State-variable modelling of CLL resonant converters

The paper presents the derivation and application of state-variable models to high-order topologies of resonant converters. In particular, a 3rd order CLL resonant circuit is considered with bridge rectification and both a capacitive output filter (voltage output), and an LC output filter (current output). The state-variable model accuracy is verified against component-based simulation packages (Spice) and practical measurements, and it is shown that the resulting models facilitate rapid analysis compared to their integration-based counterparts (Spice, Saber), without the loss of accuracy normally associated with fundamental mode approximation (FMA) techniques. Moreover, unlike FMA, the models correctly predict the resonant peaks associated with harmonic excitation of the tank resonance. Subsequently, it is shown that excitation of the resonant tank by odd harmonics of the input voltage can be utilised to provide overcurrent protection in the event of an output short-circuit. Further, through judicious control of operating frequency, it is shown that 'inductive' zero voltage switching (ZVS) can still be obtained, facilitating reductions in gate-drive switching losses, thereby improving efficiency and thermal management of the supply under fault conditions. Although the results are ultimately generic to other converter counterparts, measured results from two prototype 36 V input, 11-14.4V output, 3rd - order CLL converters are included to practically demonstrate the attributes of the proposed analysis and control schemes

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 Design of LLC Resonant Converter with Peak Gain Adjustment

The main advantages of a half-bridge LLC resonant DC/DC converter having two inductors (LL) and a single capacitor (C) compared to the other load resonant converters are its less amount of circulating currents and large bandwidth for Zero Voltage Switching (ZVS). It also has the advantage of limited tuning of operating frequency to get the regulated output when variable frequency control method is implemented on the converter. This DC/DC converter is widely used in server and telecom applications due its higher efficiency and reliability. In this paper, a novel design using peak gain adjustment is proposed for a LLC resonant DC/DC converter with a design example of 400V/12V-5A used in server based applications. For the specifications of the converter mentioned, an experimental set up is built and evaluated with the Texas instruments power switch FSFR 2100 IC in closed loop configuration. The experimental results proved an improved efficiency of 94% for the converter with the novel design proposed

Modulation scheme for the bidirectional operation of the Phase Shift Full Bridge Power Converter

This paper proposes a novel modulation technique for the bidirectional operation of the Phase Shift Full Bridge (PSFB) DC/DC power converter. The forward or buck operation of this topology is well known and widely used in medium to high power DC to DC converter applications. In contrast, backward or boost operation is less typical since it exhibits large drain voltage overshoot in devices located at the secondary or current-fed side; a known problem in isolated boost converters. For that reason other topologies of symmetric configuration are preferred in bidirectional applications, like CLLC resonant converter or Dual Active Bridge (DAB). In this work, we propose a modulation technique overcoming the drain voltage overshoot of the isolated boost converter at the secondary or current-fed side, without additional components other than the ones in a standard PSFB and still achieving full or nearly full ZVS in the primary or voltage-fed side along all the load range of the converter. The proposed modulation has been tested in a bidirectional 3.3 kW PSFB with 400 V input and 54.5 V output, achieving a 98 % of peak efficiency in buck mode and 97.5 % in boost mode operation. This demonstrates that the PSFB converter may become a relatively simple and efficient topology for bidirectional DC to DC converter applications

Analysis of an Isolated Bidirectional Ćuk Converter

The objective of this thesis is to perform an analysis of the isolated bidirectional Ćuk dc-dc converter topology and demonstrate the advantages and operation of this configuration through simulations using MATLAB/SimulinkTM and measurements collected from a 1.5-kW prototype tested at the Engineering Research Center (ENRC) laboratory of the University of Arkansas. The idea of integrating an active-clamp snubber circuit on each side of the converter, proposed by Dr. Sudip Mazumder from the University of Illinois, Chicago, limits the additional voltage stresses on the components due to the energy from the transformer’s leakage inductance. This is studied in this thesis to achieve zero voltage switching (ZVS) turn-ON functionality of all active devices, reducing the losses and size of passive components. In addition, this work evaluates three separate control parameters that are utilized for power transfer, ZVS region, and the circulating current of the converter. These three variables are the duty cycle of S_P1, namely d_1; the duty cycle of S_S1, namely d_2; and the phase-shift ratio, by the symbol ∆_∅. The theoretical analysis is validated through simulations using MATLAB/SimulinkTM and through a 1.5-kW prototype converter. In addition to the analysis of the results, conclusions and suggestions for future work are presented to enhance the system’s quality

