Automatic Positioning System for Inductive Wireless Charging Devices and Application to Mobile Robot

Inductive power transfer (IPT) remains one of the most common ways to achieve wireless power transfer (WPT), operating on the same electromagnetic principle as electrical transformers but with an air core. IPT has recently been implemented in wireless charging of consumer products such as smartphones and electric vehicles. However, one major challenge with using IPT remains ensuring precise alignment between the transmitting and receiving coils so that maximum power transfer can take place. In literature, much of the focus is on improving the electrical circuits or IPT coil geometries to allow a greater transmission range. Nevertheless, most IPT products today rely on precise alignment for efficient power transfer. In this thesis, the use of sensing coils to detect and correct lateral misalignments in a typical IPT system is modeled and tested. The sensing coils exploit magnetic-field symmetry to give a nonlinear measure of misalignment direction and magnitude. To test this idea, three experiments are performed: 1) measure the voltage of experimental sensing coils for various lateral misalignment distances, 2) implement closed-loop control and measure performance for an experimental two-dimensional (2D) automatic IPT alignment mechanism, and 3) test automatic IPT alignment on a plausible mobile robot wireless charging scenario. The experimental sensing coils give a misalignment sensing resolution of 1 mm or less in two lateral directions, allowing automatic alignment control in real time with a maximum lateral positioning error of less than √2 mm. This precise alignment allows for efficient power transfer to occur. When implemented on the mobile robot platform, the automatic positioning system gives similar results, allowing the robot to position itself above a wireless charger precisely—a task the mobile robot cannot accomplish using its navigation camera alone. The results of this experiment give confidence that similar sensing coils can be used to reduce lateral misalignments in scaled IPT systems, such as electric-vehicle wireless chargers

Double Resonant High-Frequency Converters for Wireless Power Transfer

This thesis describes novel techniques and developments in the design and implementation of a low power radio frequency (40kHz to 1MHz) wireless power transfer (WPT) system, with an application in the wireless charging of autonomous drones without physical connection to its on-board Battery Management System (BMS). The WPT system is developed around a matrix converter exploiting the benefits such as a small footprint (DC-link free), high efficiency and high power density. The overall WPT system topology discussed in this thesis is based on the current state-of-the-art found in literature, but enhancements are made through novel methods to further improve the converter’s stability, reduce control complexity and improve the wireless power efficiency. In this work, each part of the system is analysed and novel techniques are proposed to achieve improvements. The WPT system design methodology presented in this thesis commences with the use of a conventional full-bridge converter. For cost-efficiency and to improve the converters stability, a novel gate drive circuit is presented which provides self-generated negative bias such that a bipolar MOSFET drive can be driven without an additional voltage source or magnetic component. The switching control sequences for both a full-bridge and single phase to single phase matrix converter are analysed which show that the switching of a matrix converter can be considered to be the same as a full-bridge converter under certain conditions. A middleware is then presented that reduces the complexity of the control required for a matrix converter and enables control by a conventional full-bridge controller (i.e. linear controller or microcontroller). A novel technique that can maximise and maintain in real-time the WPT efficiency is presented using a maximum efficiency point tracking approach. A detailed study of potential issues that may affect the implementation of this novel approach are presented and new solutions are proposed. A novel wireless pseudo-synchronous sampling method is presented and implemented on a prototype system to realise the maximum efficiency point tracking approach. Finally, a new hybrid wireless phase-locked loop is presented and implemented to minimise the bandwidth requirements of the maximum efficiency point tracking approach. The performance and methods for implementation of the novel concepts introduced in this thesis are demonstrated through a number of prototypes that were built. These include a matrix converter and two full WPT systems with operating frequencies ranging from sub-megahertz to megahertz level. Moreover, the final prototype is applied to the charging of a quadcopter battery pack to successfully charge the pack wirelessly whilst actively balancing the cells. Hence, fast battery charging and cell balancing, which conventionally requires battery removal, can be achieved without re-balance the weight of the UAV

Power Management ICs for Internet of Things, Energy Harvesting and Biomedical Devices

