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The transformer flux unbalance in dual-activebridge (DAB) converters is a critical issue due to the electrical parameter and modulation mismatch, and load or control transients. Compared to low voltage DAB converters, the unbalance problem in medium voltage DAB converters may cause more severe problem, and become more difficult to deal with, because of the high operating voltage and insulation requirement. In this paper, a flux balancing strategy for a medium voltage (MV) DAB converter is proposed, including the transformer design with ferrite gap, current harmonic-based unbalance detection, as well as the flux balancing control scheme. With the proposed ferrite gap, nonlinear magnetizing current and its modeling are induced. Then, by analyzing the current harmonics, the flux unbalance level can be detected, and hence controlled. Test results have verified the proposed method in a MV DAB converter.

IEEE WiPDA 2022

A Flux Balancing Strategy for 10-kV SiC-Based Dual-Active-Bridge Converter

sic; converter

dual-active-bridge converters; flux balancing; medium voltage

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 The IEEE Workshop on Wide Bandgap Power Devices & Applications (WiPDA) provides a forum for device scientists, circuit designers, & application engineers from the Power Electronics & Electron Devices Societies to share technology updates, research findings, experience & potential applications.
 
 **Topics of interest**
* Heteroepitaxial & Bulk Materials Growth
* Gate Dielectrics & Surface Passivation
* Device Structures & Fabrication Techniques
* Device Characterization & Modeling
* Very-High Efficiency Or Compact Converters
* Safe Operating Areas Of Wide Bandgap Devices, including Short Circuit, Spike, &Transient Tolerance
* Harsh Environment (High Temperature) Operation & Reliability
* Packaging Power Modules & ICs
* Gate Drive & Other Auxiliary Circuits
* High-Performance Passive Components
* Hard-Switched & Soft-Switched Application Analysis
* Applications in Renewable Energy & Energy Storage, Transportation, Industrial Drives, Grid Power Systems, Space and Aerospace
* Wide Bandgap System Design Philosophies & Strategies
* Radio Frequency (RF) GaN
* Technology Roadmap of Wide Bandgap Including Devices, Applications and Packaging

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The IEEE Workshop on Wide Bandgap Power Devices & Applications (WiPDA) provides a forum for device scientists, circuit designers, & application engineers from the Power Electronics & Electron Devices Societies to share technology updates, research findings, experience & potential applications.

poster

This paper presents the initial evaluation of a 3.3- kV, SiC MOSFET power module (not fully populated) from Wolfspeed, including static, short circuit (SC), and partial discharge (PD) test results. Static characterization results are presented first. The module performance change after repetitive pulse SC tests is provided by comparing the original static characterization test results to the one performed after the SC stress tests. More electric aircrafts (MEA) require an increased electric system voltage level (e.g., 230 VAC constant or variable frequency, ± 270 VDC or 540 VDC) and make PD a very relevant and urgent issue. Thus, PD evaluation tests for the module package are included for different air pressures from Sea Level (i.e., 760 Torr) to 50,000 feet (i.e., 87 Torr) altitude. The PD inception voltage (PDIV) and extinction voltage (PDEV) obtained via experimentation are presented in this paper.

Short Circuit Ruggedness and Partial Discharge Evaluation of a 3.3 kV SiC MOSFET Power Module

SiC MOSFETs are a beneficial solution in motor inverter applications because of their remarkable intrinsic diode reverse recovery behavior. SiC MOSFETs have successfully emerged as the best choice as devices for realizing high performance and high power motor drive in, for example, electric vehicles, but have rarely been used in low power motor drive for applications. In this work, an all-in-one system integrated SiC intelligent power module, which integrates the MCU, memory, SRAM, motor control library, ADC, DAC, gate drivers, and SiC MOSFETs was proposed to explore the benefits and potential of SiC MOSFETs in highly integrated BLDC/PMSM motor drive. As a result, SiC solution generally saves over 80% of space, improves the thermal performance by 27.7°C, and enhances 3% of efficiency compared to the silicon counterparts.

A Highly Integrated Sensorless Field Oriented Control BLDC / PMSM Inverter with 99% Efficiency Enabled by an All-in-One System Integrated Full SiC Intelligent Power Module (sIPM®)

The role of an academic in the area of SiC power devices can be categorized as: (1) Fundamental Theoretical Predictions; (2) Fundamental Scientific Knowledge; (3) Fundamental Device Structures; (4) Device Structural Innovations; (5) Device Physics and Analysis; and (6) Technology Feasibility Studies. This paper provides examples of these activities during my past 40 years of effort in this field as a retrospective. New prospective device ideas that will have a strong impact on power electronics in the future are then discussed.

An Academic’s Perspective on SiC Power Devices: Retrospection and Prognostication

The adoption of SiC Schottky diodes and then SiC MOSFETs in solar inverter applications was the first wave to evaluate the capabilities of these new devices in challenging applications and environments.  With the observed and projected growth of demand for high-efficiency, high-voltage power semiconductor devices in automotive traction and EV chargers, challenges arise to supply SiC devices into these demanding applications.  Current and emerging SiC power device manufacturers are developing strategies to be able to support the accelerating need for SiC power device supply.  onsemi is building on its strength in end-to-end solutions of silicon power semiconductor devices, starting with silicon crystal growth and epitaxy, through die fabrication and final package and module assembly.  onsemi has extended its existing silicon-based power semi portfolio into SiC-based power modules.  To achieve this, we continue to invest heavily in SiC wafer and epitaxy, as well as expanding wafer fab capacity to meet the growing demand.  Additionally, onsemi continues to develop advanced SiC power modules to meet the specific needs of automotive and industrial customers. At onsemi, we strongly believe that this vertically-integrated strategy will help meet the growing customer needs for high-efficiency SiC power modules.

