Search

A detailed magnetic reluctance-based computational model of an induction machine, into which a traditional rotor-flux-orientated vector control scheme has been grafted, is used to examine the influence of saturation of both main and leakage flux paths upon vector-controlled drive performance. Individual machine teeth, windings, and conductors are incorporated, as is pseudo-3-D modeling of skew. The cross-saturation effect is therefore determined from the basic dimensional and winding design data of the machine. Effective compensation methods can then be derived for practical implementation. Direct rotor flux orientation and magnitude control is used to ensure that inaccuracies in a machine-parameter-based vector control scheme are not reflected in the results for cross saturation. Results for a 15-kW four-pole induction motor with rotor skewed one stator slot pitch show that skew leakage flux is predominantly responsible for cross saturation. The skew leakage flux is shown to heavily saturate one end of the machine and to reduce the air gap flux density at the other. At 200% rated load current, this equates to an 11% reduction in direct axis flux if [i.sub.sd] is kept constant. To compensate for this reduction, a 27% increase in [i.sub.sd] would be required. Index Terms---Cross coupling, induction machines, skew, vector control.

This paper develops the foundations of a technique for diagnosis and characterization of effects of broken bars in squirrel-cage induction motors based on the time-stepping coupled finite-element approach. These studies are performed by using the model to compute healthy case, one-broken-bar fault, and two adjacent broken bars fault performance data, which contains stator starting current waveforms, the current density on the bars, the magnetic force distribution on the rotor bars, and the distribution of magnetic field. Meanwhile, the iron core loss distributions on the rotor tooth adjacent to broken bars are computed, and the harmonic component of air-gap flux density is analyzed. From this data, the faulty signatures are extracted. Theoretical approach together with experimental results derived from a two-pole 1.1 kW induction motor confirms the validity of the proposed method. Furthermore, this method, which could help to develop diagnostics of broken bars and performance evaluation of induction motors, has great potential in future applications. Index Terms--Broken rotor bars, faults diagnosis, squirrel-cage induction motors, time-stepping coupled finite element (FE).

Fault diagnosis is gaining more attention for electric machines running critical loads, whose sudden breakdown can result in unpredictable revenue losses. Consequently, the motor drive systems with fault diagnostic and prediction features are of great concern and are becoming almost indispensable. Among all kinds of common faults, quite a few have relationship with unequal air gap. So far, work on detection of eccentricity-related faults in induction and synchronous machines has been well documented. However, a few are reported on faults resulting from axial nonuniform air gap. This paper investigates the performance of a three-phase induction machine with nonuniform static eccentricity (SE) along axial direction or inclined SE. A variant of modified winding function approach is applied to study this fault. The relationship between the number of rotor bars and poles, and the existence of fault-related current harmonics is discussed. It is shown that inclined eccentricity also demonstrates similar characteristics such as circumferential nonuniform air gap (SE). More importantly, it has been proved conclusively that inclined eccentricity symmetric to the midpoint of the machine shaft cannot be recognized from the current spectrum and would therefore require some other form of detection. Finite-element results to verify the inductance values used in simulation are also presented. The analysis is supplemented by the stator current spectra obtained from simulated results for different load and fault conditions. Finally, a four-pole 45-rotor-bar 2-kW induction motor is used to validate the theoretical and simulation results experimentally. Both current as well as vibration spectra are presented. Index Terms--Inclined static eccentricity (SE), induction motor.

This paper presents the modeling, detailed simulation, and test of an efficient medium-voltage adjustable-speed drive. The system consists of a three-level neutral-point-clamped inverter supplied by a 12-pulse rectifier. To achieve a motor-friendly supply, an LC filter is inserted between inverter output terminals and induction motor terminals. A direct torque control tunes the inverter. The full power circuits as well as the digital control scheme have been implemented and simulated. Simulation results have been compared successfully with measurements, in steady state and transients. Index Terms--Direct torque control (DTC), medium-voltage adjustable-speed drive (ASD), mixed signals regulation scheme, modeling, simulation, three-level voltage-source inverter.

We discuss the shifting magnetic field generated by a two-phase modulated wave composed of a basic wave of 60 Hz and a higher harmonic wave in terms of its use in a magnetic levitation induction linear motor. In addition, we present measurements of the propulsive and levitation forces generated by the modulated wave. When the order of the higher harmonic wave is 4, the basic wave mainly generates a propulsive force, while the higher harmonic wave generates a levitation force alone. Thus, the propulsive and levitation forces can be easily and almost independently controlled by changing the amplitude of the basic wave and that of the higher harmonic wave, respectively. When the order of the higher harmonic wave is 3 or 5, the forces can also be easily controlled, if the phase of the higher harmonic wave is the same between two phases. Index Terms--Higher harmonic wave, levitation force, linear motor, modulated wave, open core, propulsive force, two-phase electric source.