This dissertation focuses on the power management unit (PMU) and integrated circuits (ICs) for the internet of things (IoT), energy harvesting and biomedical devices. Three monolithic power harvesting methods are studied for different challenges of smart nodes of IoT networks. Firstly, we propose that an impedance tuning approach is implemented with a capacitor value modulation to eliminate the quiescent power consumption. Secondly, we develop a hill-climbing MPPT mechanism that reuses and processes the information of the hysteresis controller in the time-domain and is free of power hungry analog circuits. Furthermore, the typical power-performance tradeoff of the hysteresis controller is solved by a self-triggered one-shot mechanism. Thus, the output regulation achieves high-performance and yet low-power operations as low as 12 µW. Thirdly, we introduce a reconfigurable charge pump to provide the hybrid conversion ratios (CRs) as 1⅓× up to 8× for minimizing the charge redistribution loss. The reconfigurable feature also dynamically tunes to maximum power point tracking (MPPT) with the frequency modulation, resulting in a two-dimensional MPPT. Therefore, the voltage conversion efficiency (VCE) and the power conversion efficiency (PCE) are enhanced and flattened across a wide harvesting range as 0.45 to 3 V. In a conclusion, we successfully develop an energy harvesting method for the IoT smart nodes with lower cost, smaller size, higher conversion efficiency, and better applicability. For the biomedical devices, this dissertation presents a novel cost-effective automatic resonance tracking method with maximum power transfer (MPT) for piezoelectric transducers (PT). The proposed tracking method is based on a band-pass filter (BPF) oscillator, exploiting the PT’s intrinsic resonance point through a sensing bridge. It guarantees automatic resonance tracking and maximum electrical power converted into mechanical motion regardless of process variations and environmental interferences. Thus, the proposed BPF oscillator-based scheme was designed for an ultrasonic vessel sealing and dissecting (UVSD) system. The sealing and dissecting functions were verified experimentally in chicken tissue and glycerin. Furthermore, a combined sensing scheme circuit allows multiple surgical tissue debulking, vessel sealer and dissector (VSD) technologies to operate from the same sensing scheme board. Its advantage is that a single driver controller could be used for both systems simplifying the complexity and design cost. In a conclusion, we successfully develop an ultrasonic scalpel to replace the other electrosurgical counterparts and the conventional scalpels with lower cost and better functionality

Underwater Communications based on Resonant Inductive Links

Em anos mais recentes, os veículos não tripulados têm sofrido um avanço considerável no seu desenvolvimento. Devido ao subsequente aumento de interesse na exploração do oceano, em especial zonas de condições extremas cujo acesso está impossibilitado. Em concreto, nas aplicações subaquáticas, existem problemas substanciais relativos ao carregamento de forma wireless dos aparelhos, mais especificamente, à monitorização deste processo, assim como, na transferência dos dados recolhidos. Esta dissertação apresenta uma solução para o controlo de parâmetros associados ao carregamento wireless, reaproveitando o acoplamento indutivo ressonante para, além da transferência de potência já implementada, transmitir dados. Denote-se que o estudo e implementação foram desenvolvidos num sistema com um comutador de alta tensão, optimizado para uma resistência de carga igual a 12.5 Ohm, uma frequência de ressonância de 240 kHz para uma transferência de potência na ordem dos 80 W com uma eficiência máxima no acoplamento de 94%. O trabalho desenvolvido explora um patamar substancial de corrente disponível, desde 0.5 A a 2.5 A com um conjunto de resistências entre 1 Ohm a 11 Ohm. Com estes valores é possível determinar diferentes estados que, por sua vez, permitem uma comunicação wireless com um grande alcance dinâmico. A eficiência geral do acoplamento não sofre uma grande alteração para os diferentes estados necessários para o envio de informação. Sabendo que o teor de sal afeta diretamente o acoplamento e, consequentemente, os níveis de corrente do sistema, e ainda que os valores de salinidade do mar variam de região para região, é possível regular esta variação mudando o valor da resistência responsável pela modulação da carga, reforçando a modularidade do sistema. Este desenvolvimento apresenta uma solução simples e viável, apresentando-se como uma forte alternativa ao uso de circuitos externos adicionais.During more recent years there has been a considerable advancement in unmanned vehicles, more so in autonomous underwater vehicles, following the increasing interest in exploring unreachable parts of the ocean. Underwater autonomous work poses substantial obstacles when it comes to wirelessly charging the devices and most importantly to the monitoring of such operation, as well as the transfer of the data gathered. This thesis presents a solution for overseeing the parameters that come with the wireless charging of a system, repurposing the resonant inductive link to transmit bits of data in addition to the power transfer already in place. Furthermore, the work was developed on system designed with a high-voltage switching power driver, optimized for load resistance equal to 12.5 Ohm, having a resonance frequency of 240 kHz for a power transfer in the order of 80 W with a link efficiency up to 94%. The present work explores the substantial threshold of current available at the primary coil, from 0.5 A to 2.5 A with a variation of resistance from 1 Ohm to 11 Ohm seen at the secondary coil. This allows for a detection of different states which provide a wireless communication with a wide dynamic range. The overall efficiency of the link is not greatly affected by the different states necessary to transmit information. Knowing that the salinity value of the sea differs from region to region and in turn, both the levels of current and threshold are affected, it is possible to regulate the value of the resistance responsible for the load modulation to atone such difference, which makes for a system with a high level of modularity. This presents a simple and viable solution that is a clear alternative to the need of additional aftermarket circuits to monitor and assist the charging of devices underwater

