With rapid progress in microelectronics technology, high-performance Integrated Circuits (ICs) bring huge challenge to design the power supplies. Fast loop response is required to handle the high transient current of devices. Power solution size is demanded to reduce due to the size reduction of integrated circuits. The best way to meet these harsh requirements is to increase switching frequency of power supplies. Along with the benefits of increasing switching frequency, the power supplies will suffer from high switching loss and high gate charge loss as these losses are frequency dependant losses. This thesis investigates the best topology to minimize the switching loss. The Series-Parallel Resonant Converter (SPRC) with current-doubler is mainly analyzed for high frequency low voltage high current application. The advantages and disadvantages of SPRC with current-doubler are presented. A new adaptive synchronous rectifiers timing control scheme is also proposed. The proposed timing control scheme demonstrates it can minimize body diode conduction loss of synchronous rectifiers and therefore improve the efficiency of the converter. This thesis also proposes two families of new resonant gate drive circuits. The circuits recover a portion of gate drive energy that is total lost in conventional gate drive circuit. In addition to reducing gate charge loss, it also reduces the switching losses of the power switches. Detail operation principle, loss analysis and design guideline of the proposed drive circuits are provided. Simulation and experimental results are also presented. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2008-01-29 22:37:09.812

With the use of the simplistic equivalent circuits, loss mechanism in conventional power MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) gate drive circuits is analyzed. Resonant gate drive techniques are investigated and a new resonant gate drive circuit is presented. The presented circuit adds minor complexity to conventional gate drivers but reduces the MOSFET gate drive loss very effectively. To further expand its use in driving Half-Bridge MOSFETs, another circuit is proposed in this thesis. The later circuit simplifies the isolation circuitry for the top MOSFET and meanwhile consumes much lower power than conventional gate drivers. / Master of Science

Improved transient performance and converter miniaturization are the major driving factors behind high frequency operation of switching power supplies. However, high speed operation is limited by topology, control, semiconductor, and packaging technologies. The inherent mitigation of switching loss in resonant converters makes them prime candidates for use when the limits of switching frequency are pushed. The goal of this thesis is to address two areas that practically limit the achievable switching frequency of resonant topologies. Traditional control methods based on single cycle response are impractical at high frequency; forcing the use of pulse density modulation (PDM) techniques. However, existing pulse density modulation strategies for resonant converters in dc/dc applications suffer from: • High semiconductor current stress. • Slow response and large filter size determined by the low modulating frequency. • Possibly operating at fractions of resonant cycles leading to switching loss; thereby limiting the modulating frequency. A series resonant converter with variable frequency PDM (VF-PDM) with integral resonant cycle control is presented to overcome the limitations of existing PDM techniques to enable efficient operation with high switching frequency and modulating frequency. The operation of the circuit is presented and analyzed, with a design procedure given to achieve fast transient performance, small filter size, and high efficiency across the load range with current stress comparable to conventional control techniques. It is shown that digital implementation of the controller can achieve favourable results with a clock frequency four times greater than the switching frequency. Driving the synchronous rectifiers is a considerable challenge in high current applications operating at high switching frequency. Resonant gate drivers with continuous inductor current experience excessive conduction loss, while discontinuous current drivers are subject to slow transitions and high peak current. Current source drivers suffer from high component count and increased conduction loss when applied to complementary switches. A dual-channel current source driver is presented as a means of driving two complementary switches. A single coupled inductor with discontinuous current facilitates low conduction loss by transferring charge between the MOSFET gates to reduce the number of semiconductors in the current path, and reducing the number of conduction intervals. The operation of the circuit is analyzed, and a design procedure based on minimization of the total synchronous rectifier loss is presented. Implementation of the digital logic to control the driver is discussed. Experimental results at megahertz operating frequencies are presented for both areas addressed to verify the theoretical results. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2012-09-09 20:43:56.997

No description available.

