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

A full dc and ac analysis of a previous proposed boost-type-input soft-switching full-bridge converter is presented. The primary-side switches turn-on/off under a zero-current condition (ZCS). The soft-switching is realized by using a simple snubber, formed by two uni-directional switches and a resonant capacitor, in the primary side. The snubber's switches commute under a zero-voltage condition. The resonant energy used for getting ZCS is self-adaptable, depending only on the value of the input current. Except when the input current is at its maximum value, less resonant energy is used, keeping the conduction losses at a low value. A dc analysis allows for the calculation of the duty-cycle. The duty-cycle loss, the maximum voltage across the snubber capacitor, and the duration of the soft-switching assisted-intervals (the charging and discharging intervals of the snubber capacitor) are represented for different values of the resonant capacitor and the leakage inductance of the converter transformer. These graphics allow for an optimized design, by trading-off the voltage stress on the resonant capacitor (i.e. on the primary-side switches) with the loss of duty-cycle (i.e. with the ZCS regulation range). The range of the input voltage and load variation for which both output voltage regulation and soft-switching are assured is determined. Soft-switching is obtained for a wide line and load range. A current-controlled feedback circuit, using a digital signal processor (DSP) with a soft-start scheme was implemented. A small-signal ac analysis of the power stage allowed for the design of the digital controllers.

Modeling and Analysis of a Current-Fed ZCS Full-Bridge DC/DC Converter with Adaptive Soft-Switching Energy

A new converter using a switched-inductor cell integrated with a switched-capacitor cell within a boost-like structure is proposed. The converter can achieve a very high dc conversion ratio. It can serve as the front-end dc-dc converter for a fuel cell in a UPS system. The inductors and capacitors are switched in a parallel-series configuration. The charging circuit of the inductors from the source is separated from the load, what can benefit a DCM operation at light load. A dc analysis of the new circuit leading to the formula of the dc gain and a break-down calculation of the losses are given. Simulation results for a 100 V to 700 V, 10 kW step up converter, are given to verify the theoretical analysis.

A new large DC gain converter based on a switched-capacitor-inductor circuit in conjunction with fuel cell

By replacing the inductor in a basic boost converter by a multiple-coupled-inductor, and adding two diodes and a capacitor, a new converter with a large conversion ratio and low stresses on the switches is obtained. The additional diode helps to circulate the leakage inductance energy to the load in a non-oscillatory manner. The transistor turns on/off with soft-switching. The diodes turn on with zero-voltage switching and turn off with zero-current-switching, their reverse-recovery problem is alleviated. The voltage stress on both the transistor and diodes is less than the output voltage. Computer simulation and experimental results confirmed the theoretical expectations.

Improved circuit of the switched coupled-inductor cell for dc-dc converters with very large conversion ratio

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 closed 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 (THD). Simulations and experiments on a prototype with a five-level output confirm the theoretical analysis.

A boost-switched capacitor-inverter with a multilevel waveform

This paper investigated a novel PWM scheme for two-phase interleaved boost converter with voltage multiplier by combining Alternating Phase Shift (APS) and traditional interleaving PWM control. The APS control is used to reduce the voltage stress on switches in light load while the traditional control is used to keep better performance in heavy load. The boundary condition for swapping between APS and traditional interleaving PWM control is derived. Simulation and experimental results prove the analysis.

A. Ioinovici

Papers

Modeling and Analysis of a Current-Fed ZCS Full-Bridge DC/DC Converter with Adaptive Soft-Switching Energy

A new large DC gain converter based on a switched-capacitor-inductor circuit in conjunction with fuel cell

Improved circuit of the switched coupled-inductor cell for dc-dc converters with very large conversion ratio

A boost-switched capacitor-inverter with a multilevel waveform

Two-phase interleaved boost converter with voltage multiplier under APS control method for fuel cell power system