Dc Winding Research Articles

Single-Phase Multilevel PWM Inverter Topologies Using Coupled Inductors

The number of voltage levels available in pulsewidth modulation (PWM) voltage source inverters can be increased by using a split-wound coupled inductor within each inverter leg and interleaved PWM switching of the upper and lower switches. The magnetizing inductance of the symmetrical split-wound inductor filters the high-frequency PWM voltage differences between the upper and lower switches. The same inductor presents a three-level PWM voltage at the inverter output terminals, with the winding leakage inductance being located in series with the low-frequency output current. Deadtime PWM signal delays can be reduced as DC-rail short circuits are not possible: as a result, the quality and voltage range of the PWM output is improved. Since the inductor windings are technically exposed to high-frequency PWM AC voltages with no DC components, device voltage drops help to reduce the buildup of winding DC currents. Theoretical analysis and a sample design case are presented to illustrate how to design suitable inductors for the various topologies. Simulation and experimental results are used to illustrate the operation of the proposed inverter structures.

Experimental Verification of a Three-Phase-Laminated-Core Variable Inductor

A variable inductor, which consists of only a magnetic core and primary dc and secondary ac windings, can regulate the secondary winding inductance continuously by dc excitation from the primary winding. The variable inductor is expected to be applied to reactive power compensation in electric power systems, because it has a simple and robust structure that is extremely reliable. In a previous paper, a three-phase-laminated-core variable inductor was proposed, which has three-phase secondary ac windings installed in one laminated core to reduce the size and weight in comparison with those of a single-phase variable inductor. This paper presents an experimental verification of the proposed three-phase-laminated-core variable inductor at various ac voltages. The copper and iron losses and the efficiency of the variable inductor are also shown.

Development of a Novel Three-Phase Laminated-Core Variable Inductor for Var Compensation

This paper presents a novel three-phase laminated-core variable inductor made for the purpose of voltage stabilization in electric power systems. The proposed variable inductor has three-phase secondary ac windings together in one laminated-core to reduce the size and weight in comparison with the other single-phase ones. It can be applied as a var compensator since it can control the effective inductance of the secondary ac windings by dc excitation from the primary dc windings. First, the operating principle of the three-phase laminated-core variable inductor is described. Next, a trial 4.0 kVA variable inductor is designed based on reluctance network analysis (RNA), and then, the availability of the proposed variable inductor, which has good controllability and sinusoidal output current, is proved in experiments.

Design of a New Outer-Rotor Permanent Magnet Hybrid Machine for Wind Power Generation

This paper proposes and implements a new 36/24-pole outer-rotor permanent magnet (PM) hybrid machine for directly coupled wind power generation. The key is to design the machine with hybridization of two excitations (PMs and dc field windings) in the double-layer stator so that it can provide effective flux control, hence realizing constant voltage output over wide ranges of speeds and loads. The machine design is illustrated by finite-element analysis and then verified by experimentation.

Design and control of a flux-controllable stator-permanent magnet brushless motor drive

In this paper, a new flux-controllable stator permanent magnet (PM) brushless motor drive is proposed which is particularly attractive for electric vehicles. The key of the proposed motor is to incorporate both PM materials and dc field windings in the stator, hence offering a compact arrangement of hybrid-field excitations, while the rotor is simply composed of salient poles without windings or PMs. Thus, the flux control, including both strengthening and weakening, can be easily achieved by tuning the dc field current. Both finite element analysis and experimental results confirm that the proposed motor drive can offer effective flux control, fast speed response, wide constant-power operating range, and high efficiency over wide-speed operation.

A Single Switch Split DC-Rail Boost Converter Topology Operated Under Steady-State Unbalanced Load Conditions in Discontinuous Conduction

A single switch split dc-rail boost converter topology is described that uses a mutually coupled two winding inductor to balance the voltage drop across both of its capacitor smoothed split dc-rail input and output voltage terminals. The operation of the converter topology is described in discontinuous conduction with an unbalanced output load in steady-state. The resultant converter topology obtains balanced input and output voltages under extreme unbalanced load conditions without requiring extra converter control features. A current sharing action is described between the two coupled windings during both the switch on-time and off-time. This action is responsible for the voltage balancing feature of the converter when the converter load is unbalanced between the two output dc voltage rails. Simulations and experimental results are used to illustrate the nature of the winding current waveforms that produce this current sharing action. Load imbalances exceeding 3:1 can easily be compensated for, and simulations and experimental results show that typical deviations of the converter input and output voltages can be limited to within the range 1% to 8% for load imbalances of up to 2:1. The voltage imbalance experienced in the two dc rail output voltages is subject to design choices and linked to the winding leakage inductance and dc voltage gain.

