Influence of Conduction Angles on Single Layer Switched Reluctance Machines

This paper investigates the influence of conduction angles on the performances of two 3-phase 12-slot/8-pole short pitched switched reluctance machines (SRMs): single layer SRM with conventional winding (SL-CSRM), and single layer SRM with mutually coupled winding (SL-MCSRM). Both unipolar and bipolar excitations are employed for the SRMs with different conduction angles such as unipolar 120° elec., unipolar 180° elec., bipolar 180° elec., bipolar 240° elec., and bipolar 360° elec. Their flux distributions, self- and mutual-flux linkages and inductances are analyzed, and followed by a performance comparison in terms of on-load torque, average torque, torque ripple, using two-dimensional finite element method (2D FEM). Copper loss, iron loss and machine efficiency have also been investigated with different phase currents and rotor speeds. The predicted results show that the conduction angle of unipolar 120° elec. is the best excitation approach for SL-CSRM at low current and also modest speed, as its double layer counterpart. However, at high current, the higher average torque is achieved by a conduction angle of unipolar 180° elec. For SL-MCSRM, bipolar 180° elec. conduction is the most appropriate excitation method to generate a higher average torque but lower torque ripple than others. The lower iron loss is achieved by unipolar excitation, and the SLCSRM with unipolar 120° elec. conduction produces the highest efficiency than others at 〖10A〗_rms. In addition, the performances of single layer machines have been compared with the established double layer SRMs with conventional and mutually-coupled windings. The prototype SRMs, for both SL-CSRM and SL-MCSRM, have been built and tested to validate the predictions

Performance comparison of doubly salient reluctance machine topologies supplied by sinewave currents

This paper comprehensively investigates the electromagnetic performance of 3-phase, 12-slot, and 8-pole switched reluctance machines (SRMs) with different winding configurations, i.e. double/single layer, short pitched (concentrated) and fully pitched (distributed). These SRMs are supplied by sinewave currents so that a conventional 3-phase converter can be employed, leading to behavior which is akin to that of synchronous reluctance type machines. Comparisons in terms of static and dynamic performances such as d- and q-axis inductances, on-load torque, torque-speed curve, efficiency map, etc. have been carried out using two-dimensional finite element method (2-D FEM). It is demonstrated for the given size of machine considered, that for same copper loss and without heavy magnetic saturation, both single and double layer mutually coupled SRMs can produce higher on-load torque compared to conventional SRMs. Additionally, double layer mutually coupled SRM achieved the highest efficiency compared to other counterparts. When it comes to single layer SRMs, they are more suitable for middle speed applications and capable of producing higher average torque while lower torque ripple than their double layer counterparts at low phase current. Two prototype SRMs, both single layer and double layer, are built to validate the predictions

Recent Development of Reluctance Machines with Different Winding Configurations, Excitation Methods, and Machine Structures

This paper reviews the performances of some newly developed reluctance machines with different winding configurations, excitation methods, stator and rotor structures, and slot/pole number combinations. Both the double layer conventional (DLC-), double layer mutually-coupled (DLMC), single layer conventional (SLC-), and single layer mutuallycoupled (SLMC-), as well as fully-pitched (FP) winding configurations have been considered for both rectangular wave and sinewave excitations. Different conduction angles such as unipolar120º elec., unipolar/bipolar 180 ºelec., bipolar 240 º elec. and bipolar 360ºelec. have been adopted and the most appropriate conduction angles have been obtained for the SRMs with different winding configurations. In addition, with appropriate conduction angles, the 12-slot/14-pole SRMs with modular stator structure is found to produce similar average torque, but lower torque ripple and iron loss when compared to non-modular 12-slot/8-pole SRMs. With sinewave excitation, the doubly salient synchronous reluctance machines with the DLMC winding can produce the highest average torque at high currents and achieve the highest peak efficiency as well. In order to compare with the conventional synchronous reluctance machines (SynRMs) having flux barriers inside the rotor, the appropriate rotor topologies to obtain the maximum average torque have been investigated for different winding configurations and slot/pole number combinations. Furthermore, some prototypes have been built with different winding configurations, stator structures, and slot/pole combinations to validate the predictions

Investigation on contribution of inductance harmonics to torque production in multiphase doubly salient synchronous reluctance machines

This paper investigates the contribution of each order inductance harmonic to the torque (both average torque and torque ripple) of multiphase doubly salient synchronous reluctance machines (DS-SRMs). Such machines are similar to switched reluctance machines but supplied with sinewave currents. The investigations in this paper are as follows: first, a general analytical torque model based on Fourier Series analysis of inductances has been built for machines with different phase numbers, slot/pole number combinations and also winding configurations. The instantaneous torque for DS-SRMs with any given phase number can then be accurately predicted. Using such model, contribution of each order inductance harmonic to torque can be investigated separately. It is found that the torque ripple frequency of the DS-SRM only depends on phase number. For example, for a m-phase machine, there will be m×kth order torque ripple if mod(mk,2)=0, where m is phase number and k is a natural number. This study also explains why certain phase numbers inherently produce lower torque ripple than others. The findings in this paper provide a future direction for potential torque ripple reduction methods either from machine design or advanced control. The simulations have been validated by experiments using a 6-phase DS-SRMs

Analytical modelling of dynamic performance with harmonic current injection for doubly salient SynRMs

