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This paper analyzes the effect of unbalanced voltage over doubly fed induction generators (DFIGs) and presents a novel control strategy, named dynamic programming power control plus (DPPCW), based on dynamic programming control. The high penetration of wind energy in the electrical grids demands for new requirements for the operation of wind energy conversion systems (WECSs). DFIG is the most employed WECS, and the DPPC+ guarantees their operation under unbalance conditions achieving the required objectives. Although the technique can be implemented to control both rotor and grid converters, we hereby expound the former, which regulates stator active and reactive power. The validation of the results obtained with DPPC+ has been performed through the use of experimental tests on a 20-kW test bench, consisting of a DFIG and induction motor drive. The obtained results show that the DPPC+ is suitable for achieving a good dynamic response while controlling current distortion and power and/or torque oscillations for both steady-state conditions and unbalanced voltage dips, showing the low-voltage ride-through capability. Index Terms--Doubly fed induction generator (DFIG), dynamic programming power control plus (DPPC+), unbalanced voltage, voltage dip.

This paper presents the development and real-time implementation of a nonlinear controller for the speed control of an induction motor (IM) drive. Neglecting the iron loss in an IM model causes performance deterioration, and there has been research to investigate and cope with this problem in the vector control of an IM. However, little work has been done in the area of the nonlinear control of an IM. In this paper, an adaptive backstepping-based nonlinear controller incorporating the iron loss is developed under the parameter uncertainties. To reduce the complexity in the design of the controller, the motor model is referenced to the rotor magnetizing current, and the controller is developed in the rotor-flux-oriented control scheme. The adaptive backstepping technique is utilized to estimate the parameters online and maintain the global stability of the drive through Lyapunov. The proposed controller is successfully implemented in real time using a digital signal processor board DS 1104 for a laboratory 1/3-hp IM. Both simulation and experimental results show that the proposed controller successfully achieves the rotor-speed-tracking objective and improves dynamic responses as compared to the one without parameter adaptation. Index Terms--adaptive backstepping design, digital signal processor (DSP) and real-time implementation, induction motor (IM), iron-loss resistor, nonlinear control, speed control, vector control.

This paper investigates diagnostic techniques for electrical machines with special reference to induction machines and to papers published in the last ten years. A comprehensive list of references is reported and examined, and research activities classified into four main topics: 1) electrical faults; 2) mechanical faults; 3) signal processing for analysis and monitoring; and 4) artificial intelligence and decision-making techniques. Index Terms--Adaptive signal processing, artificial intelligence (AI), bearings, diagnostic reasoning, fault diagnosis, Fourier transforms, fuzzy neural networks, induction machines, induction motor drives, induction motor protection, industrial power system maintenance, pattern recognition, signal processing, time--frequency analysis, wavelet transforms.

This paper aims to analyze the magnetic forces on the stator end-windings of an induction machine at full load by a 3-D time-harmonic finite element analysis. Under the steady-state condition, the radial, circumferential, and axial forces all consist of a constant component and a sinusoidal component with a double-frequency. The analysis shows that the forces on the knuckle part of the upper part of a coil end are larger than on the other parts and that the constant components and the amplitudes of the sinusoidal components of the forces on the same positions of different coil ends in a phase belt are nearly different. Finally, the analysis of stresses indicates that the stresses in a coil end, corresponding to the constant components of the forces, are small. Index Terms--End-winding, finite element analysis, force.

The field-oriented control of induction machines is widely used in high-performance applications. However, detuning caused by parameter disturbances still limits the performance of these drives. In order to accomplish variable-speed operation, conventional PID-like controllers are commonly used. These controllers provide limited good performance over a wide range of operation, even under ideal field-oriented conditions. An alternate approach is to use the so-called 'fuzzy' controller. In this paper, a self-laming fuzzy controller is implemented. The proposed controller has the ability to adjust its parameters online according to the error between actual machine speed and a model reference. The scheme is compared to the conventional proportional-integral control and validated by simulation and experimental tests of both control techniques. Index Terms--Field-oriented control, fuzzy logic (FL), induction machine (IM), self-tuning, variable-speed drives.

