Very low voltage, high current output requirement have necessitated improvements in power supply's density and efficiency. Existing power conversion techniques cannot meet very stringent size and efficiency requirements. By applying the proposed magnetic integration procedure, new integrated magnetic circuits featuring low loss, simple structure, and ripple cancellation technique are then developed to overcome the limitations of prior art. Both cores and windings are integrated. Consequently, the power loss and the size of the integrated magnetic device are greatly reduced. Detailed analysis and design considerations of the proposed circuits are presented. As a result of applying the proposed technique, very high density, high efficiency, low voltage, high current power modules were developed. A typical example features an isolated 3.3V/30A power module with a power density of 130W/in3 and an efficiency of 90% at 500 KHz switching frequency. / Ph. D.

Advances in very large scale integration (VLSI) technologies impose challenges for voltage regulator modules (VRM) to deliver high-quality power to modern microprocessors. As an enabling technology, multiphase converters have become the standard practice in VRM industry. The primary objectives of this dissertation are to develop advanced topologies and innovative integrated magnetics for high-efficiency, high-power-density and fast-transient VRMs. The optimization of multiphase VRMs has also been addressed. Today's multiphase VRMs are almost universally based on the buck topology. With increased input voltage and decreased output voltage, the multiphase buck converter suffers from a very small duty cycle and cannot achieve a desirable efficiency. The multiphase tapped-inductor buck converter is one of the simplest topologies with a decent duty cycle. However, the leakage inductance of its tapped inductors causes a severe voltage spike problem. An improved topology, named the multiphase coupled-buck converter, is proposed. This innovative topology enables the use of a larger duty cycle with clamped device voltage and recovered leakage energy. Under the same transient responses, the multiphase coupled-buck converter has a significantly better efficiency than the multiphase buck converter. By integrating all the magnetic components into a single core, in which the windings are wound around the center leg and the air gaps are placed on the two outer legs, it is possible for multiphase VRMs to further improve efficiency and cut the size and cost. Unfortunately, this structure suffers from an undesirable core structure and huge leakage inductance. An improved integrated magnetic structure is proposed to overcome these limitations. All the windings are wound around the two outer legs and the air gap is placed on the center leg. The improved structure also features the flux ripple cancellation in the center leg and strongly reverse-coupled inductors. Both core loss and winding loss are reduced. The steady-state current ripples can be reduced without compromising the transient responses. The overall efficiency of the converter is improved. The input inductor can also be integrated in the improved integrated magnetic structure. Currently, selecting the appropriate number of channels for multiphase VRMs is still an empirical trial-and-error process. This dissertation proposes a methodology for determining the right number of channels for the optimal multiphase design. The problem formulation and general method for the optimization are proposed. Two examples are performed step by step to demonstrate the proposed optimization methodology. Both are focused on typical VRM 9.0 designs for the latest Pentium 4® microprocessors and their results are compared with the industry practice. / Ph. D.

The use of computers in the modern world has become prevalent in all aspects of life. The size of these machines has decreased dramatically while the capability has increased exponentially. A special DC-DC converter called a VRM (Voltage Regulator Module) is used to power these machines. The VRM faces the task of supplying high current and high di/dt to the microprocessor while maintaining a tight load regulation. As computers have advanced, so have the VRM's used to power them. Increasing the current and di/dt of the VRM to keep up with the increasing demands of the microprocessor does not come without a cost. To provide the increased di/dt, the VRM must use a higher number of capacitors to supply the transient energy. This is an undesirable solution because of the increased cost and real estate demands this would lead to in the future. Another solution to this problem is to increase the switching frequency and control bandwidth of the VRM. As the switching frequency increases the VRM is faced with efficiency and thermal problems. The current buck topologies suffer large drops in efficiency as the frequency increases from high switching losses. Resonant or soft switching topologies can provide a relief from the high switching loss for high frequency power conversion. One disadvantage of the resonant schemes is the increased conduction losses produced by the circulating energy required to produce soft switching. As the frequency rises, the additional conduction loss in the resonant schemes can be smaller than the switching loss encountered in the hard switched buck. The topology studied in this work is the 12V non-isolated ZVS self-driven presented in [1]. This scheme offered an increased efficiency over the state of the art industry design and also increased the switching frequency for capacitor reduction. The goal of this research was to study this topology and improve the magnetic design to decrease the cost while maintaining the superior performance. The magnetics used in resonant converters are very important to the success of the design. Often, the leakage inductance of the magnetics is used to control the ZVS or ZCS switching operation. This work presents a new improved magnetic solution for use in the 12V non-isolated ZVS self-driven scheme which increases circuit operation, flexibility, and production feasibility. The improved magnetic structure is simulated using 3D FEA verification and verified in hardware design. / Master of Science

