High Current Density Low Voltage Isolated Dc-dc Converterswith Fast Transient Response

With the rapid development of microprocessor and semiconductor technology, industry continues to update the requirements for power supplies. For telecommunication and computing system applications, power supplies require increasing current level while the supply voltage keeps decreasing. For example, the Intel\u27s CPU core voltage decreased from 2 volt in 1999 to 1 volt in 2005 while the supply current increased from 20A in 1999 to up to 100A in 2005. As a result, low-voltage high-current high efficiency dc-dc converters with high power-density are demanded for state-of-the-art applications and also the future applications. Half-bridge dc-dc converter with current-doubler rectification is regarded as a good topology that is suitable for high-current low-voltage applications. There are three control schemes for half-bridge dc-dc converters and in order to provide a valid unified analog model for optimal compensator design, the analog state-space modeling and small signal modeling are studied in the dissertation and unified state-space and analog small signal model are derived. In addition, the digital control gains a lot of attentions due to its flexibility and re-programmability. In this dissertation, a unified digital small signal model for half-bridge dc-dc converter with current doubler rectifier is also developed and the digital compensator based on the derived model is implemented and verified by the experiments with the TI DSP chip. In addition, although current doubler rectifier is widely used in industry, the key issue is the current sharing between two inductors. The current imbalance is well studied and solved in non-isolated multi-phase buck converters, yet few discusse this issue in the current doubler rectification topology within academia and industry. This dissertation analyze the current sharing issue in comparison with multi-phase buck and one modified current doubler rectifier topology is proposed to achieve passive current sharing. The performance is evaluated with half bridge dc-dc converter; good current sharing is achieved without additional circuitry. Due to increasing demands for high-efficiency high-power-density low-voltage high current topologies for future applications, the thermal management is challenging. Since the secondary-side conduction loss dominates the overall power loss in low-voltage high-current isolated dc-dc converters, a novel current tripler rectification topology is proposed. Theoretical analysis, comparison and experimental results verify that the proposed rectification technique has good thermal management and well-distributed power dissipation, simplified magnetic design and low copper loss for inductors and transformer. That is due to the fact that the load current is better distributed in three inductors and the rms current in transformer windings is reduced. Another challenge in telecommunication and computing applications is fast transient response of the converter to the increasing slew-rate of load current change. For instance, from Intel\u27s roadmap, it can be observed that the current slew rate of the age regulator has dramatically increased from 25A/uS in 1999 to 400A/us in 2005. One of the solutions to achieve fast transient response is secondary-side control technique to eliminate the delay of optocoupler to increase the system bandwidth. Active-clamp half bridge dc-dc converter with secondary-side control is presented and one industry standard 16th prototype is built and tested; good efficiency and transient response are shown in the experimental section. However, one key issue for implementation of secondary-side control is start-up. A new zero-voltage-switching buck-flyback isolated dc-dc converter with synchronous rectification is proposed, and it is only suitable for start-up circuit for secondary-side controlled converter, but also for house-keeping power supplies and standalone power supplies requiring multi-outputs

Low Voltage Regulator Modules and Single Stage Front-end Converters

Evolution in microprocessor technology poses new challenges for supplying power to these devices. To meet demands for faster and more efficient data processing, modem microprocessors are being designed with lower voltage implementations. More devices will be packed on a single processor chip and the processors will operate at higher frequencies, exceeding 1GHz. New high-performance microprocessors may require from 40 to 80 watts of power for the CPU alone. Load current must be supplied with up to 30A/µs slew rate while keeping the output voltage within tight regulation and response time tolerances. Therefore, special power supplies and Voltage Regulator Modules (VRMs) are needed to provide lower voltage with higher current and fast response. In the part one (chapter 2,3,4) of this dissertation, several low-voltage high-current VRM technologies are proposed for future generation microprocessors and ICs. The developed VRMs with these new technologies have advantages over conventional ones in terms of efficiency, transient response and cost. In most cases, the VRMs draw currents from DC bus for which front-end converters are used as a DC source. As the use of AC/DC frond-end converters continues to increase, more distorted mains current is drawn from the line, resulting in lower power factor and high total harmonic distortion. As a branch of active Power factor correction (PFC) techniques, the single-stage technique receives particular attention because of its low cost implementation. Moreover, with continuously demands for even higher power density, switching mode power supply operating at high-frequency is required because at high switching frequency, the size and weight of circuit components can be remarkably reduced. To boost the switching frequency, the soft-switching technique was introduced to alleviate the switching losses. The part two (chapter 5,6) of the dissertation presents several topologies for this front-end application. The design considerations, simulation results and experimental verification are discussed