This paper discusses the problems of current decoupling control and controller tuning associated with sensorless vector-controlled induction-motor (IM) drives. In field-oriented control, the d-q synchronous-frame currents should be regulated to have independent dynamics such that the torque production of the IM resembles that of a separately excited dc motor. However, these currents are not naturally decoupled, and decoupling compensators should be used. Current loop tuning is an additional problem, since controller gains obtained by theoretical methods or simulation, quite often, do not work well on the real system. This paper proposes a new approach for current control that uses integral-sliding-mode (ISM) controllers to achieve decoupling. The synchronous-frame control voltages are synthesized as the sum of two controller outputs: a traditional one (PI) that acts on an ideal plant model and an ISM controller. The ISM controller decouples the d-q currents and compensates the parameter variations in the current loops of the machine. Simulations and experimental tests on a 0.25-hp three-phase induction machine show satisfactory results. Index Terms--Current control, decoupling, induction machine, integral sliding mode (ISM), sensorless control.

The aim of this paper is to spread the sliding-mode control design technique on the new class of the ac drives: an induction motor fed by a three-level voltage-source inverter (3LVSI). A comprehensive investigation of possible drive 'variable structures' was carried out. Based on this analysis, an original two-step design procedure allows the use of the 'classical' result of sliding-mode theory for the real variable structure system with more than [2.sup.m] variable structures (m is the control space order). Based on this design procedure, the original control algorithm that includes a choice condition for 3LVSI input dc voltage and a switch table for the 3LVSI semiconductor switches are designed. The performance of the considered control structure has been examined by simulation. Index Terms--Induction motor drive, neutral-point-clamped converter, three-level converter, variable-structure systems.

In this paper, the stray load losses due to the air gap spatial harmonics effects on the rotor squirrel cage are considered and a simplified induction motor equivalent circuit able to include them in the machine power balance is reported. In the proposed model, an additional resistance appears in series with the stator impedance. This additional parameter has been defined on the basis of power balance considerations applied to the induction motor classical theory. The complete theoretical analysis together with the guidelines to measure the equivalent circuit parameters are reported in detail. Finally, the proposed approach has been experimentally verified using five total enclosed fan cooled induction motors. Index Terms--Equivalent circuit, parameter identification, stray load losses, total enclosed fan cooled (TEFC) induction motors.

Linear induction motors are under development for a variety of demanding applications including aircraft launchers and magnetically levitating trains. These applications require machines that can produce large forces, operate at high speeds, and can be controlled precisely to meet performance requirements. The design and implementation of these systems require fast and accurate techniques for performing system simulation and control system design. We present techniques for modeling and controlling linear induction machines based on a direct and quadrature (DQ) representation of the system dynamics. Simulation results using the DQ representation of the machine dynamics are presented and compared to test data from a Subscale Integration Test Bed developed for the U.S. Navy's Electromagnetic Aircraft Launch System program. Index Terms--Direct and quadrature (DQ), electromagnetic launcher, field-oriented control, linear induction motors (LIMs), vector control.

Commonly used speed-control concepts permit speed ranges up to two-three times the base speed via voltage to frequency (V/f), that is, field-weakening control. This paper teaches the extension of the speed-control range up to nine times the base speed through online reconfiguration of the motor windings via electronic switches. The switchover of the windings, either from a winding with [P.sub.1] poles to [P.sub.2] poles, or from series to parallel connection of the number of turns per phase--so-called (V/N x f) control--lasts less than a 60-Hz cycle. Such fast switchover causes small transients only, and therefore, this concept is applicable to most variable-speed drives. Index Terms--Change of number of poles, change of number of turns N, electronic switching of windings, increase of speed range, induction motor, voltage to N frequency (V/N x f) control.

This paper presents an approach for the efficient solution of multislice finite-element analysis of skewed induction machines incorporating an interbar current model. The Newton-Raphson method is applied to linearize the nonlinear field equations for each slice and domain decomposition is then utilized to reduce the field equations on to the circuit equations. Domain decomposition is implemented as both a serial and parallel algorithm. These algorithms are shown to offer significant computational efficiency improvement. The simulated performances of an induction machine with a range of interbar resistances are compared to test measurement, and the relative simulation times are compared to other algorithms. Index Terms--Domain decomposition (DD), finite-element analysis (FEA), induction motor, parallel computation.

