factor of these inter-segment air-gaps between the stator segments is investigated through 2D FEA studies where it is shown that they have a low impact. From previous studies, torque ripple is a known issue with this particular slot-pole combination of synchronous reluctance motor and the use of two different commercially available semi-magnetic slot wedges are investigated as a method to improve torque quality. An analytical analysis of continuous rotor skewing is also investigated as an attempt to reduce the torque ripple. Finally, it is shown through a combination of 2D & 3D FEA studies in conjunction with experimentally derived results on a prototype machine that axial fringing effects cannot be ignored when predicting the q-axis reactance in such machines. A comparison of measured orthogonal axis flux linkages/reactance with 3D FEA studies is presented for the first time

Oliver Heaviside's Electromagnetic Theory

The year 2018 marks the 125th anniversary of the first of three published volumes on electromagnetic theory by the eminent Victorian electrical engineer, physicist and mathematician, Oliver Heaviside FRS. This commemorative issue of Philosophical Transactions of the Royal Society A celebrates the publication of this work by collecting papers on a broad spectrum across the field of electromagnetic theory, including innovative research papers interspersed between historical perspectives and relevant reviews. Heaviside was a remarkable man, an original thinker with brilliant mathematical powers and physical insight who made many significant contributions in his fields of interest, though he is remembered primarily for his ‘step function’, commonly used today in many branches of physics, mathematics and engineering. Here, we celebrate the man and his work by illustrating his major contributions and highlighting his great success in solving some of the great telegraphic engineering problems of the Victorian era, in part due to his development and detailed understanding of the governing electromagnetic theory. We celebrate his Electromagnetic theory: three volumes of insights, techniques and understanding from mathematical, physical and engineering perspectives—as dictated by J. C. Maxwell FRS, but interpreted, reformulated and expanded by Heaviside to advance the art and science of electrical engineering beyond all expectations. This article is part of the theme issue ‘Celebrating 125 years of Oliver Heaviside's ‘Electromagnetic Theory’’

On the Influence of Increased Stator Leakage Inductance in Single Tooth Wound Synchronous Reluctance Motors

This paper explores the leakage inductance of a single tooth wound synchronous reluctance motor and its influence on motor performance. It is shown that the stator leakage inductance heavily influences the true saliency ratio in synchronous reluctance motors and a large stator leakage inductance has a serious detrimental impact on the operating power factor. It is also shown through analytical and FEA analysis that synchronous reluctance motors with single tooth windings suffer an inherent high stator leakage inductance that is dominated the air gap harmonic leakage component, derived from the significant stator MMF harmonics experienced with this winding type. This explains for the first time the experimental results showing a low operating power factor compared to a distributed wound machine. Measurement of the stator leakage inductance is attempted on a prototyped machine and the standardized method is found to be lacking when single tooth windings are employed

Leakage Inductance of a Prototyped Single Tooth Wound Synchronous Reluctance Motor

This paper explores the inductance characteristics present in single tooth wound synchronous reluctance motors, specifically the stator leakage inductance. Despite the nature of the single tooth design resulting in increased air gap harmonic content, having has consequences for the machines' design, performance & operation, the topology has been shown previously to be competitive for high efficiency drives. A key design constraint in the design of synchronous reluctance motors is maximizing the direct axis inductance and minimizing the quadrature axis inductance for a high saliency ratio. The effect of increased leakage inductance on this saliency ratio is explored with emphasis placed on design aspects of such single tooth wound synchronous reluctance motors. It is shown that careful design of the machine is required to maximize the saliency ratio in this machine topology and that the dominant leakage inductance component is the air gap harmonic leakage

Electromagnetic-Mechanical Design of Synchronous Reluctance Rotors with Fine Features

This paper explores the trade-off between electromagnetic and mechanical performance when regarding the design of a synchronous reluctance machine rotor with fine features in the lamination profile – the analyzed machine consists of four rotor poles and its stator is equipped with single tooth coils. The change in the electromagnetic characteristics of the d and q axis reactance is explored for variation in radial and tangential rib width and the impact of increased rib width on the saliency ratio of the machine. It is shown that increased radial and tangential rib width impairs electromagnetic performance, with the tangential rib having the most pronounced effect on performance in this rotor design. The mechanical performance of the design is also explored in a similar manner, where it is shown that the high stress concentration in the rotor radial & tangential ribs limits the maximum speed of the machine in the field weakening region. The radial rib is found to have the dominant impact on supporting the flux guides. It is shown that the prototyped machine can achieve good electromagnetic performance while maintaining mechanical integrity up to a 25% over speed of 10,000rpm with features as small as 0.3mm. Additionally, the challenges associated with manufacturing, selecting a higher rotor pole number and the possibility of mechanical failure are also discussed in the context of electromagnetic-mechanical design of such rotors, with important avenues of further research suggested

On Heaviside’s Contributions to Transmission Line Theory: Waves, Diffusion and Energy Flux

This paper surveys some selected contributions of Oliver Heaviside FRS (1850–1925) to classical electromagnetic theory and electrical engineering science. In particular, the paper focuses on his contributions to the development of electrical transmission line theory and his deep insights into the ‘physical’ nature of the phenomena relating to nineteenth century telegraphic problems. Following a brief historical introduction to the life of Heaviside to put his achievements in context, we explore his contributions to the reformulation of Maxwell's equations and the understanding of electromagnetic wave propagation along the external region of transmission lines. This leads naturally to his researches regarding the electromagnetic diffusion process inside the line conductors and his subsequent realization that the circuital parameters, usually assumed constant, are not always so. Finally, taking both these internal and external viewpoints of the conductors, his important work regarding the flow of energy described by his ‘energy current’ concept is presented. This article is part of the theme issue ‘Celebrating 125 years of Oliver Heaviside's ‘Electromagnetic Theory’’

Rotating Electrical Machines: Poynting Flow

This paper presents a complementary approach to the traditional Lorentz and Faraday approaches that are typically adopted in the classroom when teaching the fundamentals of electrical machines - motors and generators. The approach adopted is based upon the Poynting Vector which illustrates the 'flow' of electromagnetic energy. It is shown through simple vector analysis that the energy-flux density flow approach can provide insight into the operation of electrical machines and it is also shown that the results are in agreement with conventional Maxwell Stress based theory. The advantage of this approach is its complementary completion of the physical picture regarding the electromechanical energy conversion process - it is also a means of maintaining student interest in this subject and as an unconventional application of the Poynting vector during normal study of electromagnetism

Use of Fractional-Conductor Windings and Semi-Magnetic Slot Wedges in Synchronous Machines

This paper discusses two methods of altering the harmonic content of the spatial air-gap flux density waveform in synchronous machines (generators and motors). First, fractional-conductor windings are analysed for adoption as a replacement for a conventional distributed winding arrangement, their advantages and disadvantages briefly discussed and an example design scenario presented. Second, analysis and discussion regarding the use of semi-magnetic slot wedges as a replacement for glass-fibre type wedges is presented to complement the choice of winding in synchronous machines. Both methods are shown to benefit machine performance under certain circumstances