In this thesis, various issues regarding normally-ON silicon carbide (SiC)Junction Field-Effect Transistors (JFETs) are treated. Silicon carbide powersemiconductor devices are able to operate at higher switching frequencies,higher efficiencies, and higher temperatures compared to silicon counterparts.From a system perspective, these three advantages of silicon carbide can determinethe three possible design directions: high efficiency, high switchingfrequency, and high temperature.The structure designs of the commercially-available SiC power transistorsalong with a variety of macroscopic characteristics are presented. Apart fromthe common design and performance problems, each of these devices suffersfrom different issues and challenges which must be dealt with in order to pavethe way for mass production. Moreover, the expected characteristics of thefuture silicon carbide devices are briefly discussed. The presented investigationreveals that, from the system point-of-view, the normally-ON JFET isone of the most challenging silicon carbide devices. There are basically twoJFET designs which were proposed during the last years and they are bothconsidered.The state-of-the-art gate driver for normally-ON SiC JFETs, which wasproposed a few years ago is briefly described. Using this gate driver, theswitching performance of both Junction Field-Effect Transistor designs wasexperimentally investigated.Considering the current development state of the available normally-ONSiC JFETs, the only way to reach higher current rating is to parallel-connecteither single-chip discrete devices or to build multichip modules. Four deviceparameters as well as the stray inductances of the circuit layout might affectthe feasibility of parallel connection. The static and dynamic performance ofvarious combinations of parallel-connected normally-ON JFETs were experimentallyinvestigated using two different gate-driver configurations.A self-powered gate driver for normally-ON SiC JFETs, which is basicallya circuit solution to the “normally-ON problem” is also shown. This gatedriver is both able to turn OFF the shoot-through current during the startupprocess, while it also supplies the steady-state power to the gate-drivecircuit. From experiments, it has been shown that in a half-bridge converterconsisting of normally-ON SiC JFETs, the shoot-through current is turnedOFF within approximately 20 μs.Last but not least, the potential benefits of employing normally-ON SiCJFETs in future power electronics applications is also presented. In particular,it has been shown that using normally-ON JFETs efficiencies equal 99.8% and99.6% might be achieved for a 350 MW modular multilevel converter and a40 kVA three-phase two-level voltage source converter, respectively.Conclusions and suggestions for future work are given in the last chapterof this thesis. / I denna avhandling behandlas olika aspekter av normally–ON junction–field–effect–transistorer (JFETar) baserade på kiselkarbid (SiC). Effekthalvledarkomponenteri SiC kan arbeta vid högre switchfrekvens, högre verkningsgradoch högre temperatur än motsvarigheterna i kisel. Ur ett systemperspektivkan de tre nämnda fördelarna användas i omvandlarkonstruktionen för attuppnå antingen hög verkningsgrad, hög switchfrekvens eller hög temperaturtålighet.Såväl halvledarstrukturen som de makroskopiska egenskaperna för kommersiellttillgängliga SiC–transistorer presenteras. Bortsett från de vanligakonstruktions–och prestandaproblemen lider de olika komponenterna av ettantal tillkortakommanden som måste övervinnas för att bana väg för massproduktion.Även framtida SiC–komponenter diskuteras.Ur ett systemperspektiv är normally-ON JFETen en av de mest utmanandeSiC-komponenterna. De två varianter av denna komponent som varittillgängliga de senaste åren har båda avhandlats.State–of–the–art–drivdonet för normally-ON JFETar som presenteradesför några år sedan beskrivs i korthet. Med detta drivdon undersöks switchegenskapernaför båda JFET-typerna experimentellt.Vid beaktande av det aktuella utvecklingsstadiet av de tillgängliga normally–ON JFETarna i SiC, är det möjligt att uppnå höga märkströmmar endastom ett antal single–chip–komponenter parallellkopplas eller om multichipmodulerbyggs. Fyra komponentparametrar samt strö-induktanser för kretsenkan förutses påverka parallellkopplingen. De statiska och dynamiska egenskapernaför olika kombinationer av parallellkopplade normally-ON JFETarundersöks experimentellt med två olika gate–drivdonskonfigurationer.Ett självdrivande gate-drivdon för normally-ON JFETar presenteras också.Drivdonet är en kretslösning till “normally–ON–problemet”. Detta gatedrivdonkan både stänga av kortslutningsströmmen vid uppstart och tillhandahållaströmförsörjning vid normal drift. Med hjälp av en halvbrygga medkiselkarbidbaserade normally–ON JFETar har det visats att kortslutningsströmmenkan stängas av inom cirka 20 μs.Sist, men inte minst, presenteras de potentiella fördelarna med användningenav SiC-baserade normally-ON JFETar i framtida effektelektroniskatillämpningar. Speciellt visas att verkningsgrader av 99.8% respektive 99.5%kan uppnås i fallet av en 350 MW modular multilevel converter och i en40 kVA tvånivåväxelriktare. Sista kaplitet beskriver slutsatser och föreslagetframtida arbete. / <p>QC 20130527</p>

