Single-Stage Power Electronic Converters with Combined Voltage Step-Up/Step-Down Capability

Power electronic converters are typically either step-down converters that take an input voltage and produce an output voltage of low amplitude or step-up converters that take an input voltage and produce an output voltage of higher amplitude. There are, however, applications where a converter that can step-up voltage or step-down voltage can be very useful, such as in applications where a converter needs to operate under a wide range of input and output voltage conditions such as a grid-connected solar inverter. Such converters, however, are not as common as converters that can only step down or step up voltage because most applications require converters that need to only step down voltage or only step up voltage and such converters have better performance within a limited voltage range than do converters that are designed for very wide voltage ranges. Nonetheless, there are applications where converters with step-down and step-up capability can be used advantageously. The main objectives of this thesis are to propose new power electronic converters that can step up voltage and step down voltage and to investigate their characteristics. This will be done for two specific converter types: AC/DC single-stage converters and DC-AC inverters. In this thesis, two new AC/DC single-stage converters and a new three-phase converter are proposed and their operation and steady-state characteristics are examined in detail. The feasibility of each new converter is confirmed with results obtained from an experimental prototype and the feasibility of a control method for the inverter is confirmed with simulation work using commercially available software such as MATLAB and PSIM

A Comparison between Different Snubbers for Flyback Converters

The DC-DC flyback power converter is widely used in low power commercial and industrial applications ( \u3e 150 W) such as in computers, telecom, consumer electronics because it is one of the simplest and least expensive converter topologies with transformer isolation. Its main power circuit consists of just a semiconductor device like a MOSFET operating as a switch, a transformer, an output diode and an output filter capacitor. The converter switch, however, is susceptible to high voltage spikes due to the interaction between its output capacitance and the leakage inductance of the transformer. These spikes can exceed the ratings of the switch, thus destroying the device, and thus flyback converters are always implemented with some sort of snubber circuit that can clamp any voltage spikes that may appear across their switch. There are two types of snubbers: passive snubbers that consist of passive electrical components such as capacitors, inductors and diodes and active snubbers, that consist of passive components and an active semiconductor switch. It is generally believed that passive snubbers are less expensive but also less efficient than active snubbers, but this belief has been placed in doubt with recent advances in passive snubber technology. Flyback converter with regenerative passive snubbers that dissipate little energy have been recently proposed and have greater efficiency than traditional passive snubbers. Although the efficiency of passive snubbers has improved, no comparison has been made between these new passive snubbers and active snubbers as it is still assumed that active snubbers are always more efficient. The main focus of this thesis is to compare the performance of an example passive snubber and an example active snubber. These example snubber circuits have been selected as being among the best of their type. In this thesis, the steady-state operation of each snubber circuit is explained in detail and analyzed, the results of the analysis is used to create a procedure for the design of key components, and the procedure is demonstrated with a design example. The results of the design examples were used to build prototypes of flyback converters with each example snubber and the prototypes were used to obtain experimental results. Based on these experimental results, conclusions about the efficiency of flyback converters with passive regenerative and active snubbers operating under various input line and output load conditions are made in this thesi

Resonant Hybrid Flyback, a New Topology for High Density Power Adaptors

In this article, an innovative power adaptor based on the asymmetrical pulse width modulation (PWM) flyback topology will be presented. Its benefits compared to other state-of-the-art topologies, such as the active clamp flyback, are analyzed in detail. It will also describe the control methods to achieve high efficiency and power density using zero-voltage switching (ZVS) and zero-current switching (ZCS) techniques over the full range of the input voltage and the output load, providing comprehensive guidelines for the practical design. Finally, we demonstrate the convenience of the proposed design methods with a 65 W adaptor prototype achieving a peak efficiency of close to 95% and a minimum efficiency of 93.4% at full load over the range of the input voltage, as well as a world-class power density of 22 W/inch3 cased.This research is financed by Infineon Tecnologias AG

