IET Electric Power Applications
Volume 9, Issue 9, November 2015
Volumes & issues:
Volume 9, Issue 9
November 2015
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- Author(s): Blaž Benedik ; Katerina Taškova ; Jože Tavčar ; Jože Duhovnik
- Source: IET Electric Power Applications, Volume 9, Issue 9, p. 569 –577
- DOI: 10.1049/iet-epa.2014.0437
- Type: Article
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p.
569
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The main focus of this paper is the empirical modelling of the wear of carbon brushes. Rather than determining the dominant wear mechanisms, an approach towards the prediction of wear under a range of different conditions was used. The models were obtained by multiple regression analysis using lifetime (LT) data contributed by the biggest European manufacturer of vacuum cleaner motors. This included reliability data for 607 different test populations involving 3980 motors. Exploration of the data revealed that wear-out parameters behaved in accordance with the existing field theory, giving additional confidence to the models. The numerical appreciation of the wear-out parameters and the resulting conclusions will be beneficial to motor design and reliability engineers. Learned knowledge will be used for faster selection of optimal design and operational motor parameters to meet recent EU regulation 666/2013. Along with the more rapid design of the product, a reduced number of LT tests will result in significant energy savings.
- Author(s): Hui Zeng ; Hao Chen ; Jiaotong Shi
- Source: IET Electric Power Applications, Volume 9, Issue 9, p. 578 –585
- DOI: 10.1049/iet-epa.2015.0087
- Type: Article
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p.
578
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Owing to the constraint of the supply voltage, there is a theoretically maximum operating range of the smooth-torque operation for a switched reluctance drive (SRD). The maximum operating range can be determined by the authors previous work, based on which a novel direct instantaneous torque control (DITC) is proposed for four-phase 8/6 switched reluctance drive in this study, which can achieve the widest operating range. Compared with the conventional DITC, the proposed DITC does not need the extra optimisation strategy of the switching angle. The performance of the proposed method is identified by simulation and experiment results.
- Author(s): Guang-Jin Li ; Zi-Qiang Zhu ; Geraint Jewell
- Source: IET Electric Power Applications, Volume 9, Issue 9, p. 586 –594
- DOI: 10.1049/iet-epa.2015.0129
- Type: Article
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p.
586
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This study investigates the electromagnetic performance of a hybrid excited switched flux permanent magnet (SFPM) machine using the frozen permeability (FP) method. The flux components due to PMs, field excitation windings and armature windings have been separated using the FP method. It has been used to separate the torque components due to the PMs and excitations, providing a powerful insight into the torque generation mechanism of hybrid excited SFPM machines. It also allows the accurate calculation of d- and q-axis inductances, which will then be used to calculate the torque, power and power factor against rotor speed to compare the relative merits of hybrid excited SFPM machines with different types of PMs (i.e. NdFeB, SmCo and Ferrite). This offers the possibility of choosing appropriate PMs for different applications (maximum torque or maximum speed). Although only one type of hybrid excited PM machine has been employed to carry out the investigations, the method used in this study can also be extended to other hybrid excited PM machines. The predicted results have been validated by tests.
- Author(s): Yongchang Zhang ; Haitao Yang ; Bo Xia
- Source: IET Electric Power Applications, Volume 9, Issue 9, p. 595 –604
- DOI: 10.1049/iet-epa.2015.0138
- Type: Article
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p.
595
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Model predictive torque control (MPTC) is emerging as a high-performance control strategy for induction motor (IM) drives, due to its intuitive nature, flexibility to incorporate constraints and quick dynamic response. However, the implementation of MPTC requires high computational ability and the use of single voltage vector during one control period fails to reduce the torque ripple to the minimal value. This study proposes an improved MPTC for IM drives with reduced torque ripple and low complexity. On the basis of the relationship between stator current and stator flux, the complicated current prediction for each voltage vector is eliminated, reducing the control complexity significantly. Torque ripple reduction is achieved by allocating only a fraction of control period to the active vector selected from conventional MPTC, whereas the rest of time is allocated for a null vector. Two kinds of methods for optimising the duty ratio of the active vector are proposed and evaluated in detail. Presented experimental results prove that, compared with conventional MPTC, the proposed MPTC achieves better steady-state performance by reducing the torque ripple significantly. Meanwhile, the quick dynamic response of conventional MPTC is reserved.
- Author(s): Fahad S. Al Badawi and Mohammad AlMuhaini
- Source: IET Electric Power Applications, Volume 9, Issue 9, p. 605 –611
- DOI: 10.1049/iet-epa.2015.0089
- Type: Article
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p.
