Acoustic noise from small electronically commutated motors

An analysis of acoustic noise in electronically controlled variable speed drives is presented. The causes of vibration and acoustic noise in switched reluctance motors are discussed and it is shown that brushless d.c. motors can produce resonant vibration and acoustic noise by similar mechanisms. The flux switching motor is introduced. This new class of reluctance motor is an advance on the established switched reluctance motor, retaining many of its benefits, but with a simpler and cheaper power electronic converter. The phase windings and method of flux control are different and tests are performed to quantify the effect on the acoustic noise produced. Measurements of acoustic noise are made on one flux switching motor and one 2-phase switched reluctance motor, made from the same laminations and mechanical components. It is shown that the flux switching motor produced 2dB less acoustic noise under the same conditions. Finite element analysis is used to calculate the radical force profiles of the two motors during normal rotation, and further analysis of this data provides evidence to support the experimental results. The experimental results go on to show how the acoustic noise from a second flux switching drive was found to be comparable to that of a split phase induction motor

Investigation of skewing effects on the vibration reduction of three-phase switched reluctance motors

Switched reluctance motors (SRMs) are gaining in popularity because of their robustness, low cost, and excellent high-speed characteristics. However, they are known to cause vibration and noise primarily due to the radial pulsating force resulting from their double-saliency structure. This paper investigates the effect of skewing the stator and/or rotor on the vibration reduction of the three-phase SRMs by developing four 12/8-pole SRMs, including a conventional SRM, a skewed rotor-SRM (SR-SRM), a skewed stator-SRM (SS-SRM), and a skewed stator and rotor-SRM (SSR-SRM). The radial force distributed on the stator yoke under different skewing angles is extensively studied by the finite-element method and experimental tests on the four prototypes. The inductance and torque characteristics of the four motors are also compared, and a control strategy by modulating the turn-ON and turn-OFF angles for the SR-SRM and the SS-SRM are also presented. Furthermore, experimental results validate the numerical models and the effectiveness of the skewing in reducing the motor vibration. Test results also suggest that skewing the stator is more effective than skewing the rotor in the SRMs

Mitigation of Torque Ripple and Vibration in Switched Reluctance Motor Drives: A Switching Optimization

Switched reluctance motor (SRM) drives represents an attractive solution for industrial, transportation and domestic applications due to their rugged structure, independence from rare earth metals, modular design, wide speed range, and tolerance to harsh environments. Despite these advantages, the adequacy of SRM drives for many applications has been overshadowed by its relative high levels of torque pulsation and vibration/acoustic noise. This research aims to investigate and propose control strategies to mitigate these adverse features. To reach this goal the current shaping and switching optimization have been proposed. Two modeling methods were used in this process: i) field reconstruction method (FRM) to model the electromagnetic behavior; and ii) mechanical impulse response to model the structural behavior. This two-modeling procedure are the key innovative tools in this dissertation, since those are techniques recently proposed in the literature. Moreover, these two methods have been combined to simultaneously mitigation of torque ripple and radial vibration. Firstly, the structural vibration was investigated in detail for an 8/6 SRM. The modal analysis is carried out experimentally and through finite element model in ANSYS. Then, the mechanical impulse response concept was applied to develop a vibration prediction model that, after validated, was introduced in an optimization algorithm developed in MATLAB to design the precise switching instants to have active vibration cancellation. The method is focused on SRM operating under current control (low speed region). The experimental results show a significantly reduction. This technique is sensitive to timing without adverse impact on productivity and efficiency of the SRM drive. Moreover, the vibration mitigation also has contributed to acoustic noise reduction. In a second approach, an optimization based on the SRM model using the FRM is used to find the optimal current profile that mitigates the torque ripple. The percentage reduction reached is about 44%. Furthermore, the effect of the new current profile in the structural response is also investigated and a negative impact in the vibration has been observed. To deal with this shortcoming, an adaptive hysteresis band is implemented over the optimized current profile for torque ripple mitigation. The obtained results demonstrated a good compromise between the torque ripple and vibration mitigation

Acoustic noise and vibration of switched reluctance machines.