The intermediate bus architecture employing the 48V bus converter is one of the most popular power architecture. 48V to 12V bus converter has wide applications in telecommunications, networks, aerospace, and military, etc. However, today's state of the art products has low power rating or power density and becomes difficult to satisfy the demand of increasing power of the loads. To improve the current design, a GaN (Gallium Nitride) based two-stage solution is proposed for the bus converter. The first stage Buck converter regulates the 40V to 60V variable input to a fixed 36V bus voltage. The second stage LLC converter convert the 36V to 12V by a 3:1 transformer. The whole solution achieves the fixed frequency control. The thesis focus on the detail design and optimization of LLC converter, especially its transformer. To have high density and high efficiency, the transformer design becomes critical at MHz frequency. The matrix transformer concept is applied and a merged winding structure is used for flux cancellation, which effectively reduces the AC winding losses. A new fully interleaved termination and via design is proposed. It achieves significant reduction in loss and leakage flux. In addition, to study the current sharing of parallel winding layers, a 1-D analytic model is proposed and a symmetrical winding layer scheme is used to balance the current distribution. The hardware is built and tested. The proposed two-stage converter achieves the best performance compared to the current market. / Master of Science / Intermediate bus architecture (IBA) has wide applications in telecommunication, server and computing, and military power supplies. The intermediate bus converter (IBC) is the key stage in the IBA, where the DC bus voltage from the front-end power supply is converted to a lower intermediate bus voltage. Traditional IBC suffers from bulky magnetic components including inductors and transformers. This work illustrates the design and implementation of a two-stage IBC, where the first-stage Buck converter will provide regulation and the second stage LLC converter will provide isolation. Thanks to the soft-switching capability of LLC, the magnetic volume can be significantly reduced by raising the switching frequency of the converter. Therefore, planar magnetics can be used and placed directly inside of the printing circuit board (PCB), which allows for higher power densities and easy manufacturing of the magnetics and overall converter. However, as the frequency goes higher, the AC losses of the transformer caused by the eddy current, skin effect, and proximity effect become dominant. As a result, high-frequency transformer design becomes the key for the converter design. First, matrix transformer concept is applied to distribute the high current and reduce the conduction loss. Second, a novel merged winding structure is proposed for better transformer winding interleaving. Third, a new terminal structure of the transformer is proposed. Finally, the current sharing between parallel windings are modeled and studied. All the efforts result in great loss reduction. The prototype were verified and compared to the current converters that are on the market in the 48V – 12V area of IBCs.

In the early 1990's, with the boom of the Internet and the advancements in telecommunications, the demand for high-speed communications systems has reached every corner of the world in forms such as, phone exchanges, the internet servers, routers, and all other types of telecommunication systems. These communication systems demand more data computing, storage, and retrieval capabilities at higher speeds, these demands place a great strain on the power system. To lessen this strain, the existing power architecture must be optimized. With the arrival of the age of high speed and power hungry microprocessors, the point of load converter has become a necessity. The power delivery architecture has changed from a centralized distribution box delivering an entire system's power to a distributed architecture, in which a common DC bus voltage is distributed and further converted down at the point of load. Two common distributed bus voltages are 12 V for desktop computers and 48 V for telecommunications server applications. As industry strives to design more functionality into each circuit or motherboard, the area available for the point of load converter is continually decreasing. To meet industries demands of more power in smaller sizes power supply designers must increase the converter's switching frequencies. Unfortunately, as the converter switching frequency increases the efficiency is compromised. In particular, the switching, gate drive and body diode related losses proportionally increase with the switching frequency. This thesis introduces a loss saving self-driven method to drive the secondary side synchronous rectifiers. The loss saving self-driven method introduces two additional transformers that increase the overall footprint of the converter. Also, this thesis proposes a new magnetic integration method to eliminate the need for the two additional gate driver magnetic cores by allowing three discrete power signals to pass through one single magnetic structure. The magnetic integration reduces the overall converter footprint. / Master of Science

