Power Electronics Europe April/May Issue 2022

18 SILICON CARBIDE www.microchip.com/en-us/product/MOSFET-SIC-1700V Issue 2 2022 Power Electronics Europe www.power-mag.com called “light load conditions”. Consider a few examples: solar inverters operating on cloudy days or under shade; wind turbine converters on still days; or train doors (opened/closed by transportation APUs) that are closed nearly all the time. Under these highly common light load conditions, SiC MOSFETs offer lower conduction losses to complement its reduced switching losses, making possible the reduction of heat sinking or other thermal management measures. From a reliability standpoint, SiC MOSFETs empower designers with the ability to simplify the circuit topology and control scheme, as well as reduce component count – associated, of course, with a lower cost. Due to the higher-power delivery needs of these medium-power converters, a higher DC bus voltage is used – typically between 1000 and 1300 V. When selecting Silicon transistors for use at these high DC link voltages, efficiency requirements dictate that designers must choose among a few complex, three-level circuit architectures. Shown in Figure 3, these include the diode neutral point clamped (NPC) circuit, the active NPC circuit, or T-type circuit. In contrast, the use of 1700 V SiC MOSFETs allows designers to break free of these constraints and return to the more elegant two-level circuit shown in the right side of Figure 3, slashing device count in half and streamlining control. The importance of power packaging and proper gate driving of SiC MOSFETs is worth mentioning. Because SiC can switch high levels of power at very high speeds, care must be taken to avoid voltage overshoot and reduce noise emissions. Medium-power converters in these applications routinely turn off hundreds of amperes across a 1000-1300 V bus in under a microsecond, necessitating the lowest possible package inductance, intelligent and fast-acting gate drivers, and optimal system layout. Combining Microchip’s SP6LI power package with the AgileSwitch® family of digital gate drivers (see also the sidebar article) provides designers with ready-made solutions to get the maximum benefit out of 1700 V SiC MOSFETs without facing these common challenges. Megawatts In the multi-megawatt power range, key design factors include ease of scalability and minimal maintenance, prompting the use of modular solutions based on a basic unit cell. As shown in Figure 4, the unit cells, sometimes referred to as power electronic building blocks or sub-modules, are configured as cascade H-bridge converters or modular multi-level converters (MMCs). Megawatt-scale applications include solid-state transformers (SSTs), medium-voltage DC distribution systems, traction power units (TPUs) in commercial and heavy-duty vehicles, central solar inverters and offshore wind converters, and shipboard power conversion systems. Traditionally, the power semiconductor devices used in the unit cells have been 1200 to 1700 V Silicon IGBTs. Much like the lower power applications, the deployment of 1700 V SiC MOSFETs at the unit cell level extends their power handling capability and electrical performance. As mentioned previously, 1700 V SiC MOSFETs have much lower switching losses, making it possible to increase switching frequency and drastically reduce the size of each unit cell. Moreover, the high blocking voltage of 1700 V reduces the number of unit cells required for the same DC link voltage, which ultimately heightens system reliability while slashing cost. Summary The arrival of 1700V SiC MOSFETs benefits a variety of applications and end equipment by offering higher reliability at reduced cost – both possible even while simultaneously making converters smaller, lighter, and more efficient. From watts to megawatts, high-voltage SiC MOSFETs are allowing designers to move beyond Silicon’s compromises and make disruptive improvements to power conversion systems. Alongside the industry’s most rugged SiC power devices, advanced power packaging with ultra-low parasitic inductance and digital gate drivers are helping designers to get the most value out of SiC and accelerate time to market. Figure 4: Modular multilevel converter (left) with multiple cells to achieve required power rating and (right) two examples of how a simple, two-level unit cell configuration may be used with 1700V SiC MOSFETs To receive your own copy of Power Electronics Europe subscribe today at: www.power-mag.com