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

High-step-up, high-efficiency, and cost-effective dc–dc converters, serving as an interfacing cell to boost the low-voltage output of renewable sources to the utility voltage level, are an important part in renewable energy systems. Over the past few years, there has been a substantial amount of studies devoted to high-step-up dc–dc converters. Among them, the category of coupled-inductor boost converters is widely researched and considered to be a promising solution for high-step-up applications. In this paper, these converters are categorized into five groups according to the major topological features. The derivation process, advantages, and disadvantages of these converters are systematically discussed, compared, and scrutinized. This paper aims to provide an introduction, review, and framework for the category of high-step-up coupled-inductor boost converters. General structures for the topologies are proposed to clarify the topological derivation process and to show potential gaps. Furthermore, challenges or directions are presented in this paper for deriving new topologies in this field.

Overview of High-Step-Up Coupled-Inductor Boost Converters

This paper introduces a non-isolated high step-up dc–dc converter with dual coupled inductors suitable for distributed generation applications. By implementing an input parallel connection, the proposed dc–dc structure inherits shared input current with low ripple, which also requires small capacitive filter at its input. Moreover, this topology can reach high voltage gain by using dual coupled inductors in series connection at the output stage. The proposed converter uses active clamp circuits with a shared clamp capacitor for the main switches. In addition to the active clamp circuit, the leakage energy is recycled to the output by using an integrated regenerative snubber. Indeed, these circuits allow soft-switching conditions, i.e., zero voltage switching and zero current switching for active and passive switching devices, respectively. The mentioned features along with a common ground connection of the input and output make the proposed topology a proper candidate for transformer-less grid-connected photovoltaic systems. The operating performance, analysis and mathematical derivations of the proposed dc–dc converter have been demonstrated in the paper. Moreover, the main features of the proposed converter have been verified through experimental results of a 1-kW laboratory prototype.

High-Efficiency High Step-Up DC–DC Converter With Dual Coupled Inductors for Grid-Connected Photovoltaic Systems

A novel high step-up converter, which is suitable for renewable energy system, is proposed in this paper. Through a voltage multiplier module composed of switched capacitors and coupled inductors, a conventional interleaved boost converter obtains high step-up gain without operating at extreme duty ratio. The configuration of the proposed converter not only reduces the current stress but also constrains the input current ripple, which decreases the conduction losses and lengthens the lifetime of the input source. In addition, due to the lossless passive clamp performance, leakage energy is recycled to the output terminal. Hence, large voltage spikes across the main switches are alleviated, and the efficiency is improved. Even the low voltage stress makes the low-voltage-rated MOSFETs be adopted for reductions of conduction losses and cost. Finally, the prototype circuit with 40-V input voltage, 380-V output, and 1000-W output power is operated to verify its performance. The highest efficiency is 97.1%.

High Step-Up High-Efficiency Interleaved Converter With Voltage Multiplier Module for Renewable Energy System

A novel high step-up converter is proposed for a front-end photovoltaic system. Through a voltage multiplier module, an asymmetrical interleaved high step-up converter obtains high step-up gain without operating at an extreme duty ratio. The voltage multiplier module is composed of a conventional boost converter and coupled inductors. An extra conventional boost converter is integrated into the first phase to achieve a considerably higher voltage conversion ratio. The two-phase configuration not only reduces the current stress through each power switch, but also constrains the input current ripple, which decreases the conduction losses of metal-oxide-semiconductor field-effect transistors (MOSFETs). In addition, the proposed converter functions as an active clamp circuit, which alleviates large voltage spikes across the power switches. Thus, the low-voltage-rated MOSFETs can be adopted for reductions of conduction losses and cost. Efficiency improves because the energy stored in leakage inductances is recycled to the output terminal. Finally, the prototype circuit with a 40-V input voltage, 380-V output, and 1000- W output power is operated to verify its performance. The highest efficiency is 96.8%.

A High Step-Up Converter With a Voltage Multiplier Module for a Photovoltaic System

In this paper, a modular interleaved boost converter is first proposed by integrating a forward energy-delivering circuit with a voltage-doubler to achieve high step-up ratio and high efficiency for dc-microgrid applications. Then, steady-state analyses are made to show the merits of the proposed converter module. For closed-loop control design, the corresponding small-signal model is also derived. It is seen that, for higher power applications, more modules can be paralleled to increase the power rating and the dynamic performance. As an illustration, closed-loop control of a 450-W rating converter consisting of two paralleled modules with 24-V input and 200-V output is implemented for demonstration. Experimental results show that the modular high step-up boost converter can achieve an efficiency of 95.8% approximately.