This paper presents an analysis and control design of a doubly-fed induction generator (DFIG)-based wind generation system operating under unbalanced network conditions. A DFIG system model in the positive and negative synchronous reference frames is presented. Variations of stator active and reactive powers and generator torque are fully defined in the presence of negative sequence voltage and current. Alternative DFIG control targets during network unbalance, such as reducing stator current unbalance, torque, and power pulsations minimization, are identified. A rotor current control strategy based on positive and negative (dq) reference frames is used to provide precise control of the rotor positive and negative sequence currents. Simulation results using EMTDC/PSCAD are presented for a 2-MW DFIG wind generation system. It shows that conventional vector control of DFIG without considering network unbalance results in excessive oscillations on the stator active/reactive power, electromagnetic torque, and stator/rotor currents even with a small stator voltage unbalance. In contrast, with the proposed control strategy, enhanced system control and operation such as minimizing oscillations in either active power, or electromagnetic torque, or stator or rotor currents can be achieved. Index Terms--Control design, converter, doubly-fed induction generator (DFIG), modeling, unbalance, wind turbine.

This paper presents an improved analysis of magnetic force compensation in a bearingless induction motor with a squirrel-cage rotor. The expressions for air-gap flux linkages are derived. Simulation blocks of suspension force are constructed. A novel control system, which compensates the delay and direction error in suspension force generation for a squirrel-cage rotor, is proposed. The efficacy of the proposed control system is established by both simulation and experiment. Index Terms--Bearingless motor, component, induction motor, magnetic bearing, squirrel-cage rotor.

Most sensorless algorithms for a motor drive are based on a mathematical model including electrical variables such as motor current and voltage. Therefore, the accuracy of such variables largely influences the performance of the sensorless motor drive. However, the output voltage of the space vector pulsewidth modulation of the voltage-source inverter supplying a motor is error-prone in the motor's low-speed range because it has a poor resolution in a low-output voltage command. This letter proposes a variation of the dc-link voltage as a high-performance strategy for overcoming the above problem in a sensorless induction motor drive. The proposed strategy is verified through simulation and experimentation. Index Terms--Sensorless induction motor drive, space vector pulsewidth modulation (SVPWM), variable link voltage, voltage source inverter (VSI).

A new current regulation algorithm is presented that achieves indirect field-oriented control (IFOC) for three-phase induction motor drives using current feedback information provided by three integrated pilot sensors in the three low-side inverter switches. A new regulator is required for this configuration of pilot sensors because each sensor can measure its phase current during only half of each fundamental frequency cycle. A technique has been developed to reconstruct the three phase currents during the intervals when they are not measured so that the phase current can be used to achieve FOC of the machine. Experimental results are provided to confirm the attractive performance characteristics of the proposed control technique during both steady-state and transient operation. Key application issues including the impact of errors in the estimated machine parameters are discussed. Index Terms--Indirect field-oriented control (IFOC).

This paper proposes a strategy to minimize the losses of an induction motor propelling an electric vehicle (EV). The proposed control strategy, which is based on a direct flux and torque control scheme, utilizes the stator flux as a control variable, and the flux level is selected in accordance with the torque demand of the EV to achieve the efficiency-optimized drive performance. Moreover, among EV's motor electric propulsion features, the energy efficiency is a basic characteristic that is influenced by vehicle dynamics and system architecture. For this reason, the EV dynamics are taken into account. Simulation tests have been carried out on a 1.1-kW EV induction motor drive to evaluate the consistency and the performance of the proposed control approach. Index Terms--Direct torque control (DTC), electric vehicle (EV), induction motor, loss minimization.

In this paper, an online induction motor diagnosis system using motor current signature analysis (MCSA) with advanced signal-and-data-processing algorithms is proposed. MCSA is a method for motor diagnosis with stator-current signals. The proposed system diagnoses induction motors having four types of faults such as breakage of rotor bars and end rings, short-circuit of stator windings, bearing cracks, and air-gap eccentricity. Although MCSA is one of the most powerful online methods for diagnosing motor faults, it has some shortcomings, which degrade performance and accuracy of a motor-diagnosis system. Therefore, advanced signal-and-data-processing algorithms are proposed. They are composed of an optimal-slip-estimation algorithm, a proper-sample-selection algorithm, and a frequency auto search algorithm for achieving MCSA efficiently. The proposed system is able to ascertain four kinds of motor faults and diagnose the fault status of an induction motor. Experimental results obtained on 3.7-kW and 30-kW three-phase squirrel-cage induction motors and voltage-source inverters with a vector-control technique are discussed. Index Terms--Induction motor, motor current signature analysis (MCSA), motor diagnosis, signal processing.

