J.D. Lavers

A simple method of estimating the minor loop hysteresis loss in thin laminations

A simple and practical method of correcting the hysteresis loss in a thin lamination for the effects of minor loops is described. The necessary correction is applied to the losses that would occur under conditions of sinusoidal flux density and the required empirical factor is derived using a broad range of loss measurement data. It is shown that the correction, to a very good approximation, varies linearly with the unweighted algebraic sum of the flux density reversals in the driving waveforms. Used together with a similar factor that corrects the eddy current component of loss for the effects of flux density harmonics, the total loss can be easily estimated to an accuracy of less than 5%.

A method for circuit connections in time-dependent eddy current problems

The authors consider eddy current diffusion problems in which the electromagnetic field is computed in 2-D but external circuit connections, between the conductors with eddy currents are taken into account. The approach combines conventional circuit analysis techniques with the integro-differential finite element formulation of the transient eddy current problem. Conductors with eddy currents are treated as circuit elements with terminal voltages implicitly defined by the field equations. A numerical example is presented to illustrate the proposed formulation. >

Prediction of core losses for high flux densities and distorted flux waveforms

This paper considers the problem of estimating the core losses in a thin magnetic steel lamination when the driving flux contains not only the fundamental, but also odd harmonic components. Two numerical methods of predicting the eddy current losses due to an arbitrary flux waveform are briefly described. The important case of 3rd harmonic distortion is specifically considered. The digital simulations are used to develop a very simple model that describes the eddy current and hysteresis losses under the assumed distortion conditions with good accuracy.

A large-scale PWM solid-state synchronous condenser

The description, steady-state analysis, and the closed-loop control design of a microcontroller-based large-scale pulsewidth-modulated solid-state synchronous condenser (PWM-SSSC) for reactive power compensation are presented. The key advantage of PWM-SSSC over its predecessors is the fact that large passive magnetic components are replaced by silicon. This provides a more compact and efficient systems at a cheaper price. A series of PWM switching patterns in the low-switching-frequency range (F/sub SW/<500 Hz), which are most suitable for high-power gate turn-off (GTO) thyristors, is presented. Formulations and solutions of the Newton-Raphson method for possible low-switching-frequency PWM patterns, performance comparisons for multiple solutions, different control strategies, and the filter design are presented. Cumbersome z-domain methods for pulsed stability analysis are completely avoided by using direct s-domain computations. A systematic approach for tuning the controller parameters is introduced by extending the concept of absolute stability.<<ETX>>

Numerical solution methods for electroheat problems

This paper reviews the use of numerical methods in simulating and solving problems that arise in the electroheat industry. Particular attention is given to the coupled electrothermal and induction stirring problems that are typical of this industry. Following a brief review of the nature of electrothermal problems, the Finite Difference, Volume Integral Equation and Finite Element simulation techniques are critically examined. It is shown that each technique has a definite role and each is illustrated with practical examples. A brief discussion of unsolved problems is presented.

Sequential Optimization Method for the Design of Electromagnetic Device

Three sequential optimization methods, sequential least square method, sequential Kriging method, and sequential linear Bayesian method, are presented for the optimization design of electromagnetic device. Sequential optimization method (SOM) is composed of coarse optimization process and fine optimization process. The main purpose of the former is to reduce the design space; while the target of the latter is to update the optimal design parameters. To illustrate the performance of the proposed methods, an analytic test function and the TEAM Workshop Problem 22 are investigated. Experimental results of test function demonstrate that SOM can obtain satisfactory solutions; and practical application illustrates that the number of finite element sample points is less than 1/10 compared with that by direct optimization method, while the optimal results are even better than that by direct optimization method.

Constriction resistance at high signal frequencies

Constriction resistance arises in practical electrical interfaces because contact is made at discrete spots as defined by the surface roughness and contact pressure. This paper describes the dependence of constriction resistance on signal frequency. This dependence was calculated for circular constrictions ranging in diameter from 10 to 100 /spl mu/m, and for frequencies ranging from DC to 1 GHz. The results indicate that the magnitude of constriction resistance does not deviate appreciably from values predicted by Helms classical analytical expression, as long as the skin depth is large compared with the constriction radius. For skin depths that are much smaller than the constriction radius, constriction resistance decreases with increasing frequency to an apparent limiting value independent of the constriction radius. At high frequencies, constriction resistance constitutes only one of two components of the total connection resistance measured in practice. The second component of connection resistance is determined by details of the geometry and dimensions of the contact interface, and increases with signal frequency.

Eddy-current power loss in toroidal cores with rectangular cross section

In this paper, we investigate eddy-current power loss in toroidal cores with a rectangular cross section. An analytical method is used in which the field variables are expressed in terms of products of Bessel functions and trigonometric functions. A closed-form expression is derived for the power loss. The influence of various parameters such as skin depth and core dimensions over a wide range is discussed. Simplified expressions for the power loss at special cases such as very small and very large skin depths are provided. A comparison with measured values is presented.

Loss comparison in the design of high frequency inductors and transformers

Three design methods, widely used for high frequency inductors and transformers, are critically compared using, as a basis, the example of low profile, small footprint, low loss 500 kHz devices. In comparison to the results obtained from more detailed finite element models, it is shown that the standard methods provide surprisingly good estimates of the copper and core losses.

An Improved Multiquadric Collocation Method for 3-D Electromagnetic Problems

The multiquadric radial basis function method (MQ RBF or, simply, MQ) developed recently is a truly meshless collocation method with global basis functions. It was introduced for solving many 1- and 2-D partial differential equations (PDEs), including linear and nonlinear problems. However, few works are found for electromagnetic PDEs, especially for 3-D problems. This paper presents an improved MQ collocation method for 3-D electromagnetic problems. Numerical results show a considerable improvement in accuracy over the traditional MQ collocation method, although both methods are direct collocation method with exponential convergence