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

Solid-state switch mode AC-DC converters having high-frequency transformer isolation are developed in buck, boost, and buck-boost configurations with improved power quality in terms of reduced total harmonic distortion (THD) of input current, power-factor correction (PFC) at AC mains and precisely regulated and isolated DC output voltage feeding to loads from few Watts to several kW. This paper presents a comprehensive study on state of art of power factor corrected single-phase AC-DC converters configurations, control strategies, selection of components and design considerations, performance evaluation, power quality considerations, selection criteria and potential applications, latest trends, and future developments. Simulation results as well as comparative performance are presented and discussed for most of the proposed topologies.

Comprehensive Study of Single-Phase AC-DC Power Factor Corrected Converters With High-Frequency Isolation

Renewable sources like solar photovoltaic (PV) and fuel cell stack are preferred to be operated at low voltages. For applications such as grid-tied systems, this necessitates high voltage boosting resulting in efficiency reduction. To handle this issue, this paper proposes a novel high voltage gain, high-efficiency dc–dc converter based on coupled inductor, intermediate capacitor, and leakage energy recovery scheme. The input energy acquired from the source is first stored in the magnetic field of coupled inductor and intermediate capacitor in a lossless manner. In subsequent stages, it is passed on to the output section for load consumption. A passive clamp network around the primary inductor ensures the recovery of energy trapped in the leakage inductance, leading to drastic improvement in the voltage gain and efficiency of the system. Exorbitant duty cycle values are not required for high voltage gain, which prevents problems such as diode reverse recovery. Presence of a passive clamp network causes reduced voltage stress on the switch. This enables the use of low voltage rating switch (with low “ on -state” resistance), improving the overall efficiency of the system. Analytical details of the proposed converter and its hardware results are included.

Design and Analysis of a High-Efficiency DC–DC Converter With Soft Switching Capability for Renewable Energy Applications Requiring High Voltage Gain

The main theme of this paper is to present a new digital-controlled technique for battery charger to achieve constant current and voltage control while not requiring current feedback. The basic idea is to achieve constant current charging control by limiting the duty cycle of charger. Therefore, the current feedback signal is not required and thereby reducing the cost of A/D converter, current sensor, and computation complexity required for current control. Moreover, when the battery voltage is increased to the preset voltage level using constant current charge, the charger changes the control mode to constant voltage charge. A digital-controlled charger is designed and implemented for uninterrupted power supply (UPS) applications. The charger control is based upon the proposed control method in software. As a result, the UPS control, including boost converter, charger, and inverter control can be realized using only one low cost MCU. Experimental results demonstrate that the effectiveness of the design and implementation.

New Digital-Controlled Technique for Battery Charger With Constant Current and Voltage Control Without Current Feedback

This paper presents a dc-to-dc converter, which offers continuous input and output energy flow and low input current ripple, applicable and mandatory for photovoltaic (PV) arrays and maximum power tracking applications. The PV array yields exponential curves for current and voltage where maximum power occurs at the curve's mutual knee. Conventional dc-to-dc converters have a relatively high input current ripple which causes high power losses when connected to nonlinear sources like PV arrays. The proposed converter maximizes the power that can be sourced from the PV array, without the need of any electrolytic filtering capacitance. The effect of current ripple can be significant and decreases PV system efficiency. Converter simulations and experimental results support and extol the system concept.

/pdf/dc-to-dc-converter-with-low-input-current-ripple-for-maximum-4epk1etzz1.pdf

DC-to-DC Converter With Low Input Current Ripple for Maximum Photovoltaic Power Extraction

This paper presents a dc-dc boost converter with high voltage gain based on the three-state switching cell for split-capacitor neutral-point-clamped inverters. The proposed converter is analyzed considering the operation in continuous conduction mode and duty cycle higher than 0.5, which corresponds to overlapping mode. The main characteristics of the topology are operation at high switching frequency, whereas the input inductor is designed for twice such frequency; in order to minimize weight and volume, the voltage stress across the switches is lower than half of the output voltage and naturally clamped by one output capacitor, allowing the use of MOSFET transistors with reduced intrinsic on-resistance; the input current presents small ripple; the output voltage can be further stepped up by increasing the transformer turns ratio without compromising the voltage stress across the switches; and the output voltage is naturally balanced, thus making the converter suitable for supplying split-capacitor inverters. Several topologies where a high voltage step-up is possible are initially investigated in the literature. Then, the principle of operation and experimental results for a 1-kW prototype are presented to validate the theoretical analysis and demonstrate the converter performance.

