Alex Q. Huang

Shielded Gate SiC Trench Power MOSFET with Ultra-Low Switching Loss

A shielded gate trench silicon carbide (SiC) metal oxide semiconductor field effect transistor (SG-TMOS) is proposed and investigated by simulation in this paper. The impact of shielded gate design in SG-TMOS on Miller charge (Qgd) as well as conduction resistance (Ron) are comprehensively discussed, showing a tradeoff between Qgd and Ron. Furthermore, the Huang’s Figure of Merit (HFOM) of the SG-TMOS with reasonable design of SG is reduced more than 20%, compared with the conventional trench MOSFET (C-TMOS). Therefore, the proposed SG-TMOS is a competitive next generation device structure for ultra-high switching speed SiC MOSFET.

15-kV/40-A FREEDM Supercascode: A Cost-Effective SiC High-Voltage and High-Frequency Power Switch

High-voltage wide bandgap semiconductor devices such as the 15xa0kV SiC mosfet have attracted great attention because of their potential applications in high-voltage and high-frequency power converters. However, these devices are not commercially available at the moment, and their high cost due to expensive material growth and fabrication may limit their widespread adoption in the future. In this paper, a 15-kV 40-A SiC three-terminal power switch, the Future Renewable Electric Energy Delivery and Management (FREEDM) supercascode, is reported for the first time, which is based on a series connection of 1.2-kV SiC power devices. Compared with the monolithic 15-kV SiC mosfet, the FREEDM supercascode demonstrates obvious advantages in cost and thermal conductivity. The design and voltage-balancing mechanism of the FREEDM supercascode are introduced, and the performance including the voltage balancing, conduction characteristics over a wide range of temperatures, and dynamic switching performance, is analyzed. The FREEDM supercascodes low cost and excellent thermal dissipation capability will facilitate early applications of SiC in very high voltage and high frequency power converters.

Active Damping of Ultrafast Mechanical Switches for Hybrid AC and DC Circuit Breakers

An active damping method for Thomson coil actuated ultrafast mechanical switches is proposed, including its control. Ultrafast mechanical switches are crucial for both dc and ac circuit breakers that require fast-acting current-limiting capabilities. However, fast motion means high velocity at the end of travel resulting in over-travel, bounce, fatigue, and other undesirable effects. The active damping proposed in this paper not only avoids such issues but actually enables faster travel by removing limitations that would otherwise be necessary. This active damping mechanism is applicable in particular to medium- and high-voltage circuit breakers, but can be extended to actuators in general. A 15 kV/630 A/1 ms mechanical switch designed to enable the fast protection of medium voltage dc circuits is used as a testbed for the concept. The switch is based on the principle of repulsion forces (Thomson coil actuator). By energizing a second coil, higher opening speeds can be damped, resulting in limited over-travel range of the movable contact. The overall structure is simple and the size of the overall switch is minimized. To validate the concept and to study the timing control for best active damping performance, both finite element modeling and experimental studies have been carried out.