Multichannel Time-Domain Measurements for EMI Filter Optimization

The current energy crisis has kicked off a rapidly changing energy sector that requires society to become more sustainable. One aspect of which is regarding electrical energy, and its conversion. The number of power electronic dependent products is increasing, creating a complex electromagnetic environment (EME), often resulting in interoperability problems.

The issues of non-compatible systems have been seen across various types of complex platforms during integration, e.g. nation-sized power grids, microgrids, electric vehicle (EV)s and even on board all-electric aircraft (AEA). Several methods of mitigation exist, ranging from solutions at the source of interference to hardening the victims. This thesis focuses on solutions across the propagation path: electromagnetic interference (EMI) filters and their optimisation.

It starts with identifying the most significant practical considerations associated with the components of a generic EMI filter and providing the analytical model for the filter’s insertion loss (IL) incorporating the effects of noise and source impedance. Several critical parameters for optimised filter design were identified, such as the dominant mode of interference or required attenuation for each, differential mode (DM) and common mode (CM) emissions separately. For determining the DM and CM conducted emission (CE), the theoretical formulation of each mode in the one-phase system and a measurement technique for mode decomposition based on time-domain multichannel measurements were developed. A simplified approach for determining the dominant mode of interference using current measurements is presented for the three-phase systems.

A notch filter was designed instead of generic low-pass filter (LPF). Developing an effective notch filter for this application required analysis and incorporation of the effects of magnetic permeability on the filter’s performance. This approach can be extended towards different noise sources. It can be considered one of the main contributions of the thesis, as well as the design and analysis of the notch filter itself. Further, the multichannel time-domain measurement techniques and mode decomposition theory were extended towards EMI filter performance evaluation. A setup was developed that allows a faster, less error-prone measurement approach while reducing the drawbacks associated with
standard measurement procedures.

This thesis is a part of the project focused on developing modelling and measuring methods of evaluating complex systems and platforms, with a further goal of effectively reducing EMI in complex interconnected systems. The key objectives of the University of Twente in this project are developing measurement methods for EMI evaluation based on multichannel time-domain measurements and integrating system topology and interaction to achieve electromagnetic compatibility (EMC). The research in this thesis follows these objectives and is focused on multichannel time-domain measurement techniques for CE and EMI filter performance evaluation. The multichannel measurement techniques applied to CE assessment allow a more comprehensive analysis of system interaction, providing necessary input for optimised EMI filter design.