The power density of a switching converter is dependent on the size of the power circuit components. Converters are operated in the hundreds of kHz to achieve high power density since the size of the converter reactive components decrease as frequency increases. Most present day low power (<200W) DC-DC converters operate at switching frequencies up to 500kHz. Some research has been conducted on converters that can operate above 500kHz up to 4MHz. In the near future, most DC-DC switching converters for communications and computers will operate at switching frequencies of 1-10MHz in order to achieve greater power density and improved transient response. To meet the next generation requirements of these applications, four new ideas are proposed in this thesis. The first contribution is a new current source gate drive circuit for power MOSFETs. The circuit provides a nearly constant gate current to reduce switching transition times and therefore switching loss in power MOSFETs. In addition, it can recover a portion of the gate energy normally dissipated in a conventional driver. Demonstrated loss reduction of 24.8% at 10V/5A load are presented in comparison to a conventional voltage source driver for a boost converter switching at 1MHz. The second contribution is a new high efficiency 1MHz synchronous buck voltage regulator using an improved current source driver. The proposed circuit achieves short rise and fall times to reduce switching loss in the buck HS MOSFET. It also recovers a portion of the SR gate energy, enabling a loss reduction of 24% at 1.3V/30A load in comparison to a conventional driver. In the third contribution, a new switching loss model is proposed for synchronous buck voltage regulators. The model uses simple closed form equations to calculate the rise and fall times and piecewise linear approximations of the HS MOSFET voltage and current waveforms to allow quick and accurate calculation of switching loss. The final contribution is a new variable frequency digital control method for resonant converters, which is suitable for future applications switching at 10MHz. The proposed method uses frequency dithering to reduce the clock frequency demands of the digital controller. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2008-02-28 10:56:06.732

The future power conversion system not only must meet the characteristics demanded by the load, but also have to achieve high power density with high efficiency, high ambient temperature, and high reliability. Density and efficiency are two key drivers and metrics for the advancement of power conversion technologies. Generally speaking, a high performance active device is the first force to push power density to meet the requirement of modern systems. Silicon has been a dominant material in power management since the late 1950s. However, due to continuous device optimizations and improvements in the production process, the material properties of silicon have increasingly become the limiting factor. Workarounds like the super junction stretch the limits but usually at substantial cost. The use of gallium nitride devices is gathering momentum, with a number of recent market introductions for a wide range of applications such as point-of-load (POL) converters, off-line switching power supplies, battery chargers and motor drives. GaN devices have a much lower gate charge and lower output capacitance than silicon MOSFETs and, therefore, are capable of operating at a switching frequency 10 times greater. This can significantly impact the power density of power converters, their form factor, and even current design and manufacturing practices. To realize the benefits of GaN devices resulting from significantly higher operating frequencies, a number of issues have to be addressed, such as converter topology, soft-switching technique, high frequency gate driver, high frequency magnetics, packaging, control, and thermal management. This work studies the insight switching characteristics of high-voltage GaN devices including some specific issues related to the cascode GaN. The package impact on the switching performance and device reliability will be illustrated in details. A stack-die package is proposed for cascode GaN devices to minimize the impact of package parasitic inductance on switching transition. Comparison of hard-switching and soft-switching operation is carried based on device model and experiments, which shows the necessity of soft-switching for GaN devices at high frequency. This work also addresses high dv/dt and di/dt related gate drive issues associated with the higher switching speed of GaN devices. Particularly, the conventional driving solution could fail on the high side switch in a half-bridge configuration due to relative large common-mode noise current. Two simple and effective driving methods are proposed to improve noise immunity and maintain high driving speed. Finally, this work illustrates the utilization of GaN in an emerging application, high density AC-DC adapter. Many design considerations are presented in detail. The GaN-based adapter is capable of operating at 1-2 MHz frequency with an improved efficiency up to 94%. Several design examples at different power levels, with a power density in the range of 20~35W/in3, which is a three-fold improvement over the state-of-the-art product, are successfully demonstrated. In conclusion, this work is focus on the characterization, and evaluation of GaN devices. Packaging, high frequency driving and soft-switching technique are addressed to fully explore the potential of GaN devices. High density adapters are demonstrated to show the advance of GaN device and its impact on system design. / Ph. D.

