G. J. Li

Comparative Studies Between Classical and Mutually Coupled Switched Reluctance Motors Using Thermal-Electromagnetic Analysis for Driving Cycles

This paper presents copper and iron loss models of a classical switched reluctance motor (SRM) and a mutually coupled switched reluctance motor (MCSRM). The iron losses in different parts of machines are then detailed. Based on the power losses model, a lumped parameter (LP) transient thermal model during driving cycles is performed, the analytical results are validated by the finite-element (FE) transient thermal model. Special attention has been paid to model the salient rotor and a method to transform the salient rotor into a nonsalient one has been proposed. A comparison between the maximum temperatures obtained by using different heat source (average power losses or instantaneous power losses during driving cycles) is given. The experimental tests are also realized to verify the analytical and numerical results.

Modification in Rotor Pole Geometry of Mutually Coupled Switched Reluctance Machine for Torque Ripple Mitigating

This paper presents a new method to minimize the torque ripple of a 3-phase, 6-slot, and 4-pole mutually coupled switched reluctance motor (MCSRM 6/4). The difference between a MCSRM and a classical SRM is their winding configuration. In a MCSRM, the mutual inductances are no longer neglectable when compared to self inductance. On the contrary, due to mutual inductances, the MCSRM can produce higher average torque than a classical SRM. A literature review is firstly performed to identify the source of high torque ripple level of a MCSRM. Then, the method using punching holes in rotor poles to modify the waveforms of flux as well as derivatives of inductances with respect to rotor position (dL/d and dM/d ) is proposed. Using the 2-D finite-element method (FEM), the influence of dimensions of punching hole on the electromagnetic performances (average torque and torque ripple) is analyzed. The two MCSRM are supplied by three-phase sine wave currents, and comparisons in terms of average torque and torque ripple versus RMS current density are also carried out. In order to make sure that the presence of punching holes does not cause mechanical problems, some mechanical studies are performed. Finally, experimental tests are also realized to validate numerical results obtained by 2-D FEM.

Thermal–Electromagnetic Analysis for Driving Cycles of Embedded Flux-Switching Permanent-Magnet Motors

This paper presents a fast and precise electromagnetic-thermal model of a redundant dual-star flux-switching permanent-magnet (FSPM) motor for embedded applications with driving cycles, e.g., hybrid electrical vehicle (HEV) and aerospace. This model is based on a prior steady characterization by finite-element method (FEM) 2-D of the FSPM motor via calculating the instantaneous torque and the normal and tangential components of the magnetic flux density (Br and Bθ) of each element of the stator and the rotor for different root-mean-square (RMS) current densities and different rotor positions. These results are then used in the analytical copper and iron loss models for calculating the instantaneous copper and rotor and stator iron losses during one driving cycle. The lumped-parameter (LP) and finite-element 2-D transient thermal models are then carried out, in which the previously obtained instantaneous power losses are used as heat sources for calculating the temperatures of different motor parts during driving cycles. In the thermal studies, a transformation of an irregular slot structure into a regular (rectangular) one is applied to simplify the calculation of the winding thermal resistance. The thermal-electromagnetic analysis method in this paper can also be extended for all the other applications with driving cycles. The experimental tests are carried out to validate the analytical and numerical results.

Design of a Flux-Switching Electrical Generator for Wind Turbine Systems

This paper proposes a parametric optimization of a flux-switching electrical machine customized for a wind turbine application with a typical operating range for average and low-power wind energy sites. Statistics of wind resources are taken into consideration for the machine design for definition of the turbine power envelope. Both copper and iron losses for three different machine designs are evaluated. A very important consideration taken in this design is the elimination of gearbox requirements for coupling to the turbine. Although the developed approach makes the machine somewhat voluminous, the overall performance is highly improved because a direct-drive flux-switching electrical generator becomes very competitive for small-scale wind turbines. The design methodology presented in this paper will support widespread application of small-scale wind turbines for rural systems, farms, and villages. This paper concludes by demonstrating that a very cost-effective distributed wind system can be approached with this design.

