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Field aligned starting (FAS) is a technique for starting three-phase cage induction motors on either three-phase or single-phase supply lines under varying load conditions with minimal inrush currents. The technique starts the motor independent of the mains supply with a high transient torque before connecting the spinning motor to the mains. It is imperative to the operation of FAS that the spinning motor be connected to the mains at the correct time. Incorrectly timed mains connection can result in negative transient torques with the severity to slow, or possibly stall the already started motor. As the implementation of FAS is not possible without a predictive mechanism by which the correct moment of mains connection can be found in advance, this paper proposes a simple, low cost, yet effective self-calibrating method which ensures that the timing of the mains connection is correct under all starting conditions. Critical issues vital to a successful self-calibration under transient and varying starting conditions are investigated and presented with both experimental and simulated results to show that self-calibration is an indispensable part of FAS technique. [ABSTRACT FROM AUTHOR]

This work proposes an equivalent circuit model for a stand-alone three-phase self-excited induction generator (SEIG) with unbalanced load impedances. The SEIG supplying unbalanced loads is modelled by a two-port network that allows the steady-state performance of the generator to be analysed more easily and more efficiently. The proposed model is validated by experiments on a 0.5 Hp cage-type induction motor operated as a generator. [ABSTRACT FROM AUTHOR]

The switched reluctance (SR) motor has many benefits owing to its low cost, simple design, rugged construction and comparatively high torque-to-mass ratio. Unlike DC and induction motors, the SR motor is intended to operate in deep magnetic saturation to increase the output power density. Because of the saturation effect and the variation of magnetic reluctance with respect to rotor position, all the relevant characteristics of the machine are highly non-linear functions of both rotor position and phase current. The ultimate outcome of all these non-linearities is that the generated torque contains significant ripples. The non-linearities in the SR motor have been extensively studied and many control strategies to reduce the generated torque ripples have been proposed in the literature. Modulation of phase current profile for generating torque in the SR motor with minimum ripples was the focus of most of the research. However, the main challenge to minimise the torque ripple is to design a current controller that is able to track the modulated phase current. In this work, new techniques to optimise the widely used hysteresis current controller are studied, and experimental verifications under closed-loop speed control with the modulated reference current data are presented. The experimental results indicate that the torque ripple is reduced to lie within 5% of the desired steady torque using the proposed optimisation techniques. [ABSTRACT FROM AUTHOR]

A sensorless speed estimation method for real-time application in induction motor drives under steady-state condition is proposed. Speed harmonic component in the space vector angular fluctuation (SVAF) signal, which is caused by both dynamic and static eccentricity, is used for speed estimation. The SVAF signal is obtained from the stator currents of the induction motor. The extraction of speed information using digital signal processing techniques is considered. Experimental results are given to demonstrate the validity of the speed estimation method on an induction motor driven by an inverter. [ABSTRACT FROM AUTHOR]

A system of n complex equations, for which n=14, ... , 30 suffices, is used to determine the n unknown stator—and rotor current harmonics for each of the given terminal voltage harmonics. Correct superposition of harmonics yields the air-gap field, losses, torque and radial force. As an illustrative example, the systems of simultaneous equations are solved for an eight-pole squirrel-cage motor with different numbers of rotor slots. Parasitic effects such as supplementary losses, synchronous torques, magnetic noise or line-current harmonics depend highly on the slot number difference Z1-Z2 and on winding connections. Owing to the voltage distortion of the static converter, copper losses increased by 61%. In the case of parallel winding branches, equalising currents with 511 Hz and 37% magnitude occurred, which increased the copper losses by 152%. With Δ-connected windings, circulating currents with a magnitude of 33% have been detected, thus increasing the losses by 21%. Rules to avoid these additional losses are given. Parasitic synchronous torques are increased and emerge at additional speeds. Asynchronous dips in the torque–speed curve because of voltage harmonics are of minor importance, even for large supply voltage harmonics. The accurate determination of radial force waves enables the prediction of core vibrations and the magnetic noise, even at resonance frequency. It has been found by experiments that sound radiation of an oscillating sphere or cylinder seem not to be equivalent to that of an induction motor. [ABSTRACT FROM AUTHOR]

