Search

This paper describes a controlled-power-angle synchronous motor inverter system which provides drive characteristics similar to those of an induction motor inverter system. The system consists of a conventional synchronous motor with a shaft-position sensor which controls the firing of thyristors in an inverter. This paper investigates the steady-state properties and control strategies for the controlled-angle synchronous motor inverter system. Some experimental results are presented and compared with theoretical predictions.

Toroidal magnetic cores using ferrite materials have been applied extensively as 2-state logic and memory devices.1?4 For more complex logical operation, multiaperture ferrite cores have been used.5?8 In most of the studies of flux reversal phenomena in these cores only two final flux states have been considered, representing either of the two saturated states of the core or a leg of the core. Multiaperture cores are also capable of continuous modulation of a-c power. An example is the transfluxor, 9?11 a 2-aperture core, in which the magnitude of the output is controlled by a transient setting pulse applied to its control winding. This device is able to operate at a continuously-controllable level because the amount of magnetic flux available about one aperture for the transfer of power can be controlled by the particular magnetic state established about the other aperture.

A simple method is described whereby appropriate equivalent circuits may be developed for transformers and rotating machines. Sections of the magnetic system are represented by analogous electric elements in the equivalent circuit and in this way the effects of magnetic non-linearity are preserved. The assumptions made in the method are those usually made by the designer in reducing the magnetic field of the apparatus to a magnetic circuit. The method is demonstrated by developing equivalent circuits for 3-phase core-type transformers, polyphase induction and commutator machines and synchronous machines of both the round-rotor and the salient-pole type.

Experimental work is described which indicates the feasibility of making minor loop loss predictions in devices which use permanent magnet materials. The methods of making these loss predictions and some general conclusions about losses are discussed. Minor loop loss predictions are important in any device in which the material undergoes high-frequency operation along recoil or incremental permeability lines. However, little has been published about minor loops in permanent magnet materials. In Alnico 5, the hysteresis (zero frequency) component of the minor loop is found under certain conditions to exhibit a small secondary B/H loop superimposed upon the major loop. The behavior of this secondary B/H loop with variation of temperature gives insight into the behavior of one of the phases of the material and shows that improper metallurgical heat treatment can degrade the over-all permanent magnet characteristics.

A major constraint on the performance prediction of a hysteresis machine arises from the parasitic losses associated with the rotor magnetic material. These losses can be high enough to absorb much of the developed torque, particularly for small sizes and large numbers of poles. In this paper the phenomena which cause parasitic losses are examined in detail. Analytical expressions are developed to predict these losses in terms of the air-gap field and the stator current.

This paper describes a controllable direct-current supply in which the current is essentially independent of the load and in which very low ripple is achieved at essentially all values of controlled current output. The system consists of a 3-phase saturable reactor with a high-impedance control circuit used in conjunction with uncontrolled rectifiers. An analysis of the system is presented and experimental results are given.

A method of analysis for three-phase inverters is described. The method is based on Park vectors [1], [2] and predicts the waveforms of inverter quantities under various load conditions. The procedure discussed can be used to determine the commutation sequence of a pulsewidth modulated inverter. The current distribution of the inverter can be obtained from the current vector. The vectors of the inverter voltage and currents are determined for passive R-L and R-C loads. Oscillograms of the current vectors are shown for different loads.

Part I of this paper presented an analysis of an idealized polyphase hysteresis machine having a radial-flux type of rotor. In this Part II, a hysteresis machine with a circumferential-flux type of rotor is analyzed. Using a rectangular loop approximation to the B-H characteristic of the hysteresis material, the flux density distribution in the machine is found and an equivalent circuit is developed. An improved model of the B-H loop is then used, and two approximate analyses are developed for this improved representation of the machine.

The paper describes a method whereby the fundamental and third-harmonic quantities in the steady-state solution of a network containing certain non-linear elements may be obtained approximately. The method consists of three stages: (a) A first approximation to the fundamental-frequency solution, usually accurate to within 10%. (b) A third-harmonic solution (generally within 15%) using an equivalent circuit which is dependent on the first fundamental solution. (c) A correction to the fundamental solution, using third-harmonic quantities, which brings its accuracy to within about 3%. Adaptations of some standard techniques of solving linear steady-state problems for use with this method of analysis are described.

