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1 – 10 of over 21000Amina Mesbeh, Marwen Jarboui and Ahmed Masmoudi
The purpose of this paper is to investigate the effects of different faulty scenarios on the induction motor (IM) operation with emphasis on the currents in the rotor bar and end…
Abstract
Purpose
The purpose of this paper is to investigate the effects of different faulty scenarios on the induction motor (IM) operation with emphasis on the currents in the rotor bar and end rings.
Design/methodology/approach
The modeling of the IM followed by a graphical representation-based analysis of the rotor steady-state currents under healthy operation is treated. Then, a case study is considered in order to investigate different faulty scenarios with a focus on the rotor cage currents.
Findings
It has been found that the rotor faults greatly affect the currents in the bars and in the end rings both in amplitude and in harmonic content. These vary according to the relative positions with respect to the fault such that: the currents in the bars adjacent to the faulty one(s) have the highest amplitudes with the lowest harmonic content; and the ones in the ring portions adjacent to the faulty one have the lowest amplitudes with the highest harmonic content.
Research limitations/implications
Although the simulated model has confirmed the well known IM behavior under healthy operation, it would be appreciated if the obtained results under faulty operation would be validated by finite element analysis.
Practical implications
It is of great interest to investigate the effects of faulty scenarios on the rotor cage currents, in order to take appropriate actions starting from the design of the IM.
Originality/value
A deep investigation (including the waveforms, the phasor diagrams and the harmonic content) of the effects of different faulty scenarios on the IM rotor cage currents represents the major contribution of this work.
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Hossein Torkaman and Ebrahim Afjei
The purpose of this paper is to determine the degrees of freedom (DOF) for eccentricity fault in switched reluctance motor (SRM) based on nonlinear static torque function to…
Abstract
Purpose
The purpose of this paper is to determine the degrees of freedom (DOF) for eccentricity fault in switched reluctance motor (SRM) based on nonlinear static torque function to minimize torque ripple for maximum performance in motoring operation.
Design/methodology/approach
An algorithm based on nonlinear torque function versus rotor position and percent of rotor eccentricity for the SRM operation is introduced. This algorithm enables accurate determination of different modes of motor operations namely, healthy and faulty conditions. In this approach, SRM is first analyzed by a 3D finite element method for estimation of nonlinear torque function and then the function is approximated by least square, cubic spline and piecewise cubic Hermitian methods. The minimization is performed by random search method and genetic algorithm.
Findings
A new procedure for computing the DOF of eccentricity in SRM based on nonlinear torque function is proposed and analyzed. It computes the legal intervals for the radial airgap length as well as the regions of the motor operation under different conditions. The functionability and the feasibility of this algorithm is illustrated by employing it on a three‐phase 6/4 SRM.
Practical implications
The proposed method and its results can improve the motor control while the implementation is simple and practical. The proposed method can be used for other motors as well.
Originality/value
The boundary of motor operation under fault must be calculated to attain smooth control on motor to achieve high performance expected from the machine. To the best knowledge of the authors, this is the first time such a study has been conducted on SRM.
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Hamdi Echeikh, Hichem Kesraoui, Ramzi Trabelsi, Atif Iqbal and Mohamed Faouzi Mimouni
This paper aims to deal with direct torque controller when the five-phase induction motor drive in faulty operation. Precisely, open-phase fault condition is contemplated. Also…
Abstract
Purpose
This paper aims to deal with direct torque controller when the five-phase induction motor drive in faulty operation. Precisely, open-phase fault condition is contemplated. Also, the DTC is combined with a speed-adaptive variable-structure observer based on sliding mode observer.
Design methodology/approach
Two novel features are presented. First, the concept of the virtual voltage vector is presented, which eliminates low-frequency harmonic currents and simplifies analysis. Second, speed information is introduced into the selection of the inverter states.
Findings
Direct torque control (DTC) is largely used in traditional three-phase drives as a backup to rotor-stator flux-oriented methods. The classic DTC strategy was primarily designed on the base of hysteresis controllers to control two independent variables (speed, torque and flux). Due to the additional degrees of freedom offered by multiphase machine, extensive works have been extended on the ensemble five-phase drives in healthy operation. In addition, the ability to continue the operation in faulty conditions is considering one of the main advantages of multiphase machines. One can find in the literature different approaches treating this subject. The applicability of DTC after the appearing of a fault has not been enclosed in the literature.
Originality/value
Theoretical development is presented in details followed by simulation results using Matlab/Simulink to analyze the performance of the drive, comparing with the behavior during healthy situation.
