162 results found
Pucci N, Arteaga JM, Kwan C, et al., 2021, Induced voltage estimation from class EF switching harmonics in HF-IPT systems, IEEE Transactions on Power Electronics, Vol: 37, Pages: 4903-4916, ISSN: 0885-8993
One of the advantages of high-frequency inductive power transfer systems is the high tolerance to misalignment and large air-gaps. However, the inherently large magnetic field volumes can lead to coupling of additional foreign objects with the primary, causing possible detuning of the system and heating of the objects. These foreign objects and the conditions of the local environment can load the transmitter, which changes the induced voltage on the primary side. Unfortunately, the induced voltage is not directly measurable in an operating transmitter and the most straightforward way of calculating this variable, through a measurement of primary coil current and voltage, can cause a significant decrease in quality factor which reduces system performance. An integrated solution capable of estimating the induced voltage through other less invasive measurements in the primary is needed to ensure safety of operation through foreign object detection. Knowledge of the induced voltage can also be used to correct tuning mismatches where both sides of the link are active (i.e., in synchronous rectification and bidirectional systems). In this article, multiple candidate variables for estimating the induced voltage are assessed based on factors such as measurement practicality and estimation accuracy. It is demonstrated for the first time that a solution which is based on the measurement of only two variables, the amplitude of the fundamental frequency of the switching waveform and input current, can achieve state-of-the-art induced voltage estimation accuracy. These two variables, which can be obtained using simple cost-effective analogue circuitry, are used in a Gaussian process to generate a regression model. This is used to estimate induced voltages at any angle in an approximate magnitude range of 0–20 V with a normalized root-mean-square error of 1% for the real part and 1.5% for the imaginary part. This corresponds to detecting a plastic container with 1 kg of sal
Arteaga Saenz J, Pucci N, Lan L, et al., 2021, Load characterisation in high frequency IPT systems using Class EF switching waveforms, IEEE Transactions on Power Electronics, Vol: 36, Pages: 11036-11044, ISSN: 0885-8993
This paper introduces a technique to calculate the induced voltage generated by coupled-receivers and foreign-objects on the transmit-coil in real-time. Changes in the position or electrical quantities of the receivers, and foreign-objects, alter the induced voltage on the transmit-coil, and with it the trajectory of the switching-waveforms of the inverter driving the transmit-coil. From the shape of these waveforms, information on the phase and amplitude of the induced voltage can be extracted, thus enabling the induced voltage on the primary to be estimated with a single, easy to access, voltage measurement, which is easier than estimating the induced voltage from measurements of coil current and total coil-voltage. We used a support-vector-machine(SVM) to perform regression analysis on the drain-voltage data. The experimental setup uses a 100W, 13.56MHz Class-EF inverter, and the model was generated from a large number of samples of the drain-voltage waveforms operating at different known loads. These were generated from our in house HF-IPT test-load, which uses a Class-EF synchronous rectifier. The results allow the induced voltage on the transmit-coil to be estimated in real time from the drain-voltage waveform alone, with a normalised root-mean-square error of 1.1% for the real part~(reflected resistance) and 1.2% for the imaginary part~(reflected reactance).
Kim J, Clerckx B, Mitcheson PD, 2020, Signal and system design for wireless power transfer: prototype, experiment and validation, IEEE Transactions on Wireless Communications, Vol: 19, Pages: 7453-7469, ISSN: 1536-1276
A new line of research on communications and signals design for Wireless Power Transfer (WPT) has recently emerged in the communication literature. Promising signal strategies to maximize the power transfer efficiency of WPT rely on (energy) beamforming, waveform, modulation and transmit diversity, and a combination thereof. To a great extent, the study of those strategies has so far been limited to theoretical performance analysis. In this paper, we study the real over-the-air performance of all the aforementioned signal strategies for WPT. To that end, we have designed, prototyped and experimented an innovative radiative WPT architecture based on Software-Defined Radio (SDR) that can operate in open-loop and closed-loop (with channel acquisition at the transmitter) modes. The prototype consists of three important blocks, namely the channel estimator, the signal generator, and the energy harvester. The experiments have been conducted in a variety of deployments, including frequency flat and frequency selective channels, under static and mobility conditions. Experiments highlight that a channel-adaptive WPT architecture based on joint beamforming and waveform design offers significant performance improvements in harvested DC power over conventional single-antenna/multi-antenna continuous wave systems. The experimental results fully validate the observations predicted from the theoretical signal designs and confirm the crucial and beneficial role played by the energy harvester nonlinearity.
