High Step-down Conversion Research Articles

An Expandable Four-Phase Interleaved High Step-Down Converter With Low Switch Voltage Stress and Automatic Uniform Current Sharing

In this paper, a novel four-phase interleaved high step-down converter is presented. The proposed converter can provide an extremely high step-down voltage conversion ratio within a moderate duty cycle. There are four main advantages of the proposed converter. First, the blocking capacitors can store energy as usual. Therefore, they are used as voltage sources to reduce the input voltage as well as to reduce the switch voltage stresses. Second, due to the charge balance of the dc blocking capacitors, the converter possesses an automatic uniform current sharing characteristic of the interleaved phases without adopting any extra circuitry. Third, due to the phase shift between the interleaved phases, the architecture provides a low output current ripple. Fourth, the number of phases can be expanded or reduced to any even phases; therefore, the converter has a wide range of applications. Finally, the operating principles and analysis of this architecture are given, and an experimental prototype is also provided to verify the effectiveness of the proposed converter.

Integrated high step-down multiphase buck converter with high power density

A novel integrated implementation of a high step-down multiphase buck for low voltage power supply is presented. The design and test chip measurements of a [10.8,16]V to [0.65,2]V, 2A, 10MHz, 25.6mW/mm2, four-phases single-chip solution are presented with considerations on architecture, passive components, problems related to high frequency integration and relative improvements on power density. The experimental results confirm the theoretical predictions by simulations and are compared with respect to previous discrete implementations and integrated topologies focusing on high step-down conversion and output power. So-called “high step-down multiphase buck” topologies present advantages in terms of extended duty cycle, reduced passive components’ size and reduced switches’ breakdown voltages. However, these topologies require a more complex gate drive structure for their high side switches which are working each on a different voltage domain. A novel drive architecture that eliminates the need of any external auxiliary voltage source, being directly supplied on fractions of the input voltage, is proposed. This architecture provides also a recycling of the gate charge at the turn-off of the switches. Another problem addressed is the start up of the converter, which requires a proper pre-charging of the topology's flying capacitors. Power stage measured waveforms show the correct start-up and steady-state operation of the proposed converter design.

Nonisolated Coupled-Inductor-Based High Step-Down Converter With Zero DC Magnetizing Inductance Current and Nonpulsating Output Current

A nonisolated coupled-inductor-based high step-down converter with zero dc magnetizing inductance current and nonpulsating output current is presented. Since the dc magnetizing inductance current is zero, the magnetizing current can be positive and negative. Therefore, the entire core B–H loop can be used, ranging from the first quadrant to the third quadrant. That is, the utilization of the coupled inductor can be improved and, hence, the core loss can also be reduced. Moreover, due to a discrete output inductor, the proposed converter also features a nonpulsating output current, which makes the output current ripple smaller. In this paper, detailed theoretical analyses and experimental results are provided to verify the feasibility and effectiveness of the proposed converter.

APEC Signals Emerging Trends: A focus on advancements in GaN integration, SiC devices, high step-down converters, and passives

Continuing to bring the latest advances in power semiconductors, circuit architectures, passives, and packaging, this year's IEEE Applied Power Electronics Conference and Exposition (APEC) in Long Beach, California, signaled emerging trends in gallium nitride (GaN) integration, silicon carbide (SiC) devices, high step-down dc?dc converters, and circuit components. While the plenary session talks highlighted trends in GaN-based power integrated circuits (ICs) and very-high-frequency (VHF) power conversion and magnetics, the exhibit floor demonstrated advances in SiC discretes and modules, including silicon-based power devices, passive components, and dc?dc power conversion solutions.