High-Performance Control of a Dual Stator Winding DC Power Induction Generator

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper investigates the use of a dual stator winding squirrel-cage induction machine for generating dc power using series- or parallel-connected ac–dc pulse width modulation rectifiers. The operating principles and constraints when generating under minimum total copper-loss condition are explored using the machine steady-state model considering magnetizing flux saturation effects. Regulation of the dc voltage using concepts of the nonlinear input-output linearization method including the design of the controllers is set forth and confirmed to be effective by computer simulation results. Some experimental waveforms of the generator under load are also included in this paper. </para>

Design and Control of a PM Brushless Hybrid Generator for Wind Power Application

In this paper, a new permanent magnet (PM) brushless hybrid machine is proposed and implemented for wind power generation. The originality is that a small dc field winding and an extra air-bridge are incorporated in the machine so that the air-gap flux can be effectively strengthened or weakened to online keep the output voltage constant throughout the whole wind speed range. The characteristics of flux linkage and no-load electromotive force (EMF) are analyzed by using the finite element method (FEM), and these results agree well with those from magnetic circuit analysis. Experimental results also verify that the proposed machine can produce a constant output voltage over a wide wind speed range

Transformer derating for harmonic currents: a wide-band measurement approach for energized transformers

Power system transformers must often be derated when supplying harmonic currents to nonlinear loads. IEEE Recommended Practice C57.110 extrapolates transformer loss for harmonic frequencies based on DC winding resistance and rated eddy-current loss. This paper describes an improved derating technique based on direct measurements performed at fundamental and harmonic frequencies. The measurements can be performed regardless of whether the transformer is energized and in service or deenergized and out of service. For energized transformers, the measurement can be performed regardless of whether the transformer is fully loaded or unloaded. Measurements of several distribution transformers show the improvement of this method over C57.110.

Effects of pole flux distribution in a homopolar linear synchronous machine

Linear forms of synchronous electrical machine are at present being considered as the propulsion means in high-speed, magnetically levitated (Maglev) ground transportation systems. A homopolar form of machine is considered in which the primary member, which carries both ac and dc windings, is supported on the vehicle. Test results and theoretical predictions are presented for a design of machine intended for driving a 100 passenger vehicle at a top speed of 400 km/h. The layout of the dc magnetic circuit is examined to locate the best position for the dc winding from the point of view of minimum core weight. Measurements of flux build-up under the machine at different operating speeds are given for two types of secondary pole: solid and laminated. The solid pole results, which are confirmed theoretically, show that this form of construction is impractical for high-speed drives. Measured motoring characteristics are presented for a short length of machine which simulates conditions at the leading and trailing ends of the full-sized machine. Combination of the results with those from a cylindrical version of the machine make it possible to infer the performance of the full-sized traction machine. This gives 0.8 pf and 0.9 efficiency at 300 km/h, which is much better than the reported performance of a comparable linear induction motor (0.52 pf and 0.82 efficiency). It is therefore concluded that in any projected high-speed Maglev systems, a linear synchronous machine should be the first choice as the propulsion means.