Arteaga Saenz J, Aldhaher S, Kkelis G, et al., 2019, Dynamic capabilities of multi-MHz inductive power transfer systems demonstrated with batteryless drones, IEEE Transactions on Power Electronics, Vol: 34, Pages: 5093-5104, ISSN: 0885-8993
This paper presents the design of a multi-MHz inductive power transfer (IPT) system showcasing lightweight and energy-efficient solutions for non-radiative wireless power transfer. A proof of concept is developed by powering a drone without a battery that can hover freely in proximity to an IPT transmitter. The most challenging aspect, addressed here for the first time, is the complete system level design to provide uninterrupted power-flow efficiently while allowing for variable power demand and highly variable coupling factor. The proposed solution includes the design of lightweight air-core coils that can achieve sufficient coupling without degrading the aerodynamics of the drone, and designing newly-developed resonant power converters at both ends of the system. At the transmittingend, a load-independent Class EF inverter, which can drive a transmitting-coil with constant current amplitude and achieves zero-voltage switching (ZVS) for the entire range of operation, was developed; and at the receiving-end, a hybrid Class E rectifier, which allows tuning for large changes in coupling and power demand, was used. For the demo, the range of motion of the drone was limited by a 7.5 cm nylon string tether, connected between the centre of the transmitting-coil and the bottom of the drone. The design of the IPT system, including all the power conversion stages and the IPT link, is explained in detail. The results on performance and specific practical considerations required for the physical implementation are provided. An average end-to-end efficiency of 60% was achieved for a coupling range of 23% to 5.8%. Relevant simulations concerning human exposure to electromagnetic fields are also included to assure that the demo is safe according to the relevant guidelines. This paper is accompanied by a video featuring the proposed IPT system.
Arteaga Saenz JM, Aldhaher S, Yates DC, et al., 2019, A multi-MHz wireless power transfer system with mains power factor correction circuitry on the receiver, 34th Annual IEEE Applied Power Electronics Conference and Exposition (APEC), Publisher: IEEE, Pages: 683-688, ISSN: 1048-2334
This paper proposes the implementation of a new system topology for multi-MHz inductive power transfer (IPT) systems, which achieves unity power factor when fed from a mains power supply without traditional active circuitry in the front-end as a mains interface. Experiments were performed using an IPT-link which consists of two 20 cm two-turn air-core printed-circuit-board (pcb) coils separated by an air-gap of 13 cm. At the transmit side, a push-pull load-independent Class EF inverter fed from a rectified 60 Hz power supply with no bulk capacitor was designed to drive the transmit coil at 13.56 MHz. This inverter, which has two choke inductors between the voltage source and the two switches, similar to that of an interleaved boost converter, is suitable to be fed directly from a rectified mains source because it tolerates large changes on the input voltage. The IPT rectifier in the experiments was built using a dual current-driven Class D-based topology which allows for higher output voltage when the induced electromotive force (emf) on the receive coil is low. The final power conversion stage on the receive side is a power factor correction (PFC) boost converter that regulates the output voltage and shapes the current waveform at the input of the system. This stage is the only part of the system with closed-loop control. The end-to-end efficiency was measured at 73.3% with 99.2% power factor, when powering a load of 150 W.