Flying-Capacitor-Based Hybrid LLC Converters With Input Voltage Autobalance Ability for High Voltage Applications

An advanced hybrid LLC series resonant converter with integrated flying-capacitor cell is proposed in this paper to enable the high step-down conversion in the high input voltage applications. The inherent flying-capacitor branch in the primary side can effectively halve the primary switch voltage stress compared with the half-bridge LLC converters. And the input voltage can be shared equally and automatically between the two series half-bridge modules without additional balance circuit or control strategies due to the built-in flying-capacitor cell. Moreover, the inherent soft switching performance during wide load range that exists in the LLC converters is still kept to reduce the switching losses, which ensures the high efficiency. Besides, the proposed converter can be extended to further decrease the switch voltage stress by employing stacked connection. Finally, a 500 ∼ 640 V-input 48 V-output 1 kW prototype is built and tested to verify the effectiveness of the proposed converter. The results prove that the proposed converter is an excellent candidate for the high input voltage and high step-down dc/dc conversion systems.

A Novel Transformer-less Interleaved Four-Phase Step-Down DC Converter With Low Switch Voltage Stress and Automatic Uniform Current-Sharing Characteristics

In this paper, we propose a novel transformer-less direct current (dc) converter that features low switch voltage stress and automatic uniform current sharing. An interleaved four-phase voltage divider operating from a 400 V dc bus is used to achieve a high step-down conversion ratio with a moderate duty ratio. Based on the capacitive voltage division, the proposed converter achieves two major objectives, i.e., increased voltage conversion ratio, due to energy storage in the blocking capacitors, and reduced voltage stress of active switches and diodes. As a result, the proposed converter permits the use of lower voltage rating MOSFETs to reduce both switching and conduction losses, thereby improving the overall efficiency. In addition, due to the charge balance of the capacitors, the proposed converter enables automatic uniform current sharing of the interleaved phases without adding extra circuitry or complex control methods. The operation principles and performance analyses of the proposed converter are presented, and its effectiveness is verified by a 500 W output power prototype circuit that converts 400 V input voltage into 24 V output voltage.

Bidirectional Operation of High Step-Down Converter

In this paper, a high step-down bidirectional converter, utilizing one coupled inductor and two energy-transferring capacitors, is presented. In the step-down mode, the capacitor is connected between input voltage and coupled inductor, which plays a role to step down the input voltage. Therefore, the corresponding voltage conversion ratio is much lower than that of the traditional buck converter and also can be lower than that of the tapped-inductor buck converter. Moreover, the output voltage varies with the duty cycle linearly, making control easier. In the step-up mode, one capacitor is first charged by the coupled inductor, and then releases the energy along with the coupled inductor and the other capacitor connected in series. Therefore, a higher voltage gain can be obtained. Furthermore, the leakage inductance energy can be recycled. Therefore, the switching losses can be reduced and the efficiency can be improved. In this study, the operating principles and experimental results are provided to verify the effectiveness and performance of the proposed converter.

High step‐down interleaved buck converter with low voltage stress

This study presents a four-phase interleaved buck converter with low voltage stress and high step-down conversion ratio. The proposed converter provides an extended duty cycle and low voltage stress for switches and diodes, in high step-down applications. This makes it possible to use switches with lower voltage rating and thus reduce both switching and conduction losses to improve the overall efficiency. Extremely low output current ripple and continuous input current are two other advantages of the proposed converter. Also, the output current can be shared between interleaved modules without using additional current sharing control technique due to charge balance of input and blocking capacitors. All these benefits are obtained without adding any active auxiliary component or using transformers. The experimental results from a prototype of the proposed converter designed for 400–24 V, operating at 0.5 kW, verify the theoretical analysis.

English

English

A Novel Transformerless Interleaved High Step-Down Conversion Ratio DC–DC Converter With Low Switch Voltage Stress

In this paper, a novel transformerless interleaved high step-down conversion ratio dc-dc converter with low switch voltage stress is proposed. In the proposed converter, two input capacitors are series-charged by the input voltage and parallel-discharged by a new two-phase interleaved buck converter for providing a much higher step-down conversion ratio without adopting an extreme short duty cycle. Based on the capacitive voltage division, the main objectives of the new voltage-divider circuit in the converter are for both storing energy in the blocking capacitors for increasing the step-down conversion ratio and reducing voltage stresses of active switches. As a result, the proposed converter topology possesses the low switch voltage stress characteristic. This will allow one to choose lower voltage rating MOSFETs to reduce both switching and conduction losses, and the overall efficiency is consequently improved. Moreover, due to the charge balance of the blocking capacitor, the converter features automatic uniform current sharing characteristic of the interleaved phases without adding extra circuitry or complex control methods. The operation principles and relevant analysis of the proposed converter are presented in this paper. Finally, a 400-V input voltage, 25-V output voltage, and 400-W output power prototype circuit is implemented in the laboratory to verify the performance.