The Design, Simulation and Implementation of Inductively Powered Sensor Systems: New Applications, Design Methodologies and a Unique Coil Topology

Three case studies have been presented for new applications of inductive energy and data transfer (iEDT)-sensor systems. The first application is a condensation detection system for the windshield of an automobile. The developed iEDT-sensor prototype provides a low cost alternative for wireless dew point measurements which involves no wired connections and so can be easily replaced when the windshield is damaged. The second application involves an iEDT-sensor prototype developed wirelessly query the flow rate in a pipe. For the third application, measurement results were performed for a wireless implant system. The application involves a Wireless Sensor (WS), implanted under the dura mater, which was to be used for long term cortical measurement and stimulation with a very high resolution. A suite of tools provided two independent methods of simulating the coil self resonance, quality factor, coupling and self inductance as well as the overall system efficiency. The inductance and coupling were verified within 10% error compared to measurement results and the resonance, quality factor and efficiency to within 30% error. An accurate simulation of the efficiency was predicated by an accurate simulation of the quality factor at the operating frequency. A series of scripts were also developed to automate the construction of the coil geometry, the simulation control and the compilation of the simulation results. These scripts offered the ability to quickly analyze variations in implementation and their affect on the system parameters and efficiency. For the third application, a new and unique topology for the iEDT-sensor system was presented which resulted in three redundant and independent implant coils each capable of simultaneously delivering power to the sensor electronics. This phased array topology has never before been examined for iEDT-systems as far as is known by the author. The new topology demonstrated a similar efficiency when compared to a single implant coil system of the same dimensions and a similar quality factor. Upon implantation, simulations demonstrated that the expected loss in efficiency should be limited to 10%. SAR-value simulations showed that the ISM frequencies at or below 13.56MHz would be in compliance with FCC regulations. The coupling and self inductance measurements for the phased array coil system were confirmed within 10% error compared to the simulations and the quality factor, self-resonance and efficiency were also shown to be accurate to within 20%. The simulated maximum efficiency of the phased array system was, however, substantially lower than the analytically calculated efficiency due to parasitic effects. The outlook for the work is as follows. The scripts should be expanded to include inductors with magnetic cores in order to allow for high power and low frequency applications as well as 3-D simulations in order to allow for more complex geometries. It should also be possible to increase the efficiency per unit area of the phased array coil system by minimizing the parasitic impedance thereby leading to an efficiency per unit area that is greater than that of a single coil system. The result would be a higher efficiency system, especially important for high power applications. This type of phased array coil approach could also be employed in the coil system of the Wireless Power Supply in order to create large areas which could efficiently supply mobile wireless devices with power

Wireless Sensors and Actuators for Structural Health Monitoring of Fiber Composite Materials

This work evaluates and investigates the wireless generation and detection of Lamb-waves on fiber-reinforced materials using surface applied or embedded piezo elements. The general target is to achieve wireless systems or sensor networks for Structural Health Monitoring (SHM), a type of Non-Destructive-Evaluation (NDE). In this sense, a fully wireless measurement system that achieves power transmission implementing inductive coils is reported. This system allows a reduction of total system weight as well as better integration in the structure. A great concern is the characteristics of the material, in which the system is integrated, because the properties can have a direct impact on the strength of the magnetic field. Carbon-Fiber-Reinforced-Polymer (CFRP) is known to behave as an electrical conductor, shielding radio waves with increasing worse effects at higher frequencies. Due to the need of high power and voltage, interest is raised to evaluate the operation of piezo as actuators at the lower frequency ranges. To this end, actuating occurs at the International Scientific and Medical (ISM) band of 125 kHz or low-frequency (LF) range. The feasibility of such system is evaluated extensively in this work. Direct excitation, is done by combining the actuator bonded to the surface or embedded in the material with an inductive LF coil and setting the circuit in resonance. A more controlled possibility, also explored, is the use of electronics to generate a Hanning-windowed-sine to excite the PWAS in a narrow spectrum. In this case, only wireless power is transmitted to the actuator node, and this lastly implements a Piezo-driver to independently excite Lamb-waves. Sensing and data transfer, on the other hand, is done using the high-frequency (HF) 13.56 MHz. The HF range covers the requirements of faster sampling rate and lower energy content. A re-tuning of the antenna coils is performed to obtain better transmission qualities when the system is implemented in CFRP. Several quasi-isotropic (QI) CFRP plates with sensor and actuator nodes were made to measure the quality of transmission and the necessary energy to stimulate the actuator-sensor system. In order to produce baselines, measurements are prepared from a healthy plate under specific temperature and humidity conditions. The signals are evaluated to verify the functionality in the presence of defects. The measurements demonstrate that it is possible to wirelessly generate Lamb-waves while early results show the feasibility to determine the presence of structural failure. For instance, progress has been achieved detecting the presence of a failure in the form of drilled holes introduced to the structure. This work shows a complete set of experimental results of different sensor/-actuator nodes