Harmonic current reduction in a three-phase diode bridge rectifier

A novel method for reducing harmonic currents on the AC supply side of a three-phase bridge rectifier is presented. The principle of the method is to modify the current waveforms in the DC windings of the converter transformer by injecting a third harmonic current into the neutral point of the transformer. Passive LC filters connected between the rectifier output and the secondary neutral point act as third harmonic current sources. The effectiveness of the method is confirmed by laboratory recordings. >

Torque characteristics of swing motor with dc field winding

Torque characteristics of swing motor with dc field winding

Cage-rotor induction motor with unity power factor

The technique of using space transients in a linear induction motor in order to improve its power factor is extendable to the rotary induction machine. The transients take the form of phase jumps that cause the rotor to act as both generator of torque and as part exciter, in much the same manner as the DC winding of a synchronous machine. The technique involves novel stator winding arrangements and can be seen as an extension to the moving-coil regulator concept, whereby the short-circuited rotor acts not merely as an interphase coupling by mutual inductance, but as a combination of transformer and motional coupling. The phenomenon is clearly demonstrable in the action of a simple single-phase induction machine. A rewound conventional cage-rotor machine was tested and seen to deliver a large mechanical load while taking current at unity power factor. (See also LAITHWAITE, E.R., and KUZNETSOV, S.B.: IEEProc. B, 1981, 128, (4), pp. 190-194.)

DC magnetizing effect in the toroidal core

An effective method to give dc magnetomotive force to the toroidal core in its circumferential direction without using the dc winding is presented. This method is based on the phenomenon that dc m.m.f. appears in the circumferential direction of the tape-wound core, by applying the radial magnetic field to the core from its center. The principle of this phenomenon is made clear by FEM. Several experiments are made to demonstrate features of this phenomenon. As typical examples, applications to the voltage standard of the switching regulator and to the displacement transducer which can detect less than 1μm are reported.

Computer-aided design of air-gapped magnetic core inductors with minimum DC winding resistance

The method of computer-aided design of air-gapped inductors operating with de bias current is described. An algorithm for the minimum de resistance of the winding for a desired value of the inductance is given. Simultaneously, this permits us to determine the optimal length of the air gap, to choose a suitable operating point on the normal magnetization curve and to calculate the minimum number of turns of the winding under given inductor operation conditions, i.e., the ac voltage value across the inductor and its frequency, and the value of the de bias current superimposed in the same winding. The method presented here uses the normal magnetization curve of the core material and the family of relative incremental permeability curves of this material.

Superconducting magnets in the world of energy, especially in fusion power

Industrial applications of superconducting magnets are only feasible in the near future for superconducting homopolar machines and possibly MHD generators. In both cases there are no longer any major problems with the superconducting windings or cryogenic systems, but technological problems connected with other components are governing the chances of large scale applications. For superconducting synchronous machines, after the successful operation of machines in the MVA range, a new phase of basic investigations has started. Fundamental problems which could not be studied in the MVA machines, but which influence the design of large turbo-alternators, must now be investigated. Fusion power by magnetic confinement will probably be the largest field of application for superconducting magnets in the long run. The present research programmes require large superconducting magnets by the mid-1980s for the experimental reactors envisaged at that time. In addition to dc windings, pulse-operated superconducting windings are required in some systems, such as Tokamak. The high sensitivity of the overall plant efficiency and the active power demand of the pulsed windings require great efficiency from energy storage and transfer systems. Superconducting energy storage systems would be suitable for this, if transfer between inductances could be provided with sufficient efficiency. Basic experiments gave encouraging results. In power plant systems and electric machines an extremely high level of reliability and availability has been achieved. Less reliability will not be accepted for systems with superconducting magnets. This requires great efforts during the development work.

A DC-Type Hybrid Step Motor for Large Power Applications

The design, construction, and operation of experimental models of a dc-type hybrid step motor are discussed. This form of hybrid motor consists of a variable-reluctance step motor, the rotor of which is appropriately wound as a multipole dc motor. A computer-aided design procedure is discussed that is used to obtain the optimum parameters of the dc portion of the hybrid motor. The results obtained with two experimental models of this type of hybrid motor are presented. Both prototypes show a marked improvement in the running torque characteristics due to the dc windings. Torque-speed curves indicate load torques of 400 oz-in available at speeds up to several thousand revolutions per minute with one of the proto-types. This type of hybrid motor may be controlled in one of three different ways: a pure step motor, a pure dc motor, or a dc-aided step motor. The relative advantages, disadvantages, and application of each control mode are discussed. Several control strategies-open and closed loop-are presented for speed control as well as point-to-point type control of position. The practical feedback feasibility of this concept for high-power applications in the integral horsepower range is discussed.