Soft-switching DC-DC Converter Research Articles

Soft-switched DC-DC converter with current and voltage doubler

This paper proposes a method that consists of a phase-shift converter with a current doubler rectifier on the output side. The phase-shift converter operates at a frequency as high as 20-25 kHz (depending on the requirement of the application) to improve the power density of the converter using unity turns ratio in the isolation transformer. The size of the circuit is smaller for the same power rating. Ferrite core transformer is used instead of the conventional one, which is bulky and leads to a very large core loss. Unlike the conventional method, the number of turns of the transformer is reduced and the overall power density is increased. The current doubler rectifier doubles the input current as needed for a few vital applications. The circuit for the phase-shift converter with the current doubler was simulated using PSPICE software. For an input current of 4 A, an output of 10.2 A was obtained, which eventually settled at nearly 8.5 A. A hardware model of the proposed method validates the simulation results.

Zero-current switching resonant buck converters with small inductors

In this study two new zero-current switching resonant buck converters as soft-switching DC-DC converters are presented. In the first topology, small inductors are implemented and thus it is appropriate for integrated circuits. In the second topology, an alternative structure is presented in which not only a switch is eliminated but also higher power can be delivered. Both converters enjoy a very simple control method. The converters are analysed in details and theoretical equations are presented. The presented experimental results from the implemented prototypes confirm the theoretical analyses.

High-Efficiency Power Conditioning System for Grid-Connected Photovoltaic Modules

This paper presents a high-efficiency power conditioning system (PCS) for grid-connected photovoltaic (PV) modules. The proposed PCS consists of a step-up DC-DC converter and a single-phase DC-AC inverter for the grid-connected PV modules. A soft-switching step-up DC-DC converter is proposed to generate a high DC-link voltage from the low PV module voltage with a high-efficiency. A DC-link voltage controller is presented for constant DC-link voltage regulation. A half-bridge inverter is used for the single-phase DC-AC inverter for grid connection. A grid current controller is suggested to supply PV electrical power to the power grid with a unity power factor. Experimental results are obtained from a 180 W grid-connected PV module system using the proposed PCS. The proposed PCS achieves a high power efficiency of 93.0 % with an unity power factor for a 60 Hz / 120 Vrms AC power grid.

A Bidirectional Three-Level DC–DC Converter for the Ultracapacitor Applications

Electrochemical double-layer capacitors, which are well known as ultracapacitors, have intensively been used in power conversion applications such as controlled electric drives, active filters, power conditioners, and uninterruptible power supplies. The ultracapacitor is employed as the energy storage device that can be fully charged/discharged within a few seconds. To achieve better flexibility and efficiency, the ultracapacitor is connected to the power conversion system via an interfacing dc-dc power converter. Various topologies are used as the dc-dc power converter: nonisolated two-level single-phase or multiphase interleaved converters and many varieties of isolated soft-switched dc-dc converters. A three-level nonisolated dc-dc converter as a candidate for ultracapacitor applications is proposed and analyzed in this paper. The topology is theoretically analyzed, and design guidelines are given. The modeling and control aspects are discussed. A 5.5-kW prototype was designed, and the proposed topology was experimentally verified on a general-purpose controlled electric drive. Experimental results are presented and discussed.

Isolated Topologies of Switched-Resonator Converters

Switched-resonator converters are a new family of soft switching DC-DC converters where the energy is transferred via a resonator. This paper introduces some isolated topologies of this family. The achieved advantages include, load independent soft-switching, self short-circuit protection, and optimization capability due to topology variety. Compared to conventional seriesresonant converters, outstanding advantages such as a smaller fewer number of switches and diodes, a smaller transformer, and lower current stresses are achieved. A general synthesis scheme, functional topologies, and essential relations are included. Experimental results from a laboratory prototype confirm the presented theoretical analysis.

Practical Evaluations of a Novel Asymmetrical ZCS-PWM DC-DC Converter with High-Frequency Transformer-Link

This paper presents a novel Zero Current Switching (ZCS)-PWM controlled half-bridge DC-DC converter with High-Frequency (HF)-link. The newly-proposed soft switching DC-DC converter consists of a multi-resonant half-bridge HF-isolated inverter controlled by an asymmetrical PWM scheme and a center-tapped diode rectifier with a choke input filter. In order to attain the wide range of soft-commutation under the condition of constant switching frequency, the single Active Edge-Resonant Cell (AERC) that is composed of a lossless inductor and a switched resonant capacitor is originally employed for the half-bridge inverter arm, providing and assisting ZCS operations in the switching power devices. The ZCS-PWMDC-DC converter treated here is evaluated in experiments using the 800 W-55 kHz prototype. The practical effectiveness of the proposed soft switching DC-DC converter is actually demonstrated and discussed with the experimental results under open loop and closed loop configurations. Finally, the feasibility of the DC-DC converter topology is discussed from the view points of the high efficiency and high power density.