This Thesis examines the operation and dynamic performance of a single-stage, single-switch power factor corrector, S4 PFC, with an integrated magnetic device, IM. Also detailed isthe development and analysis of a high power light emitting diode, HP LED, power factorcorrection converter and proposed voltage regulation band control approach.The S4 PFC consists of a cascaded discontinuous current mode, DCM, boost stage anda continuous current mode, CCM, forward converter. The S4 PFC achieves a high powerfactor, low input current harmonics and a regulated voltage output, utilising a singleMOSFET. A steady-state analysis of the S4 PFC with the IM is performed, identifying theoperating boundary conditions for the DCM power factor correction stage and the CCMoutput voltage regulation stage. Integrated magnetic analysis focuses on understanding theperformance, operation and generated flux paths within the IM core, ensuring the device doesnot affect the normal operation of the converter power stage. A design method for the S4 PFCwith IM component is developed along with a cost analysis of this approach. Analysis predictsthe performance of the S4 PFC and the IM, and the theoretical work is validated by MATLABand SABER simulations and measurements of a 180 W prototype converter.It is not only the development of new topological approaches that drives theadvancement of power electronic techniques. The recent emergence of HP LEDs has led to aflurry of new application areas for these devices. A DCM buck-boost converter performs thepower factor correction and energy storage, and a cascaded boundary conduction current modebuck converter regulates the current through the LED arrays. To match the useful operatinglifetime of the HP LEDs, electrolytic capacitors are not used in the PFC converter. Analysisexamines the operation and dynamic characteristics of a PFC converter with low capacitiveenergy storage capacity and its implications on the control method. A modified regulationband control approach is proposed to ensure a high power factor, low input current harmonicsand output voltage regulation of the PFC stage. Small signal analysis describes the dynamicperformance of the PFC converter, Circle Criterion is used to determine the loop stability.Theoretical work is validated by SABER and MATLAB simulations and measurements of a180 W prototype street luminaire.

With the increasing demand for small and cost efficient DC/DC converters, the power converters are expected to operate with high efficiency. Magnetics components design is one of the biggest challenges in achieving the higher power density and higher efficiency due to the significant portion of magnetics components volume in the whole power system. At the same time, most of the experimental phenomena are related to the magnetics components. So, good magnetics components design is one of the key issues to implement low voltage high current DC/DC converter. Planar technology has many advantages. It has low profile construction, low leakage inductance and inter-winding capacitance, excellent repeatability of parasitic properties, cost efficiency, great reliability, and excellent thermal characteristics. On the other side, however, planar technology also has some disadvantages. Although it improves thermal performance, the planar format increases footprint area. The fact that windings can be placed closer in planar technology to reduce leakage inductance also often has an unwanted effect of increasing parasitic capacitances. In this dissertation, the planar magnetics designs for high current low voltage applications are thoroughly investigated and one CAD design methodology based on FEA numerical analysis is proposed. Because the frequency dependant parasitic parameters of magnetics components are included in the circuit model, the whole circuit analysis is more accurate. When it is implemented correctly, integrated magnetics technique can produce a significant reduction in the magnetic core content number and it can also result in cost efficient designs with less weight and smaller volume. These will increase the whole converter's power density and power efficiency. For high output current and low output voltage applications, half bridge in primary and current doublers in secondary are proved to be a very good solution. Based on this topology, four different integrated magnetics structures are analyzed and compared with each other. One unified model is introduced and implemented in the circuit analysis. A new integrated magnetics component core shape is proposed. All simulation and experimental results verify the integrated magnetics design. There are several new magnetics components applications shown in the dissertation. Active transient voltage compensator is a good solution to the challenging high slew rate load current transient requirement of VRM. The transformer works as an extra voltage source. During the transient periods, the transformer injects or absorbs the extra transient to or from the circuit. A peak current mode controlled integrated magnetics structure is proposed in the dissertation. Two transformers and two inductors are integrated in one core. It can force the two input capacitors of half bridge topology to have the same voltage potential and solve the voltage unbalance issue. The proposed integrated magnetics structure is simple compared with other methods implementing the current mode control to half bridge topology. Circuit analysis, simulation and experimental results verify the feasibility of these applications.

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.

