Loss Performance Evaluation of Ferrite-Cored Wireless Power System with Conductive and Magnetic Shields

This paper presents a loss evaluation of ferrite-cored wireless power transfer (WPT) systems using conductive and magnetic shield materials. The modelling and analyses of the coil systems were implemented using the finite element method. Three coil systems were modelled-circular coils, rectangular coils and flux-pipe coil system using magnetic shields (Mumetal and electrical steel) and conductive shields (aluminum and copper). From the results presented in the analyses, it was noted that ohmic losses and core losses in the WPT system are independent of the type of conductive shield used. Similarly, it was noted that the self-inductance, coupling coefficient and losses in the system is affected by the type of magnetic shield used. For the flux-pipe resonant coil system, high power losses were recorded when a magnetic shield was used as the shielding topology while low power losses were recorded in the circular coil and rectangular coil resonant systems when the magnetic shield was used as the shielding material. For optimal WPT system requiring low eddy current losses, it was established that copper shield is the appropriate choice for flux-pipe resonant coils while electrical steel is the suitable shield material for the circular resonant coil and rectangular resonant coil systems

Optimized Shield Design for Reduction of EMF from Wireless Power Transfer Systems

In this paper, we proposed an optimized shield design for electromagnetic field (EMF) reduction from the wireless power transfer (WPT) system. Three different cases of shield design are examined in terms of strength of EMF and mutual inductance, which is directly related to power transfer efficiency. Analysis results show that when using both ferrite and conducting sheets as a shield for transmitter and receiver coils, a leakage magnetic field can be significantly reduced with negligible change in mutual inductance. Additionally, the effects of the conducting sheet\u27s size and thickness on the EMF and the mutual inductance are also examined. Our investigation will be helpful to engineers designing modern WPT systems

Optimum Modelling Of Flux-pipe Resonant Coils For Static And Dynamic Bidirectional Wireless Power Transfer System Applicable To Electric Vehicles

Wireless power transfer (WPT) technology enables the transfer of electrical power from the electric grid to the electric vehicles across an airgap using electromagnetic fields with the help of wireless battery chargers. WPT technology addresses most problems associated with the “plug-in” method of charging EVs like vandalization, system power losses, and safety problems due to hanging cables and opened electrical contact in addition to the flexibility of charging electric vehicles while in a static or dynamic mode of operation. Significant research has been undertaken over the years in the development of efficient WPT topologies applicable to electric vehicles. A preliminary review of these revealed that the ferrite core WPT is a promising and efficient method of charging electric vehicles. The charging method is suitable for wireless charging of electric vehicles because of its low cost, high efficiency and high power output. This research proposed the use of the flux-pipe model as a suitable ferrite core, magnetic resonance coupled-based WPT system for the charging of the electric vehicle. The traditional flux-pipe model has some specific benefits which include high coupling coefficient, high misalignment tolerance and high efficiencies under misalignment conditions. However, it has a major drawback of low power output due to the generation of an equal amount of useful and non-useful fluxes. A set of governing equations guiding the performance output of a WPT system was presented. It was identified that the losses in the WPT system can be minimized by reducing the value of the maximum magnetic flux density while the power output and efficiency can be increased by increasing the value of the coupling factor and quality factor. Based on these findings, 3-D finite element modelling was employed for the optimal design and analysis of a typical flux-pipe model for higher coupling strength, high power output and low losses. The magnetic coupling performance of flux-pipe resonant coils was enhanced with an increased number of turns along the core length relative to increasing the width of each coil turns along the coil width. The high power transfer and efficiency was attained by splitting of the coil windings into two in order to reduce intrinsic coil resistances; copper sheet was employed as a shielding material in order to reduce the eddy current losses and finally, an air gap was introduced in the ferrite core in order to reduce the core losses and invariably increased the amount of excitation current required to drive the core into saturation. The proposed optimization methodology results in the creation of two models for application in static and dynamic charging operations respectively. From the simulation results presented, the model designed for static charging operations can transfer up to 11 kW of power across the airgap at a coil-to-coil efficiency of 99.12% while the model design for dynamic charging of electric vehicles can transfer up to 13 kW of power across the airgap at a coil-to-coil efficiency of 98.64% without exceeding the average limit specified for the exposure of human body to electromagnetic fields

Lokalisierung und freie Positionierung unter Verwendung eines kooperativen Multi-Spulensendesystems für die drahtlose Energieübertragung

