105 research outputs found

    Soft-Switching Techniques of Power Conversion System in Automotive Chargers

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    abstract: This thesis investigates different unidirectional topologies for the on-board charger in an electric vehicle and proposes soft-switching solutions in both the AC/DC and DC/DC stage of the converter with a power rating of 3.3 kW. With an overview on different charger topologies and their applicability with respect to the target specification a soft-switching technique to reduce the switching losses of a single phase boost-type PFC is proposed. This work is followed by a modification to the popular soft-switching topology, the dual active bridge (DAB) converter for application requiring unidirectional power flow. The topology named as the semi-dual active bridge (S-DAB) is obtained by replacing the fully active (four switches) bridge on the load side of a DAB by a semi-active (two switches and two diodes) bridge. The operating principles, waveforms in different intervals and expression for power transfer, which differ significantly from the basic DAB topology, are presented in detail. The zero-voltage switching (ZVS) characteristics and requirements are analyzed in detail and compared to those of DAB. A small-signal model of the new configuration is also derived. The analysis and performance of S-DAB are validated through extensive simulation and experimental results from a hardware prototype. Secondly, a low-loss auxiliary circuit for a power factor correction (PFC) circuit to achieve zero voltage transition is also proposed to improve the efficiency and operating frequency of the converter. The high dynamic energy generated in the switching node during turn-on is diverted by providing a parallel path through an auxiliary inductor and a transistor placed across the main inductor. The paper discusses the operating principles, design, and merits of the proposed scheme with hardware validation on a 3.3 kW/ 500 kHz PFC prototype. Modifications to the proposed zero voltage transition (ZVT) circuit is also investigated by implementing two topological variations. Firstly, an integrated magnetic structure is built combining the main inductor and auxiliary inductor in a single core reducing the total footprint of the circuit board. This improvement also reduces the size of the auxiliary capacitor required in the ZVT operation. The second modification redirects the ZVT energy from the input end to the DC link through additional half-bridge circuit and inductor. The half-bridge operating at constant 50% duty cycle simulates a switching leg of the following DC/DC stage of the converter. A hardware prototype of the above-mentioned PFC and DC/DC stage was developed and the operating principles were verified using the same.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

    Control And Topology Improvements In Half-bridge Dc-dc Converters

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    Efficiency and transient response are two key requirements for DC-DC converters. Topology and control are two key topics in this dissertation. A variety of techniques for DC-DC converter performance improvement are presented in this work. Focusing on the efficiency issue, a variety of clamping techniques including both active and passive methods are presented after the ringing issues in DC-DC converters are investigated. By presenting the clamping techniques, a big variety of energy management concepts are introduced. The active bridge-capacitor tank clamping and FET-diode-capacitor tank clamping are close ideas, which transfer the leakage inductor energy to clamping capacitor to prevent oscillation between leakage inductor and junction capacitor of MOSFETs. The two-FET-clamping tank employs two MOSFETs to freewheeling the leakage current when the main MOSFETs of the half-bridge are both off. Driving voltage variation on the secondary side Synchronous Rectifier (SR) MOSFETs in self-driven circuit due to input voltage variation in bus converter applications is also investigated. One solution with a variety of derivations is proposed using zerner-capacitor combination to clamping the voltage while maintaining reasonable power losses. Another efficiency improvement idea comes from phase-shift concept in DC-DC converters. By employing phase-shift scheme, the primary side and the secondary side two MOSFETs have complementary driving signals respectively, which allow the MOSFET to be turned on with Zero Voltage Switching (ZVS). Simulation verified the feasibility of the proposed phase-shifted DC-DC converter. From the control scheme point of view, a novel peak current mode control concept for half-bridge topologies is presented. Aiming at compensating the imbalanced voltage due to peak current mode control in symmetric half-bridge topologies, an additional voltage compensation loop is used to bring the half-bridge capacitor voltage back to balance. In the proposed solutions, one scheme is applied on symmetric half-bridge topology and the other one is applied on Duty-cycle-shifted (DCS) half-bridge topology. Both schemes employ simple circuitry and are suitable for integration. Loop stability issues are also investigated in this work. Modeling work shows the uncompensated half-bridge topology cannot be stabilized under all conditions and the additional compensation loop helps to prevent the voltage imbalance effectively

    Low Voltage Regulator Modules and Single Stage Front-end Converters

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    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

    Development of Efficient Soft Switching Synchronous Buck Converter Topologies for Low Voltage High Current Applications

