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）半导体开关由于较低的开关损耗而允许开关频率的显著增加，这导致磁性部件的尺寸和成本以及因此整个转换器的尺寸和成本的减小。目前，额定功率在千瓦范围内的配备GaN的工业转换器以大约1000 W的开关频率操作。50至250 kHz。可以预见的是，兆赫范围内的开关频率将很快达到。然而，在这样的频率下，在迄今为止被忽视的磁性元件中会出现一些现象，即不仅在绕组中而且在磁芯中出现集肤效应以及磁芯内的谐振或驻波。从磁性元件的传统设计的观点来看，这两种现象都不受欢迎。因此，本项目将研究可采取哪些额外措施，以尽可能避免这些令人不安的影响。这些包括磁芯的几何形状和横向和纵向气隙的熟练放置。另一方面，要研究的是，在该频率范围内的谐振效应是否甚至可以被有益地使用。例如，由于这种谐振而与频率成比例地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基本上提高开关频率的需要。该项目也将对这一假设进行调查。

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.