605
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Reliability is a significant performance index for any electrical equipment in the industry, especially for electric motor driven (EMD) systems. Modelling the reliability of an EMD system is a difficult and challenging task. However, based on field data, the dominant failure modes of some motor system parts can be used to develop a simple and credible reliability model. This study proposes a failure rate prediction model for an EMD system that is currently in use in hydrocarbon industries. In addition, a fault tree model was designed to identify the root causes of the failures and the failure mechanism of the most dominates failure modes in EMD systems. To accomplish the study's objectives, an existing failure databank of over 100 failures of EMD systems was collected and surveyed from the field. The historical information and failure rate models that were collected for the electric motors are investigated and used to model the prediction model of the EMD system. Three competing failure modes were found to dominate motor life: bearing failures, winding failures and shaft failures. A mathematical model for each of these failure modes with dominant variables is developed, and a risk failure model is established.
- Author(s): Nattapong Pothi ; Z.Q. Zhu ; Ibrahim A. A. Afinowi ; B. Lee ; Y. Ren
- Source: IET Electric Power Applications, Volume 9, Issue 9, p. 612 –619
- DOI: 10.1049/iet-epa.2015.0115
- Type: Article
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p.
612
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Hybrid-excited permanent magnet (PM) machines utilise the coordinated operation between the PM and the field excitation current. To enhance the effectiveness of the field excitation current, iron flux bridges are applied to hybrid-excited switched-flux PM machines. This study proposes a new control strategy in which the d-axis current is utilised, while the field excitation current is controlled towards zero rather than negative in the flux-weakening mode. These reference currents are determined by the voltage error regulation method. The special magnetic circuit can effectively reduce the d-axis flux-linkage by either partially short-circuiting the PM flux via the iron bridge or removing the field excitation current. The proposed method exhibits advantages, such as highly enhanced torque response in the constant torque region, extended speed range, robustness against machine parameters, and higher efficiency in flux-weakening region. The feasibility of the proposed method is verified by detailed experimental results.
- Author(s): Jianfei Pan ; Siu Wing Or ; Yu Zou ; Norbert Chow Cheung
- Source: IET Electric Power Applications, Volume 9, Issue 9, p. 620 –627
- DOI: 10.1049/iet-epa.2014.0486
- Type: Article
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620
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This study presents the performance improvement in the position control of a medium-stroke voice coil motor (VCM) using a sliding-mode controller (SMC) with a system identification observer (SIO). The proposed VCM is developed with a full stroke of 24 mm, and its non-linear electro-magneto-mechanical characteristics are analysed by the three-dimensional finite element method. A least-squares-based SIO is introduced into the VCM control system prior to the position regulation of the SMC in order to achieve a shorter rise time of 29 ms and a smaller steady-state error of <±2 μm under a square-wave excitation of 20 mm amplitude and 0.5 Hz frequency. An experimental verification between the SMC and a traditional proportion–integral–differential controller is carried out. The results demonstrate improved dynamic and static tracking responses in the SMC under load-free, frequency-varying operations.
- Author(s): Ziyuan Huang and Bangcheng Han
- Source: IET Electric Power Applications, Volume 9, Issue 9, p. 628 –633
- DOI: 10.1049/iet-epa.2014.0503
- Type: Article
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p.
628
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An effective approach is presented for large errors in calculating critical speed of rotor-shaft assembly with the commercial finite element software, is intended to develop the discrete model of the rotor-shaft assembly by using lumped mass method, which is supported by active magnetic bearings. The first two bending critical speeds are analysed by optimising the flexural rigidity coefficient based on transfer matrix method. Compared with experimental modal testing and finite element analysis, the results of the transfer matrix method are in good agreement with modal measurement, the percentage errors of the first two bending natural frequencies are 0.21 and 2.1%, respectively. Owing to the higher accuracy and numerical stability, the method used in this study is an effective way to calculate the critical speed of the rotor-shaft assembly.
- Author(s): Puvan Arumugam ; Tahar Hamiti ; Chris Gerada
- Source: IET Electric Power Applications, Volume 9, Issue 9, p. 634 –641
- DOI: 10.1049/iet-epa.2015.0020
- Type: Article
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p.
634
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This study presents a systematic study on turn–turn short circuit (SC) fault and ways to manage them to provide a basis for comparison of the various options available. The possible methods to reduce the likelihood of the winding SC fault and the fault mitigation techniques related to such faults are discussed. A finite-element analysis of a surface-mounted permanent magnet machine under application of different mitigation techniques during a turn–turn fault is presented. Both machine and drive structural adaptations for different fault mitigation techniques are addressed. Amongst the investigated fault mitigation techniques, the most promising solution is identified and validated experimentally. It is shown that the shorting terminal method adopting vertical winding arrangement is an effective method in terms of the implementation, reliability and weight.