In recent years, there is a clear trend toward increasing the demand for electric power in high-power applications. High-power converters are making major impacts on these high-power applications. Recent breakthroughs in Silicon Carbide (SiC) materials and fabrication techniques have led to the development of high-voltage, high-frequency power devices, which are at the heart of high-power converters. SiC metal-oxide semiconductor field-effect transistors (MOSFETs) have advantages over silicon (Si) devices due to their higher breakdown voltage, higher thermal capability, and lower on-state resistance. However, their fast switching frequency and high blocking voltage bring challenges to the gate-drive circuit design. The gate driver of SiC-MOSFETs requires a power supply that provides a high-voltage, high-density design, a low input-output capacitance (CI/O) transformer design, good voltage regulation, as well as good resilience to faults to enable safe and fast operation. In this thesis, a power supply that supplies multiple gate drivers for 10 kV SiC MOSFETs is presented. A transformer design approach with a single turn at the primary side is proposed. A 20 kV insulation is achieved by the primary HV cable insulation across a toroid transformer core. The CI/O is designed less than 2 pF to mitigate the Common-Mode (CM) noise. A circuit topology analysis is performed and the inductor/capacitor/capacitor/inductor (LCCL) – inductor/capacitor (LC) circuit is selected. This circuit allows Zero-Voltage Switching (ZVS) at full operation range. A Resonant-Current-Bus (RCB) is built at the transformer primary side to achieve load-independence. / Master of Science / Wide-bandgap semiconductor devices have attracted widespread attention due to their superior performance compared to their silicon devices counterpart. To utilize its full benefits, this thesis presents a complete design and optimization of a gate-drive power supply that supplies multiple gate drivers for high-voltage, high-speed semiconductor devices. Four objectives, including high density at high voltage, good noise mitigation, fair voltage regulation, resilience to faults have been achieved. During the design procedure, different topology candidates are introduced and compared, after which a resonant topology is selected. The wide-bandgap semiconductor devices are utilized to reduce the size and losses. Hardware assembly is shown and experimental testing results are provided in the end to verify the design.

No description available.

This thesis examines converter topologies suitable for Module Integrated Converters (MICs) in grid interactive photovoltaic (PV) systems, and makes a contribution to the development of the MIC topologies based on the two-inductor boost converter, which has received less research interest than other well known converters. The thesis provides a detailed analysis of the resonant two-inductor boost converter in the MIC implementations with intermediate constant DC links. Under variable frequency control, this converter is able to operate with a variable DC gain while maintaining the resonant condition. A similar study is also provided for the resonant two-inductor boost converter with the voltage clamp, which aims to increase the output voltage range while reducing the switch voltage stress. An operating point with minimized power loss can be also established under the fixed load condition. Both the hard-switched and the soft-switched current fed two-inductor boost converters are developed for the MIC implementations with unfolding stages. Nondissipative snubbers and a resonant transition gate drive circuit are respectively employed in the two converters to minimize the power loss. The simulation study of a frequency-changer-based two-inductor boost converter is also provided. This converter features a small non-polarised capacitor in a second phase output to provide the power balance in single phase inverter applications. Four magnetic integration solutions for the two-inductor boost converter have also been presented and they are promising in reducing the converter size and power loss.