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Journal ArticleDOI

Effects of eddy currents in transformer windings

01 Aug 1966-Vol. 113, Iss: 8, pp 1387-1394
TL;DR: In this article, the effect of eddy currents on transformer windings is considered and a method is derived for calculating the variation of winding resistance and leakage inductance with frequency for transformers with single-layer, multilayer and sectionalised windings.
Abstract: The effects of eddy currents in transformer windings are considered, and a method is derived for calculating the variation of winding resistance and leakage inductance with frequency for transformers with single-layer, multilayer and sectionalised windings. The method consists in dividing the winding into portions, calculating the d.c. resistances and d.c. leakage inductances of each of these portions, and then multiplying the d.c. values by appropriate factors to obtain the corresponding a.c. values. These a.c. values are then referred to, say, the primary winding and summed to give the total winding resistance and leakage inductance of the transformer. Formulas are derived and quoted for calculating the d.c. resistances and leakage inductances of the winding portions. Theoretical expressions are derived for the variation with frequency etc. of the factors by which the d.c. values must be multiplied to obtain the corresponding a.c. values. These expressions are presented in the form of graphs, permitting the factors to be read as required.
Citations
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Journal ArticleDOI
TL;DR: In this article, a double-half-bridge (DHB) inverter with two variable inductors (VIs) is proposed to reduce the conduction loss and achieve the maximum efficiency of 92.4%.
Abstract: Efficiency remains a key challenge in wireless charging in academia and industry. In this article, a new wireless power transfer (WPT) system based on a double-half-bridge (DHB) inverter with two variable inductors (VIs) is proposed. Compared with conventional full-bridge (FB) inverters, the DHB inverter can reduce the current through the mosfet s under the same output power and thus, reduce the conduction loss. Next, by adjusting the inductances of the VIs instead of using phase shift (PS) method, the output voltage or current can be controlled, while the circulating current can be eliminated and wide-range zero voltage switching operation can be achieved. Consequently, the power loss can be further reduced. Circuit analysis, VI design, as well as hardware implementation, are provided in detail. A laboratory prototype is built to verify the feasibility of the proposed method. Close agreement is obtained between simulation and experimental results. The maximum efficiency can reach 92.4%, which is 3.65% higher than traditional PS control.

17 citations

Journal ArticleDOI
TL;DR: In this paper, a 30kW 250V/530V bidirectional DC-DC converter was proposed for an electrical car. The converter has an efficiency of 95% at nominal power and works as a constant voltage in one direction and a constant current in the other to charge the batteries.
Abstract: This paper presents a design of a 30kW 250V/530V bidirectional DC-DC converter to be used in an electrical car. A detailed explanation of the design is given. The system uses two phase shifted half bridge (boost and buck) topologies to reduce the ripple current in the output capacitor. The converter has an efficiency of 95% at nominal power. It works as a constant voltage in one direction and as a constant current in the other to charge the batteries. Simulations and measurement are done at high power to test the efficiency.

17 citations

Proceedings ArticleDOI
01 Oct 2016
TL;DR: In this paper, a state-of-the-art report analyzes various materials and design tradeoffs that govern the electromagnetic behavior and loss mechanisms of the medium frequency transformer applications.
Abstract: Medium and high frequency, high power transformers play an important role in footprint reduction along with their functions of galvanic isolation, and voltage transformation in all high power converters typically used in traction power systems, offshore wind plant power converters, and solid state transformer based distribution system grids. This state of art report analysis the various materials and design tradeoffs that govern the electromagnetic behavior and loss mechanisms of the medium frequency transformer applications. Typical winding and core geometries that have been reported extensively in the literature are described, and some design procedures and flow charts are analyzed including specific optimization routines. Estimation of core loss at high frequency using Steinmetz method and other modified methods are shown in detail. Thermal modelling including static and dynamic methods available in literature are put forward with references to thermal management methods. FEM analysis for electromagnetic behavior is described and couple of commercially available tools and their limitations are analyzed. Different challenges of relevance are included in different sections and brief comparisons are drawn. Design tools which are available is given a preview and limitations are drawn. A comprehensive literature survey was done and included in the paper in the reference section.

16 citations

Proceedings ArticleDOI
20 Mar 2016
TL;DR: In this article, conductive reflectors for transmitter (Tx) and receiver (Rx) dipole coils are investigated to improve power efficiency and to mitigate electromagnetic field for human safety.
Abstract: 1m-off long distance and high efficiency inductive power transfer system (IPTS) with optimal shaped dipole-coil structure is proposed for home appliance charging applications. Conductive reflectors for transmitter (Tx) and receiver (Rx) dipole coils are investigated to improve power efficiency and to mitigate electromagnetic field for human safety. By adopting the Tx reflector behind the Tx core, the exposure level of magnetic flux density can be reduced by 94% in average verified by a finite-element method simulation. The optimal switching frequency of 200 kHz was experimentally found for maximum power efficiency, meeting an international guideline of Power Matters Alliance (PMA). It was experimentally verified that 4.2% of power efficiency reduction for the Rx reflector and 7.8% of the power efficiency improvement for the Tx reflector were observed. A prototype of the proposed IPTS for home appliances has achieved 83.1% of high efficiency with 150W of output power transfer.