In the present day, owing to the increasing number of electronic loads such as computer power supplies, Compact fluorescent lamps (CFL) and the increasing number of sources such as solar photovoltaics, fuel cells (DC sources), DC Micro-grids provide a more efficient solution compared to the AC counterpart in terms of the number of stages involved in conversion. Also, the ability to be readily buffered to storage elements is an advantage in a DC system. Apart from this, there are no issues of frequency stability, reactive power transfer and ac power losses. A DC micro-grid is effectively a multi-port dc-dc converter. The ports refer to the various sources and loads that are part of the micro-grid. Sources could be unidirectional (as in the case of PV, load) or bidirectional (as in the case of batteries). Interfacing a variety of ports and controlling power flow between these ports presents an interesting challenge. Commonly used topologies interface the various ports at the DC bus capacitor thereby making the DC bus capacitor bulky. Apart from this, the DC bus coupled topologies route power from one port to another via the central capacitor. This increases the number of stages in transferring power from one port to another. An alternative topology is to use the active bridge type converters where dynamic power flow equations are required to control inter-port power flow. But, as the number of stages increase, the computations get tedious.In this thesis, a novel topology is proposed that uses a UU type transformer core to interface all the power ports. This alleviates the problems faced in the DC bus coupled topologies. A PWM scheme to control simultaneous power flow from each of the ports is also proposed in this thesis. The PWM scheme enables the usage of simple constant frequency average current mode control to dynamically control power sharing ratio between the various ports delivering to loads. By means of the proposed PWM scheme and the control scheme, the drawbacks of the active bridge topologies are alleviated. Using the proposed topology and the PWM scheme, a prototype micro-grid system is developed for a system comprising of the utility grid, batteries, solar PVs and resistive loads. Yet another aspect of the thesis explores the concept of connecting multiple micro-grids in order to create a 'local power network'. A potential application for this could be in interconnecting residential buildings and routing power from one house to another in order to balance demand and supply among these houses. This is against the growing trend of using the utility grid to also sink power and subsequently route it to other houses connected to the grid. Unfortunately not all areas have access to the utility grid. Additionally, turning the grid bidirectional requires that a number of standards be met and policies be created. But, the standard for using a local network that only involves a unidirectional grid is fixed by the community that owns such a network. In a crude sense, this scenario can be compared to the existence of a local area network to transfer information among users of the network. In this thesis, a prototype local power network interconnecting two micro-grids has been implemented.

Growing concerns about climate change have led to the world experiencing an unprecedented push towards renewable energy. Economic drivers and government policies mean that small, distributed forms of generation, like solar photovoltaics, will play a large role in our transition to a clean energy future. In this thesis, a novel DC-DC converter known as the Coupled Inductors Combined Cuk-SEPIC' (CI-CCS) converter is explored, which is particularly attractive for these photovoltaic applications. A topological modification is investigated which provides several benefits, including increased power density, efficiency, and operational advantages for solar energy conversion. The converter, which is based on the combination of the Cuk and SEPIC converters, provides a bipolar output (i.e. both positive and negative voltages). This converter also offers both step-up and step-down capabilities with a continuous input current, and uses only a single, ground-referenced switching device. A significant enhancement to this converter is proposed: magnetic coupling of the converter's three inductors. This can substantially reduce the CI-CCS converter's input current ripple - an important benefit for maximum power point tracking (MPPT) in photovoltaic applications. The effect of this coupling is examined theoretically, and optimisations are performed - both analytically and in simulations - to inform the design of a 4 kW prototype CI-CCS converter, switched at a high frequency (100 kHz) with a silicon carbide (SiC) MOSFET. Simulation and experimental results are then presented to demonstrate the CI-CCS converter's operation and highlight the benefits of coupling its inductors. An efficiency analysis is also undertaken and its sources of losses are quantified. The converter is subsequently integrated into a domestic photovoltaic system to provide a practical demonstration of its suitability for such applications. MPPT is integrated into the CI-CCS DC-DC converter, and a combined half bridge/T-type converter is developed and paired with the CI-CCS converter to form an entirely transformerless single-phase solar energy conversion system. The combination of the CI-CCS converter's bipolar DC output with the combined half bridge/T-type converter's bipolar DC input allows grounding at both the photovoltaic panels and the AC grid's neutral point. This eliminates high frequency common mode voltages from the PV array, which in turn prevents leakage currents. The entire system can be operated in grid-connected mode - where the objective is to maximise power extracted from the photovoltaic system, and is demonstrated in stand-alone mode - where the objective is to match solar generation with the load's power demands.