November 26, 2019
Innovative power capacitor technologies for wide band-gap semiconductors
Conventional semiconductors based on silicon are being replaced by wide band-gap (WBG) technologies based on GaN and SiC. These demand a great deal from the passive components – particularly the DC link capacitors. Thanks to its supreme competence in materials and design, TDK offers innovative solutions, enabling the advantages of the new semiconductors.
For switched applications in power electronics such as power supplies and converters, WBG semiconductors offer the advantage that they can be operated with switching frequencies in the triple-digit kHz range. At the same time, they feature steep pulse edges, thereby achieving greater energy efficiency. Due to these high switching frequencies, film capacitors are increasingly being used as DC link capacitors. In order to minimize the lead lengths, and thus the parasitic inductances, the capacitors are connected directly to the WBG modules by means of busbars. The problem here is that WBG semiconductors are operated with high barrier termination temperatures, which can also be conducted via the busbars to the DC link capacitors. The temperature limit of conventional film capacitors with a dielectric of biaxially oriented polypropylene (BOPP), however, is only 105 °C.
New dielectric allows high-temperature applications
TDK has succeeded in developing a dielectric that can also be used continuously at high temperatures. This involves a combination of two basic materials. One component is semicrystalline polypropylene, which is ideal for processing into films; the other is amorphous cyclic olefin copolymer (COC), which can tolerate high temperatures. The resulting dielectric (COC-PP) can be used at temperatures in excess of 125 °C with considerably lower derating, while retaining the good self-healing properties of BOPP. In addition, this enables extremely thin films of just 3 µm to be manufactured. Figure 1 shows the significantly improved shrinking and derating behavior of COC-PP in comparison with conventional BOPP.
With the aid of CAD and FEA (finite element analysis) simulation software TDK has now developed HF (high-frequency) power capacitors with an optimized internal design. Even at the high frequencies and temperatures at which WBG semiconductors are operated, these capacitors offer high performance with low losses, thanks to a minimized ESR (Figure 3).