A Nonisolated DC–DC Boost Converter With High Voltage Gain and Balanced Output Voltage

In this paper, a new high frequency isolation on-line uninterruptible power supply (UPS) system is proposed as a viable solution for low power applications. It's composed by one half-bridge chopper that operates in open loop with fixed duty cycle, a step-up converter that operates in closed loop using the traditional average current mode control and a traditional full bridge voltage source inverter (VSI). The step-up converter control provides power factor correction to the system. The proposed circuit is suitable for the development of low power UPSs (less than 1 kVA) which few batteries are used. In such applications the battery bank voltage, can be 24 V, 36 V or 48 V. Principle of operation, as well as, experimental results for the UPS operating in both, grid and battery modes are presented. Accordingly to the experimental results for a 1 kVA assembled prototype, an efficiency of 81,3% is obtained for grid mode and 89,2% for the battery mode, confirming the effectiveness of the proposed configuration.

High frequency isolation on-line UPS system for low power applications

Electric vehicles (EVs) powered by batteries and other energy storage devices (ESDs), e.g., ultracapacitors, are expected to play an important role in the development of a more sustainable future. In this context, charging stations (CSs) are supposed to become the main sources of energy for charging the batteries, being strongly dependent on power electronic converters. This paper analyzes a bidirectional single-phase, three-level stacked neutral-point-clamped (3L-SNPC) converter for CS applications, which may behave as a rectifier or an inverter depending on the power flow direction. Besides, the derived analysis can be easily extended to the development of a three-phase version. Considering that the CS is capable of integrating the utility grid and renewable energy sources, it is possible to absorb or inject energy into the ac grid with high power factor and reduced harmonic content of the current. The main advantages of the bidirectional topology are the existence of a three-level voltage waveform across each leg and the neutral point, while filtering requirements are reduced when compared with typical two-level structures used in EV CSs; the voltage stresses on all semiconductors are equal to half of the total dc-link voltage; power factor is nearly unity in any operation mode; and the voltages across the dc-link capacitors are balanced. The thorough design of the power and control stages is presented, as well as experimental results from a laboratory prototype are discussed in detail.

/pdf/bidirectional-three-level-stacked-neutral-point-clamped-hj20lhthcx.pdf

Bidirectional Three-Level Stacked Neutral-Point-Clamped Converter for Electric Vehicle Charging Stations

This paper proposes a feasible low cost isolated battery charger converter, which is powered directly by the ac mains voltage, and with characteristics of high power factor for uninterruptible power systems (UPS) applications. The main advantage of this converter is due to the fact of its total independence of the UPS online power stage. Thus, if the batteries capacity of the system are changed (i.e., the output power of the battery charger), no such modification are required to the main power stage of the UPS, such as re-design of the input ac/dc power stage for an higher or lower output power capacity. This re-design commonly occurs in UPS topologies that the battery charger is directly fed by the dc-link bus voltage, such as common neutral connections UPS. Another advantage is that the energy supplied to charge the batteries is processed by only one power processing stage, increasing the system reliability. As disadvantage of such converter is the reasonable efficiency. Experimental results and relevant curves regarding the proposed converter operation are shown, confirming the viability of such circuit.

A low cost flyback-based high power factor battery charger for UPS applications

This paper presents a dc-dc boost converter with high voltage gain based on three-state switching cell for split-capacitor neutral-point clamped inverters. The proposed converter is analyzed considering the operation in continuous conduction mode and duty cycle higher than 0.5, which corresponds to overlapping mode. The main characteristics of the topology are: operation at high switching frequency, while the input inductor is designed for twice such frequency; in order to minimize weight and volume, the voltage stress across the switches is lower than half of the output voltage and naturally clamped by one output capacitor, allowing the use of transistors MOSFETs with reduced intrinsic on-resistance; the input current presents small ripple; the output voltage can be further step up by increasing the transformer turns ratio without compromising the voltage stress across the switches; the output voltage is balanced thus making the converter suitable for supplying split-capacitor inverters. Several topologies where high voltage step up is possible are initially investigated in literature. Then the principle of operation, the design methodology, and experimental results for a 1kW prototype are presented to validate the theoretical analysis and demonstrate the converter performance.

Luiz D. S. Bezerra

Papers

A Nonisolated DC–DC Boost Converter With High Voltage Gain and Balanced Output Voltage

High frequency isolation on-line UPS system for low power applications

Bidirectional Three-Level Stacked Neutral-Point-Clamped Converter for Electric Vehicle Charging Stations

A low cost flyback-based high power factor battery charger for UPS applications

DC-DC nonisolated boost converter with high voltage gain adequate for split-capacitor inverter applications