Harvesting energy from ultra-low-power vibration energy sources typically employs a rectifier circuit as the first power conditioning stage. The Schottky diode has a 0.15 V - 0.2 V threshold voltage and can not extract energy efficiently at low voltage. Other technologies such as MOSFET bridge or active diode are designed to minimize the voltage drop to reduce the conduction loss. However, these designs require either additional power supplies to operate comparators or have a larger threshold turn-on voltage than Schottky. Therefore, most rectifiers have an unresponsive or significant low-efficiency zone when the input power is low. This dissertation will elaborate on a backward diode based self-powered micro-circuit diode that will operate in the extremely weak or low alternating source applications, where the existing approaches offer poor outcomes. This proposed micro-circuit diode was compared to a Schottky diode in several experiment setup. The micro-circuit based half-wave rectifier circuit harvested 3.1 mV DC at a 239.5 Ohm load when the input magnitude is 50 mV while the Schottky diode was unable to convert this ultra-low AC power. This dissertation also provides the analysis of two alternating sources, the oscillatory electromagnetic generator and the piezoelectric energy harvester, to conduct experiments in a more realistic context. The micro-circuit diode shows excellent advantages in electromagnetic generator experiment, the micro-circuit based half-wave rectifier circuit harvested 5.16 mV DC at a 0.5 kOhm load when the input magnitude is 40 mV. However, due to the large leakage current in negative resistance region, this micro-circuit is unable to show advantages in piezoelectric energy harvester applications.

Switched-capacitor (SC) DC-DC converters provide a viable solution for on-chip DC-DC conversion as all the components required are available in most processes. However, power efficiency, power density characteristics of SC converters are adversely affected by the integration, and characteristics such as response time and noise can be further improved with an on-chip converter. An analysis on speed, power efficiency, and noise performance of SC converters is presented and verified using simulations. Based on the analysis two techniques, converter-gating and adaptive gain control, are developed. Converter-gating uses a combination of smaller stages and reconfiguration during transient load steps to improve the power efficiency and transient response speed. The stages of the converter are also distributed across the die to reduce the voltage drop and noise on power supply. Adaptive gain control improves transient response through manipulation of the gain of the integrator in the control loop. This technique focuses on improving the response time during converter reconfiguration and offers a general solution to transient response improvement instead of focusing on the worst case scenario which is usually the largest transient load step. The techniques developed are then implemented in ST 28nm FDSOI process and test methodologies are discussed.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16855号 / 工博第3576号 / 新制||工||1540(附属図書館) / 29530 / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 引原 隆士, 教授 木本 恒暢, 教授 小野寺 秀俊 / 学位規則第4条第1項該当

Multi-junction photovoltaic devices based on III-V semiconductors have applications in space power systems and terrestrial concentrating photovoltaics, as well as in power-over-fibre and optical power conversion systems. These devices have between two and twenty junctions arranged in tandem, connected in series with optically transparent tunnel diodes. In some cases, they may include as many as eight different materials, including ternary and quaternary alloys, and >100 epitaxial layers in total. A general method for simulating performance of these devices using drift-diffusion based device simulation tools is reviewed. This includes discussion of the geometry, discretization, and physical equations to be solved. A set of material parameters for some important materials is listed, and solutions are shown for an example of a lattice-matched four-junction GaInP / (In)AlGaAs / InGaAsN(Sb) / Ge solar cell including a dilute nitride based p-i-n junction with ∼ 0.9 eV band gap. A sample of this dilute nitride junction with a 650 nm absorber layer was grown by molecular beam epitaxy and was shown to have short-circuit current density of 15.1 mA/cm2, sufficient for use in the 4-junction structure, while transmitting sufficient light through to the bottom (germanium) junction. Open-circuit voltage was up to 0.186 V at 1-sun, increasing to 0.436 V under 1500 suns concentration. The device simulation methodology was extended to include effects of luminescent coupling and photon recycling. These effects are included by adding a term to the electron and hole continuity equations, and the resulting coupled system of equations is solved. No external iterative loop is required, as has been the case in other efforts to model these effects. A five-junction photonic power converter (PPC) is simulated and it is shown that the quantum efficiency of the device is significantly broadened through luminescent coupling. There is a 350 mV reduction in simulated open-circuit voltage (70 mV per junction) if luminescent coupling is neglected. This work was later extended to a 12-junction PPC device, where the simulation predicts a wavelength sensitivity of -1.1%/nm in the absence of luminescent coupling; this is reduced to -0.4%/nm when luminescent coupling is included in the calculation. The latter result, and the overall shape of the simulated quantum efficiency curve agree closely with experimental measurements. Finally, two specific applications of PPCs are demonstrated. The first is in a step-up DC-to-DC converter, where a linear regulator combined with a laser/PPC pair can convert a 3.3 V input (commonly available from a single lithium polymer battery cell) into 12 V. Unlike conventional switching boost converters, this ‘photonic boost converter’ is not a source of ripple. In testing, a >80 dB reduction in ripple was measured compared with an equivalent switching boost converter, limited only by input noise of the instrument.The second application is in a 60 kW, 650 V switching circuit such as might be found in a hybrid or electric vehicle drivetrain. These circuits need several isolated power supplies to power gate drivers for the IGBT or SiC MOSFET switching components. This isolation is commonly provided by a small transformer, which inherently has a parasitic capacitance between primary and secondary windings and creates a path for EMI currents to flow from the high-power components to the power supply and control circuitry. By using a laser/PPC pair to provide the needed isolation, this parasitic capacitance can be largely eliminated; a 20 dB reduction in EMI current reaching the control FPGA is demonstrated.

