DC–DC converters with voltage boost capability are widely used in a large number of power conversion applications, from fraction-of-volt to tens of thousands of volts at power levels from milliwatts to megawatts. The literature has reported on various voltage-boosting techniques, in which fundamental energy storing elements (inductors and capacitors) and/or transformers in conjunction with switch(es) and diode(s) are utilized in the circuit. These techniques include switched capacitor (charge pump), voltage multiplier, switched inductor/voltage lift, magnetic coupling, and multistage/-level, and each has its own merits and demerits depending on application, in terms of cost, complexity, power density, reliability, and efficiency. To meet the growing demand for such applications, new power converter topologies that use the above voltage-boosting techniques, as well as some active and passive components, are continuously being proposed. The permutations and combinations of the various voltage-boosting techniques with additional components in a circuit allow for numerous new topologies and configurations, which are often confusing and difficult to follow. Therefore, to present a clear picture on the general law and framework of the development of next-generation step-up dc–dc converters, this paper aims to comprehensively review and classify various step-up dc–dc converters based on their characteristics and voltage-boosting techniques. In addition, the advantages and disadvantages of these voltage-boosting techniques and associated converters are discussed in detail. Finally, broad applications of dc–dc converters are presented and summarized with comparative study of different voltage-boosting techniques.

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Step-Up DC–DC Converters: A Comprehensive Review of Voltage-Boosting Techniques, Topologies, and Applications

High-gain voltage conversion is a feature required for several applications, especially for power processing of low-voltage renewable sources in grid-connected systems. In this scope, the presented paper proposes a novel transformerless high gain step-up dc–dc converter based on an active switched-inductor and a passive switched-capacitor networks. The main advantages of the proposed converter are the high voltage gain (>10), the reduced voltage stresses across the switches and the reduced number of components when compared to topologies that provide the same voltage gain using similar principles. The detailed analysis of the proposed converter and a comparison considering other topologies previously published in the literature are also presented in this manuscript. In order to verify the proposed converter performance, a prototype has been built for a power of 200 W, input and output voltages of 20 and 260 V, respectively, and switching frequency of 50 kHz. Experimental results validate the effectiveness of the theoretical analysis proving the satisfactory converter performance, which peak efficiency is around 95.5%.

High Step-Up DC–DC Converter With Active Switched-Inductor and Passive Switched-Capacitor Networks

Over the last few decennia, power DC/DC converters have been the subject of great interest due to its extensive increment of utilization in different applications. A thorough review on recent developed power DC/DC converters is presented in this paper. The study is focused on the topologies in different applications such as renewable energy, automobile, high-voltage and medium-voltage DC power systems, telecommunication, etc. In addition, an overview of the modulation techniques, the state-of-the-art of control strategies of well-established converters are discussed. Photovoltaic (PV) systems as the noticeable renewable energy resources generally suffer from poor conversion efficiency with instability and intermittent characteristics. Therefore, DC/DC converter with Maximum Power Point Tracking (MPPT) algorithm is essential to ensure maximum available power harnessed from the PV. Important features of DC/DC converters with MPPT are also figured with various performances. Furthermore, the design and optimization of different parameters are addressed systematically. Finally, the researcher’s future challenges and focusing trends are briefly described. For the next-generation converters design and applications, these are considered in details, and will provide useful framework and point of references.

Recent progress and development on power DC-DC converter topology, control, design and applications: A review

An input-parallel, output-series dc–dc Boost converter with a wide input voltage range is proposed in this paper. An interleaved structure is adopted in the input side of this converter to reduce input current ripple. Two capacitors are connected in series on the output side to achieve a high voltage gain. The operating principles and steady-state characteristics of the converter are presented and analyzed in this paper. A 400 V/1.6 kW prototype has been created which demonstrates that a wide range of voltage gain can be achieved by this converter and it is shown that the maximum efficiency of the converter is 96.62% and minimum efficiency is 94.14%. The experimental results validate the feasibility of the proposed topology and its suitability for fuel cell vehicles.

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Input-Parallel Output-Series DC-DC Boost Converter With a Wide Input Voltage Range, For Fuel Cell Vehicles

A novel high step-up converter, which is suitable for a renewable energy system, is proposed in this paper. The proposed converter is composed of the dual switches structure, three-winding coupled inductor, and two voltage multiplier cells in order to achieve the high step-up voltage gain. The dual switches structure is beneficial to reduce the voltage stress and current stress of the switch. In addition, two multiplier capacitors are, respectively, charged during the switch-on period and switch-off period, which increases the voltage conversion gain. Meanwhile, the energy stored in the leakage inductor is recycled with the use of clamped capacitors. Thus, two main power switches with low on-resistance and low current stress are available. As the leakage inductor, diode reverse-recovery problem is also alleviated. Therefore, the efficiency is improved. This paper illustrates the operation principle of the proposed converter; discusses the effect of the leakage inductor; analyzes the influence of parasitic parameters on the voltage gain and efficiency, the voltage stresses and current stresses of power devices are shown; and a comparison between the performance of the proposed converter and the previous high step-up converters is performed. Finally, the prototype circuit with input voltage 20 V, output voltage 200 V, and rated power 200 W is operated to verify its performance.

