United States

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.

IEEE WiPDA 2022

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

gan; carnot cycle

electrocalorics

half-bridges

heat pumps

gallium nitride

energy efficiency

 **RTSS 2021** has successfully concluded. Hope you have enjoyed it, and look forward to seeing you next year in person.
    Announcement for the Awards:
 * Best Paper Award goes to: Monte Carlo Response-Time Analysis, Sergey Bozhko, Georg von der Brüggen, and Björn Brandenburg
 * Best Student Paper Award goes to: Automatic Energy-Hotspot Detection and Elimination in Real-Time Deeply Embedded Systems, Mohsen Shekarisaz, Lothar Thiele, and Mehdi Kargahi.
 * Best Solution Award for Industry Session goes to: Toward Real-Time Guaranteed Scheduling for Autonomous Driving Systems. Jinghao Sun, Tianyi Wang, Kailu Duan, Bin Lu, Jiankang Ren, Zhishan Guo, and Guozhen Tan.



IEEE RTSS 2021

The IEEE Real-Time Systems Symposium (RTSS) is the premier conference in the field of real-time systems, and is a venue for researchers and practitioners to showcase innovations covering all aspects of real-time systems, including theory, design, analysis, implementation, evaluation, and experience. 

technical paper

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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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Registration Is Required

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.

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.

A Medium-Voltage Transformer with Integrated Leakage Inductance for 10 kV SiC-Based Dual-Active-Bridge Converter

Tetra Corporation is developing a pulsed power drilling system for the geothermal industry. The system requires a high temperature switching technology to replace the existing technology based on Si thyristors with a temperature limit of 150°C. This work focuses on the development of such switch based on a Supercascode configuration using SiC JFET technology. The development presented contains thermal models, packaging design and processes, circuit simulations and prototypes of both the Supercascode switch and the high temperature packaged SiC JFETs.

Development of a 250°C 15kV SuperCascode Switch Using SiC JFET Technology

This paper investigates the failure modes of SiC MOSFETs-based passive voltage clamping dc solid-state circuit breakers (SSCBs). There are two major concerns of main SiC switch failure that are analyzed in this paper: 1) gate-source voltage ringing related switch degradation/failure when cutting off heavy fault current with high di/dt. 2) thermal runaway directly caused by the short circuit surge current in the main switch before the cut-off and transient power strike during cutoff. Two 10A/86A dc interruption experiments are conducted to demonstrate the failure caused by gate ringing due to the high di/dt issue coupled with unavoidable parasitic common source impedance of the device package. The thermal runaway failure due to the short circuit current surge and transient turn-off power strike is also demonstrated by a 631A dc interruption test. At last, an active commutation current injection scheme is discussed as future research trends to address the revealed gate ringing and cut-off power strike issues in SSCBs.

Short Circuit Fault Induced Failure of SiC MOSFETs in DC Solid-State Circuit Breakers

Insulated metal substrate (IMS) boards have been widely used in industry for their remarkable electrical and thermal performance. However, the IMS boards require a separate driver board that affects the power density. With Gallium Nitride enhancement-mode high electron mobility transistors (GaN E-HEMTs) being adopted in modern power converters, power density is becoming critical more than ever. This paper proposes the next generation of single-board IMS power stages (i.e., IMS4). In this board, the power board and the driver board are embedded into a single board. Furthermore, a CerStrate™ ceramic substrate single-board solution is proposed that maintains the exact electrical specifications as observed in IMS4 and significantly enhances the thermal performance. The superiority of these single-board solutions is verified through finite element analysis (FEA) simulations and experiments.

Next Generation of GaN Single-Board High Power Stages

In this work, Infineon’s 100V 3mΩ CoolGaN™ is evaluated and compared with a 100V similar Rdson MOSFET using OptiMOS™5 silicon technology in a three-phase inverter for battery powered motor drive applications. In order to minimize conduction losses, 30ns dead time is achieved for GaN due to its lower gate and output charge in comparison to 60ns of dead time for silicon. A motor-generator setup is developed to evaluate a 48V drone motor up to ~1kW of inverter power. For a motor speed of 4000RPM, with a bus voltage of 48V and 100 kHz switching frequency, GaN shows higher efficiency across the entire load range. At 1/3rd load (~300W), 98.67% and at full load (~900W) 98.10% power efficiency values are achieved. At light load (~45W), a significant increase of ~5% is also observed in efficiency. This experimentally demonstrates that 100V CoolGaN™ is ideal for developing high frequency switching inverters with high power densities and motor efficiencies in the kilowatt power range.

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

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

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