Novel Offline Switched Mode Power Supplies for Solid State Lighting Applications

In recent years, high brightness light emitting diodes (HBLEDs) have increasingly attracted the interest of both industrial manufacturers and academic research community. Among the several aspects that make LED technology so attractive, the most appreciated characteristics are related to their robustness, high efficiency, small size, easy dimming capability, long lifetime, very short switch-on/switch-off times and mercury free manufacturing. Even if all such qualities would seem to give to solid state lighting a clear advantage over all the other kinds of competing technologies, the issues deriving from the need of LED technology improvement, on one hand, and of the development of suitable electronic ballasts to properly drive such solid state light sources, on the other, have so far hindered the expected practical applications. The latter problem, in particular, is nowadays considered the main bottleneck in view of a widespread diffusion of solid state technology in the general lighting market, as a suitable replacement of the still dominant solutions, namely halogen and fluorescent lamps. In fact, if it is true that some aspects of the devices’ technology (e.g. temperature dependent performance, light quality, efficiency droop, high price per lumen, etc…) still need further improvements, it is now generally recognized that one of the key requirements, for a large scale spread of solid state lighting, is the optimization of the driver. In particular, the most important specifications for a LED lamp ballast are: high reliability and efficiency, high power factor, output current regulation, dimming capability, low cost and volume minimization (especially in domestic general lighting applications). From this standpoint, the main goal is, therefore, to find out simple switched mode power converter topologies, characterized by reduced component count and low current/voltage stresses, that avoid the use of short lifetime devices like electrolytic capacitors. Moreover, if compactness is a major issue, also soft switching capability becomes mandatory, in order to enable volume minimization of the reactive components by increasing the switching frequency in the range of the hundreds of kHz without significantly affecting converter’s efficiency. It is worth mentioning that, in order to optimize HBLED operation, also other matters, like the lamp thermal management concern, should be properly addressed in order to minimize the stress suffered by the light emitting devices and, consequently, the deterioration of the light quality and of the expected lamp lifetime. However, being this work focused on the issues related to the research of innovative driving solutions, the aforementioned thermal management problems, as also all the topics related to the improvement of solid state devices’ technology, will be left aside. The main goal of the work presented in this thesis is, indeed, to find out, analyze and optimize new suitable topologies, capable of matching the previously described specifications and also of successfully facing the many challenges dictated by the future of general lighting. First of all, a general overview of solid state lighting features, of the state of the art of lighting market and of the main LED driving issues will be provided. After this first introduction, the offline driving concern will be extensively discussed and different ways of approaching the problem, depending on the specific application considered, will be described. The first kind of approach investigated is based on the use of a simple structure relying on a single power conversion stage, capable of concurrently ensuring: compliance with the standards limiting the input current harmonics, regulation of the load current and also galvanic isolation. The constraints deriving from the need to fulfil the EN 61000-3-2 harmonics standard requirements, when using such kind of solution for low power (<15W) LED driving purposes, will be extensively discussed. A low cost, low component count, high switching frequency converter, based on the asymmetrical half bridge flyback topology, has been studied, developed and optimized. The simplicity and high compactness, characterizing this solution, make it a very good option for CFL and bulb replacement applications, in which volume minimization is mandatory in order to reach the goal of placing the whole driving circuitry in the standard E27 sockets. The analysis performed will be presented, together with the design procedure, the simulation outcomes and the different control and optimization techniques that were studied, implemented and tested on the converter's laboratory prototype. Another interesting approach, that will be considered, is based on the use of integrated topologies in which two different power conversion stages are merged by sharing the same power switch and control circuitry. In the resulting converter, power factor correction and LED current regulation are thus performed by two combined semi-stages in which both the input power and the output current have to be managed by the same shared switch. Compared with a conventional two-stages configuration, lower circuit complexity and cost, reduced component count and higher compactness can be achieved through integration, at cost of increased stress levels on the power switch and of losing a degree of freedom in converter design. Galvanic isolation can be provided or not depending on the topologies selected for integration. If non-isolated topologies are considered for both semi-stages, the user safety has to be guaranteed by assuring mechanical isolation throughout the LED lamp case. The issue, deriving from the need of smoothing the pulsating power absorbed from the line while avoiding the use of short lifetime electrolytic capacitors, will be addressed. A set of integrated topologies, used as HBLED lamp power supplies, will be investigated and a generalized analysis will be presented. Their input line voltage ripple attenuation capability will be examined and a general design procedure will be described. Moreover, a novel integrated solution, based on the use of a double buck converter, for an about 15W rated down-lighting application will be presented. The analysis performed, together with converter design and power factor correction concerns will be carefully discussed and the main outcomes of the tests performed at simulation level will be provided. The last kind of approach to be discussed is based on a multi-stage structure that results to be a suitable option for medium power applications, like street lighting, in which compactness is not a major concern. By adopting such kind of solution it is, indeed, possible to optimize converter’s behavior both on line and on load side, thereby guaranteeing both an effective power factor correction at the input and proper current regulation and dimming capability at the output. Galvanic isolation can be provided either by the input or the output stage, resulting in a standard two stage configuration, or by an additional intermediate isolated DC-DC stage (operating in open loop with a constant input/output voltage conversion ratio) that namely turns the AC/DC converter topology into a three stage configuration. The efficiency issue, deriving from the need of multiple energy processing along the path between the utility grid and the LED load, can be effectively addressed thanks to the high flexibility guaranteed by this structure that, relaxing the design constraint, allows to easily optimize each stage. A 150W nominal power rated ballast for street solid state lighting applications, based on the latter (three stage) topology, has been investigated. The analysis performed, the design procedure and the simulations outcomes will be carefully described, as well as the experimental results of the tests made on the implemented laboratory prototype

