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

A few simple switching structures, formed by either two capacitors and two-three diodes (C-switching), or two inductors and two-three diodes (L-switching) are proposed. These structures can be of two types: ldquostep-downrdquo and ldquostep-up.rdquo These blocks are inserted in classical converters: buck, boost, buck-boost, Cuk, Zeta, Sepic. The ldquostep-downrdquo C- or L-switching structures can be combined with the buck, buck-boost, Cuk, Zeta, Sepic converters in order to get a step-down function. When the active switch of the converter is on, the inductors in the L-switching blocks are charged in series or the capacitors in the C-switching blocks are discharged in parallel. When the active switch is off, the inductors in the L-switching blocks are discharged in parallel or the capacitors in the C-switching blocks are charged in series. The ldquostep-uprdquo C- or L-switching structures are combined with the boost, buck-boost, Cuk, Zeta, Sepic converters, to get a step-up function. The steady-state analysis of the new hybrid converters allows for determing their DC line-to-output voltage ratio. The gain formula shows that the hybrid converters are able to reduce/increase the line voltage more times than the original, classical converters. The proposed hybrid converters contain the same number of elements as the quadratic converters. Their performances (DC gain, voltage and current stresses on the active switch and diodes, currents through the inductors) are compared to those of the available quadratic converters. The superiority of the new, hybrid converters is mainly based on less energy in the magnetic field, leading to saving in the size and cost of the inductors, and less current stresses in the switching elements, leading to smaller conduction losses. Experimental results confirm the theoretical analysis.

Switched-Capacitor/Switched-Inductor Structures for Getting Transformerless Hybrid DC–DC PWM Converters

This paper introduces the use of the voltage multiplier technique applied to the classical non-isolated dc-dc converters in order to obtain high step-up static gain, reduction of the maximum switch voltage, zero current switching turn-on. The diodes reverse recovery current problem is minimized and the voltage multiplier also operates as a regenerative clamping circuit, reducing the problems with layout and the EMI generation. These characteristics allows the operation with high static again and high efficiency, making possible to design a compact circuit for applications where the isolation is not required. The operation principle, the design procedure and practical results obtained from the implemented prototypes are presented for the single-phase and multiphase dc-dc converters. A boost converter was tested with the single-phase technique, for an application requiring an output power of 100 W, operating with 12 V input voltage and 100 V output voltage, obtaining efficiency equal to 93%. The multiphase technique was tested with a boost interleaved converter operating with an output power equal to 400 W, 24 V input voltage and 400 V output voltage, obtaining efficiency equal to 95%.

Voltage Multiplier Cells Applied to Non-Isolated DC–DC Converters

The major consideration in dc-dc conversion is often associated with high efficiency, reduced stresses involving semiconductors, low cost, simplicity and robustness of the involved topologies. In the last few years, high-step-up non-isolated dc-dc converters have become quite popular because of its wide applicability, especially considering that dc-ac converters must be typically supplied with high dc voltages. The conventional non-isolated boost converter is the most popular topology for this purpose, although the conversion efficiency is limited at high duty cycle values. In order to overcome such limitation and improve the conversion ratio, derived topologies can be found in numerous publications as possible solutions for the aforementioned applications. Within this context, this work intends to classify and review some of the most important non-isolated boost-based dc-dc converters. While many structures exist, they can be basically classified as converters with and without wide conversion ratio. Some of the main advantages and drawbacks regarding the existing approaches are also discussed. Finally, a proper comparison is established among the most significant converters regarding the voltage stress across the semiconductor elements, number of components and static gain.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-pel.2014.0605

Survey on non-isolated high-voltage step-up dc–dc topologies based on the boost converter

A DC-DC converter topology is proposed. The DC-DC multilevel boost converter (MBC) is a pulse-width modulation (PWM)-based DC-DC converter, which combines the boost converter and the switched capacitor function to provide different output voltages and a self-balanced voltage using only one driven switch, one inductor, 2
 N
-1 diodes and 2
 N
-1 capacitors for an Nx
 MBC. It is proposed to be used as DC link in applications where several controlled voltage levels are required with self-balancing and unidirectional current flow, such as photovoltaic (PV) or fuel cell generation systems with multilevel inverters; each device blocks only one voltage level, achieving high-voltage converters with low-voltage devices. The major advantages of this topology are: a continuous input current, a large conversion ratio without extreme duty cycle and without transformer, which allow high switching frequency. It can be built in a modular way and more levels can be added without modifying the main circuit. The proposed converter is simulated and prototyped; experimental results prove the proposition's principle.

