GaN-Based High Efficiency Transmitter for Multiple-Receiver Wireless Power Transfer

Wireless power transfer (WPT) has attracted great attention from industry and academia due to high charging flexibility. However, the efficiency of WPT is lower and the cost is higher than the wired power transfer approaches. Efforts including converter optimization, power delivery architecture improvement, and coils have been made to increase system efficiency.In this thesis, new power delivery architectures in the WPT of consumer electronics have been proposed to improve the overall system efficiency and increase the power density.First, a two-stage transmitter architecture is designed for a 100 W WPT system. After comparing with other topologies, the front-end ac-dc power factor correction (PFC) rectifier employs a totem-pole rectifier. A full bridge 6.78 MHz resonant inverter is designed for the subsequent stage. An impedance matching network provides constant transmitter coil current. The experimental results verify the high efficiency, high PF, and low total harmonic distortion (THD).Then, a single-stage transmitter is derived based on the verified two-stage structure. By integration of the PFC rectifier and full bridge inverter, two GaN FETs are saved and high efficiency is maintained. The integrated DCM operated PFC rectifier provides high PF and low THD. By adopting a control scheme, the transmitter coil current and power are regulated. A simple auxiliary circuit is employed to improve the light load efficiency. The experimental results verify the achievement of high efficiency.A closed-loop control scheme is implemented in the single-stage transmitter to supply multiple receivers simultaneously. With a controlled constant transmitter current, the system provides a smooth transition during dynamically load change. ZVS detection circuit is proposed to protect the transmitter from continuous hard switching operation. The control scheme is verified in the experiments.The multiple-reciever WPT system with the single-stage transmitter is investigated. The system operating range is discussed. The method of tracking optimum system efficiency is studied. The system control scheme and control procedure, targeting at providing a wide system operating range, robust operation and capability of tracking the optimized system efficiency, are proposed. Experiment results demonstrate the WPT system operation

Design of Power Receiving Units for 6.78MHz Wireless Power Transfer Systems

In the last decade, the wireless power transfer (WPT) technology has been a popular topic in power electronics research and increasingly adopted by consumers. The AirFuel WPT standard utilizes resonant coils to transfer energy at 6.78 MHz, introducing many benefits such as longer charging distance, multi-device charging, and high tolerance of the coil misalignment. However, variations in coil coupling due to the change in receiving coil positions alter the equivalent load reactance, degrading efficiency. In recent studies, active full-bridge rectifiers are employed on WPT receivers because of their superior efficiency, controllability, and ability to compensate for detuned WPT networks. In order to take advantage of those characteristics, the rectifier switching actions must be synchronized with the magnetic field. In the literature, existing solutions for synchronizing the active rectifier in WPT systems are mostly not reliable and bulky, which is not suitable for small receivers. Therefore, a frequency synchronous rectifier with compact on-board control is proposed in this thesis. The rectifier power stage is designed to deliver 40 W to the load while achieving full zero-voltage switching to minimize the loss. The inherent feedback from the power stage dynamics to the sensed signal is analyzed to design stable and robust synchronization control, even at a low power of 0.02 W. The control system is accomplished using commercial components, including a low-cost microcontroller, which eliminates the need for bulky control and external sensing hardware. This high power density design allows the receiver to be integrated into daily consumer electronics such as laptops and monitors. Finally, a wide-range and high v resolution control scheme of the rectifier input phase is proposed to enable the dynamic impedance matching capability, maintaining high system efficiency over wide loading conditions. In addition, to increase the WPT technology adoption to low-power consumer electronics, a small wireless receiver replacing conventional AA batteries is developed. This receiver can supply power to existing AA battery-powered devices while providing the benefit of WPT technologies to consumers

Design and Implementation of a Wireless Charging-Based Cardiac Monitoring System Focused on Temperature Reduction and Robust Power Transfer Efficiency

Wireless power transfer systems are increasingly used as a means of charging implantable medical devices. However, the heat or thermal radiation from the wireless power transfer system can be harmful to biological tissue. In this research, we designed and implemented a wireless power transfer system-based implantable medical device with low thermal radiation, achieving 44.5% coil-to-coil efficiency. To suppress thermal radiation from the transmitting coil during charging, we minimized the ESR value of the transmitting coil. To increase power transfer efficiency, a ferrite film was applied on the receiving part. Based on analyses, we fabricated a cardiac monitoring system with dimensions of 17 x 24 x 8 mm(3) and implanted it in a rat. We confirmed that the temperature of the wireless charging device increased by only 2 degrees C during the 70 min charging, which makes it safe enough to use as an implantable medical device charging system.11Ysciescopu

