One of the key features of traditional power electronics is that its power semiconductor components take up significantly less space than the corresponding electromechanical and passive components. The use of wide-bandgap power semiconductors not only changes the form factors in power electronics; the use of SiC and GaN power semiconductors also has a profound impact on passive components such as inductors, capacitors, and resistors.
The higher switching frequencies made possible by SiC and GaN have a significant impact on passive components in at least four key areas. First, there is the potential for smaller size and reduced weight. For example, at high switching frequencies, the inductance value of inductors and transformers decreases. This results in smaller winding materials and a reduced need for copper and core material. When it comes to capacitors, the higher frequencies made possible by GaN and SiC in 400- and 800-V applications mean that MLCCs can now be used in place of bulkier film capacitors. Overall, this miniaturization results in a more compact filter assembly, thereby increasing the application’s power density. Compared to traditional silicon applications, SiC and GaN can be operated at significantly higher temperatures. This brings us to point 2: the passive components must, of course, also be able to withstand these higher temperatures. Possible improvements here include special winding insulation or the use of high-temperature capacitors. The necessary connection technology must also be taken into account. While the higher efficiency of the circuit can reduce the application’s overall heat generation, local hotspots can still occur, requiring efficient cooling measures.
Point 3: High switching frequencies naturally produce very fast switching edges. With SiC, these can exceed 50 V/ns; GaN is even faster. These fast switching edges cause significant oscillations in parasitic inductances and capacitances. In addition to the parasitic effects described, the rapid voltage changes also place extreme stress on the insulation of inductive components, such as wound products, and can lead to partial discharges and accelerated aging. Finally, increasing frequencies and faster switching edges raise the risk of electromagnetic interference. This necessitates the use of high-quality filter components.
All of this ultimately leads to point 4: the need to use high-frequency-compatible components when wide-bandgap power semiconductors are to be used in the planned power electronics circuit. The passive components used there must have very low equivalent series resistances and low equivalent series inductances to prevent potential self-heating and resonances in the circuit. For this reason, in connection with the use of wide-bandgap power semiconductors, the development of new materials suitable for higher frequencies and exhibiting lower losses is being driven forward.
The challenges posed, for example, by the upcoming transition from 400- to 800-V architectures in data centers—where 1-MW blades will be populated with up to 20,000 MLCCs—give a sense of the challenges that await manufacturers of passive components. The following articles from Würth Elektronik eiSos, TDK Electronics, and Vishay illustrate what solutions might look like. eg
