C. A. Baguley

The Effect of DC Bias Conditions on Ferrite Core Losses

In switched-mode power supplies - the predominant type of power converter in contemporary electronic equipment - ferrite magnetic components under dc bias conditions are typically large and have relatively high losses. The nature of these losses is not widely understood, and research in this area has been hampered by the difficulty of obtaining accurate core loss measurements. This paper reviews previous studies on the nature of core losses under dc bias, and presents new results, measured by a technique that has not previously been utilized for the measurement of core losses under dc bias conditions. The results show that ferrite core losses increase significantly with an increasing dc bias, and highlight the need for further research over a wider range of conditions to fully characterize the phenomenon.

A New Resonant Bidirectional DC–DC Converter Topology

This paper presents a new resonant dual active bridge (DAB) topology, which uses a tuned inductor-capacitor-inductor (LCL) network. In comparison to conventional DAB topologies, the proposed topology significantly reduces the bridge currents, lowering both conduction and switching losses and the VA rating associated with the bridges. The performance of the DAB is investigated using a mathematical model under various operating conditions. Experimental results of a 2.5-kW prototype, which has an efficiency of 96% at rated power, are also presented with discussions to demonstrate the improved performance of the tuned LCL DAB topology. Results clearly indicate that the proposed DAB topology offers higher efficiency over a wide range of both input voltage and load in comparison to conventional DAB topologies.

A New Technique for Measuring Ferrite Core Loss Under DC Bias Conditions

It is well known that the measurement of ferrite core losses is difficult, particularly under low power factor conditions for which the excitation VA drawn is large relative to the power dissipated in the ferrite core. This paper proposes a new technique, called mutual inductance neutralization, which overcomes this difficulty by compensating for the reactive power drawn by the circuit through the use of an air cored mutual inductor. Based on the technique, circuits are presented which are appropriate for core loss measurement in the absence, and the presence of a dc bias. Measured results are presented which verify the accuracy of the technique, and results are also presented showing the effect of dc bias conditions on the losses of the ferrite core under test.

A Dual-Active Bridge Topology With a Tuned CLC Network

This paper proposes a resonant dual-active bridge (DAB) converter, which uses a tuned capacitor-inductor-capacitor network. In comparison to the conventional DABs, the proposed topology significantly reduces the bridge currents, lowering both conduction and switching losses and improving the bridge power factors. A mathematical model, which predicts the behavior of the proposed system, is presented to show that both the magnitude and direction of the power flow can be controlled through either relative phase angle or pulse width modulation of voltages produced by the bridges. The viability of the proposed concept is verified through simulation. Experimental results of a 4- kW prototype converter, which has an efficiency of 95% at rated power, are also presented with discussions to demonstrate the improved performance of this topology.

The Impact of Vibration Due to Magnetostriction on the Core Losses of Ferrite Toroidals Under DC Bias

The ferrite cores of transformers and inductors are commonly excited under dc bias conditions in power electronic circuitry. Results have previously been presented showing core losses increase significantly with dc bias, along with various explanations for the cause. This paper presents measurements showing a strong correlation between core losses, and the magnetostrictive vibration caused by the presence of a dc bias. The measurements are made on power grade material ferrite toroidal cores at frequencies equal to, and distant from magnetomechanical resonance. Based on this evidence it is proposed that a mechanism causing core losses to increase with dc bias is the increase in vibration with dc bias, with losses being dependent on the amplitude and nature of the vibration waveform. The means by which core losses increase with vibration are also described.

An Investigation into the Impact of DC Bias Conditions on Ferrite Core Losses

Switch mode power supplies are the predominant form through which power conversion is currently implemented in electronic equipment. Within such power supplies magnetic components that are placed under DC bias conditions are typically large and have relatively high losses. The nature of the ferrite core losses of magnetic components under DC bias conditions is not widely understood, and research in this area has been hampered by the difficulty of performing accurate core loss measurements. This paper reviews previous studies on the nature of core losses under DC bias, and presents new results, measured using a technique that has not previously been utilized for the measurement of core losses under DC bias conditions, which show that ferrite core losses increase significantly with an increasing DC bias.