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Tarek Gallah, Badii Bouzidi and Ahmed Masmoudi
The purpose of this paper is to deal the adaptation of a direct torque control (DTC) strategy, originally dedicated to three level three leg inverter fed induction motor (IM…
Abstract
Purpose
The purpose of this paper is to deal the adaptation of a direct torque control (DTC) strategy, originally dedicated to three level three leg inverter fed induction motor (IM) drives, following a leg failure that required the reconfiguration of the inverter from three to two legs.
Design/methodology/approach
In case of troubles with one leg of a three level inverter, it is interesting in some applications to keep operating using the two remaining legs. So, after the detection and isolation of the faulty leg, the drive connection should be rearranged with the connection of the motor phase, previously linked to the faulty leg, to the mid point of the DC-bus voltage, leading to a three level two leg inverter topology (also called bridge B8-inverter).
Findings
It has been found that the IM drive exhibits better performances under the proposed DTC strategy dedicated to the reconfigured inverter than those yielded by the DTC of the IM drive under healthy operation of the inverter. It has been noticed that the only drawback affecting the reconfigured inverter fed IM drive is the speed range limitation.
Research limitations/implications
This work should be extended by an experimental validation of the proposed DTC strategies.
Originality/value
The power factor of the reconfigured three level inverter fed IM drive is higher than the one yielded by the three level three leg inverter fed one. This represents a crucial cost benefit.
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Hajer Rebai, Imen Abdennadher and Ahmed Masmoudi
The purpose of this paper is to deal with several approach to recover the torque production capability of a five phase double-layer fractional-slot PM machine under faulty…
Abstract
Purpose
The purpose of this paper is to deal with several approach to recover the torque production capability of a five phase double-layer fractional-slot PM machine under faulty operation. The considered fault is an open-circuit coil in a given phase.
Design/methodology/approach
In a first step, the mean futures, such as the phase back-EMFs and the electromagnetic torque, are computed by finite element analysis under healthy operation, and are taken as references. Then, they are investigated, under a faulty coil, for different approaches to recover the torque production capability.
Findings
A comparison of the potentialities of the torque recovery approaches has clearly highlight the superiority of the approach consisting in the re-adjustment of the current initial phases, in an attempt to equilibrate the resulting air gap MMF.
Research limitations/implications
This work should be extended by an experimental validation of the predicted results regarding the back-EMFs and the electromagnetic torque.
Practical implications
The investigation of the considered five phase fractional-slot PM machine under faulty operation should be extended to several faulty scenarios in order to fulfill the requirements of many applications such as the propulsion systems.
Originality/value
The paper proposes different approaches to recover the torque production capability of a five phase fractional-slot PM machine under faulty operation.
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Mohamed Ali Zdiri, Badii Bouzidi and Hsan Hadj Abdallah
This paper aims to analyze and investigate the performance of an improved fault detection and identification (FDI) method based on multiple criteria, applied to six-switch…
Abstract
Purpose
This paper aims to analyze and investigate the performance of an improved fault detection and identification (FDI) method based on multiple criteria, applied to six-switch three-phase inverter (SSTPI)-fed induction motor (IM) drives under both single and multiple open insulated-gate bipolar transistors(IGBT) faults.
Design/methodology/approach
This paper proposes an advanced diagnostic method for both single and multiple open IGBT faults dedicated to SSTPI-fed IM drives considering five distinct faulty operating conditions as follows: a single IGBT open-circuit fault, a single-phase open-circuit fault, a non-crossed double fault in two different legs, a crossed double fault in two different legs and a three-IGBT open-circuit fault. This is achieved because of the introduction of a new diagnosis variable provided using the information of the slope of the current vector in (α-β) frame. The proposed FDI method is based on the synthesis and the analysis, under both healthy and faulty operations, of the behaviors of the introduced diagnosis variable, the three motor phase currents and their normalized average values. Doing so, the developed FDI method allows a best compromise of fast detection and precision localization of IGBT open-circuit fault of the inverter.
Findings
Simulation works, carried out considering the implementation of the direct rotor flux oriented control in an IM fed by the conventional SSTPI, have proved the high performance of the advanced FDI method in terms of fast fault detection associated with a high robustness against false alarms, against speed and load torque fast variations and against the oscillations of the DC-bus voltage in the case of both healthy and faulty operations.
Research limitations/implications
This work should be extended considering the validation of the obtained simulation results through experiments.
Originality/value
Different from other FDI methods, which suffer from a low diagnostic effectiveness for low load levels and false alarms during transient operation, this method offers the potentialities to overcome these drawbacks because of the introduction of the new diagnosis variable. This latter, combined with the information provided from the three motor phase currents and their normalized average values allow a more efficient detection and identification of IGBT open-circuit fault.
