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

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

A design technique for geometric optimisation of resonant coil sizes in low to mid frequency inductive power transmission systems.

Wireless power transfer (WPT) is a well-established method of energising electrically-powered devices. Among the different available WPT techniques, Resonant Inductive Power Transfer (RIPT) has been adapted for use in a wide range of applications. The primary reason is the relatively higher Power Transfer Efficiency (PTE) that RIPT can provide. RIPT systems operate on the principle of magnetic resonance coupling between a Transmitter (Tx) and a Receiver (Rx) coil. Maximising the PTE is a key driver for improving the performance of RIPT systems. In a RIPT link the PTE is influenced by three factors: (i) inductive linkage between the Tx and Rx, (ii) terminating circuitry of Tx and Rx sides and (iii) the Tx/Rx coil's geometrical size. In considering these impacting factors, different techniques to improve PTE have been extensively presented in the literature and are comprehensively reviewed in this thesis. The research work undertaken focuses on the geometrical optimisation of Tx/Rx coils to help maximise PTE in RIPT systems for operation over low- and mid-frequency bands (i.e. between few kHz to several MHz). Conventional methods for maximising PTE require defining various design parameters (i.e. figure-of-merits), which assist in finding the optimum Air-Cored Coil (ACC) geometry. However, traditional techniques for working with Figure-of-Merit (FoM) parameters are very time-consuming and process-demanding. In this thesis, the number of required FoMs have been reduced to one and incorporated into a process that will accelerate production of the optimum geometry design. A unique FoM parameter (i.e. Pscf) is developed by consolidating the PTE's impacting factors. Considering the RIPT application and its physical size constraints, a proper selection method for identifying the numerical value of Pscf is investigated. A novel iterative algorithm has been developed to assist in selection of the most favourable Pscf value, which provides the optimum ACC geometry. Theoretical design examples of two RIPT systems - operating at 10 kHz (low-frequency band) and 300 kHz (mid-frequency band) - are used to investigate the functionality of the ACC design approach, for which successful results are achieved. The novel iterative algorithm is also experimentally validated by developing four prototyped Tx/Rx ACC pairs, with real-world applications, which operate over low- and mid-frequency bands: 1:06 MHz, 100 kHz, 50 kHz, 15 kHz. For the designed ACC geometries, maximum PTEs of 85:63% at 1:06 MHz, 83:10% at 100 kHz, 72:85% at 50 kHz and 34:57% at 15 kHz are practically measured in bench top tests. The measured PTE values are in close correlation (within 14%) with the calculated PTEs at these frequency ranges, and thus validate the novel ACC design procedure. The RIPT system's maximum achievable PTE can be further increased by adding ferrite cores to the Tx/Rx ACC pair. In this thesis, an advanced iterative algorithm is also presented to support the design of geometrically optimised coil pairs employing ferrite cores. The advanced iterative algorithm is an extension of the initial work on optimising ACC geometries. Optimum Ferrite-Cored Coil (FCC) geometries, produced using the advanced iterative algorithm, for RIPT systems operating at 10 kHz and 300 kHz have been investigated. In comparing the FCC and ACC geometries designed for these frequencies, it is demonstrated that RIPT systems with ferrite cores reduce the ACC's geometrical size and additionally improve PTE. To validate the performance of the advanced FCC design algorithm over low- and mid-frequency bands, two RIPT systems are physically constructed for operation at 15 kHz (low-frequency) and 50 kHz (mid-frequency). For the prototyped RIPT systems, maximum PTEs of 45:16% at 50 kHz and 50:74% at 15 kHz are practically measured. The calculated and physically measured PTE values are within 2% difference; hence validating the advanced FCC design process

A resonant system for electromagnetic induction imaging of concealed conductive targets

