Potential Application of Magneto-Optical Current Sensing in Power Modules

摘要

A magneto-optical (M-O) material causes a large rotation to the polarization, termed Faraday Rotation, of a polarizing light beam traversing through the material placed in a magnetic field. The proportionality constant relating the amount of rotation to the field strength is called the Verdet constant and it is a strong function of wavelength. In this paper, we investigate the potential of using Bismuth (Bi)-doped Yttrium-Iron Garnet (YIG) crystal, an M-O material, to sense magnetic field and thus currents in power modules. Firstly, we present data on the figure-of-merit (FOM), which is proportional to Verdet constant and inversely proportional to absorption coefficient, of the M-O material. Then the characterized sensing material is attached into a power module. The local magnetic field generated in the module is detected using DC and AC current sensing setups specifically built for this purpose. The DC current sensing results match well with those of direct measurement. For the AC current sensing, some issues on noise related to electromagnetic interference (EMI) are discussed and the sensing speed is tested up to 100 kHz. The placement location of the M-O sensing material is found by finite elemental modeling of electromagnetic filed distribution in the power module. Finally, we provide a miniaturizing design for future integration and packaging of the M-O current sensors in power modules.