Events at Department of Energy Technology

PhD defence by Naser Nourani Esfetanaj


10.06.2021 kl. 13.00 - 16.00


Naser Nourani Esfetanaj, Department of Energy Technology, will defend the thesis "Study of Spectral Characteristics of Low Frequency Conducted EMI in Power Electronic Based Systems"


Study of Spectral Characteristics of Low Frequency Conducted EMI in Power Electronic Based Systems


Naser Nourani Esfetanaj


Associate Professor Pooya Davari


Professor Huai Wang


Associate Professor Amir Sajjad Bahman


Professor, Francesco Iannuzzo, Aalborg University (Chairman)
Professor Jorma Kyyra, Aalto University
Professor Junichi Itoh, Nagaoka University of Technology 


Power electronics (PE) converters are increasingly applied in grid-connected systems. While they provide efficient and flexible control of electrical energy, they also bring new challenges concerning electromagnetic interference (EMI). In fact that, the EMC standards are in place to ensure the compatibility of power electronics. But, the current standards cover below 2 kHz and above 150 kHz. Therefore, there is a gap in standard as there is no general emission standard for 2 – 150 kHz as it only covers some specific products. The 2-150 kHz is of particular interest due to: 1) many power converters have switched in this frequency range, and 2) the mains communication systems (MCS) are communicated together to transfer the data in this frequency range. Consequently, generated noise from the PE converter may severely deteriorate MCS communication signals. Hence, to assure proper and reliable grid operation, EMI challenging issues at device and system levels should be investigated appropriately.
Firstly, seen from the technical perspective, one major concern is the lack of systematically understanding of noise propagation into the power grid within 2-150 kHz regarding the upcoming emission standard (i.e., 61000-6-3). Hence, accurate modeling of the different power converters is needed to characterize low-frequency EMI emissions up to 150 kHz. Further, this analytical model needs to extended to single-phase and three-phase applications. Further, as the penetration of power electronic systems to the grid increases, the noise level should be limited based on the standard requirement, thereby a proper EMI filter should be better designed as well in the single-phase and three-phase.
Secondly, one of the main challenges in the new frequency range is the lack of a suitable model which covers the interaction analysis between the units in multi-converter systems. Further, it is necessary to simplify the multi-converter systems analysis model. Additionally, the parallel operation of various PE converters within similar power switching frequencies has led to unprecedented emissions within high frequencies, including a beating frequency and EMI under 150 kHz. Moreover, the factory switching tolerance, which brings the unsynchronized scenario on the multi converter systems, should be included in the modeling.
To tackle those issues and thus understand noise propagation mechanism and limit the emission following the standard regulations, this Ph.D. project discusses modeling and analyzing of low-frequency noise emission. Consequently, it can provide a proper EMI filter design and identify dominant parameters leading to power converter noise model order reduction and simplification. The analytical low-frequency EMI emission model through closed-loop impedance modeling is developed up to 150 kHz throughout this project. Among different power converters, a voltage source inverter (VSI) and a boost power factor correction (PFC) converter will be intensively studied as they are common in grid-connected single-phase applications. Utilizing closed-loop models can speed up the design process, prevent time-consuming trial and error, empirical measurements, and reduce cost. Further, it is necessary to limit the noise level based on the standards requirement. Hence, designing a proper EMI filter for the frequency between 2-150 kHz based on the proposed modeling approach is analyzed. The performance of the proposed analytical approach with and without EMI filter has been validated through experiments and simulations. The reduced-order model is achieved to use in the multi-converter system analysis.
Next, the analytical model is extended to the three-phase converter to characterize noise behavior in the low-frequency EMI range. Hence, the proposed technique estimates the generated emissions of the three-phase converter by utilizing double Fourier analysis and closed-loop input/output admittance. Three-phase voltage VSI and active rectifier will be studied as the most common topologies utilized in grid-connected three-phase applications. The impact of a sampling frequency and loading conditions on the closed-loop admittance have been analyzed. The performance of the proposed method is shown through the experimental and simulation results.
Furthermore, the impact of interleaving techniques on the analytical method has also been analyzed by applying phase shift effects. Moreover, the EMI filter design is done by considering various phase shifts to decrease the filter volume. Next, the interaction current between the multi-converter is also analyzed, where unsynchronized scenarios are regarded due to the switching frequency tolerance. Moreover, the effects of the different EMI filter designs on the interaction current between the units and grid are investigated. Finally, an aggregated analytical EMI emission estimation approach is achieved on the multi-converter systems.  The proposed analytical method is validated by simulations and experiments with different phase shifts.
Accordingly, by employing the analytical proposed models for EMI noise propagation assessment and prevention, future power-electronics-based power systems may be designed and operated in a desirable fashion and compatible with the new standard. 



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