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DC short circuit fault ride-through is a critical feature for the reliability and performance of DC microgrids. This paper presents the advantage that SiC-based devices offer for designing a Dual-Active Bridge (DAB) DC-DC converter while considering DC short circuit events. It is known that SiC-MOSFET devices have a higher transient current carrying capability than Si-IGBT devices due to their superior thermal conductivity. This characteristic of SiC-MOSFET devices is utilized to improve the design of DAB for DC short circuit fault ride-through applications. An analytical model is developed to understand the performance of a DAB during DC short circuit faults. Switching and thermal simulations are used to validate the analytical model and compare DAB designs based on SiCMOSFET and Si-IGBT. The advantages of SiC-MOSFET enabled DAB compared to Si-IGBT enabled DAB are also quantified for a particular application of DAB in a DC microgrid. It is shown that for fault ride-through applications, DAB enabled with SiCMOSFET can be designed for lower phase shifts compared to Si-IGBT enabled DAB, which inherently reduces the inductor size and circulating current in a DAB.

IEEE WiPDA 2022

Advantages of SiC-Based Devices on the Design of Dual-Active Bridge DC/DC Converter for DC Faults

dual-active bridge

dc microgrid

dc fault

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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.

technical paper

In this paper, the gate driving characteristics of a SiC cascoded Junction Field Effect Transistor (JFET) is explored. Firstly, a Conventional Gate Drive (CGD) circuit is analyzed and implemented, followed by the proposal and implementation of two Active Gate Driving (AGD) methods for the cascoded JFET. Two approaches of gate control are explored: i) using the low-voltage -MOSFET gate & (ii) using the JFET gate. Switching characteristics during turn-on and turn-off for the CGD and both AGD approaches are compared, and it is observed that the proposed AGD circuits provide controllability of both switching edges and thus allowing an application optimized switching operation. Analytical, simulation and experimental results are shown to verify the proposed methods.

Active Gate Driving of Cascoded SiC JFETs

Resonant converters are used extensively for voltage regulation and isolation purposes in electric vehicles. The power level and frequency of the converters is increasing with the ongoing development of the wide-band-gap devices, which brings more challenges to the design of magnetic components. The first challenge is that such high power and frequency make it hard to make proper Litz wire. In this paper, a new current sharing method for paralleled Litz wire transformers is introduced. Using this method, the transformer can stand much higher current without increasing the cost or volume. And the power level can be further increased by integrating more matrix transformers. The second challenge is the resonant inductance integration. Different resonant inductance integration methods are summarized and compared. And controlling the leakage inductance by properly breaking the interleaving structure is proposed in this paper. Using this method, the desired leakage inductance can be reached without sacrificing too much winding loss. Comprehensive transformer design and optimization procedure is also presented in this paper. A 30 kW 100 kHz Serial Half Bridge DC-DC converter prototype is designed to verify the methods at last.

High Frequency High Power Integrated Transformer Design for Resonant Converters with SiC Devices

New semiconductor devices based on wide bandgap materials are emerging in medium voltage power electronic converter applications, presenting new opportunities to the industry relying on semiconductor devices. SiC MOSFETs with blocking voltages of 10 kV (and above) is a promising technology, however, their fast switching transitions result in increased output voltage slew rate (dv/dt), which poses challenges to the applicability of the SiC MOSFET technology. This paper examines the impact of the increased dv/dt on the applicability of an off-the-shelf closed loop hall-effect current sensor when utilized in a medium voltage SiC MOSFET based power electronics converter. Analysis of the capacitive couplings in the current sensor is presented along with an experimental determination of the parasitic capacitance between its primary conductor and secondary winding. Experimental measurements have identified two distinct noise components in the current sensor measurement path due to: 1) capacitive coupling between the primary conductor and secondary winding, and 2) an inferred capacitive coupling into the active circuitry of the current sensor

Noise Analysis of Current Sensor for Medium Voltage Power Converter Enabled by Silicon-Carbide MOSFETs

A 99% efficient power converter is applied to an electrocaloric heat pump prototype for the first time, enabling cyclic electrical field variation in electrocaloric capacitors and high heat pump performance. The electrocaloric effect is an almost fully reversible temperature change in special dielectrics caused by changed electrical field. The GaN power converter achieves high efficiency by zero-voltage switching hysteretic current control. Blocks of commercial multi-layer ceramic capacitors which exhibit an electrocaloric effect are efficiently charged and discharged, synchronized to contacting to a heat sink and source by actuators, which forms a heat pump prototype. Brayton cycles are caused by trapezoidal voltage. Then, arbitrary voltage (E-field) variation for Carnot-like cycles with quasi-isothermal heat transfer is demonstrated and verified by the measured almost constant heat flux during contact to the heat sink. The performance of electrocaloric heat pump prototypes in literature was limited by losses of LC resonant circuits, and is improved by an up to 15.5-fold decrease by this work. The work demonstrates electrocalorics as an emerging power electronics application and contributes to realize future efficient and emission-free, solid state, and electrocaloric heat pump systems.

GaN Power Converter Applied to Electrocaloric Heat Pump Prototype and Carnot Cycle

This paper demonstrates a GaN-based three-level inverter design for an electric vehicle (EV) traction application. The basic power block is a three-level active neutral point clamped (3L-ANPC) converter operating at 800 V DC bus voltage with the use of two paralleled 650 V, 60 A GaN E-HEMTs. The paper focuses on switching mode selection for better thermal performance of high-power 3L-ANPC inverters. The paper presents design details and guidelines for power layout structure and gate driver. The key parasitic inductances of the designed power block are extracted using ANSYS Q3D. A PLECS simulation model using the device loss parameters shows approximate power delivering capability of 41 kW for the designed forced air-cooled three-phase inverter. Experimental double pulse test results are presented with low voltage overshoot to verify the low inductance power loop design. Experimental results of the three-phase 3LANPC inverter operation at 70 kHz switching frequency are presented for delivered output power of 5.1 kW at 550 V DC.