High-Efficiency Modular High Step-Up Interleaved Boost Converter for DC-Microgrid Applications

In this paper, a passive ripple canceling circuit (PRCC) is proposed to eliminate the output power reduction effect of photovoltaic (PV) systems caused by the current ripple of the PV converters. Special features of the proposed PRCC include having low-cost simple modular structure and being independent of the duty ratio control of the main power circuit. Hence, it can be easily integrated to the main power circuit to achieve zero input current ripple, yielding less filter size, loss, and fast response. Meanwhile, the linear line maximum power point tracking (MPPT) control is also integrated with the proposed module integrated converter (MIC) to achieve instantaneous tracking response. Finally, a 90-W laboratory prototype is constructed to verify the effectiveness of the proposed principle. It is seen that the resulting peak-to-peak input current ripple is reduced to about 2% of the original dc converter input ripple. In other words, the input current ripple is almost zero. As a result, the harvested power of the proposed MIC can be increased by 7% as compared with that of the MIC without the proposed PRCC.

http://ieeexplore.ieee.org/iel7/28/7012131/06819430.pdf

Current-Ripple-Free Module Integrated Converter With More Precise Maximum Power Tracking Control for PV Energy Harvesting

In this paper, a novel high voltage gain single-stage dc/ac converter is proposed for distributed energy resources. A flyback-type auxiliary circuit is integrated with an isolated Cuk-derived voltage source inverter to achieve a much higher voltage gain. It is seen that through this integration, the capacitors of the flyback and the Cuk circuits are paralleled for charging and in series for discharging automatically. Due to the capacitive voltage dividing, the dc-side switch voltage stress can be reduced and the losses can be reduced as well. Besides, the low influence of coupling coefficient of flyback-type auxiliary circuit on the inverter characteristic renders the proposed inverter design rather flexible and easy. Steady-state characteristics, performance analysis, simulation and experimental results are given to show the merits of the proposed integrated inverter. Finally, based on the same integration concept, a family of different topologies is also presented for reference.

A Novel Integrated DC/AC Converter With High Voltage Gain Capability for Distributed Energy Resource Systems

This paper presents a novel integrated single-phase inverter with both high step-up ratio and buck-boost capabilities for low-voltage alternative energy source applications. An auxiliary step-up circuit is integrated with an isolated Cuk-derived voltage-source inverter to achieve a much higher voltage-conversion ratio while avoiding using extreme duty ratios in both dc-side and ac-side switches. In addition, the proposed circuit possesses the automatic energy-transfer characteristic between parallel charging and series discharging of two capacitors to achieve a much higher voltage level. Moreover, the voltage stress of dc-side active switches can be reduced to below one half as compared with that of a traditional isolated Cuk converter. Finally, steady-state characteristics, performance analyses, and representative experimental results are also made to show the merits of the proposed inverter.

A Novel Integrated Single-Phase Inverter With Auxiliary Step-Up Circuit for Low-Voltage Alternative Energy Source Applications

In this paper, a passive ripple cancelling circuit (PRCC) is proposed to eliminate the output power reduction effect of PV systems caused by the current ripple of the PV converters. Special features of the proposed PRCC include low cost, simple, modular structure, and independent of the duty ratio control of the main power circuit. Hence, it can be easily integrated to the main power circuit to achieve zero input current ripple yielding less filter size, loss, and fast response. Meanwhile, the linear line maximum power point tracking (MPPT) control is also integrated with the proposed MIC to achieve instantaneous tracking response. Finally, a 90W laboratory prototype is constructed to verify the effectiveness of the proposed principle. It is seen that the resulting peak to peak input current ripple is reduced to about 2% of the original DC converter input ripple. In other words, the input current ripple is almost zero. As a result, the harvested power of the proposed MIC can be increased by 7% as compared with that of the MIC without the proposed PRCC.

Ming-Chieh Cheng

Papers

High-Efficiency Modular High Step-Up Interleaved Boost Converter for DC-Microgrid Applications

Current-Ripple-Free Module Integrated Converter With More Precise Maximum Power Tracking Control for PV Energy Harvesting

A Novel Integrated DC/AC Converter With High Voltage Gain Capability for Distributed Energy Resource Systems

A Novel Integrated Single-Phase Inverter With Auxiliary Step-Up Circuit for Low-Voltage Alternative Energy Source Applications

Current ripple-free module integrated converter (MIC) with more precise maximum power tracking control for PV energy harvesting