A novel structure for sensorless induction motor drive is proposed based on flux vector acceleration torque control. The proposed structure combines direct torque control with speed estimation based on slip frequency evaluation. A stable drive operation is enabled in a wide range of operating speeds, including at standstill. Index Terms--Direct torque control (DTC), induction motor (IM), sensorless drive, speed estimation.

This letter describes a high-resolution technique called thermally stimulated depolarization current (TSDC) that can be used for the measurement of space charge accumulation in the medium voltage magnet wires operating on pulsewidth modulated (PWM) inverters. Index Terms--Fast rise time pulses, induction motors, inverterfed drive motors, magnet wires, space charge injection.

Finite element models are invaluable for determining expected machine performance. However, finite element analysis can be computationally intense; particularly if a large numbers of studies or high bandwidth studies are required. One method to avoid this difficulty is to extract machine parameters from the finite element model and use the parameters in lumped parameter models. While often useful, such an approach does not represent space harmonics or asymmetries in the motor. A methodology for constructing a state-variable model, based on a magnetic equivalent circuit of the motor is described herein. In addition, the parameters for this model are based solely on geometrical data. This approach is an excellent compromise between the speed of lumped parameter models and the ability of finite element methods to capture spatial effects. Experimental validation of the model is provided. Index Terms--Geometry-based modeling, induction machine modeling, magnetic equivalent circuit (MEC), space harmonics.

A new simulation approach is proposed in consideration of a saturation and a deep bar effect for the study of transients of three-phase squirrel-cage type induction motors. The mathematical model of an induction motor is expressed by the six differential equations of three-phase instantaneous voltage and current. The torque of an electric equation is related to the motion equations of motor and driven machine in the mathematical model. The values of reactance of stator and rotor are changed by the saturation of core caused by starting current. Also both the values of reactance and resistance of rotor bar are varied by the deep bar effect in the rotor core during starting. The calculation method of circuit constant that adds the influence of saturation and deep bar effect is proposed in this paper. The circuit constant of simulation model in consideration of saturation and the deep bar effect are decided by these computation methods in accordance with the conditions of rotation speed and current. If the large current flows, the leakage reactance of the stator and the rotor decreases by saturation. Moreover, the resistance of the rotor gradually decreases when the rotational speed rises from stop to synchronous speed, and the leakage reactance increases gradually. The calculated values were compared with the observed values of the examination machine of 1100 kW4P and an excellent agreement was obtained demonstrating the accuracy of the proposed simulation. Consequently, it is shown that the saturation and the deep bar effect are the essential factors to perform the accurate simulations of the induction motor. After checking the validity of the proposed approach, the simulation of the grounding faults was performed. In this study, all the simulation programs have been developed in the Maflab/Simulink environment. Index Terms--Deep bar effect, grounding fault, induction motor, saturation, transient phenomenon.

Derating a motor for operation on an unbalanced voltage system is still much of a black art although National Electrical Manufacturers Association and International Electrotechnical Commission have generic derating charts for this application. Numerous papers have been written in an attempt to provide a theory for this operating mode and the losses that may be generated. This paper will discuss the instrumentation and testing of a four-pole 1120-kW induction motor that was tested at three different levels of unbalanced voltage. Results will be presented on the stator and rotor heating, the speed-torque and locked rotor performance, as well as noise, vibration and shaft voltage. The problem has also been analyzed using time-stepping finite-element analysis. Index Terms--Induction motor, rotor, stator, temperature, unbalanced voltage.

This paper presents the results of an investigation regarding the thermal behavior of a three-phase induction motor when supplied by a reconfigured three-phase voltage source inverter with fault-tolerant capabilities. For this purpose, a fault-tolerant operating strategy based on the connection of the faulty inverter leg to the dc link middle point was considered. The experimentally obtained results show that, as far as the motor thermal characteristics are concerned, it is not necessary to reinforce the motor insulation properties since it is already prepared for such an operation. Index Terms--Alternating current (AC) motor drives, fault tolerance, thermal performance.