http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

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.

/pdf/step-up-dc-dc-converters-a-comprehensive-review-of-voltage-6dlytctzg2.pdf

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

Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

/pdf/the-2018-gan-power-electronics-roadmap-2iunv619fh.pdf

The 2018 GaN power electronics roadmap

Switching devices based on wide bandgap materials such as silicon carbide (SiC) offer a significant performance improvement on the switch level (specific on resistance, etc.) compared with Si devices. Well-known examples are SiC diodes employed, for example, in inverter drives with high switching frequencies. In this paper, the impact on the system-level performance, i.e., efficiency, power density, etc., of industrial inverter drives and of dc-dc converter resulting from the new SiC devices is evaluated based on analytical optimization procedures and prototype systems. There, normally on JFETs by SiCED and normally off JFETs by SemiSouth are considered.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/SiC.pdf

SiC versus Si—Evaluation of Potentials for Performance Improvement of Inverter and DC–DC Converter Systems by SiC Power Semiconductors

This paper points out a phenomenon of power backflow in traditional phase-shift (TPS) control of isolated bidirectional full-bridge DC-DC converter (IBDC), and analyzes the effects which backflow power act on power circulating flow and current stress. On this basis, the paper proposes a novel extended-phase-shift (EPS) control of IBDC for power distribution in microgrid. Compared with TPS control, EPS control not only expands regulating range of transmission power and enhances regulating flexibility, but also reduces current stress and improves the system efficiency. The operation principle of EPS control and the operation modes of IBDC are analyzed in the paper. By establishing mathematical models of transmission power, backflow power, and current stress, the paper comparatively analyzes control performances of TPS and EPS control. At last, experimental results verify the excellent performance of EPS control and correctness of the theoretical analysis.

Extended-Phase-Shift Control of Isolated Bidirectional DC–DC Converter for Power Distribution in Microgrid

A new design approach achieving very high conversion efficiency in low-voltage high-power isolated boost dc-dc converters is presented. The transformer eddy-current and proximity effects are analyzed, demonstrating that an extensive interleaving of primary and secondary windings is needed to avoid high winding losses. The analysis of transformer leakage inductance reveals that extremely low leakage inductance can be achieved, allowing stored energy to be dissipated. Power MOSFETs fully rated for repetitive avalanches allow primary-side voltage clamp circuits to be eliminated. The oversizing of the primary-switch voltage rating can thus be avoided, significantly reducing switch-conduction losses. Finally, silicon carbide rectifying diodes allow fast diode turn-off, further reducing losses. Detailed test results from a 1.5-kW full-bridge boost dc-dc converter verify the theoretical analysis and demonstrate very high conversion efficiency. The efficiency at minimum input voltage and maximum power is 96.8%. The maximum efficiency of the proposed converter is 98%.

High-Efficiency Isolated Boost DC–DC Converter for High-Power Low-Voltage Fuel-Cell Applications

This paper demonstrates the utilization of gallium nitride (GaN) devices to achieve an ultrahigh efficiency in an isolated dc–dc converter. This paper presents the design and implementation of high-efficiency magnetics necessary to realize such an ultrahigh efficiency converter. Synchronous rectification is also implemented to further improve the efficiency. Compared to an equivalent silicon MOSFET, GaN devices have low output charge, very low gate drive losses, and zero reverse recovery losses, this makes GaN devices more suitable for power converters to achieve high efficiency. A complete analytical loss modeling for an isolated full bridge dc–dc converter is discussed in this paper. Furthermore, the experimental demonstration of ultrahigh efficiency in a 2.4-kW isolated GaN converter is presented. Ultrahigh conversion efficiency allows the realization of a very compact dc–dc converter with a very small or no heat sink. The prototype converter has a power density of 7 kW/L and the measured efficiency is above 98.5% over a wide range of output power. The maximum measured efficiency of the converter is 98.8% at 50% of full load.

Experimental Demonstration of a 98.8% Efficient Isolated DC–DC GaN Converter

This paper proposes a comprehensive analytical LCL filter design method for three-phase two-level power factor correction rectifiers (PFCs) The high-frequency converter current ripple generates the high-frequency current harmonics that need to be attenuated with respect to the grid standards Studying the high-frequency current of each element proposes a noniterative solution for designing an LCL filter In this paper, the converter current ripple is thoroughly analyzed to generalize the current ripple behavior and find the maximum current ripple for sinusoidal pulse width modulation (PWM) and third-harmonic injection PWM Consequently, the current ripple is used to accurately determine the required filter capacitance based on the maximum charge of the filter capacitor To choose the grid-side inductance, two methods are investigated First method uses the structure of the damping to express the grid-side filter inductance as a function of the converter current ripple Reducing the power loss in the filter and optimizing the grid-side filter inductance is the main focus of the second method which is achieved by employing line impedance stabilization network (LISN) Accordingly, two LCL filters are designed for a 5 kW silicon-carbide-based three-phase PFC Various experimental scenarios are performed to verify the filters attenuation and performance

Analytical Design of Passive LCL Filter for Three-Phase Two-Level Power Factor Correction Rectifiers

Foil windings are preferable in high-current highpower inductors to realize compact designs and to reduce dc-current losses. At high frequency, however, proximity effect will cause very significant increase in ac resistance in multi-layer windings, and lead to high ac winding losses. This paper presents design, analysis and experimental verification of a two winding technique, which significantly reduces ac winding losses without compromising dc losses. The technique uses an inner auxiliary winding, which is connected in parallel with an outer main winding. The auxiliary winding is optimally designed with low ac resistance and leakage inductance to carry the ac current while the outer winding is designed for the large dc current. Detailed analysis and design of a 350 A, 10 kW inductor with the proposed technique are presented with discussions. Experimental results of a prototype 350 A inductor, used in a 10 kW fuel cell dc-dc converter, are also presented to demonstrate the validity of the proposed technique and its superior performance.

Reducing ac-winding losses in high-current high-power inductors

A new low-leakage-inductance low-resistance design approach to low-voltage high-power isolated boost converters is presented. Very low levels of parasitic circuit inductances are achieved by optimizing transformer design and circuit lay-out. Primary side voltage clamp circuits can be eliminated by the use of power MOSFETs fully rated for repetitive avalanche. Voltage rating of primary switches can now be reduced, significantly reducing switch on-state losses. Finally, silicon carbide rectifying diodes allow fast diode turn-off, further reducing losses. Test results from a 1.5 kW full-bridge boost converter verify theoretical analysis and demonstrate very high efficiency. Worst case efficiency, at minimum input voltage maximum power, is 96.8 percent and maximum efficiency reaches 98 percent.

/pdf/a-new-approach-to-high-efficiency-in-isolated-boost-2jkig0btar.pdf

Morten Nymand

Papers

High-Efficiency Isolated Boost DC–DC Converter for High-Power Low-Voltage Fuel-Cell Applications

Experimental Demonstration of a 98.8% Efficient Isolated DC–DC GaN Converter

Analytical Design of Passive LCL Filter for Three-Phase Two-Level Power Factor Correction Rectifiers

Reducing ac-winding losses in high-current high-power inductors

A new approach to high efficiency in isolated boost converters for high-power low-voltage fuel cell applications