A new analytical torque model based on dq0-axis frame has been developed for 3-phase, 12-slot/8-pole single layer doubly salient synchronous reluctance machines. This newly developed torque model, compared to the one often based on abc-axis frame, is necessary to simplify the investigation of dynamic performance such as torque-speed curve and efficiency maps. It has been found that the 3rd order current harmonic injection not only improves the torque performance (increased average torque and reduced torque ripple) in constant torque region, but also maintains a similar torque level as the fundamental current supply in the flux weakening region. Moreover, although the 5th and 7th order current harmonic injection can reduce the torque ripple of machine, their dynamic performances are compromised due to low average torque and significant voltage distortion. Finite element simulations and dynamic tests have been carried out to prove the accuracy of the developed torque model and also the efficiency of the proposed current harmonic injection method

Comparative studies of torque performance improvement for different doubly salient synchronous reluctance machines by current harmonic injection

Three types of doubly salient synchronous reluctance machines have been comparatively studied to improve the torque performance using current harmonic injection methods. These machines are derived from the switched reluctance machines (SRMs) with different winding configurations, such as the double/single layer mutually coupled SRMs (MCSRMs) and fully pitched SRMs (FPSRMs), by supplying them with sinewave current. Such current supply mode can lead to higher torque/power density, lower vibrations and acoustic noise compared to the conventional rectangular current supply. The proposed torque analytical model can predict the instantaneous torque of the doubly salient SRMs with sinewave current excitation and the current harmonics also can be selected in order to reduce the torque ripple and/or increase the average torque. It has been found that the 3rd current harmonic injection shows the best performance for single-layer MCSRMs and FPSRMs because it improves the average torque and reduces the torque ripple at the same time. However, it has little influence on doubly-layer MCSRMs. To improve the torque performance of such machines, other harmonic currents, e.g. 5th and 7th, need to be used. Both static and dynamic tests have been carried out to validate the predictions

Investigation of performance improvement of doubly salient synchronous reluctance machine with current harmonic injection

This thesis investigates some novel current harmonic injection methods to improve the electromagnetic performance of doubly salient synchronous reluctance machines (DS-SRMs). These machines will have different winding configurations, slot/pole number combinations and phase numbers. The theoretical analyses (both static and dynamic) are carried out based on Fourier Series analysis, and validated by 2-dimensional finite element method and also experiments using several prototype machines. Based on the analytical torque model in abc-axis frame, a powerful insight into the mechanism of torque generation of the DS-SRMs with pure sinewave current supply can be achieved. The electromagnetic torque (both magnitude and phase angle) produced by each order of inductance harmonic can be predicted, which allows us to obtain the dominant torque ripple components for such machines. Therefore, the appropriate current harmonic (3rd, 5th and 7th) can be injected to generate torque ripple components in order to compensate that produced by the fundamental current, and hence to achieve an overall reduced torque ripple. On the other hand, the average torque of the DS-SRMs can also be improved by properly selecting the current harmonics in terms of harmonic order, amplitude and phase angle. However, it is found that the current harmonics, although can improve torque performance, will often cause extra losses (both copper and iron losses) and undesirable distortion in the phase voltages, which could lead to negative impact on the machine efficiency and dynamic performance. Therefore, in order to fully evaluate the potential of the proposed harmonic current injection method, comprehensive studies about losses, efficiency and dynamic performances such as torque-speed curves of 3-phase and multi-phase DS-SRMs have been carried out. In order to simplify the investigation of dynamic performance analyses such as the torque speed curves and efficiency maps, novel analytical torque model in dq0-axis frame has also been proposed. The findings in this thesis can provide some useful guidelines for torque performance improvement of DS-SRMs using harmonic current injections

Energy efficient PWM induction machine drives for electric vehicles.

The viability of any electric vehicle is critically dependent on it having an acceptable range between charges, a feature which is ultimately dictated by the capacity of the battery energy store. Considerable improvements in vehicle range are possible, however, by ensuring the most effective use of this limited energy resource through the minimisation of the losses in the electric drive-train, i.e. the combined machine and power electronic controller. A particular consideration is that, for the majority of the time, the electric drive-train will be operating at part load. The thesis investigates the operation of induction motor based electric traction drive-trains, with a view to minimising the system loss over typical driving cycles. The study is based around a 26kW induction motor and IGBT inverter drive, which is typical of the technology used to power a small urban vehicle. A potential advantage of an induction motor based drive-train is the ability to vary the level of excitation field in the motor, and therefore the balance of iron and copper loss. The control of the supply voltage magnitude necessitates the use of some form of modulation on the output of the power converter. The method of modulation employed will influence the harmonic content of the supply to the motor, the level of parasitic harmonic loss in the machine and the switching losses of the power semiconductors. A theoretical study supported by experimental work on a DSP controlled drive is presented and used to determine the most appropriate modulation strategy at a given operating point to achieve an optimal balance between the motor copper, iron and harmonic loss and inverter switching and conduction loss. It is shown that compared to the established method of constant flux and fixed inverter switching frequency control, a significant reduction in the traction system loss can be achieved. Some different modulation schemes involve varying amounts of computational overhead in a DSP, the implementation of candidate modulation and control schemes has also been investigated to ensure the defined scheme is practically realisable