A Novel High-Frequency Transformer-Linked Soft-Switching Half-Bridge DC–DC Converter With Constant-Frequency Asymmetrical PWM Scheme

This paper presents a novel soft-switching half-bridge dc-dc converter with high-frequency link. The newly proposed soft-switching dc-dc converter consists of a single-ended half-bridge inverter controlled by an asymmetrical pulsewidth-modulation scheme and a center-tapped diode rectifier. In order to attain the wide range of soft commutation under constant switching frequency, the single active edge-resonant snubber cell composed of a lossless inductor and a switched capacitor is employed for the half-bridge inverter leg, providing and assisting zero-current-switching operations in the switching power devices. The practical effectiveness of the proposed soft-switching dc-dc converter is demonstrated by the experimental results from an 800 W - 55 kHz prototype. In addition, the feasibility of the dc-dc converter topology is proved from the viewpoints of the high efficiency and high power density.

Power converters and amplifiers (review of "Pulse-Width Modulated DC-DC Power Converters" by Kazimierczuk, M.K.; 2008) [Book News

This book is a comprehensive textbook in the areas of electrical, electronics, and telecommunications engineering. It consists of 17 chapters and two appendices. Some of the topics covered include: buck PWM DC-DC converters; boost PWM DC-DC converters; buck-boost-PWM DC-DC converters; half-bridge and full-bridge converters; push-pull PWM DC-DC converters; open-loop small-signal characteristics of boost converters for CCM; current-mode control of boost converters; silicon and silicon carbide power diodes; and soft-switching DC-DC converters. Appendix A is an introduction to SPICE and Appendix B provides an introduction to MATLAB. Answers to problems and the index are also included at the end of the book. The book is recommended for senior undergraduate and graduate students but also for practicing engineers working with switch-mode power supplies, within applications such as computers, telecommunications, industrial electronic systems, automobile electronics, medical equipment, radars, and aerospace power technology.

Bi-directional Zero-current Soft-switching Technique Applied for Bi-directional DC-DC Converter in Energy Capacitor Systems

In our previous work, we proposed the current-source energy capacitor system (CS-ECS), which consists of an electric double-layer capacitor, current-source inverter, and bi-directional four-quadrant DC-DC (FQ DC-DC) converter to control active/reactive power that can achieve the output leveling of wind energy system. However, this system had low conversion efficiency due to hard-switching losses. The improvement of conversion efficiency and performance are indispensable to implement the CS-ECS. This article proposes the soft-switched FQ DC-DC converter with a simple L-C resonant circuit for the CS-ECS. Since the insulated gate bipolar transistors of the converter softly turns on and off by using current-mode resonance, the conversion efficiency for the proposed system improves. In order to illustrate the operating principle of the proposed system, we analyze the transition of conversion efficiency with charge and discharge operation in detail through a theoretical approach and computer simulations with MATLAB/SIMULINK and SimPowerSystems Toolbox.

Comparative Study of Soft-Switched Isolated DC-DC Converters for Auxiliary Railway Supply

In modern railways coaches, the electrical separation between the high voltage side and the auxiliary equipments on the consumer side is realized by means of heavy and bulky 50-Hz transformers. In order to reduce the weight and size of the devices, today new power supply systems are proposed that consist in soft-switched isolated DC-DC converters with a lightweight medium frequency transformer and diverse output modules supplied by a common 600-V dc intermediate circuit. This paper aims to investigate in detail two such solutions of isolated DC-DC converters for auxiliary railway supply where zero-current transitions are achieved for the primary inverter switches. A comparison based on several criteria (overall power rating, losses in power semiconductor devices, operation in the whole range of load, etc.) is presented.

A Comparison of Soft-Switched DC-DC Converters for Fuel Cell to Utility Interface Application

High frequency (HF) transformer isolated DC-DC converter is part of a fuel cell inverter system for utility interface, required to translate the level of low fuel cell stack voltage to meet the peak utility line voltage and provides isolation between inverter and utility line. This paper presents a comparison of various soft-switched HF transformer isolated DC-DC converters for fuel-cell to utility interface application. It is shown that due to wide variation in fuel cell voltage with load variation, none of the voltage-fed converters can maintain ZVS for the complete operating range. Active clamped two-inductor current-fed converter is able to maintain ZVS for wide load and fuel cell stack voltage variations and is suitable for the present application. Analytical, simulation and experimental results are presented to evaluate the performance of the current-fed converter.

