Application of fractional slot concentrated windings to synchronous reluctance machines

Due to the advancement of electric vehicles, the desire for high torque density electric motors for traction applications is steadily increasing. It is advantageous to design such a motor with little or no rare earth permanent magnet (PM) material due to the associated environmental, political and economic challenges with its extraction and processing. This paper explores a novel synchronous reluctance machine (RSM), with fractional slot concentrated windings (cRSM) as an alternative to PM, induction machine (IM) and switched reluctance (SRM) traction motors. The impact of applying fractional slot concentrated windings to RSMs is presented and the outline of the design options for such a machine is detailed. Scaling of the fractional slot wound synchronous reluctance motor is also briefly discussed, in order to realise a torque dense synchronous reluctance machine for future traction applications. A finite element analysis comparison between IM and conventional synchronous reluctance with the proposed cRSM is also presented

Higher pole number synchronous reluctance machines with fractional slot concentrated windings

This paper presents an examination of the advantages, disadvantages and remaining challenges of the application of fractional slot concentrated windings to higher pole number (pole-pairs > 2) synchronous reluctance machines. It extends previous work by assessing the effects of the available slotpole combinations on machine performance and construction. Finite element studies and figures of merit derived from d-q axis theory are used to compare and assess performance. Manufacturing and constructional issues are also discussed

Synchronous reluctance motors with toroidal windings

This paper introduces the concept of a four-pole toroidally wound synchronous reluctance machine as an alternative to conventional and fractional slot concentrated winding designs. The toroidal windings, which are wound around the stator coreback have very short end windings, limiting the copper loss as with fractional slot concentrated windings, facilitating an increase in machine efficiency. However, unlike fractional slot concentrated windings, even space-harmonics in the air gap do not exist and the associated parasitic effects are minimized. The machine concept is described and its relationship with conventional and fractional slot concentrated winding machines is discussed. Construction methods are discussed with emphasis on manufacturability and the advantages and disadvantages of this topology are presented

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

Design of a synchronous reluctance motor with non-overlapping fractional-slot concentrated windings

This paper presents the detailed design and finite element study of a synchronous reluctance machine with a non-overlapping fractional slot concentrated windings. The machine design employs single tooth wound coils with short end windings and high fill factor, which facilitates the machines high torque density and efficiency. As no magnets are required, the machine is low cost and of robust construction like the induction motor. This machine topology is presented as a step forward in synchronous reluctance technology which are usually wound with a distributed winding with long end turns. Analytical design methodologies and performance through finite element studies are presented. Scaling and design options, along with manufacturing options are discussed, the future development of the topology for automotive traction and other demanding applications is also presented

Computationally efficient skew effect calculation in electric machines utilising harmonic Maxwellian stress decomposition

A novel finite element solution post-processing technique to determine the effects of rotor skewing is presented in this paper. It was previously proposed that a post-processing semi-numerical method to calculate the harmonic torque components in synchronous machines is useful to machine designers. Harmonic Maxwellian stress components create parasitic effects during machine operation such as torque ripple, which is extremely undesirable in many applications and is a major cause of acoustic noise and vibration which can limit the machine's application. Rotor skewing usually allows reduction of this torque ripple and this paper expands previous work to include a good approximation of skewing effects using a single 2D time stepping Finite Element (FE) study with the developed post-processing method. The method reduces computation time for skew effect calculation where a large 3D FE simulation would usually be required

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

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

Design and Validation of a Synchronous Reluctance Motor With Single Tooth Windings

This paper presents for the first time the analysis and experimental validation of a six-slot four-pole synchronous reluctance motor with nonoverlapping fractional slot-concentrated windings. The machine exhibits high torque density and efficiency due to its high fill factor coils with very short end windings, facilitated by a segmented stator and bobbin winding of the coils. These advantages are coupled with its inherent robustness and low cost. The topology is presented as a logical step forward in advancing synchronous reluctance machines that have been universally wound with a sinusoidally distributed winding. The paper presents the motor design, performance evaluation through finite element studies and validation of the electromagnetic model, and thermal specification through empirical testing. It is shown that high performance synchronous reluctance motors can be constructed with single tooth wound coils, but considerations must be given regarding torque quality and the d-q axis inductances

Winding configurations for a six phase switched reluctance machine

Winding configurations are investigated for a six phase, 12-10 switched reluctance machine having single tooth wound coils and being driven from a conventional three phase full bridge converter with the addition of six diodes. A new winding configuration is proposed and shown to develop more torque with less torque ripple than a conventional winding in this application. Finite element modelling is used to investigate the electromagnetic behaviour and compare the performance of different winding configurations. Initial experimental tests are described in verification of the modelling. The novel drive and new winding configuration offer significant advantages over a standard three phase machine and drive, giving increased mean torque with lower torque ripple and acoustic noise, as well as reduced converter complexity and potentially cost