@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} } @misc{Acquah2014, type = {Master Thesis}, author = {Acquah, Michael}, title = {Decentralized Rural Electrification in Ghana-Evaluation of Technical and Socio-Economic Aspects for Sustainable Solutions}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-29999}, school = {BTU Cottbus - Senftenberg}, year = {2014}, abstract = {Rural electrification has been one of the challenges faced by the government of Ghana due to extremely high cost of electricity extension to the rural areas. In order to meet up this challenge, the government of Ghana has been keen with the introduction of renewable energy programs as a solution for rural electrification. However, most of programs are also faced with the problem of being sustainable. After government and sponsors hand-over completed project to local users, they usually last only few years of their life span and are abandoned. This challenge has inspired this study to identify the potential barriers to the sustainability of rural electrification programs through technical and socio-economic evaluation of a solar PV rural electrification project in Ghana. The approach of this study selected an on-going solar PV project (community solar system-CSS), that has been introduced on a pilot base across the whole of Ghana, which is to be adopted as a standard system for electrification solutions in rural areas in Ghana. This project was subjected to both technical and socio-economic evaluations covering 13 rural communities across the southern part of the country. Stakeholder interviews and review of literature were additional methodologies employed to gather information pertinent to the theme of the study. The results of the study show that technically, the CSS project has simple design and operational technologies, which gives it high integration potential. However, the project faces the problem of technology misuse by the rural users and frequent failure of its components. The socio-economic barriers identified are: (1) ineffective management of the project due to a long chain of bureaucratic administrative management system, inadequate monitoring and supervision, and inconsistency in standardizing the cash flow of the project, and (2) low electricity capacity of the CSS project and other similar small scale renewable projects to meet the electricity requirements of the rural populates. These problems lead to gradual decline of users' interest for such small scale renewable energy projects and subsequently result in project abandonment. It was concluded that small scale renewable energy programs lack the capacity to fully meet the energy requirement of rural populates; however, they are crucial as intervening solutions and play key role in rural development.}, subject = {Ghana; Ghana; L{\"a}ndliche Elektrifizierung; Bewertung; Nachhaltigkeit; Rural Electrification; Evaluation; Sustainability}, language = {en} } @phdthesis{Schmuck2005, author = {Schmuck, J{\"o}rg}, title = {Entwurf einfach strukturierter Regler mit Robustheitskriterien im Frequenzbereich}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-000000659}, school = {BTU Cottbus - Senftenberg}, year = {2005}, abstract = {Zentraler Gegenstand der Arbeit ist die Anwendung von Robustheitskriterien im Frequenzbereich f{\"u}r den Entwurf robuster Regler mit einfacher Struktur. Im Blickpunkt stehen dabei unkomplizierte Regelstrecken aus Energie- und Verfahrenstechnik. Die gemessene Sprungantwort der Regelstrecke ist Ansatzpunkt f{\"u}r die hier vorgeschlagene Modellierungsmethode. Bevorzugt f{\"u}r die Kombination von PT1-Glied als nominelles Modell und PI-Regler folgen Untersuchungen zum erreichbaren Regelverhalten und die {\"U}berf{\"u}hrung von Zeitbereichsvorgaben in eine frequenzabh{\"a}ngige Wichtungsfunktion. Die Robustheitskriterien werden grafisch durch punktweise Analyse auf dem gerasterten Parametergebiet ausgewertet, worin alle geeigneten Kombinationen der Reglerparameter als L{\"o}sung markiert werden. Die Algorithmen wurden in MATLAB-Programmen realisiert. Als Anwendungsbeispiele enth{\"a}lt die Arbeit den Reglerentwurf f{\"u}r einen Neutralisationsprozess, ein instabiles System und eine Druckregelstrecke.