This thesis describes a systematic investigation into the sources of acoustic noise and vibration in switched reluctance machines, and encompasses the vibrational behaviour of the stator, the influence of control parameters, and an evaluation of the effectiveness of active vibration cancellation. The influence of leading design parameters, such as the width and number of poles and the yoke thickness, and geometric asymmetries, such as lamination notches in the stator core, and the effect of the stator windings, the frame, the end-caps and the mounting assembly, on the natural frequencies and modes of vibration are investigated, Chapter 3. Both two-dimensional and three-dimensional finite element analyses are employed, the predicted results being validated by measurements on various experimental models, which consequently highlights the limitation of the finite element technique for highly complex structures with discontinuities in their fabrication. The influence of the mass and stiffness of the laminated stator core and the stator windings on the natural frequencies and vibration modes is investigated, and effective material properties are deduced for the analyses. It is found that the number of poles and lamination notches on the stator influence the number of vibrational modes which occur in the audible frequency range due to the introduction of dual natural frequencies, viz. symmetrical and anti-symmetrical modes, which are shown to separate further in value as the asymmetries become more profound. As the diameter of the stator yoke is reduced the natural frequencies increase, whereas increasing the thickness of the yoke and the adding of a frame and end-caps significantly increase the natural frequencies. The effect of the stator poles is to significantly reduce the stator natural frequencies, which are irrespective to a variation to the width of the poles, a variation in their mass being annulled by the resulting change in stiffness. Similarly, it is shown that the winding mass and stiffness offset each other so that their influence is also relatively small, whereas, although quantification of the damping is not within the aims of this thesis, it is apparent that the windings introduce a high level of damping which consequently limits the magnitude of the vibrations and hence acoustic noise. Finally, the laminated nature of the core is quantified and is shown to affect the effective material properties compared to an equivalent solid core, and to increase the effective damping. Previous investigations have studied the influence of the drive control parameters, but generally limit the analysis to either the frequency or time domain or to measurements of the sound pressure level, and are generally carried out in isolation. Therefore. the influence of alternative operating modes and their associated control parameters on the acoustic noise and vibration of an SR machine is thoroughly investigated. the results being analysed in both the frequency and time domains, and compared with measurements of the sound pressure level, Chapter 4. The noise and vibration which results when the SR machine is operated under both voltage and current control. with both hard and soft chopping techniques, and various switching angles, and for various sampling and switching frequencies, is measured. The influence of speed and load is also investigated, and the vibration and noise are also investigated under single pulse mode operation. It is found that hard chopping results in a noisier operation than with soft chopping due to increased current ripple, especially under current control. The noise and vibration is clearly shown to differ under current control compared to voltage control and single pulse mode, due to the random switching of the phase voltages resulting in wideband harmonic spectra, thereby increasing the levels of all the mechanical resonances. Further, it is found that the noise and vibration increase with both speed and load. In general, the increases in noise and vibration are attributed to an increase in the rate of decay of current at phase turn-off, regardless of the control parameter under investigation. Finally, the effectiveness of active vibration cancellation for nOIse reduction is investigated under typical operating modes in Chapter 5, which, for the first time, is analysed in both the frequency and time domains, and validated by measurements of the sound pressure level. It is found that active vibration cancellation is less effective for machine stators which have more than one dominant vibration mode within the audible frequency range, since the technique is only capable of applying active cancellation for a single vibration mode, thus any further resonances remain unaffected. Further, during chopping control, especially current control which results in random switching, it has been shown, for the first time, that the effective time-delay varies to that applied, thus rendering the technique less effective. This is found to be attributed to the asynchronism of the final chopping edge and point of phase turn-off, therefore preventing the vibrations from being excited in anti-phase, as explained in section 5.6

Critical Aspects of Electric Motor Drive Controllers and Mitigation of Torque Ripple - Review