- Author(s): Luca Peretti ; Paul Sandulescu ; Giovanni Zanuso
- Source: IET Electric Power Applications, Volume 9, Issue 9, p. 642 –651
- DOI: 10.1049/iet-epa.2015.0070
- Type: Article
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p.
642
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This study presents a self-commissioning procedure for the estimation of the flux linkage curves of synchronous reluctance machines. The procedure exploits a quasi-standstill condition obtained by imposing fast torque oscillations. The flux linkage is calculated by means of a pure integration of the voltages and currents. With respect to the existing procedures, the proposed one tackles the problem of the limited knowledge of the core losses in the electrical machine, which is shown to induce erroneous estimation results for the case under investigation. A theoretical analysis supported by extensive laboratory measurements is shown, proving the effectiveness of the proposed approach.
- Author(s): Pedro Lobato ; Joaquim A. Dente ; João F. Martins ; Armando J. Pires
- Source: IET Electric Power Applications, Volume 9, Issue 9, p. 652 –659
- DOI: 10.1049/iet-epa.2014.0451
- Type: Article
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p.
652
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This study presents a design methodology based on scale models for low speed switched reluctance generators (SRG). This study is motivated by the application of SRG to direct-drive wind turbines and other low speed renewable energy systems. In direct drive energy converters considerable simplifications result from the elimination of the gear box which has generally been used to interface a slowly rotating shaft with the generator shaft. The comparison and evaluation of magnetic structures plays an important role in the SRG design. General design methodologies are usually oriented towards the evaluation of stator/rotor poles combinations for regular switched reluctance machines. Besides covering that feature, the formulation of scale laws proposed is also suitable to compare other SRG topologies distinguished by different characteristics of electric and magnetic circuits and their own relative position. In addition, this methodology can be extended to other physical phenomena such as thermal changes and magnetic saturation by introducing some constraints. The running example compares a modular short flux-path topology versus a low speed 20 kW prototype SRG designed for a direct drive wind turbine. The modular topology can optimise the efficiency and weight taking benefits from the significant gain of power per unit of volume and lower losses.
- Author(s): Fenghua Wang ; Chao Geng ; Lei Su
- Source: IET Electric Power Applications, Volume 9, Issue 9, p. 660 –669
- DOI: 10.1049/iet-epa.2015.0034
- Type: Article
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p.
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This study presents a novel approach for the modelling of transformer core magnetisation characteristics under DC bias condition by using the inverse Jiles–Atherton (J–A) model. An improved shuffled frog leaping algorithm (SFLA) is proposed to identify the five parameters of J–A model, where an adaptive chaotic mutation operation is added in the global searching process to increase the identification accuracy. With the proposed algorithm, the J–A model parameters under different DC components are identified based on the DC-bias experiment on the real transformer. The conventional SFLA and particle swarm optimisation (PSO) method are also applied to identify the parameters of J–A model. All the identified results are compared with the measured B–H curves to verify their identification accuracy. Moreover, the least square support vector machine (LSSVM) algorithm is used to predict the J–A model parameters of transformer under larger DC component from the previously identified parameters in smaller DC. The calculated results have shown that the improved SFLA has higher identification accuracy than the conventional SFLA and PSO methods. Furthermore, LSSVM algorithm can effectively forecast the transformer magnetisation character under large DC bias condition, which is beneficial for the research of transformer DC bias problem.
Prediction of vacuum cleaner motor brush life: a regression approach
Direct instantaneous torque control with wide operating range for switched reluctance motors
Performance investigation of hybrid excited switched flux permanent magnet machines using frozen permeability method
Model predictive torque control of induction motor drives with reduced torque ripple
Reliability modelling and assessment of electric motor driven systems in hydrocarbon industries
Control strategy for hybrid-excited switched-flux permanent magnet machines
Sliding-mode position control of medium-stroke voice coil motor based on system identification observer
Effective approach for calculating critical speeds of high-speed permanent magnet motor rotor-shaft assemblies
Turn–turn short circuit fault management in permanent magnet machines
Self-commissioning of flux linkage curves of synchronous reluctance machines in quasi-standstill condition
Scale models formulation of switched reluctance generators for low speed energy converters
Parameter identification and prediction of Jiles–Atherton model for DC-biased transformer using improved shuffled frog leaping algorithm and least square support vector machine
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