An improved calculation of ferrite core loss for nonsinusoidal waveforms separates a flux trajectory into major and minor loops via a new recursive algorithm. It is highly accurate and outperforms two previous methods for our measured data. The only characteristics of the material required are the standard Steinmetz-equation parameters.

/pdf/accurate-prediction-of-ferrite-core-loss-with-nonsinusoidal-3bljaupm8k.pdf

Accurate prediction of ferrite core loss with nonsinusoidal waveforms using only Steinmetz parameters

Interleaving technique is used in some applications due to its advantages regarding filter reduction, dynamic response, and power management. In dual battery system vehicles, the bidirectional dc-dc converter takes advantage of this technique using three-to-five paralleled buck stages. In this paper, we propose the use of a much higher number of phases in parallel together with digital control. It will be shown that this approach opens new possibilities since changes in the technology are possible. Thus, two 1000-W prototypes have been designed using surface mount technology devices (SO-8 transistors). An additional important feature is that due to the accuracy of the digital device [field-programmable gate array (FPGA)], current loops have been eliminated, greatly simplifying the implementation of the control stage

Automotive DC-DC bidirectional converter made with many interleaved buck stages

THIS paper explores opportunities and challenges in power conversion in the VHF frequency range of 30-300 MHz. The scaling of magnetic component size with frequency is investigated, and it is shown that substantial miniaturization is possible with increased frequencies even considering material and heat transfer limitations. Likewise, dramatic frequency increases are possible with existing and emerging semiconductor devices, but necessitate circuit designs that either compensate for or utilize device parasitics. We outline the characteristics of topologies and control methods that can meet the requirements of VHF power conversion, and present supporting examples from power converters operating at frequencies of up to 110 MHz.

/pdf/opportunities-and-challenges-in-very-high-frequency-power-2j4vslax8q.pdf

Opportunities and Challenges in Very High Frequency Power Conversion

A dynamic core loss model is proposed to estimate core loss in both soft ferromagnetic and power ferrite materials with arbitrary flux waveforms. The required parameters are the standard core loss coefficients that are either directly provided by manufacturers or extracted from the loss curve associated with sinusoidal excitation. The model is applied to calculating core loss in both two-dimensional and three-dimensional transient finite element analysis, and the results are compared with measured data.

A dynamic core loss model for soft ferromagnetic and power ferrite materials in transient finite element analysis

The trend toward high power density, high operating frequency, and low profile in power converters has exposed a number of limitations in the use of conventional wire-wound magnetic component structures. A planar magnetic is a low-profile transformer or inductor utilizing planar windings, instead of the traditional windings made of Cu wires. In this paper, the most important factors for planar transformer (PT) design including winding loss, core loss, leakage inductance, and stray capacitance have individually been investigated. The tradeoffs among these factors have to be analyzed in order to achieve optimal parameters. Combined with an application, four typical winding arrangements have been compared to illustrate their advantages and disadvantages. An improved interleaving structure with optimal behaviors is proposed, which constructs the top layer paralleling with the bottom layer and then in series with the other turns of the primary, so that a lower magnetomotive force ratio m can be obtained, as well as minimized ac resistance, leakage inductance, and even stray capacitance. A 1.2-kW full-bridge dc-dc converter prototype employing the improved PT structure has been constructed, over 96% efficiency is achieved, and a 2.7% improvement, compared with the noninterleaving structure, is obtained.

https://orbit.dtu.dk/files/4566316/Ouyang.pdf

Optimal Design and Tradeoff Analysis of Planar Transformer in High-Power DC–DC Converters

An extension to the Steinmetz equation is proposed, to enable estimation of hysteresis losses in magnetic core materials with nonsinusoidal flux waveforms The new formulation is shown to avoid anomalies present in previous modified-Steinmetz-equation calculations of loss with nonsinusoidal waveforms Comparison with experimental measurements in MnZn ferrite shows improved accuracy The result may be optionally formulated in terms of an effective frequency and an effective amplitude, and options for defining these are discussed

/pdf/improved-calculation-of-core-loss-with-nonsinusoidal-3yge4hur60.pdf

Improved calculation of core loss with nonsinusoidal waveforms

Multiphase voltage regulator modules (VRMs) for microprocessor power delivery with coupled output inductors are discussed. Strong coupling is shown to be feasible and effective at reducing ripple if the correct magnetic topology is used. For more than two phases, this can be a "ladder" core with windings around each rung. Typical ripple reduction is better than a factor of six with no effect on response time. One can also chose to improve response time while still significantly reducing ripple. A simultaneous numerical optimization of the magnetics and the circuit is used to minimize loss in a fast-response 100 A design.

/pdf/coupled-inductor-design-optimization-for-fast-response-low-3g2zk5tu1t.pdf

Coupled-inductor design optimization for fast-response low-voltage DC-DC converters

Motivated by modern microprocessors' demand for high-current, low-voltage power with large transient load steps, a scalable multi-phase coupled inductor buck circuit is presented which delivers 80 A at 1.2 V from a 12 V input. 4-phase coupling and 1 MHz per-phase switching frequency enable the use of 50 nil per-phase leakage inductance so that the system is capable of supporting 15%-to-full-to-15% load transient steps with a 72 mV output voltage window using only a small bank of MLCC output capacitors.

Using coupled inductors to enhance transient performance of multi-phase buck converters

Methods and structures for constructing a magnetic core of a coupled inductor. The method provides for constructing N-phase coupled inductors as both single and scalable magnetic structures, where N is an integer greater than 1. The method additionally describes how such a construction of the magnetic core may enhance the benefits of using the scalable N-phase coupled inductor. The first and second magnetic cores may be formed into shapes that, when coupled together, may form a single scalable magnetic core. For example, the cores can be fashioned into shapes such as a U, an I, an H, a ring, a rectangle, and a comb, that cooperatively form the single magnetic core.

Method For Making Magnetic Components With M-Phase Coupling, And Related Inductor Structures

A set of four coupled inductors is applied to a four-phase interleaved 1 kW bi-directional 14 V to 42 V DC/DC converter for automotive applications. The coupled-inductor structure is optimized, and the performance is examined through simulations and experimental measurements. Although coupled inductors offer bigger advantages in applications that require fast transient response, they also have significant advantages in this type of application.

/pdf/automotive-application-of-multi-phase-coupled-inductor-dc-dc-5rxuhhzvyz.pdf

Jieli Li

Papers

Improved calculation of core loss with nonsinusoidal waveforms

Coupled-inductor design optimization for fast-response low-voltage DC-DC converters

Using coupled inductors to enhance transient performance of multi-phase buck converters

Method For Making Magnetic Components With M-Phase Coupling, And Related Inductor Structures

Automotive application of multi-phase coupled-inductor DC-DC converter