A variable-speed drive is described in which a 2-phase induction motor is energized by power modulators of the frequency-doubler type. The system provides continuous and reversible control of motor torque. In comparison with similar drives using conventional magnetic amplifiers this system has the advantages of simplicity, high efficiency, inherent zero stability, and reasonably flat torque-speed characteristics. Both steady-state and transient characteristics of the drive are described and analyzed.

The paper deals with the use of voltage transformers as multipliers for complex quantities and describes how they may be used to form a network analyser. The analyser consists of a measuring section and a number of identical panels each containing two multiplying units. These panels may be used to represent impedances, admittances, voltage or current sources, phase-shifting auto-transformers or mutual inductances. Valuable features of the analyser are the ease with which negative resistance and unilateral mutual inductance may be introduced. The accuracy of the analyser depends on the suppression of amplitude and phase errors in the voltage ratios of the transformers, and each transformer is supplied with the required exciting current from special compensators. The paper concludes with examples of the principles to be adopted in applying the analyser to common problems concerning the behaviour of power networks, electrical machines and closed-loop control systems as well as to the solution of linear simultaneous equations.

Electric traction vehicles usually employ two or more axles to transmit the drive torque to the wheels. Several ac squirrel cage induction motors driven in parallel from a common inverter produce poor torque sharing and large motor derating even for very small (less than one percent) differences in the diameters of the wheel sets attached to different axles of the vehicle. This paper presents two new converter systems using a common chopper current source and two current source inverters. The two inverters are in series and parallel connections for the converter systems A and B respectively. The two converter systems have been analyzed in this paper. A method of calculating the torque and thrust distribution using the equivalent circuits has been developed. Theoretical results have been obtained to show that the converter system A (series connection) is stable in both motoring and braking regions. On the other hand, the converter system B (parallel connection) has lower losses, is stable in the motoring region and is unstable in the braking region. A method to stabilize the converter system B in the braking region is briefly discussed. Experimental results have been obtained to verify the theoretical predictions.

Keen interest in the design of Permanent Magnet (P.M.) synchronous motors is being fuelled by continuing developments in permanent magnet material technology. The most recent of these developments has been in the introduction of Neodymium-Boron-Iron (N d BF e ) with residual flux density of 1.23 T and energy product (BH max ) of 320 kJ/m3. However a continuing difficulty with the analysis of permanent magnet motors, irrespective of their magnet composition, is the prediction of the direct and quadrature axis reactances. This is particularly the case with motors having permanent magnets imbedded in the rotor iron below the cage winding. The purpose of this paper is to present equivalent circuit models for such interior-type P.M. motors and develop simple analytical expressions for the calculation of axis reactances. Computed reactances including saturation effects are presented along with experimental values for verification.

Cogging torque in a permanent magnet motor, which arises from the interaction of the rotor magnets with the steel teeth on the stator, can be reduced by skewing the stator teeth, but only at the expense of added complexity in stator construction and some loss of output torque. It is shown that by appropriate choice of the angular width of the magnet relative to the tooth-plus-slot dimension, the cogging torque can be reduced to about 1% of rated torque. A further reduction to about 0.3% resulted from a rotational shift of one pair of poles with respect to the other pair in a four-pole motor. The analysis of cogging torques with both surface mounted and inset magnet rotors as well as experimental confirmation are reported. >

The reference design for the Canadian electrodynamically-levitated Maglev system makes use of a single-stator linear synchronous motor (LSM) and provides lateral stabilization by the use of figure-eight null flux loops. This paper presents an alternative approach using two independently-controlled linear synchronous motors with lateral stabilization provided by a simple null flux ladder. Some of the advantages of this approach are (1) a stiffer lateral stabilization is provided with much less material in the guidance loops, (2) active damping of roll and yaw moments can be provided by the dual LSM as well as the heave and surge damping which is available from a single LSM, and (3) the magnetic field in the passenger compartment is reduced.

Effects of samarium cobalt permanent magnet on the steady-state performance of hysteresis-reluctance motors are presented. Based on the parallelogram approximation of the B-H loop for the semi-hard hysteresis materials of 36% colbalt-steel and Alnico 5, analytical expressions to predict the motor terminal characteristics are given. Experimental verification of the theoretical analysis is also provided. It leads to some useful conclusions, enabling the designers to choose between the types of permanent magnet materials for different drive requirements.