The area of multiphase variable-speed motor drives in general and multiphase induction motor drives in particular has experienced a substantial growth since the beginning of this century. Research has been conducted worldwide and numerous interesting developments have been reported in the literature. An attempt is made to provide a detailed overview of the current state-of-the-art in this area. The elaborated aspects include advantages of multiphase induction machines, modelling of multiphase induction machines, basic vector control and direct torque control schemes and PWM control of multiphase voltage source inverters. The authors also provide a detailed survey of the control strategies for five-phase and asymmetrical six-phase induction motor drives, as well as an overview of the approaches to the design of fault tolerant strategies for post-fault drive operation, and a discussion of multiphase multi-motor drives with single inverter supply. Experimental results, collected from various multiphase induction motor drive laboratory rigs, are also included to facilitate the understanding of the drive operation. [ABSTRACT FROM AUTHOR]

The paper evaluates the impact that the relationship between purely rotational and alternating losses has on the computation of core losses in induction motors. At frequencies other than 50 Hz, the analysis is simplified if statistical loss theory is considered, as discussed in the paper. The paper outlines a practical method of computation of hysteresis and excess losses when the rotation of flux is considered and loss data for these terms at 50 Hz are available. An imposed constraint is that the quantity of experimental loss data available for the motor designer is, in general, reduced. To deal with the problem, Kochmann general relationships for 36 NO grades, covering the main spectrum of electrical steel grades at 50 Hz, have been found to be helpful. An approach is proposed to convert these relationships, so that they can be fitted into the statistical loss theory. The results are validated using FEA and bench tests. As a conclusion, the loss estimate is improved in all cases, not incurring an overestimation with respect to bench results. [ABSTRACT FROM AUTHOR]

An adaptive fuzzy total-sliding-mode controller (AFTSMC) with a total switching surface is proposed to control the position of an electrical servodrive. The proposed controller comprises a special fuzzy total-sliding-mode controller (FTSMC) and an adaptive tuner. The FTSMC acts as the main tracking controller, which is designed via a fuzzy system to mimic the merits of a total-sliding-mode controller (TSMC). In addition, a translation width is embedded into fuzzy rules to reduce the chattering phenomena. The adaptive tuner, which is derived in the sense of Lyapunov stability theorem, is utilised to adjust the translation width on-line for further assuring robust and optimal performance. In the AFTSMC, the fuzzy-control-rules base is compact and only one parameter needs to be adjusted. An electrical servodrive with the proposed position-control system possesses the advantages of a simple control framework, reduced chattering, stable performance and robustness to uncertainties. The effectiveness is demonstrated by simulated and experimental results, and its advantages are indicated in comparison with conventional TSMC and adaptive TSMC for a field-oriented control induction-motor (IM) drive. [ABSTRACT FROM AUTHOR]

An unbalanced DC-link voltage regulation strategy is proposed for a three-level voltage source inverter used in the rotor cascade of a double-fed asynchronous motor-generator. The major problem in determining the presence of the unbalanced component is investigated and a solution is proposed using an adaptable filter. This latter is only of a low order and is designed to ensure easy implementation into a (DSP). The regulator is based on the injection of a second order harmonic and its design is presented as well as an investigation of the critical point for correct action of the regulator. Real measurements performed on a low-power test bench after implementation into a DSP validate the accuracy and quality of the filter as well as the control strategy proposed. [ABSTRACT FROM AUTHOR]

During startup an electric motor can be subject to severe electrical and thermal loads. These loads, despite their relatively short durations, significantly affect motor's lifetime and reliability. The use of the double squirrel-cage arrangement has resulted in the improvement of the startup coefficients for induction motors. However, the cage is still subject to non-uniform thermal loads and, in consequence, to overheating. These transient loads are particularly heavy during a prolonged startup, routinely encountered under tough industrial operating conditions, for example when attempting to start a motor with a locked rotor. Typical examples are starting a motor powering a longwall shearer buried under a collapsed coal face or an overloaded coal mill. A methodology is presented to compute the temperature field of a double squirrel-cage and the core of an induction motor. The procedure employs a three-dimensional model of the motor heating obtained using the control volume method. The model provides the basis for calculating the stress field within the cage. The input data to the model can be obtained from the motor windings specification sheet. The thermomechanical analyses can be performed during the design and construction phases, and may facilitate motor performance optimisation. [ABSTRACT FROM AUTHOR]

