In-Circuit Impedance Extraction of Individual Components in Power Converter Using Capacitive Coupling Fixture Adapters Method for Electromagnetic Interference Estimation

In-circuit impedances of individual components in power converters, such as semiconductor power switches and inductors, can deviate from their off-circuit impedances, affecting electromagnetic interference (EMI) estimation. Existing methods pose challenges in extracting in-circuit impedances of these components. To overcome this limitation, this article proposes a method based on capacitive coupling fixture adapters (CFAs), where compact-sized CFAs serve as interconnections between the vector network analyzer (VNA) and the measured nodes of the power converter. Unlike the traditional capacitive coupling method, the CFAs consist of a five-stage structure with flexible end (FE), coaxial cable, dc blocker, protector, and attenuator; and also facilitate easy configuration into an operating power converter. Additionally, the FEs can be configured into reflection, parallel-through, and series-through capacitive coupling topologies to accommodate different component types. Moreover, a simple deembedding procedure is utilized to eliminate the parasitic effects of CFAs. Using a 450 W dc–dc converter as a case study, the proposed method effectively extracts the in-circuit impedances of individual components within the power converter, enabling the creation of precise component models and finally realizing the accurate estimation of conducted EMI from 150 kHz to 30 MHz.