Frequency-dependent resistance in Litz-wire planar windings for domestic induction heating appliances

Abstract-High-Frequency (HF) litz wires are extensively used for the windings of Medium-Frequency (MF) magnetic components in order to reduce the impact of eddy current losses that originate from skin and proximity effects. Literature documents different methods to calculate eddy current losses in HF litz wires, however, most of the computation methods rely on perfect twisting of the strands, which is often not present in practice. This paper analyzes the implications of imperfect twisting on the current distribution among the different strands of HF litz wires and the corresponding losses by means of a fast 2.5D PEEC (Partial Element Equivalent Circuit) method. The effects of different types of twisting imperfections (at the bundle-, subbundle-, or strand-level) are examined. It is found that imperfect twisting can lead to increased losses (more than 100 %). However, perfect twisting of the strands, which is difficult to achieve, is often not required, i.e. suboptimal twisting is sufficient. Analytical expressions are given for distinguishing between critical and uncritical imperfections. The experimental results, conducted with a 7.5 kHz / 65 kW transformer, reveal a reduction of the error on the predicted losses from 52 % (ideal HF litz wire model) to 8 % (presented model) and, thus, confirm the accuracy improvement achieved with the proposed approach.

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“…The exact packing pattern is modeled and the magnetic field is computed with a Biot-Savart summation [5].…”

Section: Perfect Twistingmentioning

confidence: 99%

“…Roebel bars or HF litz wires. In this regard, HF litz wires are very popular since they allow for low losses and great flexibility in the design of the magnetic component [1]- [5].…”

Section: Introductionmentioning

confidence: 99%

Litz wire losses: Effects of twisting imperfections

Guillod

Huber

Krismer

et al. 2017

2017 IEEE 18th Workshop on Control and Modeling for Power Electronics (COMPEL)

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“…Electric heating system requires heat energy which can be obtained from the heat loss occurring in the process of electromagnetic induction. Many industries have benefited from this new breakthrough by implementing induction heating for furnacing, quenching and welding [9]. In these applications, induction heating has made it easier to set the parameters without the need of external power source.…”

Section: Introductionmentioning

confidence: 99%

Design and Analysis of Zero Current Switching Resonant Inverter based High Frequency Induction Heating

Rathi¹,

Kumar²

2017

IJERT

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Abstract-This paper deals with design and analysis of Zero Current Switching (ZCS) resonant inverter based high frequency induction heating. The basic circuits consist of a half bridge inverter and an induction heating coil. This equipment works on the principle of eddy current induction. The high frequency current is given to the coil which acts as a primary winding of the transformer. The work piece acts like a short circuited secondary of the transformer. The heating effect is obtained by the eddy current induced in the work piece. Since eddy current is proportional to square of the frequency, heating effect will be high at high frequency. The heat can be varied by varying the frequency. When high frequency in the range of several hundred kHz is used, the switching losses will be more. To reduce the switching losses ZCS soft switching is employed in this work. Simulations are performed in MATLAB to understand the working of ZCS based high frequency induction heating. Also, hardware results are obtained using ZCS IC UC3865N.

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“…For coils in free-space, matches to experimental data can be achieved using a variety of simplified models, employing prior knowledge of the expected field and current density distributions, as well as symmetry between the strands in each bundle [6]- [9]. However, for lossy-magnetic multilayer structures, each strand of the coil experiences a proximity effect not only due to the nearby strands, but also due to the multilayer structure, complicating the overall analysis [7], [10].…”

Section: Introductionmentioning

confidence: 99%

Fast Simulation of Complicated 3-D Structures Above Lossy Magnetic Media

2014

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A fast numerical method is presented for the simulation of complicated 3D structures, such as inductors constructed from litz or stranded wires, above or sandwiched between planar lossy magnetic media. Basing upon its smoothness, the quasistatic multilayer Green's function is numerically computed using finite differences, and its source height dependence is computed using an optimal Toeplitz-plus-Hankel decomposition. We show that a modified precorrected FFT method can be applied to reduce the dense linear algebra problem to near-linear time, and that frequency-dependent setups can be avoided to result in a considerable speed-up. Experimental verifications are made for a 16-strand litz wire coil, realistically modeled down to each individual strand. Results are obtained in 2-3 hours, showing an excellent agreement to measurements, and can be used to study the impact of transposition patterns in litz wire construction.

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Frequency-dependent resistance in Litz-wire planar windings for domestic induction heating appliances

Cited by 155 publications

References 15 publications

Litz wire losses: Effects of twisting imperfections

Litz wire losses: Effects of twisting imperfections

Design and Analysis of Zero Current Switching Resonant Inverter based High Frequency Induction Heating

Fast Simulation of Complicated 3-D Structures Above Lossy Magnetic Media

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