h1

TY  - THES
AU  - Gurumurthy, Sriram Karthik
TI  - Advanced harmonic stability monitoring and control of power-electronics dominated grids; 1. Auflage
VL  - 141
PB  - RWTH Aachen University
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2025-06020
SN  - 978-3-948234-55-3
T2  - E.ON Energy Research Center
SP  - 1 Online-Ressource : Illustrationen
PY  - 2025
N1  - Druckausgabe: 2025. - Auch veröffentlicht auf dem Publikationsserver der RWTH Aachen University
N1  - Dissertation, RWTH Aachen University, 2024
AB  - A new paradigm has emerged with the increased proliferation of renewable energy sources (RES), which is enabled by the large-scale integration of grid-connected power electronic converters. These power electronic-dominated grids (PEDGs) pose new challenges to stability over a wide range of frequencies. Interaction among the power electronic-interfaced sources and non-linear loads may lead to the presence of undesirable harmonics and inter-harmonics, which distort the grid voltage and affect power quality. Depending on the operating conditions and damping in the power system, these inter-harmonics could remain sustained and resonate; the harmonic content may increase over a period, cause tripping of breakers, and potentially fully destabilize the grid. This phenomenon is known as harmonic instability. Due to the growing number of instances and failures experienced by grid operators, it is essential to develop methods to monitor and detect harmonic stability conditions. Over the last decade, several research studies have identified that harmonic stability can be characterized as an impedance phenomenon, and thus the impedance of converters would be required. Converter manufacturers protect the hardware and control systems of converters through Intellectual Property Rights (IPR), and thus black-box or non-parametric models of converters are required. Consequently, the choice of measurement method for rapid impedance extraction becomes vital, as does the characterization of such measurement devices. Aggregation of the extracted impedance data on a system level is crucial for system-level harmonic stability studies. To address harmonic stability issues, local compensation schemes are necessary to adjust the impedance of power converters and effectively introduce the desired damping. This dissertation aims to develop a standalone impedance measurement device, a harmonic stability monitoring algorithm for a multi-bus network, and a harmonic instability mitigation method. This dissertation proposes four major scientific contributions which enable harmonic stability monitoring and a safe operation of PEDGs: 1) a standalone impedance measurement device to extract the grid impedance in a non-parametric manner; 2) a Frequency Coupling Matrix (FCM) measurement method for power converters; 3) a non-parametric harmonic stability monitoring method for multi-bus power systems; and 4) an advanced virtual damping control strategy for grid-connected power electronic converters. The initial part of the thesis deals with the measurement of non-parametric impedances. A standalone plug-play measurement device called Wideband-frequency Grid Impedance (WFZ) measurement device is developed for the measurement of grid impedances. A low-power prototype of the proposed device is constructed. Linear impedance measurement is verified formerly by simulations followed by experimental measurements. Uncertainty characterization of the WFZ device is performed to validate the device. The second part of this thesis considers non-linearity through the FCM and extends the measurement algorithm of the WFZ device to accommodate FCM measurements. Characterization parameters are developed for the analysis and interpretation of the extracted FCM. Simulative and experimental measurements were carried out to extract the FCM of a grid-connected converter, followed by validation of the extracted FCM. The third part of the thesis proposes a non-parametric harmonic stability monitoring method. The proposed method requires non-parametric impedance measurements of active components in the network. A bus admittance matrix approach is considered to aggregate the non-parametric impedances of the power converters within the network. The proposed method enables the calculation of the minimum phase margin and the critical frequency where damping is required. The effectiveness of the method is demonstrated empirically through validation on both star and meshed power networks, showcasing its broad applicability across different network configurations. In the last part of the thesis, a non-parametric approach to harmonic instability mitigation is proposed. The proposed method consists of a centralized non-parametric stability monitoring tool that identifies the critical frequency and bandwidth, which are then published to the local converters. The converters implement the damping through the proposed adaptive Virtual Damping Controller, which is implemented as a digital Infinite Impulse Response (IIR) filter with adaptive parameters such as the critical frequency and bandwidth; furthermore, a look-up table-based approach is proposed to select the optimal gain of the VDC based on the critical frequency and bandwidth. The proposed VDC controller only requires grid current measurement, establishing a two-degree-of-freedom (2-DoF) control structure. Experimental validations were conducted to show the efficacy of the proposed approach. This thesis makes significant contributions in the areas of impedance measurement devices, system-level monitoring of harmonic stability, and the development of an advanced VDC, resulting in advancements in these fields.
LB  - PUB:(DE-HGF)11 ; PUB:(DE-HGF)3
DO  - DOI:10.18154/RWTH-2025-06020
UR  - https://publications.rwth-aachen.de/record/1014325
ER  -