Lawson J, Yates DC, Mitcheson PD, 2019, High Q Coil Measurement for Inductive Power Transfer, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol: 67, Pages: 1962-1973, ISSN: 0018-9480
Arteaga Saenz J, Lan L, Aldhaher S, et al., 2019, A multi-MHz IPT-link developed for load characterisation at highly variable coupling factor, Wireless Power Transfer Conference, Pages: 1-4
This paper presents the development and characterisation of an inductive link to assess and compare inductive power transfer (IPT) systems that operate at 6.78 or 13.56 MHz. First, the properties of two equal air-core coils were obtained from simulations and corroborated experimentally. Then, the coupling factor between the coils was calculated in function of separation and misalignment. A receiving-end circuit, comprised of a capacitance and a resistive load, was also characterised in order to reflect different loads to the transmitter at different tunings and couplings, and therefore represent the effects produced by changes in coupling and variations in the rectifier's input impedance. The link was tested, firstly using a Class E inverter and then a load-independent Class EF inverter, both at power levels lower than 200 W. The reflected load was changed by altering coupling, and the tuning capacitance. A comparison between these inverter topologies handling highly reactive loads is shown here for the first time.
Kim J, Clerckx B, Mitcheson PD, 2019, Experimental Analysis of Harvested Energy and Throughput Trade-off in a Realistic SWIPT System, 2019 IEEE MTT-S WIRELESS POWER TRANSFER CONFERENCE (WPTC) / IEEE PELS WORKSHOP ON EMERGING TECHNOLOGIES: WIRELESS POWER (WOW) / WIRELESS POWER WEEK (WPW 2019), Pages: 1-5, ISSN: 2474-0225
Kwan CH, Yates DC, Mitcheson PD, 2019, Reducing human body heating and temperature rises due to inductively-powered implantable medical devices, 18th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications, Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
Aldhaher S, Yates D, Mitcheson P, 2018, Load-independent class E/EF inverters and rectifiers for MHz-switching applications, IEEE Transactions on Power Electronics, Vol: 33, Pages: 8270-8287, ISSN: 0885-8993
This paper presents a unified framework for the modeling, analysis, and design of load-independent Class E and Class EF inverters and rectifiers. These circuits are able to maintain zero-voltage switching and, hence, high efficiency for a wide load range without requiring tuning or use of a feedback loop, and to simultaneously achieve a constant amplitude ac voltage or current in inversion and a constant dc output voltage or current in rectification. As switching frequencies are gradually stepping into the megahertz (MHz) region with the use of wide-bandgap (WBG) devices such as GaN and SiC, switching loss, implementing fast control loops, and current sensing become a challenge, which load-independent operation is able to address, thus allowing exploitation of the high-frequency capability of WBG devices. The traditional Class E and EF topologies are first presented, and the conditions for load-independent operation are derived mathematically; then, a thorough analytical characterization of the circuit performance is carried out in terms of voltage and current stresses and the power-output capability. From this, design contours and tables are presented to enable the rapid implementation of these converters given particular power and load requirements. Three different design examples are used to showcase the capability of these converters in typical MHz power conversion applications using the design equations and methods presented in this paper. The design examples are chosen toward enabling efficient and high-power-density MHz converters for wireless power transfer (WPT) applications and dc/dc conversion. Specifically, a 150-W 13.56-MHz Class EF inverter for WPT, a 150-W 10-MHz miniature Class E boost converter, and a lightweight wirelessly powered drone using a 20-W 13.56-MHz Class E synchronous rectifier have been designed and are presented here.
Lan L, Ting NM, Aldhaher S, et al., 2018, Foreign Object Detection for Wireless Power Transfer, 2nd URSI Atlantic Radio Science Meeting (AT-RASC), Publisher: IEEE
This paper presents foreign object detection (FOD) methods for MHz wireless power transfer (WPT) systems. Unlike current FOD implementations, the presented methods can operate without requiring a feedback loop from the wireless power receiver to the transmitter. This allows complete decoupling of the transmitter and receiver and therefore reduces the design complexity and cost of the system. The developed FOD methods were implemented on a 13.56 MHz WPT and experimental results are presented showing successful detection of a wide range of objects regardless of the loading condition of the system.
