The solid-state transformer (SST), which has been regarded as one of the 10 most emerging technologies by Massachusetts Institute of Technology (MIT) Technology Review in 2010, has gained increasing importance in the future power distribution system. This paper presents a systematical technology review essential for the development and application of SST in the distribution system. The state-of-the-art technologies of four critical areas are reviewed, including high-voltage power devices, high-power and high-frequency transformers, ac/ac converter topologies, and applications of SST in the distribution system. In addition, future research directions are presented. It is concluded that the SST is an emerging technology for the future distribution system.

Review of Solid-State Transformer Technologies and Their Application in Power Distribution Systems

Silicon carbide (SiC) power devices have been investigated extensively in the past two decades, and there are many devices commercially available now. Owing to the intrinsic material advantages of SiC over silicon (Si), SiC power devices can operate at higher voltage, higher switching frequency, and higher temperature. This paper reviews the technology progress of SiC power devices and their emerging applications. The design challenges and future trends are summarized at the end of the paper.

https://ieeexplore.ieee.org/ielaam/41/8031005/7815312-aam.pdf

Review of Silicon Carbide Power Devices and Their Applications

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

During recent years, silicon carbide (SiC) power electronics has gone from being a promising future technology to being a potent alternative to state-of-the-art silicon (Si) technology in high-efficiency, highfrequency, and high-temperature applications. The reasons for this are that SiC power electronics may have higher voltage ratings, lower voltage drops, higher maximum temperatures, and higher thermal conductivities. It is now a fact that several manufacturers are capable of developing and processing high-quality transistors at cost that permit introduction of new products in application areas where the benefits of the SiC technology can provide significant system advantages.

Silicon Carbide Power Transistors: A New Era in Power Electronics Is Initiated

Medium-voltage (MV) SiC devices have been developed recently which can be used for three-phase MV grid tie applications. Two such devices, 15 kV SiC insulated-gate bipolar transistor (IGBT) and 10 kV SiC MOSFET, have opened up the possibilities of looking into different converter topologies for the MV distribution grid interface. These can be used in MV drives, active filter applications, or as the active front end converter for solid-state transformers (SSTs). The transformerless intelligent power substation (TIPS) is one such application for these devices. TIPS is proposed as a three-phase SST interconnecting a 13.8 kV distribution grid with a 480 V utility grid. It is an all SiC device-based multistage SST. This paper focuses on the advantages, design considerations, and challenges associated with the operation of converters using these devices keeping TIPS as the topology of reference. The efficiency of the TIPS topology is also calculated using the experimentally measured loss data of the devices and the high-frequency transformer. Experimental results captured on a developed prototype of TIPS along with its measured efficiency are also given.

Solid-State Transformer and MV Grid Tie Applications Enabled by 15 kV SiC IGBTs and 10 kV SiC MOSFETs Based Multilevel Converters

Ten-kilovolt SiC MOSFETs are currently under development by a number of organizations in the United States, with the aim of enabling their applications in high-voltage high-frequency power conversions. The aim of this paper is to obtain the key device characteristics of SiC MOSFETs so that their realistic application prospect can be provided. In particular, the emphasis is on obtaining their losses in various operation conditions from the extensive characterization study and a proposed behavioral SPICE model. Using the validated MOSFET SPICE model, a 20-kHz 370-W dc/dc boost converter based on a 10-kV 4H-SiC DMOSFET and diodes is designed and experimentally demonstrated. In the steady state of the boost converter, the total power loss in the 15.45-mm2 SiC MOSFET is 23.6 W for the input power of 428 W. The characterization study of the experimental SiC MOSFET and the experiment of the SiC MOSFET-based boost converter indicate that the turn-on losses of SiC MOSFETs are the dominant factors in determining their maximum operation frequency in hard-switched circuits with conventional thermal management. Replacing a 10-kV SiC PiN diode with a 10-kV SiC JBS diode as a boost diode and using a small external gate resistor, the turn-on loss of the SiC MOSFET can be reduced, and the 10-kV 5-A SiC MOSFET-based boost converter is predicted to be capable of a 20-kHz operation with a 5-kV dc output voltage and a 1.25-kW output power by the PSpice simulation with the MOSFET model. The low losses and fast switching speed of 10-kV SiC MOSFETs shown in the characterization study and the preliminary demonstration of the boost converter make them attractive in high-frequency high-voltage power-conversion applications.

Characterization, Modeling, and Application of 10-kV SiC MOSFET

W kV SiC MOSFETs are currently under development by a number of organizations in the United States with the aim to enable their applications in high voltage high frequency power conversion applications. The aim of this study is to demonstrate their high frequency high temperature operation capability in the application of a DC/DC boost converter. A DC/DC boost converter based on a 10 kV 10 A SiC MOSFET and a 10 kV 5A Junction Barrier Schottky (JBS) diode is designed and tested for continuous conditions up to a switching frequency of 25 kHz, an output voltage of 4 kV, an output power of 4 kW and a junction temperature of 174degC for the SiC MOSFET. In the steady state of the 20 kHz boost converter operation, the input power is 4335 W, the output power is 4030 kW and the efficiency is 93%. The power loss analysis shows the total power loss in the 30.45 mm2 SiC MOSFET is 115 W, and the operating junction temperature of the SiC MOSFET is 140degC at the 20 kHz switching frequency. The power losses and the junction temperature of the SiC MOSFET as a function of the switching frequency, load current and input voltage in the boost converter are investigated extensively. The fast switching, low loss and high temperature operation capability of 10 kV SiC MOSFETs demonstrated in the DC/DC boost converter make them attractive in high frequency high voltage power conversion applications.

10 kV SiC MOSFET Based Boost Converter

High-voltage p-channel 4H-SiC insulated gate bipolar transistors (IGBTs) have been fabricated and characterized. The devices have a forward voltage drop of 7.2 V at 100 A/cm2 and a -16 V gate bias at 25degC, corresponding to a specific on-resistance of 72 mOmega ldr cm2 and a differential on-resistance of 26 mmOmega ldr cm2. Hole mobility of 12 cm2/V ldr s in the inversion channel with a threshold voltage of -6 V was achieved by optimizing the n+ well doping profile and gate oxidation process. A novel current enhancement layer was adopted to reduce the JFET resistance and enhance conductivity modulation by improving hole current spreading and suppressing the electron current conduction through the top n-p-n transistor. Inductive switching results have shown that the p-IGBT exhibited a turn-off time of ~1 mus and a turn-off energy loss of 12 m J at 4-kV dc-link voltage and 6-A load current at 25degC. The turn-off trajectory from the measured inductive load switching waveforms and numerical simulations shows that the p-IGBT had a near-square reverse bias safe operating area. Numerical simulations have been conducted to achieve an improved tradeoff between forward voltage drop and switching off energy by investigating the effects of drift layer lifetime and p-buffer layer parameters. The advantages of SiC p-IGBTs, such as the potential of very low ON-state resistance, slightly positive temperature coefficient, high switching speed, small switching losses, and large safe operating area, make them suitable and attractive for high-power high-frequency applications.

R. Callanan

Papers

Characterization, Modeling, and Application of 10-kV SiC MOSFET

10 kV SiC MOSFET Based Boost Converter

Design and Characterization of High-Voltage 4H-SiC p-IGBTs