This paper presents a comparative analysis involving several fault-tolerant operating strategies, applied to three-phase induction-motor drives, that intend to compensate for inverter faults. The results presented show the advantages and the inconveniences of several fault-tolerant drive structures, under different control techniques, such as the field-oriented control and the direct torque control. Experimental results concerning the performance of the three-phase induction motor, based on the analysis of some key parameters, like induction-motor efficiency, motor power factor, and harmonic distortion of both motor line currents and phase voltages, will be presented. Index Terms--AC motor drives, fault tolerance, induction-motor drives, reliability.

This paper presents a new approach of optimizing the efficiency of induction-motor drives through minimizing the copper and core losses. The induction-machine model, which accounts for the varying core-loss resistance and saturation dependent magnetizing inductance, uses natural and reference frame independent quantities as state variables. Utilization of the nonlinear geometric control methodology of input-output linearization with decoupling permits the implementation of the control in the stationary reference frame. This approach eliminates the need of synchronous reference transformation and flux alignment required in classical vector control schemes. The new efficiency optimizing formulation yields a reference rotor flux, which ensures a minimum loss and yields an improved efficiency of the drive system especially when driving part load. The proposed scheme and its advantages are demonstrated both by computer simulations and some experimental results for motor speed control. Index Terms--Butterworth filter, efficiency optimization, induction motor, linearizing control, speed control.

Optimal time trajectories, based on the Pontryagin's maximum principle, are deduced for a squirrel-cage induction motor with constant load torque. These trajectories are valid for acceleration and deceleration with or without the load torque and for a loaded or unloaded motor, and ensure the minimal time transients with the stator current limited to the previously fixed value. Moreover, the optimal trajectories place the motor at the end of the transient at the minimum current point, which is close to the one of maximum efficiency, thus combining the brevity of the transients with the saving of energy. An optimal-time control system that implements these trajectories is designed. The results of the simulation of the proposed control system and the results of the experiments on a real drive are presented. Index Terms--Constant load torque, energy saving, maximum principle, optimal control, squirrel-cage motors.

A robust interturn fault diagnostic approach based on the concept of magnetic field pendulous oscillation, which occurs in induction motors under faulty conditions, is introduced in this paper. This approach enables one to distinguish and classify an unbalanced voltage power supply and machine manufacturing/construction imperfections from an interturn fault. The experimental results for the two case studies of a set of 5-hp and 2-hp induction motors verify the validity of the proposed approach. Moreover, it can be concluded from the experimental results that if the circulating current level in the shorted loop increases beyond the phase current level, an interturn fault can be easily detected using the proposed approach even in the presence of the existence of motor manufacturing imperfection effects. Index Terms--Broken-bar, condition monitoring, induction motor, interturn short circuit, stator fault, transient modeling.

Based on the stator-flux-oriented electromechanical model of a doubly fed induction machine (DFIM), this paper presents two different approaches to wind farm modeling. Particularly, the overall control system of the DFIM is modeled in detail, so that tuning equations that allow adjusting the parameters of its proportional-integral (PI) compensators straightforwardly are provided. In addition to validating the wind generator model proposed, experimental tests carried out on a 660-kW doubly fed induction generator (DFIG) prove that such a control system makes it possible to govern separately its stator-side or net active and reactive powers. The two wind farm models proposed, which are assumed to be made up of DFIM type generators exclusively, are mainly devised to assist the design and test of closed-loop control algorithms for the wind farm total power factor. They generally imply significantly different computational loads, so that the second may be regarded as a simplified version of the first one. The net active and reactive power performances of both wind farm models are finally compared via simulation, which allows identifying the stronger and weaker points associated to each model. Index Terms--Active power, doubly fed induction generators (DFIGs), pole assignment, reactive power, simplified model, vector control, wind farms, wind power generation.