This paper proposes solutions for an IPT system to operate efficiently when large changes in coupling take place. To achieve high power-efficiency independent of coupling, we utilise inherent regulation properties of resonant converters to avoid losing soft switching for any coupling value, and present the optimal load to the IPT-link at the maximum energy-throughput coupling. A probability-based model is introduced to assess and optimise the IPT system by analysing coupling as a distribution in time, which depends on the dynamic behaviour of the wireless charging system. The proposed circuits are a Class D rectifier with a resistance compression network (RCN) in the receiving-end and a load-independent Class EF inverter in the transmitting-end. Experiments were performed at 6.78 and 13.56 MHz verifying high efficiency for dynamic coupling and variable load resistance. End-to-end efficiencies of up to 88% are achieved at a coil separation larger than one coil-radius for a system capable of supplying 150 W to the load, and the energy-efficiency was measured at 80% when performing a uniformly-distributed linear-misalignment of 0-12.5 cm, corresponding to a receiver moving at constant velocity over a transmitter without power throughput control.
Arteaga Saenz JM, Kkelis G, Aldhaher S, et al., 2018, Probability-based optimisation for a multi-MHz IPT system with variable coupling, IEEE PELS Workshop on Emerging Technologies - Wireless Power Transfer (Wow), Publisher: IEEE
This paper presents the analysis and design of a dynamic inductive power transfer (IPT) system, in which coupling is treated as a stochastic variable and is therefore modelled as a probability distribution. The purpose of this formulation is to optimise the tuning of the inverter and the rectifier to the coupling value that achieves the highest charging energy-efficiency when operating at a broad range of coupling. The analysis is supported by a case study in which two rectifier designs, using the hybrid Class E topology, are tuned at different coupling values in order to verify which version achieves the highest charging efficiency. The load in the experiments is a wirelessly powered drone without a battery hovering randomly over the charging pad, and the range of motion is set by a nylon string tether. The experiments show lower energy consumption when the rectifier is tuned to present the optimal load of the link at the coupling value with the highest probability, as opposed to the first, which was designed to present the optimal load of the link at minimum coupling.
Mitcheson PD, Kkelis G, Aldhaher S, et al., 2018, Power Electronics for Wireless Power Delivery in Synthetic Sensor Networks, 17th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
Gadoue S, Chen K-W, Mitcheson P, et al., 2018, Electrochemical Impedance Spectroscopy State of Charge Measurement for Batteries using Power Converter Modulation, 9th International Renewable Energy Congress (IREC), Publisher: IEEE, ISSN: 2378-3435
Aldhaher S, Mitcheson PD, 2018, Sate-Space Modelling and Design of a 10MHz 180W Class E DC/DC Converter using WBG Devices, 33nd Annual IEEE Applied Power Electronics Conference and Exposition (APEC), Publisher: IEEE, Pages: 2918-2921, ISSN: 1048-2334
Ouda MHI, Mitcheson P, Clerckx B, 2018, Optimal Operation of Multi-Tone Waveforms inLow RF-Power Receivers, IEEE MTT-S Wireless Power Transfer Conference
Aldhaher S, Yates DC, Mitcheson PD, 2018, 13.56MHz 50W Load-Independent Synchronous Class E Rectifier using GaN devices for Space-Constrained Applications, IEEE Wireless Power Transfer Conference (WPTC), Publisher: IEEE, ISSN: 2474-0225
Mitcheson PD, Boyle D, Kkelis G, et al., 2017, Energy-Autonomous Sensing Systems Using Drones, 16th IEEE SENSORS CONFERENCE, Publisher: IEEE, Pages: 648-650, ISSN: 1930-0395
This paper describes the system concept and initial results for end-to-end energy-autonomous sensor systems using unmanned aerial vehicles (drones) as agents for power delivery to and data gathering from sensing devices. Such systems may be particularly useful for delay tolerant monitoring scenarios, where sensing devices may be deployed in remote, harsh conditions, often with sparse connectivity, long life and high reliability requirements. This paper discusses the latest advances in wireless power delivery that makes this it possible to fly wireless power delivery systems on drones that have little payload capability.