This paper describes a track-powered propulsion system for automated urban transit vehicles. It is a linear synchronous motor which is similar in principle to the motor previously designed for the Canadian 500 km/h Maglev system. The urban vehicle has an array of samarium-cobalt magnets fixed to a backing plate on the underside of the vehicle. These magnets interact with insulated aluminum cables imbedded in the track surface and carrying variable-frequency current supplied from periodically-placed track-side inverter stations. No iron is used in the track. The vehicle is suspended on wheels. The air gap clearance between the vehicle magnets and the track surface is about 40 mm. The paper describes a typical design in which the propulsion system, operating at maximum power output of 240 kW, has an efficiency of 77% and a power factor of 88%, using inverters with 200 m spacing. The system appears to have excellent technical and control features. Its economy will depend on the future cost of rare-earth magnet material.

A permanent magnet motor with power semiconductor supply and shaft position sensing can be constructed using radially- directed high energy magnets on its rotor. This paper presents equivalent circuit models for such motors. The model parameters are related to the motor structure and dimensions. Computed values of parameters are compared with those measured from two experimental motors with different rotor construction.

The dilithium derivatives of the ditertiary 1,2-diols, cis- and trans-1,2-dimethyl-1,2-cyclo-hexanediol, fail to undergo base-induced stereochemical equilibration under conditions that lead to such equilibration with the dilithium derivatives of the disecondary 1,2-diols, cis- and trans-1,2-cyclohexanediol. This casts doubt on the proposal that the latter equilibration proceeds by carbon–carbon bond cleavage of the dialkoxide to give a diketyl intermediate. It is highly probable that it involves oxidation–reduction as established by Doering in the case of monohydric alcohols. Examination of steroidal secondary-tertiary 1,2-diols under similar conditions shows that such systems can epimerize at both carbinol centres; this is interpreted in terms of sequential oxidation, α-ketol rearrangement, and reduction.

This study developed a situation-specific instrument that measures assertiveness of adolescents. The Assertiveness Scale for Adolescents (ASA), which contains 33 items, was constructed using a multiple-choice format with three response alternatives. Based on data from 682 elementary and secondary school students, adequate reliability and validity of the ASA were obtained when tested against several variables about which predictions could be made. Potential use of the instrument in clinical diagnosis and research was discussed.

This report describes the design of the hardware and software system which will support the training envisioned for the experimental prototype Ground Controlled Approach Controller Training System (GCA-CTS). Included as appendices are a facilities report, system interface drawings, trainee and instructor panel drawings, and programming variable definitions and file structures. (Author)

The fictions Malcolm Lowry wrote subsequent to Under the Volcano seem to demonstrate little of the technical expertise he manifests in the earlier work, and one of the few unanimously held findings of his critics is that in Lowry's later fictions something has gone wrong. This thesis explores the "problem" of the later fiction. It shows how Lowry, throughout his writing career, experiments with fictional form, and how each of his later works marks an intermediate point in a process of fictional evolution towards a "new form." This "new form," although never fully realized, is initially shaped in the notebooks Lowry used to record the events which he later transformed into the material of his autobiographical fictions. Lowry's "new form" is in fact a development out of the structure of his notebooks: the journal form. The journal form inherently creates opposing perspectives upon events; conflicting narrative rhythms ensue from this. The "new form" is an ideal Lowry aspires towards: it is intended to structure a new type of realism -- the means by which human beings assimilate and order what has happened to them —• and to contain, and thus make contiguous, Lowry's diverse themes, images, and oppositional narrative technique. Lowry's theoretical approach to the "new form" is discussed in the Introduction. Chronology is then reversed. Chapter I discusses "Ghostkeeper" as Lowry's reflection upon his fictional method. Chapter II approaches "Through the Panama" as Lowry's use of the journal form to unify disparate narrative voices. Chapter III examines and compares the manuscript and the printed version of Dark As the Grave Wherein My Friend Is Laid. It shows that this book is Lowry's first direct experiment with temporal inversions which are used to attempt to reconcile narrative mode with thematic action. Chapter IV demonstrates that Lowry uses an oppositional system as the fictional unifying principle for Under the Volcano, and examines the formal dimensions which Lowry only retrospectively discovers operating in this book. Each chapter focuses upon fictional form and argues that Lowry's themes and narrative techniques grow out of the form he employs. The Conclusion examines Lowry's "new form" in relation to his philosophical outlook, shows how the new form reconciles Lowry's borrowings from Ortega y Gasset and J.W. Dunne and suggests a critical approach that will elucidate the literary and philosophical function of the journal-narrative method.