Toward Vertical Integration to Scale the Supply of High Performance SiC Power Modules for Demanding Applications

There is little debate nowadays about the merit of GaN or SiC material for Power Electronics applications compared to the Silicon-based technologies. Power supplies and power inverter continue to drive most of the Wide Bandgap material adoption with Gallium Nitride used nowadays in nearly every power supply and Silicon Carbide as the material of choice for high efficiency power inverters for long range Electric Vehicle (EV). To enable such widespread adoption into new applications, MOCVD equipment needs to ensure not only to meet the tightest material performance requirements but also to provide solutions enabling cost reduction year after year. In addition, the current semiconductor ramps, and material constraints are accelerate the transition to larger substrate size and the focus on integrability into Silicon factory as well as tool productivity per unit for clean room floor area. We will present how AIXTRON is addressing those markets with new series of high throughput solutions for Wide Bandgap materials and how this contribute to bolst the output of existing factories.

New high throughout solutions for Wide Bandgap power semiconductors

As the world looks beyond silicon for the next generation of power electronics, NexGen Vertical GaN™, the world’s first GaN-on-GaN power semiconductor, unlocks the full potential of Gallium Nitride (GaN). It is the only wide band gap power semiconductor that provides high-voltage capabilities up to 4kV, switching frequencies up to 10MHz, and avalanche and short-circuit robustness. This makes it an ideal power semiconductor for applications from LED Lighting and Computing to Data Centers and Electric Vehicles. NexGen is reinventing power electronics by leveraging this breakthrough technology and building a scalable, software-configurable power platform that enables the smallest, lightest, and most efficient power systems.

Vertical GaN “Technology of Future” – Now a Reality with NexGen Power Systems

Ultra-wide-bandgap (UWBG) AlGaN alloys (Eg > 4 eV) are appealing for the next-generation of high-voltage power devices due to their superior material properties. Most notable is that the critical electrical field scales as the bandgap to the ~ 2.0-2.5 power. Thus, power diodes employing Al-rich AlGaN alloys (4.0 < Eg < 6.2 eV) are expected to operate at higher breakdown voltages with thinner and more heavily-doped drift regions, leading to lower resistive losses and higher power density compared to Si-, SiC- and even GaN-based devices. Additionally, the formation of AlGaN-based heterojunctions and the utilization of polarization fields for doping offer device design options not currently possible for devices based on SiC and other ultra-wide bandgap semiconductors such as diamond and b-Ga2O3. We will present polarization doping of both p- and n-type AlGaN alloys in compositions where conventional impurity doping fails and employ polarization doping to fabricate Al0.7Ga0.3N PN diodes with kilovolt breakdown voltages. In addition to appealing material properties such has high critical electric field, we have found that the electrical characteristics of Schottky diodes and regrown PN junctions in AlGaN alloys show a surprising robustness to residual, sub-surface etch damage that degrades the performance and thus complicates the fabrication of GaN devices. This robustness to etch damage has led to the demonstration of PN diodes where the p-anode was formed by regrowth in an etched well which resulted in diodes that exhibit reverse breakdown voltages of 1.8 kV and are indistinguishable from continuously grown PN diodes. A major challenge to realizing vertically conducting AlGaN power devices is the lack of a native, conducting substrate. To address the need for vertically conducting device architectures, we present an AlGaN overgrowth process on previously-patterned, conducting GaN substrates that have been used to fabricate PN diodes with 7 mm thick drift layers in Al0.3Ga0.7N that reach breakdown voltages of 1 kV. These and other examples to be presented illustrate the potential of AlGaN alloys for realizing kilovolt-class power diodes and transistors for next generation power systems.

Ultra-Wide Bandgap AlGaN Alloys for Power Electronics

Supply and Cost of Substrates for Compound Semiconductors

A new Dodecagonal (polygon with twelve sides, short for Dod) cell topology is designed for 4H-SiC planar power MOSFETs. The Dod cell is used in the layout design of the 650 V SiC MOSFETs. The nominal Hexagonal (Hex) cell and a recently published Octagonal (Oct) cell are also used on the 650 V SiC MOSFET layout designs for comparisons. The devices are fabricated, diced, and packaged for static and dynamic characterizations. Experimental results show that the Hex-cell MOSFET has the lowest specific ON-resistance (Ron,sp) and is suitable for high-power applications. The Dod and Oct-cell MOSFETs have much smaller gate-drain capacitance than Hexcell MOSFETs, making them good candidates for high-frequency applications. The new Dod cell is designed with optimized channel density to have reduced Ron,sp compared to the Oct cell.

A New Cell Topology for 4H-SiC Planar Power MOSFETs and Comparison with Hexagonal and Octagonal Cell Topologies

Several different designs of 1.2kV-rated 4HSiC JBS diode integrated MOSFETs (JBSFETs) have been successfully fabricated to increase the 3rd quadrant device performance while maintaining the electrical characteristics on both the forward and blocking modes of operation when compared to its MOSFET counterpart. Incorporating the Schottky area in an efficient manner to improve overall device performance has been a critical path in the development and adoption of 4H-SiC JBSFETs rather than MOSFETs copackaged with JBS Diodes. Device design, fabrication, and electrical performances are discussed in this paper and as a result, an optimum JBSFET design is proposed.

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Short Circuit Ruggedness and Partial Discharge Evaluation of a 3.3 kV SiC MOSFET Power Module

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