Diang Xing

This paper presents a review and comparison of high voltage-step-down ratio dc/dc converters based on the modular multilevel converter (MMC) or quasi-MMC, specifically designed for medium-voltage direct current (MVDC) grid-tied energy storage systems (ESS). The paper discusses various topology configurations and their operational features. The surveyed topologies are compared in terms of switching device cost, switching device power losses, passive component volumes, voltage-step-down ratios, and frequency multiplication ratios. Case studies are performed on selected topologies using specifications of 7-kV input voltage, 250-V-to-450-V output voltage, and 250-kW transferred power. This review highlights the potentials of MMC-based dc/dc converters and provides an analysis of the pros and cons of different topologies.

This article presents the short-circuit (SC) capability evaluation of TO-247-3 packaged silicon carbide (SiC) metal–oxide–semiconductor field-effect transistors (MOSFETs) based on tests under different drain biases and gate biases. Compared with the 900-V Si super-junction MOSFET and the 1200-V Si trench-gate field-stop insulated gate bipolar transistor (IGBT), SiC devices show higher saturation current per die area, which requires more rigorous chip design consideration to reach an acceptable SC withstand time (SCWT). The test results also reveal that the SC withstand capability of SiC MOSFETs can still be enhanced. Thus, in both chip design and detection circuits, several novel approaches investigated in recent years, which could potentially improve SC ruggedness of SiC device-based systems, are discussed at the end of this article.

Compared to Silicon counterparts, SiC power MOSFETs have lower on-state resistance and faster switching speed, which in-turn makes them better candidates for high-voltage power switching applications. This creates a growing need to develop device models for such SiC Power devices. In this study we show a sub-circuit model based on the analytical study using non-linear curve fitting method for modeling of dynamic switching behavior. Using a 1.2 KV, 17 A MOSFET as a testbed, this sub-circuit model is validated by implementing the model into Synopsys Saber in comparison with the measured DC characteristics, the Saber MOSFET tool model, and the manufacturer's model. The switching behavior of the device at 800 V/17 A and 800 V/5.5 A based on the sub-circuit model were also compared and validated with experimental measurements, the Saber MOSFET model, and manufacturer's model. Excellent agreements were achieved on both DC characteristics and switching behaviors. On the LTspice platform, the computation time of the analytical sub-circuit model is 4.5 times faster than the manufacturer's model. This sub-circuit model is adoptable and suitable for real time hardware in loop simulations and power converter designs.

Medium voltage (MV) Silicon Carbide (SiC) power devices have become available as engineering samples. Recent studies show that they outperform their Silicon (Si) counterparts regarding voltage blocking capability, specific on-state resistance, switching speed and maximum allowable junction temperature. It is projected that MV SiC power devices will bring revolutionary changes in medium and high voltage applications such as traction drives for locomotives, industrial motor drives, utility power transmission systems, etc. This paper presents a summary of recent advances in MV SiC power devices, including MOSFETs, IGBTs, GTOs and super-cascode devices. Technical challenges of their applications such as device packaging, gate drive design and gate drive auxiliary power supply design are discussed. Testing results of three state-of-the-art MV SiC devices, including a 4 kV, 5 A discrete SiC MOSFET, a 4.5 kV, 40 A SiC super-cascode device and a 10 kV, 40 A SiC MOSFET power module, are presented as examples.