Comparative Study of Classical and Mutually Coupled Switched Reluctance Motors Using Multiphysics Finite-Element Modeling

This paper presents the numerical modeling of a classical switched reluctance motor (SRM) and a mutually coupled SRM (MCSRM); both have three phases with 12 slots and 8 poles. The multiphysics models have been developed, which can take into account the electromagnetic characteristics, mechanical vibration, and acoustic noise of the foregoing machines. A 2-D electromagnetic model has been used to calculate the magnetic force which is the main source of vibration of the entire motor system. The vibration of the motor is calculated by a mode superposition method, while the acoustic noise is predicted by a 3-D finite-element acoustic model. In order to validate the numerical models, experiments have been carried out. A good agreement between measured and numerical results has been observed, and it is found that the vibration and the noise levels of MCSRM are considerably lower than those of classical SRM.

Influence of Flux Gaps on Electromagnetic Performance of Novel Modular PM Machines

In order to simplify manufacture processes and improve fault-tolerant capabilities, modular electrical machines, especially the ones with segmented stators, are increasingly employed. However, flux gaps between segments are often inevitable. In this paper, to take advantage of these flux gaps to enhance the machine performance, novel modular permanent magnet machines with different slot/pole combinations have been proposed. The influence of these flux gaps on the electromagnetic performance of modular PM machines, such as winding factor, open-circuit air-gap flux densities, back-EMFs, cogging torque, on-load torque, inductances, magnetic saturation and copper losses, are comprehensively investigated and general rules have been established. It is found that for modular machines having slot number higher than pole number, the flux gaps between stator segments degrade the electromagnetic performance due to the lower winding factor and the flux defocusing effect. However, for modular machines having slot number lower than pole number, the electromagnetic performances can be significantly improved using proper flux gap width due to the higher winding factor and the flux focusing effect. The finite element results are validated by experiments using two prototype modular machines.

Comparative study of Switched Reluctance Motors performances for two current distributions and excitation modes

This paper presents a 3-phase, 6-slot, and 4-pole Mutually Coupled Switched Reluctance Motor (MCSRM 6/4) with new current distribution. This kind of SRMs has both the merits of conventional SRMs and Fully Pitched SRMs, i.e. shorter end-windings and higher torque density. A comparison based on Finite Element Method (FEM) between conventional and mutually coupled SRMs, in terms of self flux-linkage and inductance per phase, mutual flux-linkage and inductance between phases, and output torque is realized. The conventional SRM is excited in unipolar mode, while the MCSRM is excited in bipolar overlapping mode. With a high coupling between phases for MCSRM, mutual inductances are employed to produce torque. Furthermore, the flux pathways are separated and distributed between phases, this leads to a less sensitivity to magnetic saturation. At high current density and high conduction angle, the MCSRM has a higher output torque and a lower torque ripple. Thus, comparing to conventional SRMs, the MCSRM is more outstanding for starter-generator applications (hybrid vehicles, aerospace) which needs high output torque.

Thermal modelling of switched flux permanent magnet machines

This paper presents the electromagnetic loss and thermal modelling of a switched flux permanent magnet (SFPM) machine. A 2D finite element method is first used to calculate the stator and rotor iron losses as well as PM eddy current losses. Then, 3-D thermal modelling has been performed for analysing the temperature distribution within the SFPM machine, the calculated power losses have been applied to different machine components as heat sources to predict the temperature distributions throughout the SFPM machine. A prototype of 50 kW SFPM machine has been used for thermal tests under both open-circuit and on-load conditions. Good agreement between measured and simulated results has been achieved.

Fault diagnosis using vibration measurements of a Flux-Switching permanent magnet motor

This paper examines the fault diagnosis (including detection and localization) of a Flux Switching permanent magnet Motor (FSM). Electrical and mechanical models of fault due to a partial short-circuit on one phase is described and used on a numerical simulation in order to detect and localize the fault. Fault detection is realized by a diagnostic observer (Kalman filter) which generates residual functions depending on the kind of fault. This diagnostic observer is designed by the Luenberger method and uses vibration measures to generate these residual functions.

Double and single layers flux-switching permanent magnet motors: Fault tolerant model for critical applications

This paper deals a double layer and a single layer Flux-Switching Permanent Magnet (FSPM) motors for a fault tolerant application. The self and mutual inductances of these two machines are calculated, which are then applied for establishing a faulty model. A three phase short-circuit problem is simulated for these two motors. A comparison between these two machines is carried out, which is in terms of normal phase currents and the output torque before and after the failure as well as the short-circuit peak currents against the rotor velocity.