Magnetic components for Power Electronics Operated in the Megahertz Range Using the Example of an LLC Converter

新型电力电子碳化硅(SIC)或氮化镓(GaN)半导体开关由于开关损耗较低而显著提高了开关频率，从而减小了磁性元件的尺寸和成本，从而降低了整个转换器的成本。目前，配备GaN的额定功率在千瓦范围内的工业转换器的开关频率约为。50到250千赫。可以预见，兆赫范围内的开关频率将很快达到。然而，在这样的频率下，直到现在被忽视的磁性部件中将出现现象，即不仅在绕组中而且在铁心中出现集肤效应，以及铁心内的共振或驻波。从磁性部件的常规设计角度来看，这两种现象都是不受欢迎的。因此，该项目将调查可以采取哪些额外措施来尽可能避免这些令人不安的影响。其中包括磁芯的几何形状以及横向和纵向气隙的巧妙放置。另一方面，这个频率范围内的共振效应是否能得到有益的利用，还有待研究。例如，由于这种谐振而与频率成比例增长的电抗可以用在LLC转换器中，以避免在低负载和小输出输入电压比的关键情况下大幅提高开关频率。这一假设也将在该项目中得到研究。

Novel power electronic silicon carbide (SiC) or gallium nitride (GaN) semiconductor switches allow a considerable increase of the switching frequency due to lower switching losses, which leads to a reduction in size and costs of the magnetic components and thus of the entire converter. Currently, GaN-equipped industrial converters of ratings in the kilowatt range are operated at switching frequencies of approx. 50 to 250 kHz. It is foreseeable that switching frequencies in the megahertz range will soon be reached. At such frequencies, however, phenomena will turn up in magnetic components neglected up to now, namely the emergence of a skin effect not only in the winding but also in the core as well as resonances or standing waves within the core. Both phenomena are not welcome from the viewpoint of the conventional design of magnetic components. The project will therefore investigate which additional measures can be taken to avoid these disturbing effects as far as possible. These include the geometric shaping of the magnetic core and skilled placement of transverse and longitudinal airgaps. On the other hand, it is to be investigated whether the resonance effects in this frequency range can even be beneficially used. For example, a reactance that grows over-proportionally with frequency due to such a resonance can be used in an LLC converter to avoid the need to raise the switching frequency substantially in the crucial situation of low load and small output-input voltage ratio. This hypothesis will also be investigated in the project.