High-frequency-link (HFL) power conversion systems (PCSs) are attracting more and more attentions in academia and industry for high power density, reduced weight, and low noise without compromising efficiency, cost, and reliability. In HFL PCSs, dual-active-bridge (DAB) isolated bidirectional dc-dc converter (IBDC) serves as the core circuit. This paper gives an overview of DAB-IBDC for HFL PCSs. First, the research necessity and development history are introduced. Second, the research subjects about basic characterization, control strategy, soft-switching solution and variant, as well as hardware design and optimization are reviewed and analyzed. On this basis, several typical application schemes of DAB-IBDC for HPL PCSs are presented in a worldwide scope. Finally, design recommendations and future trends are presented. As the core circuit of HFL PCSs, DAB-IBDC has wide prospects. The large-scale practical application of DAB-IBDC for HFL PCSs is expected with the recent advances in solid-state semiconductors, magnetic and capacitive materials, and microelectronic technologies.

Overview of Dual-Active-Bridge Isolated Bidirectional DC–DC Converter for High-Frequency-Link Power-Conversion System

This paper presents an architecture for a future electric power distribution system that is suitable for plug-and-play of distributed renewable energy and distributed energy storage devices. Motivated by the success of the (information) Internet, the architecture described in this paper was proposed by the NSF FREEDM Systems Center, Raleigh, NC, as a roadmap for a future automated and flexible electric power distribution system. In the envisioned “Energy Internet,” a system that enables flexible energy sharing is proposed for consumers in a residential distribution system. The key technologies required to achieve such a vision are presented in this paper as a result of the research partnership of the FREEDM Systems Center.

The Future Renewable Electric Energy Delivery and Management (FREEDM) System: The Energy Internet

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

In the first part of this paper, three-phase power factor correction (PFC) rectifier topologies with sinusoidal input currents and controlled output voltage are derived from known single-phase PFC rectifier systems and/or passive three-phase diode rectifiers. The systems are classified into hybrid and fully active pulsewidth modulation boost-type or buck-type rectifiers, and their functionality and basic control concepts are briefly described. This facilitates the understanding of the operating principle of three-phase PFC rectifiers starting from single-phase systems, and organizes and completes the knowledge base with a new hybrid three-phase buck-type PFC rectifier topology denominated as Swiss Rectifier. Finally, core topics of future research on three-phase PFC rectifier systems are discussed, such as the analysis of novel hybrid buck-type PFC rectifier topologies, the direct input current control of buck-type systems, and the multi-objective optimization of PFC rectifier systems. The second part of this paper is dedicated to a comparative evaluation of four rectifier systems offering a high potential for industrial applications based on simple and demonstrative performance metrics concerning the semiconductor stresses, the loading and volume of the main passive components, the differential mode and common mode electromagnetic interference noise level, and ultimately the achievable converter efficiency and power density. The results are substantiated with selected examples of hardware prototypes that are optimized for efficiency and/or power density.

The Essence of Three-Phase PFC Rectifier Systems—Part II

The dual-active-bridge (DAB) topology is ideally suited for high-power dc-dc conversion, especially when bidirectional power transfer is required. However, it has the drawback of high circulating currents and hard switching at light loads, if wide variation in input and output is expected. To address these issues, this paper presents a comprehensive analysis and experimental results with pulsewidth-modulation (PWM) control of the DAB. The PWM control is in addition to phase-shift modulation between the two H-bridges. The analysis addresses PWM of one bridge at a time and of both bridges simultaneously. In the latter, five distinct modes arise based on the choice of PWM and load condition. The possibilities are analyzed for optimizing power density and efficiency for low-load operation. Finally, a composite scheme combining single and dual PWM is proposed that extends the soft-switching range down to zero-load condition, reduces rms and peak currents, and results in significant size reduction of the transformer. Experimental results are presented with a 10-kW prototype.

Pwm control of dual active bridge: Comprehensive analysis and experimental verification

In the area of power electronics there is a general trend to higher power densities and efficiency. In order to continue this trend new devices, which enable high switching frequencies at higher power levels or show reduced losses at moderate switching frequencies are required. High voltage switches based on a series connection of SiC JFETs and one MOSFET in cascode connection meet these demands. For investigating the performance of the SiC based switch and its influence on the power density/efficiency a dual active bridge, which could transfer 25 kW bidirectionally between a 5 kV and a 700 V dc bus at a switching frequency of 50 kHz, is presented in this paper. There, especially the design of the high voltage/high frequency transformer and the switching as well as the static behaviour of the SiC switch is investigated in detail by simulations and experimental results in this paper.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/04522813_01.pdf