This paper presents a general mathematical model of a five-phase induction machine including the effects of higher space and time harmonics in the air gap field. These harmonic waves play a decisive role in the behavior of machines with more than three phases. Mathematical expressions for the calculation of the self and mutual inductances are presented, and results are compared with values obtained by finite element analysis and measurements. Based on the air gap field distribution produced by the stator and rotor, all the field harmonics are included in a direct and simple way in the self-inductances. The mutual inductances are obtained from a Fourier series description of the air gap field, resulting in a different inductance for each harmonic field. The machine equations are then simplified using coordinate transformations, which result in equivalent d-q models and equivalent circuits for given harmonic groups. In their final form, the equations are appropriated for the simulation of the machine behavior and developing new control strategies including higher space and time harmonics. Finally, practical results of a prototype machine are compared with simulations demonstrating the accuracy of the model. Index Terms--Finite element method, induction machines, induction motors, modeling.

Transient performance of a 1.7--MW wind-power doubly fed induction generator (DFIG) under network disturbances is studied using a coupled field-circuit simulator. The simulator consists of the finite-element method model of a DFIG coupled with the circuit model of the frequency converter, a transformer, and a simple model of the network. The simulation results show the transient behavior of the DFIG when a sudden voltage dip is introduced. The field-circuit simulator is experimentally validated by full-power measurement. Index Terms--Coupled model, crowbar, doubly fed induction generator (DFIG), finite-element method (FEM), measurement, voltage dip.

In this paper, the application of an additional excitation in induction motor (IM) drives for static, dynamic, and mixed eccentricity diagnosis is proposed. The additional excitation consists in a predefined inverter-switching pattern that is applied on the motor for a short time, while the fundamental excitation is canceled. This excitation was used previously to implement a position estimation strategy. The strategy obtains information about the rotor position from the motor saliencies effects over the zero-sequence voltage. The air-gap eccentricity is a kind of saliency that affects the zero-sequence voltage and allows the use of the additional excitation for eccentricity diagnosis. For the evaluation of the feasibility of this proposal, a multiple-coupled circuit model of the IM is used. The effects of series and series-parallel stator winding connections on the diagnosis signals are shown. Experimental results to validate the proposal are also given. These results show that it is possible to use the diagnosis strategy in a self-commissioning scheme. Index Terms--Air-gap eccentricity, fault diagnosis, induction motor drives, position estimation.

This paper estimates motor life when a motor is supplied with a combination of over- or undervoltages with unbalanced voltages. The motor life is predicted by estimating the stator winding insulation life of squirrel cage motors using Arrhenius' equations. Electrical and thermal models are used to calculate motor losses and temperatures, respectively. The thermal model parameters are obtained from simple motor testing techniques rather than from complex methods requiring motor design data. Index Terms--Motor life and temperature rise, voltage unbalance.

In this paper, an analytical model with a new spacevector modulation strategy for a four-switch (B4), inverter feeding an induction motor drive is derived. The proposed modulation strategy for the B4 operation has the same symmetry as in a classical B6 inverter. The analysis is based on a novel space-vector decomposition technique. The analytical results of the machine are accomplished in an [alpha][beta] complex plane by space vector decomposition and by using a mixed p-z approach. As shown, good agreement exists between the analytically calculated waveforms and the experimentally determined ones. Therefore, the proposed analytical model becomes a very useful method for motor investigation under unbalanced as well as balanced supply conditions. Index Terms--Induction motors, inverters, modeling, PWM, time-domain analysis.

Direct torque control (DTC) is an induction motor control technique that has been successful because it explicitly considers the inverter stage and uses few machine parameters, while being more robust to parameter uncertainty than field-oriented control (FOC). This paper presents a formal derivation of DTC based on singular perturbation and nonlinear control tools. The derivation elaborates an explicit relationship between DTC performance and machine characteristics; low-leakage machines are expected to perform better under DTC. It is shown that DTC is a special case of a sliding-mode controller based on the multiple time-scale properties of the induction machine. The known troublesome machine operating regimes are predicted and justified. Explicit conditions to guarantee stability are presented. DTC is shown to be a suboptimal controller because it uses more control effort than is required for flux regulation. Finally, compensation strategies that extend DTC are discussed. The derivation does not require space vector concepts thus, it is established that the traditional link between DTC and space vectors is not fundamental. Index Terms--AC motors, direct torque control (DTC), induction motor drives, singularly perturbed systems, vector control.

The hazards associated with high-voltage three-phase inverters and high-powered large electrical machines have resulted in most of the engineering courses covering three-phase machines and drives theoretically. This paper describes a set of purpose-built, low-voltage, and low-cost teaching equipment that allows the hands-on instruction of three-phase inverters and rotating machines. The motivation for moving towards a system running at low voltages is that the students can safely experiment freely with the motors and inverter. The students can also access all of the current and voltage waveforms, which until now could only be studied in textbooks or observed as part of laboratory demonstrations. Both the motor and the inverter designs are for teaching purposes and require minimal effort and cost. Index Terms--Brushless dc motor, course, induction motor, inverter, teaching.