A DC-DC multilevel boost converter

Two structures, a switched-capacitor (SC)-based boost converter and a two-level inverter, are connected in cascade. The dc multilevel voltage of the first stage becomes the input voltage of the classical inverter, resulting in a staircase waveform for the inverter output voltage. Such a multilevel waveform is close to a sinusoid; its harmonics content can be reduced by multiplying the stage number of the SC converter. The output low-pass filter, customary after a two-level inverter, becomes obsolete, resulting in a small size of the system, as the SC circuit can be miniaturized. Both stages are operated at a high switching frequency, resulting in a high-frequency inverter output, as required by some industrial applications. A Fourier analysis of the output waveform is performed. The design is optimized with reference to the nominal duty-cycle for obtaining the minimum total harmonic distortion. Simulations and experiments on two prototypes, one with a five-level output and one with a seven-level output, confirm the theoretical analysis.

A cascade boost-switched-capacitor-converter - two level inverter with an optimized multilevel output waveform

The energy-transfer-capacitor in basic Cuk, Zeta and Sepic converters is split into two capacitors. The rectifier diode is replaced by two diodes that form with the two capacitors a switched-capacitor circuit, which appears connected between the input and output inductances of the original converter. As a result, hybrid circuits, presenting a higher DC voltage ratio than the classical Cuk, Zeta and Sepic converters, are obtained. Even if the new hybrid structures do not reach the DC gain of quadratic converters, they present a higher efficiency in processing the energy: unlike the cascaded converters whose efficiency is a product of the efficiencies of each block, the hybrid converters do not require an additional level of energy processing. A DC analysis, simulation and experimental results concerning the proposed circuits are presented.

Hybrid switched-capacitor-Cuk/Zeta/Sepic converters in step-up mode

The switched-capacitor (SC) converters are ideal switching-mode power supplies for consumer portable electronic devices due to their nature of being light weight, small size, and high-power density. However, they suffer from a discontinuous input-current waveform with large di/dt, which leads to significant electromagnetic interference emission. This paper proposes a configuration of SC converters connected in parallel, with their inputs and outputs interleaved and adaptively controlled. The interleaving operation is performed by using an original type of control in which both the capacitors' charging time TON and switching frequency are adjusted to get the line and load regulation. It is shown that, for a given range of variation of the supply voltage and load, there always exists a solution [TON, TS] that assures both output-voltage regulation and perfect interleaving. Experimental results are provided to validate the feasibility of the proposed scheme. Precise interleaving, and good line and load regulation are maintained for all the designated range, including the transient periods.

Adaptive Mixed On-Time and Switching Frequency Control of a System of Interleaved Switched-Capacitor Converters

A new type of DC-to-DC converter is proposed by using dual basic quasi-switched-capacitor (QSC) converter cells. The prominent feature of this converter is its improved input current waveform, which can reduce the electromagnetic interference due to the conducted emissions as compared to the classical PWM-type and SC-based converters. The concept of energy transfer is realized by two symmetrical converter cells, operating in two cyclical phases. The d.c. voltage conversion ratio is determined by the voltage applied to the quasi-switch in each cell for controlling the charging trajectory of the capacitors in order to maintain a constant output voltage for a wide range of load and supply voltage. As the converter does not contain any inductive element, it makes the converter of small size, light weight, high power density and possible in IC form. The small-signal frequency response shows that the designed converter has good operation stability. A prototype of 36 W, 12 V/9 V, step-down DC-to-DC converter has been built, giving an overall efficiency of 73% with power density of 20 W/in/sup 3/.

Switched-capacitor-based DC-to-DC converter with improved input current waveform

A new soft-switched, current-driven full-bridge converter is presented. The structure utilizes a simple snubber formed by two unidirectional switches and a capacitor to realize soft-switching operation over a wide line and load range. All primary-side switches are operated with zero-current switching (ZCS) and the snubber switches are operated with zero-voltage switching. The energy used for soft-switching is self-adaptable. For a given input current, the snubber capacitor is charged to the minimum required energy for ZCS of the switches. Thus, less resonant energy is used and the conduction loss can be kept minimal. The cyclical switching operation and control of the converter will be discussed. By compromising the voltage stress on the switches and loss of duty cycle (i.e., the regulation range), an optimized design procedure of the circuit elements is derived. The input voltage range and load variation that ensure both output voltage regulation and soft switching are determined. By studying the small-signal characteristics of the entire system, a current-controlled feedback control circuit has been implemented with a DSP. The experimental results measured on a 5-kW, 530-V/15-kV prototype confirms the advantages of the proposed converter.

A. Ioinovici

Papers

A cascade boost-switched-capacitor-converter - two level inverter with an optimized multilevel output waveform

Hybrid switched-capacitor-Cuk/Zeta/Sepic converters in step-up mode

Adaptive Mixed On-Time and Switching Frequency Control of a System of Interleaved Switched-Capacitor Converters

Switched-capacitor-based DC-to-DC converter with improved input current waveform

A ZCS Current-Fed Full-Bridge PWM Converter With Self-Adaptable Soft-Switching Snubber Energy