A compact, high voltage 25 kW, 50 kHz DC-DC converter based on SiC JFETs

Switching devices based on SiC offer outstanding performance with respect to operating frequency, junction temperature, and conduction losses enabling significant improvement of the performance of converter systems. There, the cascode consisting of a MOSFET and a JFET has additionally the advantage of being a normally off device and offering a simple control via the gate of the MOSFET. Without dv /dt-control, however, the transients for hard commutation reach values of up to 45kV/μs, which could lead to electromagnetic interference problems. Especially in drive systems, problems could occur, which are related to earth currents (bearing currents) due to parasitic capacitances. Therefore, new dv/d t-control methods for the SiC JFET/Si MOSFET cascode as well as measurement results are presented in this paper. Based on this new concepts, the outstanding performance of the SiC devices can be fully utilized without impairing electromagnetic compatibility.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/06365336.pdf

D $v$ /D $t$ -Control Methods for the SiC JFET/Si MOSFET Cascode

In this paper two bi-directional DC-DC converters for a 1MW next-generation BTB system of a distribution system, as it is applied in Japan, are presented and compared with respect to design, efficiency and power density. One DC-DC converter applies commercially available Si-devices and the other one high voltage SiC switch, which consists of a SiC JFET cascode (MOSFET+1 JFET) in series with five SiC JFETs. In the comparison also the high frequency, high voltage transformer, which ensures galvanic isolation and which is a core element of the DC-DC converter, is examined in detail by analytic calculations and FEM simulations. For validating the analytical considerations a 20kW SiC DC-DC converter has been designed in detail. Measurement results for the switching and conduction losses have been acquired from the SiC and also for a Si system for calculating the losses of the scaled 1MW system.

https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/aggeler_IEEJ_SiCDualActiveBridge_1__01.pdf

Bi-Directional Isolated DC-DC Converter for Next-Generation Power Distribution - Comparison of Converters using Si and SiC Devices

In many pulsed-power applications, there is a trend to modulators based on semiconductor technology For these modulators, high-voltage and high-current semiconductor switches are required in order to achieve a high pulsed power Therefore, often, high-power IGBT modules or IGCT devices are used Since these devices are based on bipolar technology, the switching speed is limited, and the switching losses are higher In contrast to bipolar devices, unipolar ones (eg, SiC JFETs) basically offer a better switching performance Moreover, these devices enable high blocking voltages in the case where wide-band-gap materials, for example, SiC, are used At the moment, SiC JFET devices with a blocking voltage of 12 kV per JFET are available Alternatively, the operating voltage could be increased by connecting N JFETs and a low-voltage MOSFET in series, resulting in a super cascode switch with a blocking voltage N times higher than the blocking voltage of a single JFET For the super cascode, auxiliary elements are required for achieving a statically and dynamically balanced voltage distribution in the cascode In this paper, a new balancing circuit, which results in faster switching transients and higher possible operating pulse currents, is presented and validated by measurement results

Balancing Circuit for a 5-kV/50-ns Pulsed-Power Switch Based on SiC-JFET Super Cascode

Inthis papertwobi-directional DC-DCconverters fora1MW next-generation BTBsystemofadistribution system, asitisapplied inJapan,arepresented andcomparedwith respect todesign, efficiency andpowerdensity. OneDC-DC converter applies commercially available Si-devices andtheother onehighvoltage SiCswitch, whichconsists ofaSiCJFETcascode (MOSFET+1JFET)inseries withfive SiCJFETs. In thecomparison alsothehighfrequency, highvoltage transformer, whichensures galvanic isolation andwhichisa coreelement oftheDC-DCconverter, isexamined indetail by analytic calculations andFEM simulations. Forvalidating theanalytical considerations a20kWSiCDC- DC converter hasbeendesigned indetail. Measurement results fortheswitching andconduction losses havebeenacquired from theSiCandalsoforaSisystemforcalculating thelosses ofthe scaled 1MW system.

Daniel Aggeler

Papers

A compact, high voltage 25 kW, 50 kHz DC-DC converter based on SiC JFETs

D $v$ /D $t$ -Control Methods for the SiC JFET/Si MOSFET Cascode

Bi-Directional Isolated DC-DC Converter for Next-Generation Power Distribution - Comparison of Converters using Si and SiC Devices

Balancing Circuit for a 5-kV/50-ns Pulsed-Power Switch Based on SiC-JFET Super Cascode

Bi-Directional Isolated DC-DCConverter forNext-Generation PowerDistribution - Comparison ofConverters using SiandSiCDevices