A novel square-wave converter with bidirectional power flow

Author name used in this publication: K. W. E. ChengAuthor name used in this publication: D. SutantoVersion of RecordPublishe

A New ZVS-PWM Full-Bridge Boost Converter

Pulse-width modulated (PWM) full-bridge boost converters are used in applications where the output voltage is considerably higher than the input voltage. Zero-voltage-switching (ZVS) is typically implemented in these converters. The objective of this thesis is to propose, analyze, design, implement, and experimentally confirm the operation of a new Zero-Voltage-Switching PWM DC-DC full-bridge boost converter that does not have any of the drawbacks that other converters of this type have, such as a complicated auxiliary circuit, increased current stresses in the main power switches and load dependent ZVS operation. In this thesis, the general operating principles of the converter are reviewed, and the converter’s operation is discussed in detail and analyzed mathematically. As a result of the mathematical analysis, key voltage and current equations that describe the operation of the auxiliary circuit and other converter devices have been derived. The steady state equations of each mode of operation are used as the basis of a MATLAB program that is used to generate steady-state characteristic curves that shows the effect that individual circuit parameters have on the operation of the auxiliary circuit and the boost converter. Observations as to their steady-state characteristics are made and the curves are used as part of a design procedure to select the components of the converter, especially those of the auxiliary circuit. An experimental full-bridge DC-DC boost converter prototype is built based on the converter design and typically waveforms are presented to confirm the feasibility of the converter, as well as computer simulation results. The efficiency of the proposed converter operating with the auxiliary circuit is compared to that of a hard-switched PWM DC-DC full-bridge boost converter and the increased efficiency of the proposed converter is confirmed. Keywords: Power conversion, DC-DC converter, Full-bridge converter, Boost Converter, Zero-voltage-switching, Soft-switching

Analysis of an Isolated Bidirectional Ćuk Converter

The objective of this thesis is to perform an analysis of the isolated bidirectional Ćuk dc-dc converter topology and demonstrate the advantages and operation of this configuration through simulations using MATLAB/SimulinkTM and measurements collected from a 1.5-kW prototype tested at the Engineering Research Center (ENRC) laboratory of the University of Arkansas. The idea of integrating an active-clamp snubber circuit on each side of the converter, proposed by Dr. Sudip Mazumder from the University of Illinois, Chicago, limits the additional voltage stresses on the components due to the energy from the transformer’s leakage inductance. This is studied in this thesis to achieve zero voltage switching (ZVS) turn-ON functionality of all active devices, reducing the losses and size of passive components. In addition, this work evaluates three separate control parameters that are utilized for power transfer, ZVS region, and the circulating current of the converter. These three variables are the duty cycle of S_P1, namely d_1; the duty cycle of S_S1, namely d_2; and the phase-shift ratio, by the symbol ∆_∅. The theoretical analysis is validated through simulations using MATLAB/SimulinkTM and through a 1.5-kW prototype converter. In addition to the analysis of the results, conclusions and suggestions for future work are presented to enhance the system’s quality

A Three-Phase Single-Stage AC-DC ZVZCS PWM Full-Bridge Converter

It is standard practice to use two separate power converters to convert an ac input voltage to a desired and isolated dc output voltage. A front-end ac-dc converter is used to convert the input ac voltage into an intermediate dc voltage which is then fed into a dc-dc converter with transformer isolation. The front-end converter also performs input power factor correction (PFC) to shape the input currents to be sinusoidal and in phase with the input voltages to maximize the use of the available source power. Conventional two-stage power conversion, however, requires two power con­ verters and there has been considerable interest to try to integrate the PFC and dc-dc conversion functions in a single power converter to reduce cost and complexity. Although many of these single-stage converters have been proposed for low power, single-phase applications, there have been relatively few higher power three-phase converters that have been proposed. This is due to the challenges faced when trying to perform PFC and dc-dc conversion for a wider load range. A new three-phase, single-stage ac-dc full-bridge converter is proposed in this thesis. The outstanding features of the new converter are that it is relatively simple and it can perform PFC using standard phase-shift pulse width modulation (PWM). In the thesis, derivation of the converter is discussed and its general operation is re­ viewed. The modes of operation of the converter are explained in detail and analyzed and the results of the analysis are used to develop guidelines for its design. The feasibility of the proposed converter is confirmed with experimental results that were obtained from a prototype and are presented in this thesis