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    Switched mode power supplies (SMPS) have emerged as the popular candidate in all the power processing applications. The demand is soaring to design high power density converters. For reducing the size, weight, it is imperative to channelize the power at high switching frequency. High switching frequency converters insist upon soft switching techniques to curtail the switching losses. Several soft switching topologies have been evolved in the recent years. Nowadays, the soft switching converters are vastly applied modules and the demand is increasing for high power density and high efficiency modules by minimizing the conduction and switching losses. These modules are generally observed in many applications such as laptops, desktop processors for the enhancement of the battery life time. Apart from these applications, solar and spacecraft applications demand is increasing progressively for stressless and more efficient modules for maximizing the storage capacity which inturn enhances the power density that improves the battery life to supply in the uneven times. Modern trends in the consumer electronic market focus increases in the demand of lower voltage supplies. Conduction losses are significantly reduced by synchronous rectifiers i.e., MOSFET’s are essentially used in many of the low voltage power supplies. Active and passive auxiliary circuits are used in tandem with synchronous rectifier to diminish the crucial loss i.e., switching loss and also it minimizes the voltage and current stresses of the semiconductor devices. The rapid progress in the technology and emerging portable applications poses serious challenges to power supply design engineers for an efficient power converter design at high power density. The primary aim is to design and develop high efficiency, high power density topologies like: buck, synchronous buck and multiphase buck converters with the integration of soft switching techniques to minimize conduction and switching losses sustaining the voltage and current stresses within the tolerable range. In this work, two ZVT-ZCT PWM synchronous buck converters are introduced, one with active auxiliary circuit and the other one with passive auxiliary circuit. The operating principle and comprehensive steady state analysis of the ZVT-ZCT PWM synchronous buck converters are presented. The converters are designed to have high efficiency and low voltage that is suitable for high power density application. The semiconductor devices used in the topologies in addition to the main switch operate with soft switching conditions. The viii Abstract topologies proposed render a large overall efficiency in contrast to the contemporary topologies. In addition the circuit’s size is less, reliable and have high performance-cost ratio. The new generation microprocessor demands the features such as low voltage, high current, high power density and high efficiency etc., in the design of power supplies. The supply voltage for the future generation microprocessors must be low, in order to decrease the power consumption. The voltage levels are dripping to a level even less than 0.7V, and the power consumption increases as there is an increase in the current requirement for the processor. In order to meet the demands of the new generation microprocessor power supply, a soft switching multiphase PWM synchronous buck converter is proposed. The losses in the proposed topology due to increasing components are pared down by the proposed soft switching technique. The proposed converters in this research work are precisely described by the mathematical modelling and their operational modes. The practicality of the proposed converters for different applications is authenticated by their simulation and experimental results

    Analysis and design of a dual series-resonant DC-DC converter

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    DC-DC conversion systems are vital components in DC distribution systems, renewable energy generation systems, telecommunication systems, and portable electronics devices. The extensive applications of DC-DC converter have resulted in continuous improvement in the topologies and control methods in these converters. The challenge is to build a converter that improves factors such as efficiency of conversion and power density with a simple topology, which incorporates simplified switching and control schemes and fewer numbers of active and passive components to reduce the manufacturing cost. This thesis addresses this challenge by proposing an alternative topology of a DC-DC converter based on dual series-resonant circuits. The proposed topology operates under zero voltage switching (ZVS) and zero current switching (ZCS) conditions to reduce the switching losses. It achieves two degrees of freedom (i.e., duty ratio and switching frequency) to control the output voltage of the converter, which results in both step-down and step-up voltage conversions. The number of active components is limited to two semiconductor switches and two rectifying diodes, which reduces the manufacturing cost of the converter. Detailed analytical analysis is carried out using the extended describing function methodology to characterize the steady state and small signal operation of the converter. Small-signal transfer functions are developed and used to propose a simple closed-loop control scheme to control the output voltage of the converter. An experimental 10 V, 40 W prototype of the proposed converter is built and tested to investigate its operation and confirm its features. The improvement in the efficiency of the converter and power transfer capability of the proposed dual series-resonant converter compared with the traditional single series-resonant circuit, which is used in the interleaved topologies are experimentally verified. In addition, soft switching operation of the converter is realized and a simple control scheme is developed to control the output voltage of the converter. A detailed and step-by-step design procedure is developed, which can be used to customize the design of the converter for different levels of power and voltage. It is shown that the proposed dual series-resonant DC-DC converter provides significant improvement regarding power density, efficiency of power conversion, simplicity of switching and control schemes, and reduced number of converter components resulting in a low cost and compact converter

    Inductorless bi-directional piezoelectric transformerbased converters: Design and control considerations.