Wireless Power Transfer

Wireless power transfer techniques have been gaining researchers' and industry attention due to the increasing number of battery-powered devices, such as mobile computers, mobile phones, smart devices, intelligent sensors, mainly as a way to replace the standard cable charging, but also for powering battery-less equipment. The storage capacity of batteries is an extremely important element of how a device can be used. If we talk about battery-powered electronic equipment, the autonomy is one factor that may be essential in choosing a device or another, making the solution of remote powering very attractive. A distinction has to be made between the two forms of wireless power transmission, as seen in terms of how the transmitted energy is used at the receiving point: - Transmission of information or data, when it is essential for an amount of energy to reach the receiver to restore the transmitted information; - Transmission of electric energy in the form of electromagnetic field, when the energy transfer efficiency is essential, the power being used to energize the receiving equipment. The second form of energy transfer is the subject of this book

High-Performance Power Converters for Telecom and Datacenter Applications

Telecommunication systems and datacenters require compact isolated power converters that maintain high efficiencies across wide operating ranges. This thesis introduces high-efficiency high-power-density isolated dc-dc converters suitable for such applications. These converters are based on the impedance control network (ICN) resonant converter architecture, which enables high performance by achieving soft-switching across wide variations in operating conditions. First, an ICN-based telecom bus converter is developed. The design of this ICN converter is optimized using an enhanced augmented state-space analysis approach. A 1-MHz 550-W prototype of this ICN converter achieves a peak efficiency of 97.6%, maintains &gt;95.3% full-power efficiency across 2:1 ranges of input voltage and output voltage, and &gt;93.6% efficiency across a 10:1 range of output power. Next, an approach to reduce the size of this ICN converter is developed, in which the three inductors of the converter are combined into a single integrated magnetic structure utilizing two coupled windings. The integrated magnetic structure is designed and optimized using 3D finite element analysis. This results in a very high performance 550-W quarter-brick ICN converter prototype, which maintains efficiencies comparable to those described above, while achieving a much higher power density of 462 W/in3. The ICN converter architecture is then applied to a large step-down conversion application &ndash; a single-stage isolated 48V-to-1.8V point-of-load (PoL) converter for datacenters. Three generations of this PoL ICN converter are developed, progressively achieving higher efficiencies and reduced size through innovations in the design of magnetically integrated matching networks and transformers, and through the utilization of transformer and rectifier architectures suitable for providing large voltage step-down. The final 1-MHz 90-W PoL ICN converter prototype provides up to 33:1 voltage step-down while achieving a peak efficiency of 92.6% and a power density of 314 W/in3. This thesis also describes an improved approach to optimizing the design of high-efficiency high-gain matching networks, with applications in large-conversion-ratio resonant converters and in wireless power transfer (WPT) systems. Finally, a high-frequency inverter architecture building upon the concepts of the ICN is developed, which compensates for coupling variations in WPT systems while maintaining high power transfer and high efficiency.</p

Wireless Power Transfer System for Battery-Less Body Implantable Devices

Department of Electrical EngineeringAs the life expectancy is increased and the welfare is promoted, researches on the body implantable medical devices (BIMD) are actively being carried out, and products providing more various functions are being released. On the other hand, due to these various functions, the power consumption of the BIMD is also increased, so that the primary battery alone cannot provide sufficient power for the devices. The limited capacity and life time of batteries force patients to make an additional payment and suffering for the power supply of the BIMD. Wireless power transfer technology is the technology which has been making remarkable progress mainly in wireless charging for personal portable devices and electric vehicles. Convergence of wireless power transfer technology (WPT) and rechargeable battery can extend the life time of the BIMD and reduce the suffering and the cost for battery replacements. Furthermore, WPT enables the devices which do not need to operate consistently such as body implantable sensor devices to be used without batteries. In this dissertation, techniques to support WPT for BIMD are introduced and proposed. First, basic researches on magnetic coupled WPT are presented. The basics which are important factors to analyze power transmission are introduced. In addition, circuits that make up the WPT system are described. There are three common technical challenges in WPT. Those are efficiency degradation on coil geometry, voltage gain variation with coil geometry, and power losses in WPT. The common challenges are discussed in chapter II. Moreover, additional challenges which are arisen in WPT for BIMD and approaches to resolve the challenges are addressed in chapter II. Then, efficiency improvement techniques and control techniques in WPT are presented in chapter III. The presented techniques to improve efficiency are applied in coil parts and circuit parts. In coil parts, efficiency enhancement technique by geometric variation is proposed. In circuit parts, instantaneous power consuming technique for step-down converter is suggested. Li-ion battery charger is also discussed in chapter III. Additionally, the wireless controlled constant current / constant voltage charging mode and the proposed step charging method are described. After that, WPT system for BIMD is discussed one by one with the proposed techniques for each part in chapter IV. A load transformation is suggested to improve efficiency in weak coupling, and suppress voltage gain variation under coil displacement. Power conversion efficiency improvement techniques for rectifier and converter are also proposed. By using the proposed technique for the converter, we can remove the bootstrap capacitors, and reduce the overall size of power circuits. In conclusion, techniques in coil parts and circuit parts to handle challenges in WPT for BIMD are fully investigated in this thesis in addition to the efficiency improvement and control techniques in common WPT. All the techniques are verified through simulations or experiments. The approaches realized in the thesis can be applied to other applications employing the WPT.clos