Broken rotor bars in induction motors can be detected by monitoring any abnormality of the spectrum amplitudes at certain frequencies in the motor-current spectrum. It has been shown that these broken-rotor-bar specific frequencies are located around the fundamental stator current frequency and are termed lower and upper sideband components. Broken-rotor-bar fault-detection schemes should rely on multiple signatures in order to overcome or reduce the effect of any misinterpretation of the signatures that are obscured by factors such as measurement noises and different load conditions. Multiple discriminant analysis (MDA) and artificial neural networks (ANNs) provide appropriate environments to develop such fault-detection schemes because of their multiinput-processing capabilities. This paper describes two fault-detection schemes for a broken-rotor-bar fault detection with a multiple signature processing and demonstrates that the multiple signature processing is more efficient than a single signature processing. The first scheme, which will be named the 'monolith scheme,' is based on a single large-scale MDA or ANN unit representing the complete operating load-torque region of the motor, while the second scheme, which will be named the 'partition scheme,' consists of many small-scale MDA or ANN units, each unit representing a particular load-torque operating region. Fault-detection performance comparison between the MDA and the ANN with respect to the two schemes is investigated using the experimental data collected for a healthy and a broken-rotor-bar case. Partition scheme distributes the computational load and complexity of the large-scale single units in a monolith scheme to many smaller units, which results in the increase of the broken-rotor-bar fault-detection performance, as is confirmed with the experimental results. Index Terms--Artificial neural networks (ANNs), broken rotor bar, discriminant analysis, fault diagnosis, induction motors.

This paper deals with the speed sensorless vector control of an induction motor in a special case where the output voltage of the pulsewidth-modulated inverter is filtered by an inductance-capacitance (LC) filter. The system states are estimated by means of an adaptive full-order observer, and no additional voltage, current, or speed measurements are needed. The rotor speed adaptation is based on the estimation error of the inverter output current. Quasi-steady-state and linearization analyses are used to design an observer that enables a wide operation region, including very low and very high speeds. A torque-maximizing control method is applied in the field-weakening region. Simulation and experimental results show that the performance is comparable to that of a drive without the LC filter. Index Terms--Adaptive full-order observer, induction motor (IM) drives, inverter output filter, speed sensorless, vector control.

Investigations were carried out on a novel sensorless drive for induction motors, based on the combination of an open-loop (OL) estimator and a steady-state (SS) estimator. The novelty of this new sensorless structure is obtained by an intelligent mixing of the OL estimator response with the SS one. A fuzzy system weights the two estimated speed values according to the motor operating point. Then, the final speed value is obtained averaging the previously weighted speed values. Moreover, the OL estimator response is improved by means of using a fuzzy-controlled adaptive filter that selects the optimum cutoff frequency. The aim of this paper is to obtain a moderate performance sensorless drive for induction motors that could be easily implemented for industrial applications without a high computational effort. Simulation and experimental results illustrate the operation and performance of the proposed fuzzy-logic-based sensorless drive. Index Terms--Fuzzy control, induction motors, sensorless.

The flywheel energy-storage systems (FESSs) are suitable for improving the quality of the electric power delivered by the wind generators and for helping these generators to contribute to the ancillary services. Supervisors must be used for controlling the power flow from a variable-speed wind generator (VSWG) to the power grid or to an isolated load. This paper investigates the control method and the energetic performances of a low-speed FESS with a classical squirrel-cage induction machine in the view of its association to a VSWG. A test bench is developed, and experimental results are presented and discussed. Index Terms--Efficiency, energy storage, induction machine, losses, low-speed flywheel, power-flow control, supervisory, wind energy conversion system.

This paper reports on the development of a spherical actuator with two actuated degrees of freedom (DOFs). The electromechanical conversion principle is that of an induction motor. The paper first discusses possibilities of adapting the actuator to a spherical rotor actuated with an unlimited angular range along two DOFs. These concepts are then characterized and compared by analytical and numerical modeling, and the final shape of the actuator, composed of a two-layer rotor with teeth surrounded by five inductors, is described. A prototype has been built, and its performance, in terms of characteristic torque-speed and efficiency, has been measured. Index Terms--Design, induction motor, modeling, multi degrees of freedom, spherical motor.