Study and design of topologies and components for high power density DC-DC converters

Size reduction of low power electronic DC–DC converters is a topic of major interest for power electronics which requires the study and design of circuits and components working under redefined requirements. For this purpose, novel circuital topologies provide advantages in terms of power density increment, especially where a single chip design is feasible. These concepts have been applied to design and implement an integrated high step-down multiphase buck converter and to study the miniaturization of a stackable fiflyback architecture. Particular attention has been dedicated to power inductors, focusing on the modeling and measurement of magnetic materials’ hysteresis and core losses

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

A New Smart Grid Hybrid DC–DC Converter with Improved Voltage Gain and Synchronized Multiple Outputs

This paper introduces a new hybrid DC-DC converter with enhanced voltage gain and synchronized multiple output capabilities, specifically tailored for smart grid applications. The proposed converter is based on the integration of non-isolated Zeta and Mahafzah converters, comprising a single controlled switch, two diodes, three inductors, and two coupling capacitors. The primary objective of this novel hybrid converter is to improve voltage gain as compared to conventional Zeta and Mahafzah topologies. By achieving higher voltage gain at lower duty cycles, the converter effectively reduces voltage stress on semiconductor switches and output diodes, thereby enhancing overall performance and reliability. A comprehensive examination of the hybrid converter's operating principle is presented, along with detailed calculations of duty cycle and switching losses. The paper also explores the converter's application in smart grids, specifically in the context of renewable energy systems and electric vehicles. Two distinct scenarios are analyzed to evaluate the converter's efficacy. Firstly, the converter is assessed as a DC-DC converter for renewable energy systems, highlighting its relevance in sustainable energy applications. Secondly, the converter is evaluated as an electric vehicle adapter, showcasing its potential in the transportation sector. To validate the converter's performance, extensive simulations are carried out using MATLAB/SIMULINK with parameters set at 25 kW, 200 V, and 130 A. The simulation results demonstrate the converter's ability to efficiently supply multiple loads with opposing energy flows, making it a promising technology for optimized grid management and energy distribution. Moreover, the paper investigates the total harmonic distortion (THD) of the grid current, focusing on its impact in smart grid environments. Notably, the new hybrid converter topology achieves a THD of 21.11% for the grid current, indicating its ability to effectively mitigate harmonics and improve power quality. Overall, this research introduces a cutting-edge hybrid DC-DC converter that enhances voltage gain and synchronizes multiple outputs, specifically catering to the requirements of smart grid applications. The findings underscore the converter's potential to significantly contribute to the advancement of efficient and resilient power conversion technologies for smart grids, enabling seamless integration of renewable energy systems and electric vehicles into the grid

Concept of an efficient self-startup voltage converter with dynamic maximum power point tracking for microscale thermoelectric generators

