Single probe in-circuit impedance extraction based on inductive coupling approach

• Main Author: Weerasinghe, Sudharma Deshapriya Kotuwegedara Harsha Yashoman Arjuna
• Other Authors: See Kye Yak
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Electrical and electronic engineering::Electronic systems::Signal processing; Engineering::Electrical and electronic engineering::Antennas, wave guides, microwaves, radar, radio
• Online Access: https://hdl.handle.net/10356/156196
• Institution: Nanyang Technological University

The in-circuit impedance of a critical electrical system provides valuable information on its operating status and health. There are three common in-circuit impedance measurement approaches, namely the voltage-current (V-I) measurement approach, the capacitive coupling approach, and the inductive coupling approach. Among them, the inductive coupling approach does not require a direct electrical contact to the energized system-under-test (SUT) and therefore greatly simplifies the implementation without the need to shut down the system and eliminates the concern of electrical safety hazards. The conventional measurement setup of the inductive coupling approach requires two inductive probes and a two-port vector network analyzer (VNA) or a signal generation and data acquisition system (SGAS). This well-established two-probe setup (TPS) has been refined and improved over the years. Despite all these recent improvements, it still cannot eliminate the inherent probe-to-probe coupling which compromises the measurement accuracy when the two probes are placed very close to each other. This thesis develops an in-circuit impedance measurement setup with the use of only one inductive probe and it is experimentally verified. By introducing a single-probe setup (SPS), not only reduces the hardware overhead of the measurement setup but also fundamentally addresses the concern of probe-to-probe coupling. In addition, the proposed SPS incorporates power amplification and protection devices to maintain the measurement system’s accuracy and improve the ruggedness for in-circuit impedance measurement of electrical systems in harsh electromagnetic environments with the presence of strong background noise and transient events. An error correction scheme has also been developed to recover measurement results contaminated with errors if the available signal-to-noise ratio (SNR) of the SPS is poor due to correlated noise interfering with the excitation signal. The proposed SPS has also been designed so that it has the flexibility to extract in-circuit impedance using either frequency-domain (FD) or time-domain (TD) based instrumentation so that the application scope is broadened. The SPS TD-based instrumentation is capable of measuring time-varying in-circuit impedance at multiple frequencies simultaneously to improve its measurement efficiency. To demonstrate the practical value of the proposed SPS, firstly, it is applied to extract the in-circuit differential-mode (DM) and common-mode (CM) impedances of a variable frequency drive (VFD) under different operating modes using FD-based instrumentation. Then, the in-circuit impedance of a grid-connected induction motor is extracted based on both FD and TD-based instrumentations. The measured in-circuit impedance of the induction motor is also compared against the conventional V-I measurement approach to showcase the measurement accuracy of the proposed SPS.