16 citations

Journal ArticleDOI
TL;DR: In this paper, a load-dependent soft-switching method has been proposed with an auxiliary circuit that includes inductor, diode, and MOSFETs so that the hard switching issue of typical symmetrical controlled half-bridge converters is resolved.
Abstract: With the increased cloud computing and digital information storage, the energy requirement of data centers keeps increasing. A high-voltage point of load (HV POL) with an input series output parallel structure is proposed to convert 400 to 1 VDC within a single stage to increase the power conversion efficiency. The symmetrical controlled half-bridge current doubler is selected as the converter topology in the HV POL. A load-dependent soft-switching method has been proposed with an auxiliary circuit that includes inductor, diode, and MOSFETs so that the hard-switching issue of typical symmetrical controlled half-bridge converters is resolved. The operation principles of the proposed soft-switching half-bridge current doubler have been analyzed in detail. Then, the necessity of adjusting the timing with the loading in the proposed method is analyzed based on losses, and a controller is designed to realize the load-dependent operation. A lossless RCD current sensing method is used to sense the output inductor current value in the proposed load-dependent operation. Experimental efficiency of a hardware prototype is provided to show that the proposed method can increase the converter's efficiency in both heavy- and light-load conditions.

16 citations

References
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Journal ArticleDOI
TL;DR: In this article, a multilayer winding carrying an alternating current, such as the windings illustrated in figures 1, 2, and 3, each layer of copper lies in the alternating magnetic field set up by the current in all the other layers.
Abstract: IN any multilayer winding carrying an alternating current, such as the windings illustrated in figures 1, 2, and 3, each layer of copper lies in the alternating magnetic field set up by the current in all the other layers. Eddy currents are set up in each layer in a direction to partly neutralize the magnetic intensities in the interior of the copper wire in each layer. As a result of the eddy-current losses in the copper, the effective resistance of the winding to the alternating current it carries may be many times its resistance to continuous currents.

103 citations

Journal ArticleDOI
TL;DR: In this article, the authors discuss the more important causes of eddy currents in heavy conductors carrying alternating currents and surrounded on three sides by iron, and propose a method to identify the most important causes.
Abstract: The object of the present paper is the discussion of the more important causes of eddy currents in heavy conductors carrying alternating currents and surrounded on three sides by iron.

93 citations

Journal ArticleDOI
TL;DR: In this article, it is shown that a considerable proportion of the effective resistance of inductive coils when used at radio frequencies is caused by the eddy-currents set up in the wires of the coils by the alternating magnetic field in which they are situated, and that in extreme cases the alternating current resistance may amount to more than one hundred times the direct current resistance.
Abstract: It is well-known that a considerable proportion of the effective resistance of inductive coils when used at radio frequencies is caused by the eddy-currents set up in the wires of the coils by the alternating magnetic field in which they are situated, and that in extreme cases the alternating current resistance may amount to more than one hundred times the direct current resistance. It is therefore important to have reliable formulae for the eddy-current resistance of such coils in order to determine the conditions which will reduce the eddy-current losses to a minimum. The simplest case, that of a long straight cylindrical wire under the action of its own current, has been treated by Kelvin, Rayleigh, Heaviside, and others. The general effect is known as the “skin effect,” because the current tends to concentrate more and more upon the skin of the conductor as the frequency increases.

49 citations

Journal ArticleDOI
TL;DR: In this article, the authors show how hyperbolic functions of complex angles may be applied to the solution of the problem of heat losses in rectangular conductors that are embedded in open slots.
Abstract: The principal object of this paper is to show how hyperbolic functions of complex angles may be applied to the solution of the problem of heat losses in rectangular conductors that are embedded in open slots. A certain knowledge of the functions themselves is presupposed. Inasmuch, however, as they are handled like trigometric functions of real angles?except in regard to the plus and minus signs?it is a simple matter to acquire the requisite technical skill to use them. The hyperbolic function of a complex angle, consisting as it does of a real and an imaginary part, may represent a vector?the real part being the component of the vector along the horizontal, and the imaginary part, component along the vertical. Thus, for example, A sinh (x + j x) represents a vector just as A e j ? A/?, A (cos ? + j sin ?) represent vectors. Considerable experience has shown that the vector method for handling a-c. problems is much superior to the original method in which simple trigonometric functions were used. With this lesson before us, it should require but little contact with the problem at hand to demonstrate the superiority of the vector method, even though it employs the possibly unfamiliar hyperbolic quantities. These hyperbolic vectors have been used for a number of years in the analysis of problems involving a-c. circuits, which have distributed inductance and capacitance, and have proved their usefulness.

27 citations