A Novel High Step-Up Dual Switches Converter With Coupled Inductor and Voltage Multiplier Cell for a Renewable Energy System

In applications where the high voltage gain is required, such as photovoltaic grid-connected system, fuel-cell and high-intensity discharge lamps for automobile, high step-up dc-dc converters have been introduced to boost the low voltage to a high bus voltage. The voltage gain of traditional boost converter is limited, considering the issues such as the system efficiency and current ripple. This paper proposes a class of hybrid switched-inductor converters (H-SLCs) for high step-up voltage gain conversion. First, the topological derivation of H-SLCs is deduced by combining the passive and active switched-inductor unit; second, this paper illustrates the operation modes of the proposed asymmetrical and symmetrical converters; third, the performance of the proposed converters is analyzed in detail and compared with existing converters; finally, a prototype is established in the laboratory, and the experimental results are given to verify the correctness of the analysis.

Hybrid Switched-Inductor Converters for High Step-Up Conversion

High step-up voltage gain dc–dc converters are widely applied in fuel cell stacks, photovoltaic arrays, battery sources, and high intensity discharge lamps power systems. Active-network converters with coupled inductors (CL-ANC) are derived from switched inductor active-network converters (SL-ANC). The proposed converter contains two coupled inductors which can be integrated into one magnetic core and two power switches. The converter can provide a relatively high voltage conversion ratio with a small duty cycle; the voltage and current stress of power switches are low which is helpful to reduce the losses. This paper shows the key waveforms of the CL-ANC and detailed derivation of the steady-state operation principle. The voltage conversion ratio and the effect of the leakage inductance on voltage gain are discussed. The voltage stress and current stress on the power devices are illustrated and the comparison between the proposed converter and SL-ANC are given. Finally, the prototype has been established in the lab with 200 V and 400 V output under different turn ratios. Experimental results are given to verify the correctness of the analysis.

Analysis of Active-Network Converter With Coupled Inductors

This paper proposes an air-core transformer integration method, which mounts the transformer straight into the multilayer printed circuit board (PCB), and maintains a proper distance between the inner transformer and other components on the top layer. The integration method reduces the PCB area significantly, ensuring higher power density. The design of the complete structure is accomplished with finite element analysis (FEA) to ensure that the unconstrained transformer magnetic field does not affect other components. It is applied to three resonant flyback converters operating at 20 MHz with Si mosfet s, 30 MHz, and 50 MHz with enhancement-mode gallium nitride (eGaN) high-electron mobility transistors, respectively. The 30-MHz eGaN prototype achieves the full load efficiency of 80.1% (an increase of 1.1% compared with the 20-MHz Si prototype) and power density of 32 W/in3 at 5-V input and 5 V/ 2 W output. The 50-MHz eGaN prototype achieves the power density of 39.4 W/in3, which is 41% higher than the 20-MHz Si prototype. With the similar efficiency, the overall height of the converters in this paper is less than half of the commercial products, very suitable for low thickness and profile applications.

GaN VHF Converters With Integrated Air-Core Transformers

A 1-kV input SiC LLC converter with the matrix planar transformers is proposed to achieve high efficiency and high power density. With fast switching speed 140 ns of SiC mosfet s at 1-kV input voltage, high dv/dt of 11.8 kV/ μ s can cause large displacement current via the parasitic capacitance between the primary and secondary sides of high-frequency planar transformers. The displacement current via the interwinding capacitance can distort the resonant current seriously. This causes the control mosfet s not to realize ZVS and induces high switching loss at 1 kV. An LLC topology with split resonant tanks is proposed for high input voltage applications. The resonant tank is split into two identical resonant tanks to provide symmetrical resonant current with the same impedance. Compared with the conventional LLC converters, the input and output current of the resonant tank is symmetrical, avoiding the current distortion. Therefore, all of the control mosfet s can realize ZVS. The transformer interwinding capacitance modeling and a reduction solution are presented, which reduces the waveform distortion by 68%. Two SiC prototypes of 3 and 4 kW with an input of 1 kV and output of 32 and 48 V were built, respectively. The efficiency is 94.9% at full load at 300 kHz for a 3-kW module and 96.0% at full load for a 4-kW module. The power density is 3.87 kW/L (63.4 W/in3) and 4.11 kW/kg for the 4-kW module.

A 1-kV Input SiC LLC Converter With Split Resonant Tanks and Matrix Transformers

Pulse power converters demands single high voltage and current pulse shape waveform in high temperature, heavy neutrons, and ions radiation environment, where ${\text{50}}\% \sim {\text{75}}\%$ voltage derating margin is typically required for the power devices. silicon carbide (SiC) mosfet s are promising to improve radiation reliability owing to wide band-gap. However, the conventional converters with off-the-shelf commercial SiC mosfet s cannot provide enough voltage margin accordingly. A stack-capacitor pulse converter topology is proposed to reduce the voltage stress of switching devices and capacitors and improve the voltage derating capability significantly. The main idea is to build high voltage with multiple low voltage stacks instead of single high voltage capacitors, so that SiC mosfet s can be applied with improved voltage margin. The method is to charge the stack-capacitors in parallel with fast charging speed, and discharge in series for high pulse voltage. The converter operates at higher switching frequency, which reduces the weight and size of the magnetic components. A 300-kHz prototype with 18–28 V input and 1  kV/ 100 A output was built using 650 V SiC devices, demonstrating 75% reduction of the voltage stress of the capacitors and power devices compared with the conventional converters.

Zhi-Wei Xu

Papers

Hybrid Switched-Inductor Converters for High Step-Up Conversion

Analysis of Active-Network Converter With Coupled Inductors

GaN VHF Converters With Integrated Air-Core Transformers

A 1-kV Input SiC LLC Converter With Split Resonant Tanks and Matrix Transformers

SiC Stacked-Capacitor Converters for Pulse Applications