Household appliances utilize single-phase motors to perform everyday jobs whether it is to run a fan in an air conditioner or the compressor in a refrigerator. With the movement of the world going “green” and trying to make everything more efficient, it is a logical step to start with the items that we use every day. This can be done by replacing single-phase motors with three-phase motors in household appliances. Three-phase motors are 14% more efficient than single-phase motors when running at full load and typically cost less over a large range of sizes [1]. One major downside of incorporating three-phase motors in household appliance is that three-phase power is not readily available in homes. With the motor replacement, a single to three-phase converter is necessary to convert the single-phase wall power into the required three-phase input of the motor. One option is active conversion, which uses switches and introduces different stages that produce power loss [2]. An alternative solution is passive conversion that utilizes the resistances within the motor windings along with additional capacitors and inductors, which in theory are lossless. This study focuses on three different single to three-phase passive converters to run both wye and delta-connected three-phase induction motors, and a possible third winding configuration that utilizes one of the three converters. There will be an emphasis on proving the equivalency of two converters, one proposed by Stuart Marinus and Michel Malengret [11] and the other by Otto Smith [12]. Sensitivity analysis is performed to study the effects of variation of torque and converter component tolerances on the system.

This report explains how an SMES is operated and how SMES systems could be used to increase the efficiency of the CERN Large Hadron Collider (LHC) and the Future Circular Collider (FCC) as well as to reduce the very high power needs of a future Muon Collider (MC). The performance of SMES for other applications and late developments of the technique will also be described.

Strategic use of energy storage systems alleviates imbalance between energy generation and consumption. Battery storage of various chemistries is favorable for its relatively high energy density and high charge and discharge rates. Battery voltage is in dc, while the distribution of electricity is still predominantly in ac. To effectively harness the battery energy, a dc-ac inverter is required. A conventional inverter contains two high-frequency switching stages. The battery-interfacing stage provides galvanic isolation and switches at high frequency to minimize the isolation transformer size. The grid-interfacing stage also operates at high frequency to obtain sinusoidal grid currents and the desired power. Negative consequences of high-frequency switching include increased switching loss and the generation of large voltage harmonics that require filtering. This dissertation proposes an alternative two-stage inverter topology aimed at reducing converter size and weight. This is achieved by reducing the number of high-frequency switching stages and associated filter requirements. The grid-interfacing stage is operated at the line frequency, while only the battery-interfacing stage operates at high frequency to shape the line currents and control power flow. The line-frequency operation generates negligible switching loss and minimal current harmonics in the grid-interfacing stage. As a result, the required filter is reduced in size. Hardware designs are performed and compared between the conventional and proposed converters to quantify expected size reduction. Control methods are developed and verified in simulation and experiment to obtain high-quality line currents at all power factors.

