Design and Development of Low Torque Ripple Variable-Speed Drive System With Six-Phase Switched Reluctance Motors

Switched reluctance motor (SRM) drives conventionally use current control techniques at low speed and voltage control techniques at high speed. However, these conventional methods usually fail to restrain the torque ripple, which is normally associated with this type of machine. Compared with conventional three-phase SRMs, higher phase SRMs have the advantage of lower torque ripple: To further reduce their torque ripple, this paper presents a control method for torque ripple reduction in six-phase SRM drives. A constant instantaneous torque is obtained by regulating the rotational speed of the stator flux linkage. This torque control method is subsequently developed for a conventional converter and a proposed novel converter with fewer switching devices. Moreover, modeling and simulation of this six-phase SRM drive system has been conducted in detail and validated experimentally using a 4.0-kW six-phase SRM drive system. Test results demonstrate that the proposed torque control method has outstanding performance of restraining the torque ripple with both converters for the six-phase SRM, showing superior performance to the conventional control techniques

Cost-Effective and High-Efficiency Variable-Speed Switched Reluctance Drives With Ring-Connected Winding Configuration

This paper presents a novel converter topology for six-phase switched reluctance motor (SRM) drives, which reduces the number of switches and diodes by half, compared with the conventional asymmetric half-bridge converter, but needs no additional energy storage component. A dynamic model of a six-phase SRM is developed in the MATLAB/SIMULINK environment and conventional current chopping and angle position control techniques are applied to the proposed converter, demonstrating successful operation across the full speed range with modified conventional control techniques, lower converter losses, and higher system efficiency compared with the asymmetric half-bridge converter. Experimental tests comparing two versions of the proposed converter with an asymmetric half-bridge are described and verify the predictions of the simulations

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

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

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

A torque ripple minimization method for six-phase switched reluctance motor drives

This paper presents a direct torque control (DTC) method on a six-phase SRM driven by a six-phase asymmetric half bridge converter. Modeling and simulations of the proposed drive system have been built with MATLAB/SIMULINK. In the proposed DTC method, instantaneous output torque of the six-phase SRM is directly controlled by flux-linkage magnitude and rotating speed regulation (acceleration or deceleration) respective to rotor movement. The simulation and test results accurately reflect the actual operation states of the SRM. Compared with traditional current chopping control (CCC), the DTC method can effectively reduce the torque ripple for the six-phase SRM

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

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