The possibility of revealing the presence and identifying the nature of electrically conductive targets is of central interest in many fields, including security, medicine, industry, archaeology and geophysics. In many applications, these targets are electromagnetically shielded by other external materials and thus cannot be directly accessed and detected. Hence, material interrogation techniques are required that allow penetration through the shielding materials, in order for the targets to be identified. Electromagnetic interrogation techniques represent a powerful solution to this challenge, as they enable penetration through conductive shields. Two resonant electromagnetic induction imaging (EII) methods, based on the use of LCR circuits, were developed in this research work. These proof-of-principle EII methods were based, respectively, on position-resolved-measurements of resonant frequency and Q-factor shifts, which occurred as a consequence of eddy current induction inside the conductive targets to be detected. The proposed techniques were applied to 2D imaging of conductive targets (having conductivities σ ranging from 0.54 to 59.77 MSm-1), both unshielded and shielded by an aluminium shield (1.5-mm-thick). The experimental results achieved in the first part of this work highlighted a limitation in the LCR resonant circuits used for EII investigations, linked to the Q-factor low absolute 5 values (between 7 and 23). Therefore, investigations were conducted, leading to the implementation of an improved version of the EII system, based on active bandpass filters. The sensitivity of the novel EII system was found to be larger by a factor of 3.5 compared to the previously used LCR-based system, when both systems were used for imaging copper. Additionally, the new system allowed achieving images with higher contrast. The research work reported in this thesis led to establishing a proof-of-principle method for EII of conductive samples, also in the interesting scenario where the samples were shielded by conductive shields preventing them from being directly accessed

Wireless power transfer for electric vehicle

Wireless Power Transfer (WPT) systems transfer electric energy from a source to a load without any wired connection. WPTs are attractive for many industrial applications because of their advantages compared to the wired counterpart, such as no exposed wires, ease of charging, and fearless transmission of power in adverse environmental conditions. Adoption of WPTs to charge the on-board batteries of an electric vehicle (EV) has got attention from some companies, and efforts are being made for development and improvement of the various associated topologies. WPT is achieved through the affordable inductive coupling between two coils termed as transmitter and receiver coil. In EV charging applications, transmitter coils are buried in the road and receiver coils are placed in the vehicle. Inductive WPT of resonant type is commonly used for medium-high power transfer applications like EV charging because it exhibits a greater efficiency. This thesis refers to a WPT system to charge the on-board batteries of an electric city-car considered as a study case. The electric city-car uses four series connected 12V, 100A•h VRLA batteries and two in-wheel motors fitted in the rear wheels, each of them able to develop a peak power of 4 kW to propel the car. The work done has been carried out mainly in three different stages; at first an overview on the wired EV battery chargers and the charging methodologies was carried out. Afterwards, background of different WPT technologies are discussed; a full set of Figures of Merit (FOM) have been defined and are used to characterize the resonant WPTs to the variations in resistive load and coupling coefficient. In the second stage, the WPT system for the study case has been designed. In the third stage, a prototypal of the WPT system has been developed and tested. Design of the WPT system is started by assessing the parameters of the various sections and by estimating the impact of the parameters of the system on its performance. The design process of the coil-coupling has come after an analysis of different structures for the windings, namely helix and spiral, and different shapes for the magnetic core; further to the preliminary results that have shown the advantages of the spiral structure, a more detailed analysis has then been executed on this structure. The coil design has encompassed the determination of the inductive parameters of the two-coil coupling as a function of the coil distance and axial misalignment. Both the analysis and the design was assisted by a FEM-approach based on the COMSOL code. Design of the power supply stages of the WPT system has consisted of the assessment of values and ratings of a) the capacitors that make resonant the coil-coupling, b) the power devices of the PFC rectifier and of the high frequency inverter (HF) that feeds the transmitting coil, c) the power devices of the converters supplied by the receiver coil: the rectifier diode and the in-cascade chopper that feeds the battery in a controlled way. For the converters that operate at high frequency (inverter and the rectifier in the receiver section), power electronic devices of the latest generation (the so-called Wide Band Gap (WBG) devices) have been used in order to maximize the efficiency of the WPT system. A prototypal WPT battery charger was arranged by using available cards with the power and signal circuits. Relevant experimental activities were: a) measurement of the parameters of the coils, b) desk assembling of the prototype, and c) conducting tests to verify proper operation of the prototype. The thesis work includes also a brief overview of i) emerging topics on WPT systems such as on-line electric vehicle (OLEV), ii) shielding of the magnetic fields produced by a WPT system, and iii) standards on WPT operation. These three issues play a significant role in the advancement of the WPT technology. The thesis work has been carried out at the Laboratory of “Electric systems for automation and automotive” headed by Prof. Giuseppe Buja. The laboratory belongs to the Department of Industrial Engineering of the University of Padova, Italy