At high angular velocity, the induction motor is operated in the field weakening range due to the voltage limit of the inverter. Field oriented vector control (FOC) is unsuitable for this operation due to coupling, non-linearities, and saturation of linear current controllers. A proposed direct torque control space vector modulation (DTC-SVM) scheme using SVM does not use coordinate transforms or current controllers to achieve DTC. Control of the stator flux vector allows for dynamic change in the torque in all regions, including field weakening with the six-step operation. This paper describes the torque control dynamic in the field weakening range, using a step change in stator flux vector magnitude and it's angular velocity. The method is demonstrated experimentally. Index Terms--Constant power speed range (CPSR), direct torque control (DTC), field-weakening.

Current source inverter (CSI) fed drives are employed in high power applications. The conventional CSI drives suffer from drawbacks such as harmonic resonance, unstable operation at low speed ranges, and torque pulsation. This paper presents a novel CSI drive which overcomes all these drawbacks and results in sinusoidal motor voltage and current even with CSI switching at fundamental frequency. The proposed CSI drive uses a three-level inverter as an active filter across motor terminals replacing the bulky ac capacitors used in the conventional drive. A sensorless vector controlled CSI drive based on proposed configuration is developed. The simulation and experimental results are presented. Experimental results show that the proposed drive has stable operation even at low speeds. Comparative results show that the proposed CSI drive has improved torque ripple compared to the conventional configuration. Index Terms--Active filters, current control, current source inverters (CSI), harmonic distortion, induction motor drives, multi-level inverters, pulsewidth modulation (PWM).

In high frequency motor-drives such as direct torque controlled (DTC) induction motor drives, the motor harmonic loss, and electromagnetic interference are largely affected by the spectrum of the motor input voltage. Nonlinear elements in the control loop of DTC drive make harmonic analysis of the drive very complex compared to classical pulsewidth modulated controlled drives. In this paper, a probabilistic method to study the harmonic contents of voltage in DTC of induction motors is presented. The DTC voltage chain is simulated with a random process. Then, the autocorrelation function of voltage vectors is calculated and its power spectrum density is obtained. The effect of flux and torque hysteresis controller bands, machine parameters, and inverter dc-link voltage on the motor voltage spectrum is investigated. Major harmonics in the DTC voltage spectrum are specified and their behaviors are described. Simulation and experimental results are presented to justify the theoretical analysis. Index Terms--Autocorrelation function, direct torque control (DTC), induction motor drive, power spectral density, random process, voltage harmonics.

Conventional space vector pulsewidth modulation (CSVPWM) employs conventional switching sequence, which divides the zero vector time equally between the two zero states in every subcycle. Existing bus-clamping PWM (BCPWM) techniques employ clamping sequences, which use only one zero state in a subcycle. This paper deals with a special type of switching sequences, termed here as 'double-switching clamping sequences,' which use only one zero state and apply an active vector twice in a subcycle. The present work brings out a class of bus-clamping PWM techniques, which employ such sequences. It is shown analytically as well as experimentally that the proposed BCPWM techniques result in reduced harmonic distortion in the line currents over CSVPWM as well as existing BCPWM techniques at high modulation indices for a given average switching frequency of [F.sub.sw]. At high modulation indices, the dominant harmonic components in the line voltages are around 2 [F.sub.sw] with the proposed BCPWM techniques, while the dominant components are around [F.sub.sw] and 1.5 [F.sub.sw], respectively, with CSVPWM and existing BCPWM techniques. The proposed techniques also reduce the inverter switching losses at high power factors over CSVPWM and existing BCPWM techniques. Index Terms--Bus clamping pulsewidth modulation (BCPWM), discontinuous PWM, harmonic distortion, induction motor drives, PWM inverters, space vector PWM, stator flux ripple, switching sequences.

This paper deals with the pulse doubling in a 12-pulse ac-dc converter for improving power quality in vector-controlled induction motor drives (VCIMDs). The design of proposed magnetics shows the flexibility in varying the voltage ratio of the autotransformer for making it suitable for retrofit applications, where presently a six-pulse diode bridge rectifier is being used. The proposed ac-dc converter is capable of eliminating up to 21st harmonics in the supply current. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter. A set of power quality indices on input ac mains and on dc bus for a VCIMD fed from proposed ac-dc converter are also given to compare its performance with six-pulse and twelve-pulse ac-dc converters. Index Terms--Autotransformer, multipulse ac--dc converter, pulse multiplication, vector-controlled induction motor drive (VCIMD).