A high efficiency, soft switching DC-DC converter with adaptive current-ripple control for portable applications

A novel control scheme for improving the power efficiency of low-voltage dc-dc converters for battery-powered, portable applications is presented. In such applications, light-load efficiency is crucial for extending battery life, since mobile devices operate in stand-by mode for most of the time. The proposed technique adaptively reduces the inductor current ripple with decreasing load current while soft switching the converter to also reduce switching losses, thereby significantly improving light-load efficiency and therefore extending the operation life of battery-powered devices. A load-dependent, mode-hopping strategy is employed to maintain high efficiency over a wide load range. Hysteretic (sliding-mode) control with user programmable hysteresis is implemented to adaptively regulate the current ripple and therefore optimize conduction and switching losses. Experimental results show that for a 1-A, 5- to 1.8-V buck regulator, the proposed technique achieved 5% power efficiency improvement (from 72% to 77%) at 100 mA of load current and a 1.5% improvement (from 84% to 85.5%) at 300 mA, which constitute light-load efficiency improvements, when compared to the best reported, state-of-the-art techniques. As a result, the battery life in a typical digital signal processing microprocessor application is improved by 7%, which demonstrates the effectiveness of the proposed solution.

Reduced-order averaged modeling of active-clamp converters

Reduced-order averaged modeling and analysis of soft-switching dc-dc converters employing active clamping techniques are presented in this paper. A general modeling method based on time-scale separation of converter state variables is used to develop large-signal averaged models that accurately represent the converter dynamics up to half the switching frequency. The fast-changing resonant variables of the active clamping circuits are eliminated in the modeling process, resulting in reduced-order models that are much simpler than existing full-order models. A method is also presented to account for the effects of switching-frequency ripple on converter dynamics in the low-frequency region. A transformer-coupled active-clamp single-ended primary inductance converter (SEPIC) is studied in detail to demonstrate the application of the method. Numerical simulation and experimental measurement of frequency responses of a experimental SEPIC converter are presented to validate the developed models. Additionally, an active-clamp flyback converter is briefly studied to demonstrate the general applicability of the method to other active-clamp converter topologies.

Pulse current regenerative resonant snubber‐assisted two‐switch flyback‐type ZVS PWM DC‐DC converter

AbstractIn this paper, a two‐switch high‐frequency flyback transformer‐type zero voltage soft‐switching PWM DC‐DC converter using IGBTs is proposed. Effective applications for this power converter can be found in auxiliary power supplies of rolling stock transportation and electric vehicles. This power converter is basically composed of two active power switches and a flyback high‐frequency transformer. In addition to these, two passive lossless snubbers with power regeneration loops for energy recovery, consisting of a three‐winding auxiliary high‐frequency transformer, auxiliary capacitors and diodes are introduced to achieve zero voltage soft switching from light to full load conditions. Furthermore, this power converter has some advantages such as low cost circuit configuration, simple control scheme, and high efficiency.Its operating principle is described and to determine circuit parameters, some practical design considerations are discussed. The effectiveness of the proposed power converter is evaluated and compared with the hard switching PWM DC‐DC converter from an experimental point of view, and the comparative electromagnetic conduction and radiation noise characteristics of both DC‐DC power converter circuits are also depicted. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(3): 74–81, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20081

Tapped-inductor filter assisted soft-switching PWM DC-DC power converter

A novel high-frequency transformer linked full-bridge type soft-switching phase-shift pulsewidth modulated (PWM) controlled dc-dc power converter is presented, which can be used as a power conditioner for small-scale photovoltaic and fuel cell power generation systems as well as isolated boost dc-dc power converter for automotive ac power supply. In these applications with low-voltage large-current sources, the full-bridge circuit is the most attractive topology due to the possibility of using low-voltage high-performance metal-oxide-semiconductor field-effect transistor (MOSFET) and achieving high efficiency of the dc-dc power converter. A tapped-inductor filter including the freewheeling diode is newly implemented in the output stage of the full-bridge phase-shift PWM dc-dc converter to achieve soft-switching operation for the wide load variation range. Moreover, in the proposed converter circuit, the circulating current is effectively minimized without using additional resonant circuit and auxiliary power switching devices. The practical effectiveness of the proposed soft-switching dc-dc power converter was verified in laboratory level experiment with 1 kW 100 kHz breadboard setup using power MOSFETs. Actual efficiency of 94-97% was obtained for the wide duty cycle and load variation ranges.

A 25-MW Soft-Switching HVDC Tap for<tex>$pm$</tex>500-kV Transmission Lines

This paper presents an optimization of a previously proposed high-voltage dc current transmission system (HVDC) tap system where the power rating of the soft-switching dc-dc converter has been increased to supply medium loads (up to 25 MW) from /spl plusmn/500-kV HVDC transmission lines. This dc-dc converter is connected in series with a pole of the HVDC transmission line. It drains energy to a dc capacitor through an air-core transformer and a single-phase diode rectifier connected at the secondary. A pulsewidth-modulation (PWM) voltage-source converter is directly connected to this dc capacitor to supply ac loads. The HVDC tap comprises all those components and can supply high-quality power to isolated or interconnected load areas. The controller of the HVDC tap is independent from the control systems of the main HVDC converter stations. It does not need any communication channel to the control of the main HVDC converter stations. A complete bipolar /spl plusmn/500-kV HVDC system, together with a refined model of dc transmission line were implemented to simulate the performance of the proposed HVDC tap. It has revealed to be very robust and to be an attractive solution for feeding small loads from long dc transmission lines.