Fourier Analysis and Optimization of Inductive Wireless Power Transfer for Electric Vehicle Charging

With the growth of electric vehicle (EV) popularity, different charging options to increase user convenience and reduce charging time such as high power wireless charging are increasingly being developed and researched. Inductive wireless power transfer (WPT) systems for EVs must meet specifications such as stray field, battery power and voltage operating range, efficiency, and ground clearance. The coil geometry and design have a large impact in meeting these constraints. Typical design approaches include iterative analysis of predetermined coil geometries to identify candidates that meet these constraints. This work instead directly generates WPT coil shapes and magnetic fields to meet specifications and constraints through the optimization of Fourier basis function coefficients and that can be used to predict system efficiency and performance. The proposed Fourier Analysis Method (FAM) applies to arbitrary planar coil geometries and does not rely on iterative finite-element analysis (FEA) simulations. This flexibility allows for rapid design evaluation across a larger range of coil geometries and specifications. The method is used to consider the trade-off of coil current and stray field for given power levels to illustrate the flexibility and generality of the method. A 6.6 kW proof-of-concept demonstrator WPT system is built from the optimization result to compare model efficiency, stray fields, and performance to experimental measurements. The methodology is then used in the optimization, design, analysis, and testing of two 120 kW demonstrators, including thermal modeling and integration

Compact Multi-Coil Inductive Power Transfer System with a Dynamic Receiver Position Estimation

Inductive power transfer (IPT) systems with tolerance to the lateral misalignment are advantageous for enhancing the transmitted power, usability and security of the system. In this thesis, a misalignment tolerant multi-coil design is proposed to supply stationary and dynamic battery-free wireless devices. A compact architecture composed of individually switchable 3 layers of printed coils arranged with overlap for excellent surface coverage. A hybrid architecture based on three compact AC supply modules reduces the supply circuit complexity on the sending Seite 2 von 4side. It detects the position of the receiver coil quickly, controls the activation of the transmitting coils and estimates the next receiver position. The proposed architecture reduces the circuit footprint by a factor of 62% compared to common architectures. A transmitter coil activation strategy is proposed based on the detection of the transmitting coils voltage and communication between sending side and receiving side to detect devices to supply nature and position and to differentiate them from other conductive objects in the sending area to the supplying security. The experimental results prove that the proposed architecture has a good performance for different trajectories when the device speed does not exceed 15 mm/s. Besides, the maximum detection time for the initial device position is about 1.6 s. The maximal time interval to check the transmitter coils is around 0.7 s.:1. INTRODUCTION 2. THEORETICAL BACKGROUND 3. STATE OF THE ART OF MULTI-COIL IPT SYSTEMS 4. NOVEL DESIGN OF A MULTI-COIL IPT SYSTEM 5. MULTI-COIL ACTIVATION PROCEDURE 6. EXPERIMENTAL INVESTIGATIONS 7. CONCLUSION AND OUTLOOKInduktive Energieübertragungssysteme (IPT) mit Toleranz gegenüber seitlichem Versatz sind vorteilhaft, um die übertragene Leistung, die Nutzbarkeit und die Sicherheit des Systems zu verbessern. In dieser Arbeit wird ein versatztolerantes Multispulen-Design vorgeschlagen, um stationäre und dynamische batterielose drahtlose Geräte zu versorgen. Die kompakte Architektur besteht aus 3 einzeln schaltbaren Schichten gedruckter Spulen, die überlappend angeordnet sind, um eine hervorragende Oberflächenabdeckung zu gewährleisten. Eine hybride Architektur, die auf drei kompakten AC-Versorgungsmodulen basiert, reduziert die Komplexität der Versorgungsschaltung auf der Senderseite. Sie erkennt die Position der Empfängerspule schnell, steuert die Aktivierung der Sendespulen und schätzt die nächste Empfängerposition. Die vorgeschlagene Architektur reduziert den Platzbedarf der Schaltung um einen Faktor von 62 % im Vergleich zu herkömmlichen Architekturen. Es wird eine Aktivierungsstrategie für die Sendespulen vorgeschlagen, die auf der Erkennung der Spannung der Sendespulen und der Kommunikation zwischen Sende- und Empfangsseite basiert, um die Art und Position der zu versorgenden Geräte zu erkennen und sie von anderen leitfähigen Objekten im Sendebereich zu unterscheiden. Die experimentellen Ergebnisse zeigen, dass die vorgeschlagene Architektur eine gute Leistung für verschiedene Trajektorien hat, wenn die Geschwindigkeit der Geräte 15 mm/s nicht überschreitet. Außerdem beträgt die maximale Erkennungszeit für die anfängliche Geräteposition etwa 1,6 s. Das maximale Zeitintervall für die Überprüfung der Senderspulen beträgt etwa 0,7 s.:1. INTRODUCTION 2. THEORETICAL BACKGROUND 3. STATE OF THE ART OF MULTI-COIL IPT SYSTEMS 4. NOVEL DESIGN OF A MULTI-COIL IPT SYSTEM 5. MULTI-COIL ACTIVATION PROCEDURE 6. EXPERIMENTAL INVESTIGATIONS 7. CONCLUSION AND OUTLOO