In this paper, the authors give a new model of squirrel-cage induction motors under stator and rotor faults. First, they study an original model that takes into account the effects of interturn faults resulting in the shorting of one or more circuits of stator-phase winding. They introduce, thus, additional parameters to explain the fault in the three stator phases. Then, they propose a new faulty model dedicated to broken rotor bars detection. The corresponding diagnosis procedure based on parameter estimation of the stator and rotor faulty model is proposed. The estimation technique is performed by taking into account prior information available on the sale system operating in nominal conditions. A special three-phase induction machine has been designed and constructed in order to simulate true faulty experiments. Experimental test results show good agreement and demonstrate the possibility of detection and localization of previous failures. Index Terms--Broken rotor bars, faults diagnosis, induction motors, modeling, parameter estimation, prior information, short circuit.

Vector control accuracy of induction motor drives is affected by variations of motor parameters that are treated in the control algorithm as constant values, and by the phenomena that are not modeled at all and are therefore unaccounted for in the controller. Detuning sources of the first type include variations of rotor and stator resistance, mutual inductance, and leakage inductances, while the second category includes stator iron (core) losses. All these sources of detuned operation have been studied in a considerable depth in the past. It appears that the only potential source of detuned operation, which has never been studied before, is the stray load loss (SLL), which belongs to the category of unmodeled phenomena. This paper develops an analytical model that characterizes detuning due to SLLs in indirect rotor-flux-oriented (RFO) current-fed induction motor drives in steady-state operation by means of the orientation angle error, actual to reference rotor-flux ratio, and actual to reference-torque ratio. A quantitative assessment of the impact of SLL on accuracy of rotor-flux-oriented control is performed, with the necessary motor parameters obtained from IEEE 112-B standard measurements and subsequent equivalent circuit parameter fitting. Detuning is also examined in transient operation. It is shown that, although SLLs are comparable to the iron losses in the studied machine (of approximately the same value in the rated operating point), their impact on accuracy of vector control is much smaller when compared to the iron loss induced detuning. Index Terms--Induction machines, stray load losses, vector control.

In this paper, an autotransformer with reduced kilo-voltampere rating for 24-pulse ac-dc converter fed vector controlled induction motor drives (VCIMDs) is presented for harmonic current reduction. The 24-pulse operation is achieved using dc ripple reinjection technique in 12-pulse ac-dc converters. The proposed novel harmonic mitigator is found capable of suppressing up to 21st harmonic in the supply current. The procedure for the design of autotransformer for proposed ac-dc converter is presented to show the flexibility in the design for making it a cost-effective replacement suitable for retrofit applications, where presently a 6-pulse diode bridge rectifier is used. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed ac-dc converter. A set of power quality indices on input ac mains and on dc bus for a VCIMD fed from other 24-pulse ac-dc converters are also given to compare their performance. The laboratory prototypes of proposed autotransformers based 12-pulse and 24-pulse ac-dc converters are developed and test results are presented to validate the developed design procedure and the simulation models of these ac-dc converters under varying loads. Index Terms--Autotransformer, multipulse ac-dc converter, pulse multiplication, vector controlled induction motor drives (VCIMD).

The thermal modeling of the machine adopted here results from the association of two methods: a nodal approach that models the diffusion in the structure and a computational fluid dynamics approach that characterizes the convective heat exchanges that operate in the end-bracket cavities. This thermal model is then validated after experimentation carried out on an induction machine equipped with thermal sensors. This enables us to evaluate the thermal behavior of the machine in normal operating mode. In particular, the modeling of the convection heat exchanges in the internal cavities has to be done in detail to reproduce the thermal behavior of the machine accurately. Index Terms--Electric machines, fluid mechanics, heat transfer, thermal factors, thermal modeling.

This paper (also presented at [27]) presents an integrated design approach to small drives for emerging 42-V automotive systems. The emphasis is on motors for ancillary loads. The final result offers a simple and low cost solution with high efficiency and high power density. Motor and inverter designs are combined to gain advantages in power factor and operating range. A near-minimum-distortion method is introduced for the overmodulation regime to improve power factor without sacrificing harmonic performance. The design is addressed in several steps: integration of the induction motor into a 42-V environment, selection of the inverter modulation scheme, and final system integration. The proposed system consists of an induction motor wound for the proper voltage range and driven by an inverter. The inverter is used partly in the overmodulation regime when bus voltage is low. A signal is formed based on triangle injection to minimize distortion. Some alternative modulation approaches are also analyzed and compared with the proposed solution. Experimental results confirm that a low-distortion overmodulation approach can be implemented successfully. Index Terms--Automobile auxiliary loads, dc bus utilization, 42-V automotive power, induction motor, overmodulation, pulse-width modulation (PWM), three-phase inverter.

