High-Precision Broadband Impedance Measurements of Three-Phase Common-Mode Chokes Using Single-Port Circuit De-Embedding and Three-Port Network Calibration Methods

Common-mode chokes (CMCs) are essential components of electromagnetic interference (EMI) filters. Obtaining precise common-mode (CM) and differential-mode (DM) impedance information of CMCs facilitates their performance evaluation and behavioral modeling, ultimately contributing to optimal EMI filter design. Among existing impedance extraction approaches, measurement methods are the most straightforward, not requiring CMC's detailed geometry and material properties. These methods typically use an impedance analyzer (IA) or vector network analyzer (VNA) with specific fixture adapters for measurements. However, these adapters introduce parasitics, which can affect measurement accuracy, particularly at high frequencies. Some solutions have been proposed but limited to single-phase CMCs. This article presents two impedance measurement methods for three-phase CMCs: single-port circuit de-embedding (SCD) and three-port network calibration (TNC). Both methods consider the parasitics of fixture adapters and provide unique solutions for accurate broadband measurements for the CM and DM impedances of three-phase CMCs. The SCD method has good versatility as it can be implemented using either an IA or VNA; however, it requires fixture adapter details for the de-embedding process. Conversely, the TNC method does not need these details but can only be implemented using an IA. Both methods are validated experimentally with good accuracy from 150 kHz to 120 MHz.