This dissertation presents to our knowledge the first demonstration of a quantum well (QW) laser monolithically integrated with internal optical pump based on a light emitting diode (LED). The LED with high efficiency is operated in a thermoelectrophotonic (TEP) regime for which it can absorb both its own emitted light and heat. The LED optical pump can reduce internal optical loss in the QW laser, and enables monolithically integrated TEP heat pumps to the semiconductor laser. The design, growth and fabrication processes of the laser chip are discussed, and its experimental data is presented. In order to further increase the TEP laser efficiency the development of QDs as the active region for TEP edge emitting laser (EEL) is studied. The usage of QD as TEP laser's active region is significant in terms of its low threshold current density, low internal optical loss and high reliability, which are mainly due to low transparency in QD laser. The crystal growth of self-organized QDs in molecular beam epitaxial (MBE) system and characterization of QDs are mentioned. The design, growth, processing and fabrication of a QD laser structure are detailed. The characteristics of laser devices with different cavity length are reported. QD active regions with different amount of material are grown to improve the active region performance. Theoretical calculations based on material parameters and semiconductor physics indicate that with proper design, the combination of high efficiency LED in TEP regime with a QD laser can result in the integrated laser chip power conversion efficiency exceeding unity.

The development in power conversion technology is in constant demand of high power efficiency and high power density. The DC-DC power conversion is an indispensable stage for numerous power supplies and energy related applications. Particularly, in PV micro-inverters and front-end converter of power supplies, great challenges are imposed on the power performances of the DC-DC converter stage, which not only require high efficiency and density but also the capability to regulate a wide variation range of input voltage and load conditions. The resonant DC-DC converters are good candidates to meet these challenges with the advantages of achieving soft switching and low EMI. Among various resonant converter topologies, the LLC converter is very attractive for its wide gain range and providing ZVS for switches from full load to zero load condition. The operation of the LLC converter is complicated due to its multiple resonant stage mechanism. A literature review of different analysis methods are presented, and it shows that the study on the LLC is still incomplete. Therefore, an operation mode analysis method is proposed, which divides the operation into six major modes based on the occurrence of resonant stages. The resonant currents, voltages and the DC gain characteristics for each mode is investigated. To obtain a thorough view of the converter behavior, the boundaries of every mode are studied, and mode distribution regarding the gain, load and frequency is presented and discussed. As this operation mode model is a precise model, an experimental prototype is designed and built to demonstrate its accuracy in operation waveforms and gain prediction. iv Since most of the LLC modes have no closed-form solutions, simplification is necessary in order to utilize this mode model in practical design. Some prior approximation methods for converter’s gain characteristics are discussed. Instead of getting an entire gain-vs.-frequency curve, we focus on peak gains, which is an important design parameters indicating the LLC’s operating limit of input voltage and switching frequency. A numerical peak gain approximation method is developed, which provide a direct way to calculate the peak gain and its corresponding load and frequency condition. The approximated results are compared with experiments and simulations, and are proved to be accurate. In addition, as PO mode is the most favorable operation mode of the LLC, its operation region is investigated and an approximation approach is developed to determine its boundary. The design optimization of the LLC has always been a difficult problem as there are many parameters affecting the design and it lacks clear design guidance in selecting the optimal resonant tank parameters. Based on the operation mode model, three optimization methods are proposed according to the design scenarios. These methods focus on minimize the conduction loss of resonant tank while maintaining the required voltage gain level, and the approximations of peak gains and PO mode boundary can be applied here to facilitate the design. A design example is presented using one of the proposed optimization methods. As a comparison, the L-C component values are reselected and tested for the same design specifications. The experiments show that the optimal design has better efficiency performance. Finally, a generalized approach for resonant converter analysis is developed. It can be implemented by computer programs or numerical analysis tools to derive the operation waveforms and DC characteristics of resonant converters

In this work an n-channel In0.65Ga0.35As LDMOS with Al2O3 as gate dielectric is investigated. Instead of using traditional Si process for LDMOS, we suggest In0.65Ga0.35As as substitute material due to its higher electron mobility and its promising for power applications. The proposed 0.5-µm channel-length LDMOS cell is studied through device TCAD simulation tools. Due to different gate dielectric, comprehensive comparisons between In0.65Ga0.35As LDMOS and Si LDMOS are made in two ways, structure with the same cross-sectional dimension, and structure with different thickness of gate dielectric to achieve the same gate capacitance. The on-resistance of the new device shows a big improvement with no degradation on breakdown voltage over traditional device. Also it is indicated from these comparisons that the figure of merit(FOM) Ron·Qg of In0.65Ga0.35As LDMOS shows an average of 91.9% improvement to that of Si LDMOS. To further explore the benefit of using In0.65Ga0.35As LDMOS as switch in power applications, DC-DC buck converter is utilized to observe the performance of LDMOS in terms of power efficiency. The LDMOS performance is experimented with operation frequency of the circuit sweeping in the range from 100 KHz to 100 MHz. It turns out InGaAs LDMOS is good candidate for power applications.