Electronic identification systems for asset management

Electronic identification is an increasingly pervasive technology that permits rapid data recovery from low-power transponders whenever they are placed within the vicinity of an interrogator device. Fundamental benefits include proximity detection not requiring line-of-sight, multiple transponder access and data security. In this document, electronic identification methods for asset management are devised for the new target application of electrical appliance testing. In this application mains-powered apparatus are periodically subjected a prescribed series of electrical tests performed by a Portable Appliance Tester (PAT). The intention is to enhance the process of appliance identification and management, and to automate the test process as far as possible. Three principal methods of electronic identification were designed and analysed for this application: proximity Radio Frequency Identification (RFID), cable RFID and power- line signalling. Each method relies on an inductively coupled mechanism that utilities a signalling technique called direct-load modulation. This is particularly suited to low- cost passive transponder designs. Physical limitations to proximity RFID are identified including coil size, orientation and susceptibility to nearby conducting surfaces. A novel inductive signalling method called cable RFID is then described that permits automatic appliance identification. This method uses the appliance power cable and inlet filter to establish a communication channel between interrogator and transponder. Prior to commencing the test phase, an appliance is plugged into the PAT and identified automatically via cable RFID. An attempt is made to extend the scope of cable RFID by developing a novel mains power-line signalling method that uses direct-load modulation and passive transponders. Finally, two different implementations of RFID interrogator are described. The first takes the form of an embeddable module intended for incorporation into electronic identification products such as RFID enabled PAT units. Software Defined Radio (SDR) principles are applied to the second interrogator design in an effort to render the device reconfigurable

Distributed light sources for photocatalytic water treatment

In dit proefschrift wordt een nieuwe fotokatalytische reactor met gedistribueerde lichtbronnen gepresenteerd. De nieuwe fotokatalytische reactor maakt gebruik van draadloze energie overdracht om ultraviolet-licht-emitterende diodes (UV-LEDs) van energie te voorzien. De draadloze UV-LEDs worden gedistribueerd door de reactor en verdelen hun licht over het oppervlakte van de fotokatalyst