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This book is a policy proposal aimed at the democratic left. It is concerned with gradual but radical reform of the socio‐economic system. An integrated policy of industrial and…
Abstract
This book is a policy proposal aimed at the democratic left. It is concerned with gradual but radical reform of the socio‐economic system. An integrated policy of industrial and economic democracy, which centres around the establishment of a new sector of employee‐controlled enterprises, is presented. The proposal would retain the mix‐ed economy, but transform it into a much better “mixture”, with increased employee‐power in all sectors. While there is much of enduring value in our liberal western way of life, gross inequalities of wealth and power persist in our society.
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Elvira Anna Graziano, Fabio Fiano, Antonio Usai and Nadia Cipullo
The purpose of the study is to analyse the stock market response to a spin-off announcement concerning a food and beverage (F&B) business unit.
Abstract
Purpose
The purpose of the study is to analyse the stock market response to a spin-off announcement concerning a food and beverage (F&B) business unit.
Design/methodology/approach
The study uses a sample of approximately 107 spin-offs, 84 of which are operating in the F&B sector surveyed by the Zephyr–Bureau Van Dijk database. The event study approach is applied to the identified sample. The results demonstrate that the effect of an event on the stock price of a firm allows identification of the abnormal return as the difference between the current and expected returns.
Findings
The study finds that investors adjust positively to the closing of the spin-off deal. The peak of performance is reached on the day of the announcement.
Research limitations/implications
Empirical evidence could be distorted by the mono-industry database, analysed in a “favourable time span.” The role of information transfer on spin-offs, in terms of diffusion and reduction of information asymmetries, could be developed.
Originality/value
The study represents a pioneering investigation of a category of mono-industry spin-offs. Previous doctrinal contributions underline the fact that abnormal returns corresponding to announcement effects are amplified in the case of information asymmetries but underestimate the effects deriving from the strategic business unit's nature as a spin-off.
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Sunhee (Sunny) Seo and Hyunjeong Lee
The purpose of this paper is to uncover what affected restaurateurs in their intention to participate in the healthy restaurant initiative.
Abstract
Purpose
The purpose of this paper is to uncover what affected restaurateurs in their intention to participate in the healthy restaurant initiative.
Design/methodology/approach
In all, 53 restaurateurs who participated in healthy restaurant initiatives in Korea responded to a survey. Multiple regression analysis was conducted to reveal the influences of perceived innovation characteristics (PICs), attitudes, subjective norm, and perceived behavioral control (PBC) on the intention to sustain a healthy restaurant.
Findings
The results showed that PBC, attitudes toward healthy restaurants, relative advantage for restaurants, and complexity among PICs were significant influences on the intention to sustain healthy restaurant initiatives.
Research limitations/implications
This research has made the first attempt to evaluate healthy restaurant initiatives using the perspectives of restaurateurs who actually participated in healthy restaurant initiatives. Also, this study extends the research model testing behavior intention using the theory of planned behavior and the innovation adoption theory to investigate the influences on restaurateur intentions to sustain healthy restaurant initiatives.
Practical implications
The findings indicate that operators must have access to sufficient technical resources and a sense of self-efficacy, which encourage restaurateurs to maintain healthy restaurant initiatives. Enhancing positive attitudes and the relative advantages of the healthy restaurant initiatives also encouraged participation. Finally, voluntary and continuous participation and expansion of healthy restaurant initiatives require community and government support, a simple use of process to change, and a good understanding of the relative advantages of healthy restaurant initiatives.
Originality/value
This study first illustrates the factors that best explain the intention to sustain a healthy restaurant from the perspective of restaurateurs. PICs shed light on how complexity and relative advantage for customers helps predict intentions to sustain healthy restaurant initiatives.
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Ali Hajary, Seyed Ghodratollah Seifossadat, Reza Kianinezhad, Alireza Saffarian and Seyed Saeedollah Mortazavi
This paper aims to present a novel robust control method based on an adaptive PI controller (APIC) to compensate for different disturbances and unknown dynamics for multi-phase…
Abstract
Purpose
This paper aims to present a novel robust control method based on an adaptive PI controller (APIC) to compensate for different disturbances and unknown dynamics for multi-phase induction machines.
Design/methodology/approach
The gains of the APIC are adapted online according to the tracking error. Proposed APIC is accompanied with designed linear disturbance observer (LDO) to present robust behavior to machine parameter variations and fault disturbances.
Findings
The results show remarkable dynamic performance in both healthy and faulty conditions when the six-phase induction machine works under APIC and LDO schemes.
Originality/value
The proposed controller need not readjust current controllers for the post-fault condition. The developed Simulink model efficiency is confirmed through experimental tests.
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