Inductively Coupled in-Circuit Measurement of Two-Port Admittance Parameters

In-circuit impedance and admittance measurements are widely exploited in power electronics, from control stability analysis to electromagnetic interference modeling. In particular, the use of clamp-on inductive probes allows nonintrusive measurements of systems in real operating conditions. However, available methods are limited to a single port and cannot evaluate mutual impedances or admittances, hence they cannot properly characterize multiport systems described by impedance or admittance matrices. In this article, a two-port inductively coupled in-circuit measurement method is proposed. Specifically, two inductive probes connected to a vector network analyzer define two longitudinal ports along the clamped wires of the system under test and allow measurement of its two-by-two admittance matrix. The proposed method is firstly verified with a set of known passive loads, then applied to measure the unknown admittance matrix of a single-phase motor drive system. Experimental results prove the effectiveness of the proposed method in providing accurate measurement of admittance parameters, including mutual terms, both for active and passive two-port devices. Additionally, such two-port admittance matrix measurements are suitable for the identification of the behavioral circuit model of a system, in general for any number of ports.