Electric vehicles (EVs) are playing a vital role in sustainable transportation. It is estimated that by 2030, Battery EVs will become mainstream for passenger car transportation. Even though EVs are gaining interest in sustainable transportation, the future of EV power transmission is facing vital concerns and open research challenges. Considering the case of torque ripple mitigation and improved reliability control techniques in motors, many motor drive control algorithms fail to provide efficient control. To efficiently address this issue, control techniques such as Field Orientation Control (FOC), Direct Torque Control (DTC), Model Predictive Control (MPC), Sliding Mode Control (SMC), and Intelligent Control (IC) techniques are used in the motor drive control algorithms. This literature survey exclusively compares the various advanced control techniques for conventionally used EV motors such as Permanent Magnet Synchronous Motor (PMSM), Brushless Direct Current Motor (BLDC), Switched Reluctance Motor (SRM), and Induction Motors (IM). Furthermore, this paper discusses the EV-motors history, types of EVmotors, EV-motor drives powertrain mathematical modelling, and design procedure of EV-motors. The hardware results have also been compared with different control techniques for BLDC and SRM hub motors. Future direction towards the design of EV by critical selection of motors and their control techniques to minimize the torque ripple and other research opportunities to enhance the performance of EVs are also presented.publishedVersio

Mitigation techniques for acoustic noise and vibration in switched reluctance drives

PhD ThesisSwitched reluctance machines (SRM) have become an attractive rotating electrical machine in many applications because they have no permanent magnets, have robust structures and high fault tolerance. However, the crucial drawback of the SRM that limits the range of applications, is the acoustic noise and vibration often associated with this technology. The major source of vibration comes from the high deformation of the SRM stator stack, caused primarily by high radial magnetic forces. Vibration behaviour of di erent SRM topologies is analyzed by using nite element software to calculate the magnitude, mode shape and the resonant frequencies of the SRM. This includes determination of the generating magnetic force characteristic for each topology. To improve the accuracy of the vibration model of the SRM stator, which is built from laminated steel sheet, calculation of the mechanical material properties of the stator are developed for structural simulations. The simulation and testing results of the resonant frequency of the SRM are compared to determine the accuracy of the simulation model. There are two main strategies for reducing the vibration in an SRM. I) structural design and II) control technique. In this thesis, the structural design of six types of SRM segmented stator, each shrink- tted into an aluminium housing, are investigated, both in terms of the structural sti ness and resonant frequency. The impact of varying temperature on the resonant frequency of the stator is tested to show the rate of change of the resonant frequency and damping ratio of the stator structure. Furthermore, the control technique of the SRM has also been shown to have a signi cant impact on the vibration produced in the SRM. Improvement of the control technique based on an active vibration cancellation (AVC) method is implemented under load conditions with di erent operating speeds of the SRM and compared with the conventional control method.Royal Thai governmen

Overview of permanent-magnet brushless drives for electric and hybrid electric vehicles

With ever-increasing concerns on our environment, there is a fast growing interest in electric vehicles (EVs) and hybrid EVs (HEVs) from automakers, governments, and customers. As electric drives are the core of both EVs and HEVs, it is a pressing need for researchers to develop advanced electric-drive systems. In this paper, an overview of permanent-magnet (PM) brushless (BL) drives for EVs and HEVs is presented, with emphasis on machine topologies, drive operations, and control strategies. Then, three major research directions of the PM BL drive systems are elaborated, namely, the magnetic-geared outer-rotor PM BL drive system, the PM BL integrated starter-generator system, and the PM BL electric variable-transmission system. © 2008 IEEE.published_or_final_versio

Investigation on synchronous reluctance machines with different rotor topologies and winding configurations

This paper investigates the influence of rotor topologies and winding configurations on the electromagnetic performance of 3-phase synchronous reluctance machines with different slot/pole number combinations, e.g. 12-slot/4-pole and 12-slot/8-pole. Transversally laminated synchronous reluctance rotors with both round flux barrier and angled flux barrier have been considered, as well as the doubly-salient rotor as that used in switched reluctance machines. Both concentrated and distributed winding configurations are accounted for, i.e., single layer and double layer conventional and mutually coupled windings, as well as fully-pitched winding. The machine performance in terms of d- and q-axis inductances, on-load torque, copper loss, and iron loss have been investigated using 2-D finite-element analysis. With appropriate rotor topology, 12-slot/4-pole and 12-slot/8-pole machines with fully-pitched and double layer mutually coupled windings can achieve similar torque capacity, which are higher than the machines with other winding configurations. In addition, the synchronous reluctance machine with round flux barrier can have lower iron loss than doubly salient reluctance machine under different working conditions. The prototypes of 12-slot/8-pole single layer and double layer, doubly salient synchronous reluctance machines have been built to validate the predictions in terms of inductances and torques