With the continuous development of communication technology there are more and more portable devices requiring periodic charging with a cable and power socket. Wireless power transfer (WPT) technology provides a promising solution to overcome the inconvenience, potential safety hazard and unsightliness of power supply cables. The result of this thesis is a conceptual design for an optimized 100 kHz WPT system having a large charging pad allowing free placement of the device to be charged. The system has high efficiency and is Electromagnetic Compatibility friendly. The three-coil system, composed of a single transmitter coil and two coils in the receiver, is operating in series resonance and has been optimized by synthesis of the coupling coefficient and quality factor to provide maximum efficiency and power simultaneously. Unique to the proposed design is that the single transmitter coil is replaced with 4-coil structure which enables field forming to strengthen the field in the center of the 4-coil structure and reduce it at the margins. A transmitter matrix consisting of cooperative multiple coils is proposed to increase the charging pad area and reduce the external magnetic field. A 16 coils system is selected as most cost efficiency. The transmitter coil radius is optimized using the criterion of weighted overall efficiency, which results in high efficiency with minimal emission to the surroundings. During charging, the appropriate 4-coil structure is activated, depending on the device location, with the other coils turned off. Several algorithms are presented that enable localization of the receiver position including: grid search, Gauss-Newton and reflected impedance for combined coils. COMSOL simulation is used to investigate the effects of using ferrite, aluminum loading and a reactive resonant coil to improve system efficiency and reduce external fields below specified human exposure limits. This thesis provides a WPT solution for charging mobile and portable devices that has many advantages. The proposed 100 kHz 16 coils transmitter matrix WPT system, consisting of individually activated 4-coil sub structures, allows free placement within the charging area, more than 65% transfer efficiency at 10 cm transmission distance and electromagnetic field emission considerably less than required by guidelines.Mit fortschreitender Entwicklung der Kommunikationstechnik steigt die Anzahl tragbarer Geräte, die einen wiederholten Ladevorgang über ein Kabel benötigen, kontinuierlich. Drahtlose Energieübertragung (Wireless Power Transfer, WPT) umgeht die damit verbundenen Sicherheitsrisiken sowie die Unbequemlichkeiten und Unansehnlichkeit, die eine große Zahl an Ladekabeln mit sich bringt. Im Rahmen dieser Arbeit ist ein konzeptueller Entwurf für ein optimiertes 100 kHz WPT-System entstanden, welcher einen großen Ladebereich mit der Möglichkeit zur freien Platzierung des zu ladenden Gerätes erlaubt. Das System zeichnet sich durch eine hohe Effizienz und elektromagnetische Verträglichkeit aus. Ein Dreispulensystem, bestehend aus einer Sendespule und zwei Empfängerspulen in Serienresonanz, wird hinsichtlich Kopplungsfaktor und Gütefaktor optimiert. Die Sendespule wird durch eine 4-Spulen Struktur ersetzt, die eine Feldformung ermöglicht, so dass eine Verstärkung des Feldes im Zentrum der Struktur erreicht wird bei gleichzeitiger Abschwächung an den Rändern. Sendermatrizen aus kooperativen Mehrspulensystemen werden untersucht mit dem Ziel, die Fläche des Ladefeldes zu vergrößern und das externe magnetische Feld zu reduzieren. Ein System aus 16 Spulen wird als das mit dem besten Kosten-Effizienz Verhältnis identifiziert. Der Radius der Senderspulen wird nach einem Kriterium der gewichteten Gesamteffizienz optimiert. Ziel ist eine hohe Effizienz bei gleichzeitig minimalen Emissionen in die Umgebung. Beim Ladevorgang wird in Abhängigkeit von der Position des zu ladenden Geräts die passende 4-Spulen Struktur aktiviert während die übrigen deaktiviert bleiben. Zur Lokalisierung des Empfängers werden die Algorithmen Rastersuche, Gauss-Newton und reflektierte Impedanz für kombinierte Spulen vorgestellt. Zur Untersuchung der Effekte von Ferriten und Aluminium sowie reaktiver resonanter Spulen wurden Simulationen mit COMSOL durchgeführt, mit dem Ziel die Effizienz zu erhöhen und die externen Felder zu reduzieren, so dass die Grenzwerte für die menschliche Exposition unterschritten werden. Diese Arbeit liefert eine WPT-Lösung für das Laden mobiler und portabler Geräte welche zahlreiche Vorteile bietet. Das vorgeschlagene 100 kHz 16-Spulen Matrixsystem, bestehend aus individuell aktivierbaren 4-Spulen Teilstrukturen, ermöglicht eine freie Platzierung auf dem Ladebereich, mehr als 65 % Übertragungseffizient im Abstand von 10 cm sowie deutlich geringere Elektromagnetische Feld Emissionen als in den Richtlinien gefordert