The simultaneous elimination of common-mode voltage and DC-link capacitor voltage imbalance is achieved in a five-level inverter scheme for an induction motor drive throughout its operating range. A dual five-level inverter-fed open-end-winding induction motor structure is used for the proposed drive. Initially, the operating limitations of achieving this dual task for the five-level inverter configuration are investigated for a single DC power supply. Subsequently, a switching strategy for a five-level inverter topology with two DC power supplies is proposed to achieve the dual task over the entire speed range of the drive. The proposed drive offers a simple power-bus structure with more redundant switching combinations for inverter voltage vectors, and requires a lower voltage-blocking capacity of the power devices as compared with the conventional single five-level inverter-fed drive. As only the availability of redundant switching combinations for inverter voltage vectors is exploited, the dual task is achieved without disturbing the fundamental component of the inverter output voltage and the scheme does not need any extra control circuit hardware. Experimental verification of the proposed scheme is done on a 1.5 kW induction motor drive in the linear as well as overmodulation range. [ABSTRACT FROM AUTHOR]

The movement of a linear induction motor (LIM) causes eddy currents in the secondary conductor sheet at the entry and the exit of the primary core. The eddy currents of the sheet tend to resist sudden flux variation, allowing only gradual change along the airgap. Hence, the so-called ‘end effect’ causes not only the losses but also airgap flux profile variation changes depending on the speed. In this work, an equivalent circuit model of LIM is developed following Duncan's per phase model. It is then transformed into a synchronous reference frame which is aligned with the secondary flux. Also, a field orientation control scheme is developed which accounts for the end effect. The validity of the proposed LIM model is demonstrated by comparing experimental and simulated voltage current relations. With the proposed control scheme, the (secondary) flux-attenuation problem due to the end effect is shown to be resolved in the high-speed range. [ABSTRACT FROM AUTHOR]

Most induction motor analyses that allow for the presence of inter-bar currents are based on a rotor model in which the inter-bar currents are assumed to flow between adjacent pairs of bars. An alternative model is proposed in which the inter-bar currents flow into and around the rotor core. The validity of the new model is verified by means of measurements made on 54 rotors of identical design, which have been subjected to a range of treatments during manufacture to produce bar-to-bar resistances that differ by up to three orders of magnitude. It is shown that the new rotor model may readily be incorporated into existing analyses by redefining a single inter-bar resistance parameter. An alternative viewpoint of this is that the new rotor model redefines the relationship between the resistance parameter used in analytical models and the bar-to-bar resistance measured under test. [ABSTRACT FROM AUTHOR]

The paper addresses the bearingless induction motor based on the concept of dual-pole windings, one controlling the motor torque and the other the generated radial forces. Such machines have been investigated experimentally in the past. The paper presents a simulation model capable of investigating the effect of induction-machine design on the generation and control of the radial force. The simulation is based on the dynamic reluctance-mesh field model embedded in vector control systems for the decoupled control of torque, flux and radial force. In the paper, the rotor is constrained by a mechanical bearing so that the radial force is used to cancel the rotor weight to effect 'bearing relief'. The paper summarises the modelling method, investigates the radial force production in both cage and wound rotor machines, and introduces a mixed field orientation method for the decoupled control of the torque and radial forces. Simulations are undertaken showing good generation of radial force under zero speed, acceleration and transient load conditions. [ABSTRACT FROM AUTHOR]

The speed control of a field-weakened (FW) indirect field-oriented (IFO) induction motor drive with compensations for system dead-time and parameter variations is presented. Firstly, the DSP-based motor drive with a field-weakening mechanism is designed. To handle the command tracking and load rejection speed controls simultaneously, the proposed control scheme consists of a feedback controller and a command feedforward controller (FC) to possess two degrees of freedom (2DOF). The feedback controller is designed according to the given load rejection control requirements, and the command FC is set as the inverse plant model to let the tracking response follow the one defined by a reference model. Then, to reduce the effects of system dead-time and parameter variations on the speed control performance, a dead-time and disturbance compensator (DTDC) is proposed with its parameters being adapted by a variable-structure system (VSS). In addition to dead-time compensation, an estimated signal containing plant uncertainties and disturbances is generated and used for cancelling their effects on dead-time compensation control. Moreover, the tracking response is further enhanced by adaptively adjusting the parameters set in the FC and the DTDC according to the estimated mechanical inertia change. The practical considerations for simultaneously providing a good load rejection control response are also presented. Finally, the closed-loop regulation control is provided by adding a linear model following control (LMFC) scheme. [ABSTRACT FROM AUTHOR]