Design of Power Management Integrated Circuits and High-Performance ADCs

A battery-powered system has widely expanded its applications to implantable medical devices (IMDs) and portable electronic devices. Since portable devices or IMDs operate in the energy-constrained environment, their low-power operations in combination with efficiently sourcing energy to them are key problems to extend device life. This research proposes novel circuit techniques for two essential functions of a power receiving unit (PRU) in the energy-constrained environment, which are power management and signal processing. The first part of this dissertation discusses power management integrated circuits for a PRU. From a power management perspective, the most critical two circuit blocks are a front-end rectifier and a battery charger. The front-end CMOS active rectifier converts transmitted AC power into DC power. High power conversion efficiency (PCE) is required to reduce power loss during the power transfer, and high voltage conversion ratio (VCR) is required for the rectifier to enable low-voltage operations. The proposed 13.56-MHz CMOS active rectifier presents low-power circuit techniques for comparators and controllers to reduce increasing power loss of an active diode with offset/delay calibration. It is implemented with 5-V devices of a 0.35 µm CMOS process to support high voltage. A peak PCE of 89.0%, a peak VCR of 90.1%, and a maximum output power of 126.7 mW are measured for 200Ω loading. The linear battery charger stores the converted DC power into a battery. Since even small power saving can be enough to run the low-power PRU, a battery charger with low IvQ is desirable. The presented battery charger is based on a single amplifier for regulation and the charging phase transition from the constant-current (CC) phase to the constant-voltage (CV) phase. The proposed unified amplifier is based on stacked differential pairs which share the bias current. Its current-steering property removes multiple amplifiers for regulation and the CC-CV transition, and achieves high unity-gain loop bandwidth for fast regulation. The charger with the maximum charging current of 25 mA is implemented in 0.35 µm CMOS. A peak charger efficiency of 94% and average charger efficiency of 88% are achieved with an 80-mAh Li-ion polymer battery. The second part of this dissertation focuses on analog-to-digital converters (ADCs). From a signal processing perspective, an ADC is one of the most important circuit blocks in the PRU. Hence, an energy-efficient ADC is essential in the energy-constrained environment. A pipelined successive approximation register (SAR) ADC has good energy efficiency in a design space of moderate-to-high speeds and resolutions. Process-Voltage-Temperature variations of a dynamic amplifier in the pipelined-SAR ADC is a key design issue. This research presents two dynamic amplifier architectures for temperature compensation. One is based on a voltage-to-time converter (VTC) and a time-to-voltage converter (TVC), and the other is based on a temperature-dependent common-mode detector. The former amplifier is adopted in a 13-bit 10-50 MS/s subranging pipelined-SAR ADC fabricated in 0.13-µm CMOS. The ADC can operate under the power supply voltage of 0.8-1.2 V. Figure-of-Merits (FoMs) of 4-11.3 fJ/conversion-step are achieved. The latter amplifier is also implemented in 0.13-µm CMOS, consuming 0.11 mW at 50 MS/s. Its measured gain variation is 2.1% across the temperature range of -20°C to 85 °C

Using Radio Frequency and Motion Sensing to Improve Camera Sensor Systems

Camera-based sensor systems have advanced significantly in recent years. This advancement is a combination of camera CMOS (complementary metal-oxide-semiconductor) hardware technology improvement and new computer vision (CV) algorithms that can better process the rich information captured. As the world becoming more connected and digitized through increased deployment of various sensors, cameras have become a cost-effective solution with the advantages of small sensor size, intuitive sensing results, rich visual information, and neural network-friendly. The increased deployment and advantages of camera-based sensor systems have fueled applications such as surveillance, object detection, person re-identification, scene reconstruction, visual tracking, pose estimation, and localization. However, camera-based sensor systems have fundamental limitations such as extreme power consumption, privacy-intrusive, and inability to see-through obstacles and other non-ideal visual conditions such as darkness, smoke, and fog. In this dissertation, we aim to improve the capability and performance of camera-based sensor systems by utilizing additional sensing modalities such as commodity WiFi and mmWave (millimeter wave) radios, and ultra-low-power and low-cost sensors such as inertial measurement units (IMU). In particular, we set out to study three problems: (1) power and storage consumption of continuous-vision wearable cameras, (2) human presence detection, localization, and re-identification in both indoor and outdoor spaces, and (3) augmenting the sensing capability of camera-based systems in non-ideal situations. We propose to use an ultra-low-power, low-cost IMU sensor, along with readily available camera information, to solve the first problem. WiFi devices will be utilized in the second problem, where our goal is to reduce the hardware deployment cost and leverage existing WiFi infrastructure as much as possible. Finally, we will use a low-cost, off-the-shelf mmWave radar to extend the sensing capability of a camera in non-ideal visual sensing situations.Doctor of Philosoph