Microscale Thermoelectric Generators (microTEGs) have a high application potential for energy harvesting for autonomous microsystems. In contrast to conventional thermoelectric generators, microTEGs can only supply small output-voltages. Therefore, voltage converters are required to provide supply-voltages that are sufficiently high to power microelectronics. However, for high conversion efficiency, voltage converters need to be optimized for the limited input voltage range and the typically high internal resistance of microTEGs. To overcome the limitations of conventional voltage converters we present an optimized self-startup voltage converter with dynamic maximum power point tracking. The performance potential of our concept is theoretically and experimentally analyzed. The voltage conversion interface demonstrates energy harvesting from open-circuit voltages as low as 30.7 mV, and enables independent and full start-up from 131 mV. No additional external power supply is required at any time during operation. It can be operated with a wide range of internal resistances from 20.6 to − 4 kΩ with a conversation efficiency between η = 68–79%

Passive and Active Topologies Investigation for LED Driver Circuits

In this chapter, a survey of LED driver circuits is presented. The driver circuit is a crucial component in the LED light system. It provides the correct voltage and current values for the best brightness and long life. Furthermore, the driver circuits contribute to obtaining high efficiency and reliability light system. Several lighting applications need different driver topologies that meet the use requirement and the energy sources available. In actual applications, passive and active circuits are implemented to satisfy the LED driver electrical requirements and cost-effective demands. The LED driver circuits investigation evaluate the issues and the solutions in the LED lighting systems connected to a DC source such as a battery or AC line. The AC line connection requisites such as the power factor correction and the harmonic distortion are dealt with both the driver topology and control optimization. Also, the volume reduction need is examined in the circuitry choice. Moreover, the different topologies of the power converters isolated and not isolated used in the driver circuits based on both the power request and supply source are described and critically evaluated

Modeling And Design Of Multi-port Dc/dc Converters

In this dissertation, a new satellite platform power architecture based on paralleled three-port DC/DC converters is proposed to reduce the total satellite power system mass. Moreover, a fourport DC/DC converter is proposed for renewable energy applications where several renewable sources are employed. Compared to the traditional two-port converter, three-port or four-port converters are classified as multi-port converters. Multi-port converters have less component count and less conversion stage than the traditional power processing solution which adopts several independent two-port converters. Due to their advantages multi-port converters recently have attracted much attention in academia, resulting in many topologies for various applications. But all proposed topologies have at least one of the following disadvantages: 1) no bidirectional port; 2) lack of proper isolation; 3) too many active and passive components; 4) no softswitching. In addition, most existing research focuses on the topology investigation, but lacks study on the multi-port converter’s control aspects, which are actually very challenging since it is a multi-input multi-output control system and has so many cross-coupled control loops. A three-port converter is proposed and used for space applications. The topology features bidirectional capability, low component count and soft-switching for all active switches, and has one output port to meet certain isolating requirements. For the system level control strategy, the multi-functional central controller has to achieve maximal power harvesting for the solar panel, the battery charge control for the battery, and output voltage regulation for the dc bus. In order to design these various controllers, a good dynamic model of the control object should be obtained first. Therefore, a modeling procedure based on a traditional state-space averaging method is v proposed to characterize the dynamic behavior of such a multi-port converter. The proposed modeling method is clear and easy to follow, and can be extended for other multi-port converters. In order to boost the power level of the multi-port converter system and allow redundancy, the three-port converters are paralleled together. The current sharing control for the multi-port converters has rarely been reported. A so called “dual loop” current sharing control structure is identified to be suitable for the paralleled multi-port converters, since its current loop and the voltage loop can be considered and designed independently, which simplifies the multi-port converter’s loop analysis. The design criteria for that dual loop structure are also studied to achieve good current sharing dynamics while guaranteeing the system stability. The renewable energy applications are continuously demanding the low cost solution, so that the renewable energy might have a more competitive dollar per kilowatt figure than the traditional fossil fuel power generation. For this reason, the multi-port converter is a good candidate for such applications due to the low component count and low cost. Especially when several renewable sources are combined to increase the power delivering certainty, the multi-port solution is more beneficial since it can replace more separate converters. A four-port converter is proposed to interface two different renewable sources, such as the wind turbine and the solar panel, one bidirectional battery device, and the galvanically isolated load. The four-port converter is based on the traditional half-bridge topology making it easy for the practicing power electronics engineer to follow the circuit design. Moreover, this topology can be extended into n input ports which allow more input renewable sources. vi Finally, the work is summarized and concluded, and references are listed