DC-DC and AC-DC Converters Based on Three-Phase DC-DC Topologies

Power electronics is the field of electrical engineering that uses power semiconductor devices along with passive elements such as inductors, capacitor and transistors to convert electrical power that can be generated by a source to a form that is suitable for user loads. The main focus of this thesis is on the development of new DC-DC and AC-DC topologies that are based on three-phase DC-DC converters. Three-phase DC-DC converters take an input DC voltage, convert it into a high-frequency AC voltage that is then stepped up or down, then rectify and filter this voltage to produce an output DC voltage. They are implemented with a high-frequency three-phase transformer in their topology rather than a single-phase transformer. These converters are very attractive over other topologies that have a single-phase transformer in their topologies for several reasons. First, just one three-phase DC-DC converter can be used instead of using three DC-DC converters in parallel for particular applications; this advantage is especially attractive for higher power applications. In addition, by using three-phase DC-DC converters, the ripple of the source current is significantly reduced and that means less filtering is needed. Moreover, the components of the converter will have less current stress because current is split among three-phases. In this thesis, new DC-DC and AC-DC converters that are based on three-phase DC-DC topology are proposed. The proposed converters use fewer active switches than other previously proposed converters of similar type, thus resulting in lower cost and simpler operation. For each of the proposed converters, its steady-state characteristics are determined by mathematical analysis and procedure for the design of key converter components is developed. The feasibility of each proposed converter has been confirmed with results that have been obtained from experimental prototypes. For one of the proposed converters, a comparison between the operation of one of the proposed converters operating with traditional silicon devices (Si) and that with the converter operating with new silicon-carbide devices (SiC) was made to examine its performance with both types of devices

A Control Scheme for an AC-DC Single-Stage Buck-Boost PFC Converter with Improved Output Ripple Reduction

AC-DC power factor correction (PFC) single-stage converters are attractive because of their cost and their simplicity. In these converters, both PFC and power conversion are done at the same time using a single converter that regulates the output. Since they have only a single controller, these converters operate with an intermediate transformer primary-side DC bus voltage that is unregulated and is dependent on the converters’ operating conditions and component values. This means that the DC bus voltage can vary significantly as line and load conditions are changed. Such a variable DC bus voltage makes it difficult to optimally design the converter transformer as well as the DC bus capacitor. One previously proposed single-stage AC-DC converter, the Single-Stage Buck-Boost Direct Energy Transfer (SSBBDET) converter has a clamping mechanism that can clamp the DC bus voltage to a pre-set limit. The clamping mechanism, however, superimposes a low frequency 120 Hz AC component on the output DC voltage so that some means must be taken to reduce this component. These means, however, make the converter transient slow and sluggish. The main objective of this thesis is to minimize the 120 Hz output ripple component and to improve the dynamic response of the SSBBDET converter by using a new control scheme. In the thesis, the operation of the SSBBDET converter is reviewed and the proposed control method is introduced and explained in detail. Key design considerations for the design of the converter controller are discussed and the converter’s ability to operate with fixed DC bus voltage, low output ripple and fast dynamic response is confirmed with experimental results obtained from a prototype converter

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

Highly Integrated Dc-dc Converters

A monolithically integrated smart rectifier has been presented first in this work. The smart rectifier, which integrates a power MOSFET, gate driver and control circuitry, operates in a self-synchronized fashion based on its drain-source voltage, and does not need external control input. The analysis, simulation, and design considerations are described in detail. A 5V, 5-µm CMOS process was used to fabricate the prototype. Experimental results show that the proposed rectifier functions as expected in the design. Since no dead-time control needs to be used to switch the sync-FET and ctrl-FET, it is expected that the body diode losses can be reduced substantially, compared to the conventional synchronous rectifier. The proposed self-synchronized rectifier (SSR) can be operated at high frequencies and maintains high efficiency over a wide load range. As an example of the smart rectifier\u27s application in isolated DC-DC converter, a synchronous flyback converter with SSR is analyzed, designed and tested. Experimental results show that the operating frequency could be as high as 4MHz and the efficiency could be improved by more than 10% compared to that when a hyper fast diode rectifier is used. Based on a new current-source gate driver scheme, an integrated gate driver for buck converter is also developed in this work by using a 0.35µm CMOS process with optional high voltage (50V) power MOSFET. The integrated gate driver consists both the current-source driver for high-side power MOSFET and low-power driver for low-side power iv MOSFET. Compared with the conventional gate driver circuit, the current-source gate driver can recovery some gate charging energy and reduce switching loss. So the current-source driver (CSD) can be used to improve the efficiency performance in high frequency power converters. This work also presents a new implementation of a power supply in package (PSiP) 5MHz buck converter, which is different from all the prior-of-art PSiP solutions by using a high-Q bondwire inductor. The high-Q bondwire inductor can be manufactured by applying ferrite epoxy to the common bondwire during standard IC packaging process, so the new implementation of PSiP is expected to be a cost-effective way of power supply integration