Pacini A, Costanzo A, Aldhaher S, et al., 2017, Load- and Position-Independent Moving MHz WPT System Based on GaN-Distributed Current Sources, IEEE Transactions on Microwave Theory and Techniques, Vol: 65, Pages: 5367-5376, ISSN: 0018-9480
This paper describes the modeling, analysis, and design of a complete (dc-to-dc) inductive wireless power transfer (WPT) system for industrial moving applications. The system operates at 6.78 MHz and delivers up to 150 W to a load moving along a linear path, providing a quasi-constant dc output voltage and maintaining a zero voltage switching operation, regardless of position and load, without any retuning or feedback. The inductive link consists of an array of stationary transmitting coils and a moving receiving coil whose length is optimized to achieve a constant coupling coefficient along the path. Each Tx coil is individually driven by a constant amplitude and phase sinusoidal current that is generated from a GaN-based coupled load-independent Class EF inverter. Two adjacent transmitters are activated at a given time depending on the receiver’s position; this effectively creates a virtual series connection between the two transmitting coils. The Rx coil is connected to a passive Class E rectifier that is designed to maintain a constant dc output voltage independent of its load and position. Extensive experimental results are presented to show the performance over different loading conditions and positions. A peak dc-to-dc efficiency of 80% is achieved at 100 W of dc output power and a dc output voltage variation of less than 5% is measured over a load range from 30 to 500 Ω . The work in this paper is foreseen as a design solution for a high-efficient, maintenance-free, and reliable WPT system for powering sliders and mass movers in industrial automation plants.
Douthwaite M, Koutsos E, Yates DC, et al., 2017, A thermally powered ISFET array for on-body pH measurement, IEEE Transactions on Biomedical Circuits and Systems, Vol: 11, Pages: 1324-1334, ISSN: 1932-4545
Recent advances in electronics and electrochemical sensors have led to an emerging class of next generation wearables, detecting analytes in biofluids such as perspiration. Most of these devices utilize ion-selective electrodes (ISEs) as a detection method; however, ion-sensitive field-effect transistors (ISFETs) offer a solution with improved integration and a low power consumption. This work presents a wearable, thermoelectrically powered system composed of an application-specific integrated circuit (ASIC), two commercial power management integrated circuits and a network of commercial thermoelectric generators (TEGs). The ASIC is fabricated in 0.35 μm CMOS and contains an ISFET array designed to read pH as a current, a processing module which averages the signal to reduce noise and encodes it into a frequency, and a transmitter. The output frequency has a measured sensitivity of 6 to 8 kHz/pH for a pH range of 7-5. It is shown that the sensing array and processing module has a power consumption 6 μW and, therefore, can be entirely powered by body heat using a TEG. Array averaging is shown to reduce noise at these low power levels to 104 μV (input referred integrated noise), reducing the minimum detectable limit of the ASIC to 0.008 pH units. The work forms the foundation and proves the feasibility of battery-less, on-body electrochemical for perspiration analysis in sports science and healthcare applications.
Douthwaite M, Koutsos E, Yates DC, et al., 2017, A Thermally Powered ISFET Array for On-Body pH Measurement., IEEE Trans. Biomed. Circuits and Systems, Vol: 11, Pages: 1324-1334
Lawson J, 2017, High frequency electromagnetic links for wireless power transfer
This thesis investigates inductive links used in wireless power transfer systems. Inductive power transfer can be used as a power delivery method for a variety of portable devices, from medical implants to electric vehicles and is gaining increased interest. The focus is on high quality factor coils and MHz operation, where accurate measurements are difficult to achieve. Fast models of all pertinent aspects of inductive power transfer systems for constant cross section coils are developed. These models are used to optimise a new coil winding pattern that aims to increase efficiency in volume constrained scenarios. Measurement systems are developed to measure coil Q factors in excess of 1,000. The prototype measurement systems are verified against models of that system, as well as finite element simulations of the coil under test. Shielding of inductive power transfer systems is then investigated. A structure typically used at GHz frequencies, the artificial magnetic conductor, is miniaturised as an alternative to conventional ferrite backed ground plane shielding. Finite element simulation shows this structure significantly improves link efficiency. The artificial magnetic conductor prototype does not result in a gain in efficiency expected, however it does display the properties expected of an artificial magnetic conductor, including increased coupling factor. Finally, an unconventional inductive power transfer system is presented where transmitter and receiver are up to 6m away from each other and of radically different size. This system provides mW level power to remote devices in a room, for example thermostats or e-ink displays. Conventional approaches to design do not consider the distortion of the magnetic field caused by metallic objects in the room. It was found that treating the system as a decoupled receiver and transmitter provides a better prediction of received power in real world environments.