High-frequency flyback-type soft-switching PWM DC-DC power converter with energy recovery transformer and auxiliary passive lossless snubbers

A two-switch high-frequency flyback-type zero voltage soft-switching PWM DC-DC power converter for use in auxilary power supplies is proposed. Its basic building block is composed of two active power switches and a flyback high frequency transformer. In addition, two passive lossless snubbers with power regeneration loops for energy recovery that consist of a three-turn auxiliary high frequency transformer, auxiliary capacitors and diodes, are introduced to achieve zero voltage soft switching in the full range of light to full load conditions. The power converter has the advantages of a low cost circuit configuration, a simple control scheme and a high efficiency.The converter's operating principle is described and to in order determine circuit parameters, some practical design considerations are discussed. The effectiveness of the proposed power converter is evaluated and is compared to a hard-switching PWM DC-DC converter. The comparative electromagnetic conductive noise characteristics of both DC-DC power converter circuits are also investigated.

Novel soft-commutation DC–DC power converter with high-frequency transformer secondary side phase-shifted PWM active rectifier

This paper presents a novel circuit topology of the voltage source type zero voltage soft-switching (ZVS) full bridge DC-DC power converter with an isolated high-frequency transformer, which incorporates zero-current soft-switching (ZCS) phase-shifted (PS)-PWM active power switches in series with diodes of two bridge arms of a full-bridge rectifier on the high-frequency transformer secondary side. This high-frequency linked DC-DC power converter can achieve ZVS for noncontrolled active power switches on the primary side of the transformer and ZCS for PS-PWM active switches on the secondary side of the transformer under wide load variations as well as a wide PS-PWM regulation range. The switching power losses and conduction power losses of the active devices of the proposed DC-DC converter can be considerably reduced. The proposed DC-DC converter blocks circulating current flowing through the semiconductor switching devices on the transformer primary side as compared to the lossless snubbing capacitor and transformer leakage and magnetising inductor-assisted soft-switching full-bridge DC-DC converter with ZVS PS-PWM scheme on the transformer primary side. The steady-state operating principles of the proposed DC-DC converter are evaluated and discussed, based on the simulation and experimental results obtained from a 2 kW-40 kHz breadboard set-up using IGBTs.

ZVS PWM昇圧チョッパ・ZVSフルブリッジDC-DCコンバータ構成の2ステージ電力変換システム

The high-frequency isolated power supply with low-voltage large-current output and widely fluctuating input voltage is discussed in this paper. It is described that it is difficult to achieve high efficiency of the power supply with ZVS phase-shift PWM controlled DC-DC power converter mainly due to high conduction power losses in the rectifier stage. The 2-stage DC-DC converter system configuration, which consists of boost ZVS-PWM DC-DC chopper and ZVS full-bridge high-frequency isolated DC-DC converter operating with maximum duty cycle, is presented. An ability to improve efficiency of the power conversion by using 2 stages DC-DC circuit configuration is discussed. 900W-100kHz DC-DC conversion system prototypes were built and tested. An efficiency comparison between full-bridge ZVS phase-shift PWM DC-DC power converter and 2-stage soft-switching DC-DC converter has been made. It is proved that using 2-stage DC-DC converter can improve efficiency under full load.

Double two-switch forward transformer linked soft-switching PWM DC–DC power converter using IGBTs

A double two-switch forward type high-frequency transformer linked zero-voltage and zero-current mode soft-switching (ZVZCS) pulse width modulation (PWM) DC-DC power converter using IGBTs is presented. A new circuit configuration of the isolated type PWM softly switching converter is proposed to reduce idling and circulating currents in the main circuit without using complex additional active auxiliary resonant snubber circuits and power semiconductor devices, and to decrease the peak voltage across power devices, and their peak current stresses. This soft-switching PWM DC-DC power converter has the unique advantages of less power circuit components and power semiconductor devices, high power conversion efficiency, constant frequency duty cycle control scheme, cost-effective and stable soft-switching operating range under wide load variations for high power applications. The basic operating principle of the soft-switching power converter treated here is illustrated using periodic steady-state circuit analysis for each mode equivalent circuit. The effectiveness of the proposed soft-switching DC-DC power converter built and tested as a 500 W-100 kHz breadboard setup using IGBTs is verified and evaluated on the basis of simulation and theoretical circuit analysis.