Analysis, design and implementation of isolated bidirectional converter with winding‐cross‐coupled inductors for high step‐up and high step‐down conversion system

In this study, a zero voltage switching (ZVS) isolated bidirectional DC/DC converter is proposed for high step-up and high step-down conversion systems. In the low voltage side, an interleaved Buck and Boost converter is employed to reduce the current ripple and improve the power level. In the high voltage side, a modified three-level structure is adopted to bring each power switch sustain half of the high bus voltage, which makes the low voltage rated MOSFETs available for the performance improvement. Two coupled inductors are interleaved in the low voltage side and in series in the high voltage side, which can not only serve as the filter inductors for the current ripple cancellation, but also as the transformer for isolation, which is named as winding-cross-coupled inductors. As a result, the magnetic size can be reduced to enhance the power density. ZVS operation is ensured from light load to full load conditions by the advanced pulse width modulation plus phase shift control strategy. The voltage regulation and transferred power are decoupled for easy design and implementation. Finally, a 1.5 kW 48 V/800 V prototype is built to verify the effectiveness of the proposed converter.

Transformerless Three-Level DC-DC Buck Converter with a High Step-Down Conversion Ratio

For high power high step-down dc-dc conversion applications, conventional three-level dc-dc converters are subject to extreme duty cycles or increased volume and cost due to the use of transformers. In this paper, a transformerless three-level dc-dc buck converter with a high step-down conversion ratio is proposed. The converter comprises two asymmetrical half bridges, which are of the neutral point clamped structures. Therefore, the output pulse voltage of the converter can be obtained in terms of the voltage difference between the two half bridges. In order to realize harmonious switching of the converter, a modulation strategy with capacitor voltages self balance is presented. According to the deduced output dc voltage function, transformerless operation without extreme duty cycles can be implemented. Experimental results from a 1kW prototype verify the validity of the proposed converter. It is suitable for ship electric power distribution systems.

Comparison between Phase-Shift Full-Bridge Converters with Noncoupled and Coupled Current-Doubler Rectifier

This paper presents comparison between phase-shift full-bridge converters with noncoupled and coupled current-doubler rectifier. In high current capability and high step-down voltage conversion, a phase-shift full-bridge converter with a conventional current-doubler rectifier has the common limitations of extremely low duty ratio and high component stresses. To overcome these limitations, a phase-shift full-bridge converter with a noncoupled current-doubler rectifier (NCDR) or a coupled current-doubler rectifier (CCDR) is, respectively, proposed and implemented. In this study, performance analysis and efficiency obtained from a 500 W phase-shift full-bridge converter with two improved current-doubler rectifiers are presented and compared. From their prototypes, experimental results have verified that the phase-shift full-bridge converter with NCDR has optimal duty ratio, lower component stresses, and output current ripple. In component count and efficiency comparison, CCDR has fewer components and higher efficiency at full load condition. For small size and high efficiency requirements, CCDR is relatively suitable for high step-down voltage and high efficiency applications.

5 kW DC/DC converter for hydrogen generation from photovoltaic sources

This paper covers the design of a DC–DC power converter aimed for hydrogen production from photovoltaic sources. Power conditioning for such application is usually driven by different constraints: high step-down conversion ratio is required if the input voltage of such equipment has to be compatible with photovoltaic sources that are connected to grid-connected inverters; galvanic isolation; high efficiency and low mass. Taking into account those factors, this work proposes a push–pull DC/DC converter for power levels up to 5 kW. The operation and features of the converter are presented and analyzed. Design guidelines are suggested and experimental validation is also given.