Design Considerations of a GaN-Based Three-Level Traction Inverter for Electric Vehicles

In this paper, a novel structure of three-port with zero voltage switching (ZVS) dc-dc converter is proposed. Three-port dc-dc converters are widely applicable in hybrid energy generating systems to provide substantial power to sensitive loads. One of the ports of the proposed converter is interfaced with a storage such as a battery which makes the converter capable of supplying the load even if the main renewable energy supply of the proposed converter (e.g. photovoltaic cells) is not able to generate power. The proposed converter operates in two operations of charging the battery port and the mode when the battery discharges to the load. In addition, it has ZVS operation for all utilized switches and can eliminate the input current ripple. The ZVS of the switches is provided by the leakage inductances of the used coupled inductors. Also, the voltage control of each of the terminals is achieved by three active switches. In this paper, the proposed topology is analyzed theoretically for all operating modes, also, the voltage and current equations of all components are calculated. Furthermore, the required soft switching and zero input currents ripple conditions are analyzed. Finally, the accuracy performance of the proposed converter and the analytical results is verified by the PSCAD/EMTDC simulation and experimental results for 1MHz switching frequency operation. Applying high frequency and using GaN Fets leads to achieve a more compact prototype of the proposed topology.

Novel High-Voltage-Gain High-Frequency Non-Isolated Three-Port DC-DC Converter with Zero Input Current Ripple and Soft Switching Capability

In this work an approach for a direct experimental comparison of the application-oriented performance between two high current GaN DC/DC converters based on 7 mΩ, 100 V GaN HEMTs in a commercial off-the-shelf top-cooled package and 5 mΩ, 100 V GaN HEMTs embedded in a thermally-optimized single-chip package is given. The two packaging versions are compared by a maximally identical implementation of the power and gate loops in a 48 V, 300 kHz buck converter with two parallel GaN HEMTs. In the single-chip package the die is directly mounted on a 12×6 mm2 copper-heat spreader offering a significantly lower thermal resistance to heatsink (1.69 K W−1) in comparison to the commercial off-the-shelf version (2.45 K W−1). For a direct benchmark, the COTS-based converter has an identical power-loop to the SCP-version with a novel gate-drive concept. Both versions have an efficiency of 96.8 % at 65 A output current (output power: 1.5 kW), while the commercial off-theshelf version has a better efficiency for lower currents, due to its better hard-switching Figure-of-Merits and therefore lower switching losses and reaches an output current of up to 80 A (output power: 1.75 kW). A detailed analytical loss breakdown for the different transistors in dependence of the temperature and output current is given to proof the measured current point, where the efficiencies of both converters are identical, since the higher switching losses of the SCP version are compensated by lower conduction losses at higher currents and temperatures compared to the smaller COTS transistor. Finally, an outlook on further improvements for reaching higher output currents and potential converters for a more fair comparison of different thermally optimized SMD packages are given.

Comparison of Thermally Optimized SMD Packages for 100 V GaN HEMTs in 300 kHz Buck Converter High Current Applications

With the development of SiC technology, the onresistance of discrete devices drops rapidly and can potentially replace the expensive power modules in high power converters. Unlike parallel discrete devices or a power module with built-in parallel dies, using a single device does not need to slow down the gate driver speed hence can achieve lower switching loss. However, there are still many challenges that need meticulous design considerations. This paper uses the 1200V TO-247-4 package device as an example to provide detailed guidance on device selection, loop optimization, insulation, thermal management, and mounting. A DC-DC converter design example is given with a very low loop inductance and excellent thermal performance. The aircooled hardware demonstrates the hardware limitation is around 40kW in an 800V to 470V buck operation. Normalized to the Ron of the two devices used, this demonstrates an extremely high power density figure of merit of PDFOM=87kW/cm2 .

Design of High Power Converter with Single Low Ron Discrete SiC Device

The purpose of this paper is to investigate the impact of the SiC device packages on the commutation performance characteristics of current-source inverters (CSIs). The parasitic components in the CSI current commutation loop between the two-phase legs and output capacitors have a significant impact on the high-frequency performance of the SiC devices. To meet the elevated current requirements of high-power CSIs, it is often necessary to connect multiple discrete devices in parallel which increases the current commutation loop length. The selection of compact high-power SiC MOSFET and Schottky diode modules instead of discrete devices can be highly desirable to reduce the loop inductance and improve the system performance and power density. Two CSI benchtop prototype units, one with SiC discrete devices and the other with power modules, have been designed and tested, and the performances of the two CSIs are compared. The CSI with SiC power modules significantly reduces the inverter volume and lowers the parasitic inductance by 60% and the voltage ripple amplitude by 20% compared to the CSI unit with discrete devices.

Comparative Investigation of Current-Source Inverters Using SiC Discrete Devices and Power Modules

Medium-voltage (MV) dual-active-bridge (DAB) converters have become an emerging technology thanks to highvoltage silicon carbide (SiC) devices and nanocrystalline magnetic materials. However, the need of phase-shift inductance and insulation requirements for the MV DAB may complicate the design of the transformer and the MV DAB converter, which can also induce higher loss and occupy more space. In this paper, the leakage integration and insulation techniques are discussed for a 6.7-kV/850-V DAB converter, meeting both the inductance and insulation requirements of the MV DAB converter. Ferrite cores with air gaps are inserted between the LV and MV windings without introducing high loss, and the MV winding is selectively shielded to avoid high parasitics and meet the insulation requirement. Test results have verified the effectiveness of this design.

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Active Gate Driving of Cascoded SiC JFETs

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