Power Electronics Europe February/March 2022

www.wolfspeed.com/products/power/sic-power-modules SIC POWER MODULES 31 www.power-mag.com Issue 1 2022 Power Electronics Europe junction temperature (Tj) reaches 130°C and the separate diode chip junction temperature reaching 140°C. This required a large heat sink and two fans per module even after limiting the switching frequency to 8 kHz. The SiC-based system used a Wolfspeed XM3 power module, the XAB400M12XM3. The system can switch at a much higher 25 kHz, and uses a 30 µH inductor. For the same 40°C ambient temperature, the MOSFET junction temperature reaches 164°C. Again, each red box shown in Figure 3 comprises the module and it’s much lower cooling requirements. Power modules compared Wolfspeed’s XM3 power module platform occupies 60% less volume and 55% less area than an equivalently rated 62-mm module. Compared with a similarly rated EconoDUAL® IGBT module, the reduction in size, volume, as well as weight is significantly more. The XM3 platform’s key features include: • A high power density of up to 32 kW/l • Junction temperature of up to 175°C • Low inductance (6.7 nH) • >5X lower switching losses • Low conduction losses without intrinsic knee-voltage • High reliability Silicon Nitride power substrate for enhanced power cycling capability In the AFE under consideration, Table 1 compares the IGBT power module losses against the XAB400M12XM3. As shown, using Wolfpseed SiC technology helps overcome the first broad design challenge by reducing the total switching and conduction losses, which enables the remaining broad challenges to be addressed. Smaller and lighter cooling The high MOSFET junction temperature allowed by SiC technology and the XM3’s low losses have an immediate effect on the cooling requirements. With a loss per module of 1.11 kW, every EconoDUAL® needs to be mounted on a large heatsink with a pusher and puller fan each to achieve sufficient airflow for cooling efficiency. The cooling system volume is 6.4 l/module. Given the 40% lower losses, the XM3 needs a smaller heatsink and just one fan to achieve the same result (@40°C). The cooling system volume is just 3.7 l. This 42 % reduction in cooling system volume is accompanied by yet another advantage — a 70 % reduction in the AFE system thermal solution cost. The impact on passives By enabling an increase in the switching frequency by a factor of three, from 8 kHz to 25 kHz, the SiC-based AFE needs smaller passives (Figure 6). As mentioned earlier, the required inductance can also be reduced by a factor of three, from the IGBT design’s 100 µH to 30 µH. The resulting reduction in the physical size is about 37%. Moreover, I2R losses in the inductor are also reduced by close to 20%. For the power levels required by the AFE example, the cost of the magnetics, including the core and the copper windings, is lower in the XM3 design by 75% over the IGBT-based AFE. The effect on the required DC link capacitance is similar due to the increased switching frequency. While for the IGBT variant 1800 µF are required, the SiC MOSFET-based design only needs 550 µF capacitance. The side-by-side comparison in Figure 6 illustrates the reduction in the volume of the needed capacitance by 54 %. AFE system-level comparison At the system level, the 3X increase in switching enabled by SiC translates to a 3X improvement in control bandwidth that in turn means faster response time to dynamic conditions. The easing up of the demand on passives, including the cooling system, results in a 37 % reduction in the BOM costs toward those components put together. ABOVE Figure 4: The XM3 platform represents a drastic reduction in area and volume over the EconoDUAL® LEFT Figure 5: The XM3 lowers cooling system volume by 42 % and cost by 70 %