@phdthesis{JaramilloCajica2024, author = {Jaramillo Cajica, Ismael}, title = {A switched systems approach for voltage regulation in smart grids}, doi = {10.26127/BTUOpen-6873}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-68734}, school = {BTU Cottbus - Senftenberg}, year = {2024}, abstract = {Smart grids provide state-of-the-art communication and information technologies that facilitate the integration of distributed generation units (DGUs) as well as the design of novel and flexible control strategies. In particular, the design of control strategies for DGUs in medium- and low-voltage (MV/LV) distribution microgrids, as well as for load tap changer transformers (LTCs) in extra high- and high-voltage (EHV/HV) transmission grids, is considered in this work. On the one hand, the DGUs are enabled to provide voltage control support by adopting a grid-aware operation paradigm, which allows them to autonomously switch between grid-forming and grid-feeding schemes whenever necessary. On the other hand, LTCs are equipped with a control strategy that imposes a coordinated sequence of discrete tap changes to ensure voltage regulation and prevent undesired transient phenomena. From a control systems perspective, ensuring stability in the presence of discontinuous phenomena, e.g., grid-aware switches and LTC taps, demands the explicit consideration of such features. Hence, the contributions of the present work are derived within the framework of switched systems theory and are characterized by the following aspects: (i) A passivity-based grid-feeding DGU controller is designed by taking inspiration from a similar grid-forming controller proposed in the literature. By taking this approach, stabilization results can be extended to microgrids with an arbitrary topology. (ii) A grid-aware DGU control strategy for autonomously switching between controllers is designed as a state- and time-dependent switching logic, which ensures that the closed-loop switched microgrid dynamics possesses a unique equilibrium point. (iii) Stability guarantees of the equilibrium point are provided by deriving sufficient tuning conditions for the control parameters via dwell-time methods within a multiple Lyapunov functions framework. The points (i)-(iii) are addressed separately for DC and AC microgrids. (iv) The discontinuous features of a class of LTC-controlled AC transmission grids are captured by a switched dynamic model. Based on this, a coordinated control strategy for LTCs is proposed, together with sufficient tuning conditions for its control parameters that ensure convergence of the regulated voltage and prevent undesired voltage oscillations known as voltage hunting. The viability of the abovementioned results is validated via illustrative simulation examples.}, subject = {Grid-aware control; Switched systems; Voltage hunting; Netzbewusste Regelung; Geschaltete Systeme; Intelligentes Stromnetz; Spannungsregelung; Schaltvorgang; Regelungssystem}, language = {en} } @phdthesis{LorenzMeyer2024, author = {Lorenz-Meyer, Maximilian Nicolai Lorenz}, title = {State and parameter estimation approaches for online dynamic security assessment in power systems}, doi = {10.26127/BTUOpen-6911}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-69114}, school = {BTU Cottbus - Senftenberg}, year = {2024}, abstract = {With the global effort to decarbonize the energy sector, major changes are being implemented in power systems. This shift drastically alters the system dynamics, prompting the need for innovative online dynamic security assessment (DSA) tools. Such tools are crucial for system operators to gain situational awareness and make corrective or preventive operational decisions, ensuring reliable, secure, and cost-efficient system operation. A key component of online DSA tools is power system dynamic state estimation (DSE), used to obtain real-time estimates of critical system states and parameters, such as the inertia constant or the states and parameters of synchronous generators. Motivated by this, control theory-based approaches for DSE that focus on two key challenges are developed in the present thesis. Firstly, the topic of multi-area inertia estimation is addressed. Secondly, the problem of decentralized state and parameter estimation for synchronous generators is considered. Unlike much of the existing literature on the topic, rigorous analytical convergence guarantees are provided. More specifically, the main contributions of this work are as follows: 1) A robust tuning method for consensus + innovations-based distributed parameter estimation in the presence of disturbances is derived. This technique allows for systematic gain tuning, while providing guaranteed robustness properties and avoiding trial-and-error gain selection. As disturbances, such as measurement noise, perturbations in the communication channels, and model mismatches, arise in any real-world application, the tuning procedure can be utilized for various distributed estimation problems in the context of DSE and other fields. 2) The method presented under Item 1 is employed to develop a robust distributed inertia estimation approach for interconnected power systems. Differing from similar approaches, the proposed scheme requires only peer-to-peer communication of local parameter estimates between neighboring control areas, avoiding the need for a central entity with access to global measurement information. The performance of the approach is validated by simulations. 3) A decentralized unknown input scheme for reconstructing the states of synchronous generators in a multi-machine power system along with critical machine parameters is proposed. Only phasor measurements from a substation near a power plant are required for this. Such a location is more accessible to system operators than the generator's terminal bus, which is the usual measurement location assumed in the literature. Lastly, the performance is validated in a simulation study and using real-world measurement data from the German high-voltage grid.}, subject = {Online dynamic security assessment; Power grid monitoring; Dynamic state and parameter estimation; Robust distributed estimation; Dynamische Sicherheitsbewertung; Stromnetz{\"u}berwachung; Dynamische Zustands- und Parametersch{\"a}tzung; Robuste verteilte Sch{\"a}tzung; Regelungstheorie; Verbundnetz; Sicherheit; Bewertung; Synchrongenerator; Parametersch{\"a}tzung}, language = {en} }