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    Soft-Switching DC-DC Converters

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    Power electronics converters are implemented with switching devices that turn on and off while power is being converted from one form to another. They operate with high switching frequencies to reduce the size of the converters\u27 inductors, transformers and capacitors. Such high switching frequency operation, however, increases the amount of power that is lost due to switching losses and thus reduces power converter efficiency. Switching losses are caused by the overlap of switch voltage and switch current during a switching transition. If, however, either the voltage across or the current flowing through a switch is zero during a switching transition, then there is no overlap of switch voltage and switch current so in theory, there are no switching losses. Techniques that ensure that this happens are referred to as soft-switching techniques in the power electronics literature and there are two types: zero-voltage switching (ZVS) and zero-current switching (ZCS). For pulse-width modulated (PWM) Dc-Dc converters, both ZVS and ZCS are typically implemented with auxiliary circuits that help the main power switches operate with soft-switching. Although these auxiliary circuits do help improve the efficiency of the converters, they increase their cost. There is, therefore, motivation to try to make these auxiliary circuits as simple and as inexpensive as possible. Three new soft-switching Dc-Dc PWM converters are proposed in this thesis. For each converter, a very simple auxiliary circuit that consists of only a single active switching device and a few passive components is used to reduce the switching losses in the main power switches. The outstanding feature of each converter is the simplicity of its auxiliary circuit, which unlike most other previously proposed converters of similar type, avoids the use of multiple active auxiliary switches. In this thesis, the operation of each proposed converter is explained, analyzed, and the results of the analysis are used to develop a design procedure to select key component values. This design procedure is demonstrated with an example that was used in the implementation of an experimental prototype. The feasibility of each proposed converter is confirmed with experimental result obtained from a prototype converter

    Phase shifted bridge converter for a high voltage application

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    High-efficiency voltage source converters with silicon super-junction MOSFETs

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    High-efficiency power converters have the benefits of minimising energy consumption, reducing costs, and realising high power densities. The silicon super-junction (SJ) MOSFET is an attractive device for high-efficiency applications. However, its highly non-linear output capacitance and the reverse recovery properties of its intrinsic diode must be addressed when used in voltage source converters (VSCs). The research in this thesis aims at addressing these two problems and realising high efficiency. Initially, state-of-art techniques in the literature are reviewed. In order to develop a solution with simple hardware, no major auxiliary magnetic components, and no onerous timing requirements, a dual-mode switching technique is proposed. The technique is demonstrated using a SJ MOSFET based bridge-leg circuit. The hardware performance is then experimentally investigated with different power semiconductor device permutations. The transition conditions between the two switching modes do not have to be tightly set in order to maintain a high efficiency. The dual-mode switching technique is then further investigated with a current transformer (CT) arrangement embedded in the MOSFET’s gate driver circuit in order to control the profile of the MOSFET’s incoming drain current at turn on. The dual-mode switching technique, with or without a CT scheme, is shown to achieve high efficiency with minimal additional hardware.High-efficiency power converters have the benefits of minimising energy consumption, reducing costs, and realising high power densities. The silicon super-junction (SJ) MOSFET is an attractive device for high-efficiency applications. However, its highly non-linear output capacitance and the reverse recovery properties of its intrinsic diode must be addressed when used in voltage source converters (VSCs). The research in this thesis aims at addressing these two problems and realising high efficiency. Initially, state-of-art techniques in the literature are reviewed. In order to develop a solution with simple hardware, no major auxiliary magnetic components, and no onerous timing requirements, a dual-mode switching technique is proposed. The technique is demonstrated using a SJ MOSFET based bridge-leg circuit. The hardware performance is then experimentally investigated with different power semiconductor device permutations. The transition conditions between the two switching modes do not have to be tightly set in order to maintain a high efficiency. The dual-mode switching technique is then further investigated with a current transformer (CT) arrangement embedded in the MOSFET’s gate driver circuit in order to control the profile of the MOSFET’s incoming drain current at turn on. The dual-mode switching technique, with or without a CT scheme, is shown to achieve high efficiency with minimal additional hardware
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