Master of Science

thesisFully integrated, implantable, and wireless neural interface systems typically re-quire a forward data link in addition to the telemetry link that transmits data from the chip. One popular way to create this forward data link is to amplitude modulate the magnetic fi eld of the inductive link that provides the device with wireless power. However, the limitations of these channels when loaded with a recti fier and amplitude modulated have not previously been characterized, and this lack of understanding caused previous versions of the Integrated Neural Interface (INI) to have forward data communication issues, which needed to be corrected for the next generation of the device, INIR8. This thesis first develops an analytical method of characterizing this sort of wireless channel. It then shows measurement data that verifies the validity of the model in the desired region of operation. The available bandwidth as determined by this analytical method, and confirmed by simulation, is insufficient for many applications. Therefore, the next subject of this thesis is to increase the data rate beyond what the bandwidth of the system can intrinsically support by using an equalization technique. This technique is shown to support very robust data recovery under a variety of operating conditions and to data rates much higher than otherwise possible. Another way to improve the reliability of data recovery is to develop a robust digital control system with error detection capabilities. This was done for INIR8, and works very reliably. The end result of this eff ort is a very robust forward data communication in INIR8, as well as a new analytical method for characterizing inductively coupled channels with certain loads and modulation techniques

A WIRELESS SENSOR SYSTEM WITH DIGITALLY CONTROLLED SIGNAL CONDITIONING CIRCUIT FOR FORCE MONITORING AT BONE FIXATION PLATES

Post-rehabilitation of orthopedic surgery is critical for bone fracture treatments. Current protocols are not based on quantitative assessments of the patient condition but they are conservative estimations mostly based on prior experience and physician’s opinions. While there are quantitative methods for assessing the recovery of orthopedic surgery, they are typically very expensive and provide only snapshots during the healing process. A standalone, reconfigurable, embedded wireless sensor system with digitally controlled signal conditioning system capable of providing continuous monitoring of bone healing is developed. Strain sensor measurements were validated against a commercial mechanical loading instrument for relevant loads that an animal (ovine) would experience during in vivo testing (up to 250 N). The loader was configured to apply a maximum force of 250 N to the bone fixation plate at a rate of 1000 N/min. Cyclic testing of the system showed optimal stability and no observable drift in the sensor. The sensor was also implemented in a rodent model for monitoring force loading at an internal bone fixation plate. The platform’s small, robust, and low power nature is usefulness for continuous wireless monitoring and actuation in many biomedical applications

Design and integration of a dynamic IPT system for automotive applications

Inductive power transmission (IPT) for electric vehicles (EVs) is a promising emergent technology that seems able to improve the electric mobility acceptance. In the last two decades many researchers have proved its feasibility and the possibility to use it to replace the common conductive systems for the charge of the on-board battery. Many efforts are currently aimed to extend the IPT technology towards its use for the charge during the vehicle motion. This application, commonly indicated as dynamic IPT, is aimed to overcome the limit represented by the long stops needed for the recharge introducing also the possibility of reducing the battery capacity installed on vehicle. An IPT system is essentially based on the resonance of two magnetically coupled inductors, the transmitter, placed on or under the ground, and the receiver, placed under the vehicle floor. The typical operating frequency range for the EVs application goes from 20 kHz to approximately 100 kHz. The coupling between the two inductors takes place through a large air-gap, usually about 10-30 cm. This thesis presents the results of the research activities aimed to the creation of a prototype for the dynamic IPT oriented to the private transport. Starting from an analysis of the state of the art and the current research projects on this domain, this work presents the development of a circuit model able to describe the electromagnetic phenomena at the base of the power transfer and the interface with the power electronics. This model provides the information at the base of the design and the implementation of a dedicated low cost-high effciency H-bridge converter for the supply of the transmitter side. A general architecture of the power electronics that manages the receiver side is proposed together with the additional protection circuits. A methodology for the integrated design of the magnetic structure is illustrated covering the aspects of the matching with the power electronics, the integration on an existing vehicle and the installation on the road infrastructure. A series of activities aimed to the implementation of a dedicated test site are presented and discussed. In particular, the activities related to the creation of the electrical infrastructure and the issues and methods for the embedding of the transmitters in the road pavement are presented. The final goal is the creation of a dedicated IPT charging line one hundred meters long. Finally, a methodology for the assessment of the human exposure is presented and applied to the developed solution