A Review of E-textiles in Neurological Rehabilitation: How Close Are We?

Textiles able to perform electronic functions are known as e-textiles, and are poised to revolutionise the manner in which rehabilitation and assistive technology is provided. With numerous reports in mainstream media of the possibilities and promise of e-textiles it is timely to review research work in this area related to neurological rehabilitation.This paper provides a review based on a systematic search conducted using EBSCO- Health, Scopus, AMED, PEDro and ProQuest databases, complemented by articles sourced from reference lists. Articles were included if the e-textile technology described had the potential for use in neurological rehabilitation and had been trialled on human participants. A total of 108 records were identified and screened, with 20 meeting the broad review inclusion criteria. Nineteen user trials of healthy people and one pilot study with stroke participants have been reported.The review identifies two areas of research focus; motion sensing, and the measurement of, or stimulation of, muscle activity. In terms of motion sensing, E-textiles appear able to reliably measure gross movement and whether an individual has achieved a predetermined movement pattern. However, the technology still remains somewhat cumbersome and lacking in resolution at present. The measurement of muscle activity and the provision of functional electrical stimulation via e-textiles is in the initial stages of development but shows potential for e-textile expansion into assistive technologies.The review identified a lack of high quality clinical evidence and, in some cases, a lack of practicality for clinical application. These issues may be overcome by engagement of clinicians in e-textile research and using their expertise to develop products that augment and enhance neurological rehabilitation practice.

Transient Modeling and Parameter Estimation of Field Aligned Starting

Field aligned starting (FAS) is a new technique for starting three-phase cage induction motors on single-phase supply lines with minimal inrush currents. It uses a simple energy storage system to generate a very high impulsive torque by which the motor is started before being connected to the mains supply. The spinning motor can then be connected to the mains to operate in a standard Steinmetz connection without incurring high inrush currents, if the moment of mains connection is properly timed. This paper presents a transient model and an accompanying parameter estimation method through which the transient behavior of three-phase induction motors operated with FAS can be analyzed. The proposed model is based on instantaneous symmetrical components and is used to investigate a 3 kW motor started under various operating conditions. The proposed parameter estimation method and the developed transient model are both validated by experimental results.

The Impact of Magnetomechanical Effects on Ferrite B–H Loop Shapes

Under high dc bias conditions, experimental observations show B-H loops can exhibit a figure-eight shape, as energy is returned from the magnetic core back to the magnetic excitation supply during a portion of the excitation cycle. However, an explanation for this phenomenon is yet to be reported. In this paper, experimental evidence is presented showing a correlation between the asymmetrical nature of vibration due to magnetostriction and figure-eight B-H loops. Based on this evidence, it is proposed that mechanical energy generated during part of a magnetization cycle can be converted to magnetic energy during another part, aiding the magnetization process to such an extent that energy is returned to the excitation supply. The proposed theory is supported by a modified Jiles-Atherton (J-A) model, showing that a stress related H-field component caused by magnetomechanical iteractions is responsible for generating figure-eight shaped B-H loops.

Unusual Effects Measured Under DC Bias Conditions on MnZn Ferrite Material

Switch mode power supplies are the predominant form through which power conversion is currently implemented in electronic equipment. Within such power supplies, ferrite cored magnetic components are commonly placed under dc bias conditions which, due to magnetomechanical effects, can result in higher than expected core losses. This paper presents measurements that show the impact of magnetomechanical effects on the losses of a MnZn ferrite core material under low ac excitation and high dc bias conditions. The measurements are made using an accurate measurement circuit, and the results show the impact on losses of magnetomechanical resonance. In addition distorted, figure-eight shaped B-H loops are measured, which are also believed to manifest from magnetomechanical interactions. These B-H loops show that, on a transient basis, magnetomechanical interactions may take place in a manner that is not only lossless, but returns energy back to the excitation supply.