Kkelis G, Yates DC, Mitcheson PD, 2017, Class-E half-wave zero dv/dt rectifiers for inductive power transfer, IEEE Transactions on Power Electronics, Vol: 32, Pages: 8322-8337, ISSN: 0885-8993
This paper analyses and compares candidate zero dv/dt half-wave Class-E rectifier topologies for integration into multi-MHz inductive power transfer (IPT) systems. Furthermore, a hybrid Class-E topology comprising advantageous properties from all existing Class-E half-wave zero dv/dt rectifiers is analysed for the first time. From the analysis, it is shown that the hybrid Class-E rectifier provides an extra degree of design freedom which enables optimal IPT operation over a wider range of operating conditions. Furthermore, it is shown that by designing both the hybrid and the current driven rectifiers to operate below resonance provides a low deviation input reactance and inherent output voltage regulation with duty cycle allowing efficient IPT operation over wider dc load range than would otherwise be achieved. A set of case studies demonstrated the following performances: 1) For a constant dc load resistance, a receiving end efficiency of 95% was achieved when utilising the hybrid rectifier, with a tolerance in required input resistance of 2.4% over the tested output power range (50W to 200W). 2) For a variable dc load in the range of 100% to 10%, the hybrid and current driven rectifiers presented an input reactance deviation less than 2% of the impedance of the magnetising inductance of the inductive link respectively and receiving end efficiencies greater than 90%. 3) For a constant current in the receiving coil, both the hybrid and the current driven rectifier achieve inherent output voltage regulation in the order of 3% and 8% of the nominal value respectively, for a variable dc load range from 100% to 10%.
Pacini A, Costanzo A, Aldhaher S, et al., 2017, Design of a Position-Independent End-to-End Inductive WPT link for Industrial Dynamic Systems, IEEE-Microwave-Theory-and-Techniques-Society International Microwave Symposium (IMS) / Session on Women in Microwaves (WIM), Publisher: IEEE, Pages: 1049-1052, ISSN: 0149-645X
Allmen L, Bailleul G, Becker T, et al., 2017, Aircraft strain WSN powered by heat storage harvesting, IEEE Transactions on Industrial Electronics, Vol: 64, Pages: 7284-7292, ISSN: 0278-0046
The combination of ultra-low-power wireless communications and energy harvesting enables the realization of autonomous wireless sensor networks. Such networks can be usefully applied in commercial aircraft where wireless sensing solutions contribute to weight reduction and increased ease of installation and maintenance. This paper presents, for the first time, a complete energy-autonomous wireless strain monitoring system for aircraft. The system is based on a multimode wireless time-division multiple access (TDMA) medium access control (MAC) protocol that supports automatic configuration and a time-stamping accuracy better than 1 ms. The energy supply depends solely on an innovative thermoelectric energy harvester, which takes advantage of the changes in environmental temperature during takeoff and landing. The system was successfully integrated and passed the functional and flight-clearance tests that qualify it for use in a flight-test installation.
Kim J, Clerckx B, Mitcheson PD, 2017, Prototyping and Experimentation of a Closed-Loop Wireless Power Transmission with Channel Acquisition and Waveform Optimization, IEEE Wireless Power Transfer Conference (WPTC), Publisher: IEEE, ISSN: 2474-0225
Kkelis G, Aldhaher S, Arteaga JM, et al., 2017, Hybrid Class-E Synchronous Rectifier for Wireless Powering of Quadcopters, IEEE Wireless Power Transfer Conference (WPTC), Publisher: IEEE, ISSN: 2474-0225
Aldhaher S, Mitcheson PD, Arteaga JM, et al., 2017, Light-Weight Wireless Power Transfer for Mid-Air Charging of Drones, 11th European Conference on Antennas and Propagation (EUCAP), Publisher: IEEE, Pages: 336-340, ISSN: 2164-3342
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