In this paper, to make a compromise between accuracy and efficiency in the design of single-phase induction motors, voltage source complex finite-element model, which is combined with the equivalent circuit method to carry out the performance analysis, is presented. The voltage source complex finite-element method is used to determine equivalent circuit parameters by simulating the no-load tests and locked-rotor tests, while the conventional method is adopted to calculate the performances. Good agreement is achieved between the calculated results and test results, which verifies the effectiveness of the presented method. Index Terms--Finite-element method (FEM), induction motors, performance analysis.

Abstract: In this paper we present the comparison results of induction motor fault detection using stator current, vibration, and acoustic methods. A broken rotor bar fault and a combination of [...]

A closed-loop synchronous-frame current regulator for an induction machine drive that is capable of delivering high-quality performance characteristics using integrated pilot current sensors in the three low-side switches of a three-phase bridge inverter has been developed. However, the necessary current reconstruction exhibits sensitivity to errors in the machine parameters, which has been documented during this investigation. This paper presents a technique for introducing a gated integrator into the controller gain amplifier that compensates for parameter errors using feedback information from all three of the phase currents during the periodic intervals when it is available. A numerical singularity in the current reconstruction algorithm during light-load operation is overcome by introducing an alternative first-order current estimator that is activated over narrow angular spans of the fundamental component vector rotation. This paper also presents an in situ technique to compensate gain differences between the three pilot devices in the inverter unit. The effectiveness of these improvements is verified using experimental results. Index Terms--Decoupling voltage, indirect field-oriented control, integrated pilot current sensor, three-phase induction motor drives.

A direct torque control (DTC) strategy for dual three-phase induction motor drives is discussed in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The DTC strategy is based on a predictive algorithm and is implemented in a synchronous reference frame aligned with the machine stator flux vector. The advantages of the discussed control strategy are constant inverter switching frequency, good transient and steady-state performance, and low distortion of machine currents with respect to direct self-control (DSC) and other DTC schemes with variable switching frequency. Experimental results are presented for a 10-kW DTC dual three-phase induction motor drive prototype. Index Terms--Deadbeat algorithm, digital control, direct torque control, dual three-phase induction machine, multiphase drives.

Instability of electrohydrodynamic (EHD) induction pumps can manifest itself in a sudden drop/jump in pump output. The instability can also result in alternating/bidirectional flow. To understand and avoid this erratic behavior of the pump operation, a nondimensional stability analysis of EHD induction pumping of liquid film in a vertical annular configuration in the presence of an external load (i.e., pressure gradient and gravitational force) for repulsion mode is carried out. A general nondimensional stability criterion is presented, indicating that the stability of the pump depends on the nondimensionai geometric parameters of the pump as well as the nondimensional electric properties of the liquid film. A stability map based on dimensionless electric conductivity and liquid-film thickness is presented. The effect of the dimensionless angular velocity on the nondimensional interfacial velocity under the influence of a pressure gradient and gravitational force is investigated. It is also shown that the erratic behavior of the unstable pump can be eliminated by a proper selection of geometric and liquid-film parameters, as well as the traveling electric-wave frequency. Index Terms--Electrohydrodynamics (EHDs), interface, pumping, two-phase flow.

This paper presents the analysis, design, fabrication, and testing of a planar electric induction micromotor. The micromotor is a 6-phase motor with 131 pole pairs distributed on a stator having a 4 mm outer diameter. The axial air gap is 3 [micro]m. With a 90 V stator excitation, applied at a 300-kHz slip frequency, the motor produces a torque of 2 [micro]N * m. Special attention is paid to the limitations that microfabrication places on the design of the motor. [1086] Index Terms--Deep reactive ion etching (DRIE), duffing oscillator, electrostatic actuator modeling design analysis, micromotor, power microelectromechanical systems (Power MEMS) fabrication, quasi-static electric induction machine motor generator, torque measurement.

This paper presents a technique for accurate discrimination between transient voltage stability and voltage sag by combining damped sinusoids-based transient modeling with neural networks. Transient modeling is accomplished by energy adapted matching pursuits with an over-complete dictionary of damped sinusoids. In our approach, the information provided by the damped sinusoids-based transient modeling stage is applied to a Neural Network, which determine in a fast and accurate fashion the class to which the waveform belongs. The simulated results clearly show that the proposed technique can accurately discriminate between transient voltage stability and voltage sag in power system protection. Index Terms--Damped sinusoids, induction motor drives, load modeling, matching pursuit, signal modeling.