}, subject = {Reglerentwurf; Mehrgr{\"o}ßenregelung; Prozessregelung; Robuste Regelung; Frequenzbereich; H-unendlich-Methode; Robuste Regelung; Frequenzbereichskriterium; PI-Regler}, language = {de} } @phdthesis{Handreg2016, author = {Handreg, Martin}, title = {Entwurf von k{\"u}nstlichen neuronalen Netzen zur Regelung von Prozessgr{\"o}ßen in einer Schmelzwanne f{\"u}r Flachglas}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-39471}, school = {BTU Cottbus - Senftenberg}, year = {2016}, abstract = {In der vorliegenden Arbeit wird die Eignung von K{\"u}nstlichen Neuronalen Netzen hinsichtlich der Modellierung des komplexen Prozessverhaltens in einer Flachglasschmelzanlage analysiert. Die Identifikation und das Training der neuronalen Prozessmodelle erfolgen mit Messdaten einer Schmelzwanne f{\"u}r Flachglas. Im Vordergrund steht die Evaluation einer geeigneten Netzstruktur und die Parametrierung der Netzparameter. Dabei wird der Einfluss der einzelnen Netzparameter in Bezug auf die Genauigkeit der Netze eingehend untersucht. Anhand von Testdaten wird nachgewiesen, dass die qualit{\"a}tsbestimmenden Temperaturen und der Glasstand mit K{\"u}nstlichen Neuronalen Netzen hinreichend genau berechnet werden k{\"o}nnen. Auf Basis der entwickelten neuronalen Prozessmodelle wird anschließend eine modellbasierte pr{\"a}diktive Regelstrategie beschrieben. Neben der Auswahl des G{\"u}tekriteriums und des Optimierungsalgorithmus zur Berechnung zuk{\"u}nftiger Stellgr{\"o}ßen werden Richtlinien zur Dimensionierung der verf{\"u}gbaren Reglerparameter abgeleitet.}, subject = {K{\"u}nstliches Neuronales Netz; Pr{\"a}diktive Regelung; Levenberg-Marquardt-Algorithmus; Flachglas; Schmelzprozess; Artifical Neural Networks; Predictive control; Algorithm of Levenberg-Marquardt; Floatglas; Melting process; Neuronales Netz; Flachglas; Schmelzen}, language = {de} } @article{KrishnaSchifferRaisch, author = {Krishna, Ajay and Schiffer, Johannes and Raisch, J{\"o}rg}, title = {Distributed secondary frequency control in microgrids : robustness and steady-state performance in the presence of clock drifts}, doi = {10.26127/BTUOpen-5969}, abstract = {Microgrids are distributed systems with high share of inverter-interfaced renewable energy sources where stable and reliable system operation is realized by suitably controlling the inverters. In this work, we focus on secondary frequency control, which is an important ancillary service provided by the inverters. In the literature on secondary frequency control, the effect of clock drifts has often been neglected. However, clock drifts are practically unavoidable parameter uncertainties in inverter-based microgrids and we show that the most commonly employed distributed secondary frequency controllers exhibit performance deteriorations when taking clock drifts explicitly into consideration. Motivated by this, we propose a novel alternative control law called generalized distributed averaging integral (GDAI) control, which achieves the secondary control objectives of steady-state accurate frequency restoration and proportional power sharing in the presence of clock drifts. In addition, we derive a sufficient tuning criterion in the form of a set of linear matrix inequalities (LMIs) which guarantees robust stability of the closed-loop equilibrium point in the presence of uncertain clock drifts. Finally, our analysis is validated extensively via simulation with comprehensive comparisons to other related distributed control approaches.}, subject = {Microgrids; Distributed control; Consensus algorithms; Power systems; Secondary frequency control; Sekund{\"a}rfrequenzregelung; Mikronetze; Robustheit; Taktdifferenzen; Wechselrichter; Microgrid ; Wechselrichter; Taktfrequenz}, language = {en} } @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} } @inproceedings{RuedaEscobedoMorenoSchiffer, author = {Rueda-Escobedo, Juan G. and Moreno, Jaime A. and Schiffer, Johannes}, title = {Finite-time estimation of time-varying frequency signals in low-inertia power systems}, doi = {10.26127/BTUOpen-5988}, pages = {2108 -- 2114}, abstract = {The ongoing and unprecedented transformation of power systems leads to a reduction in the number of conventional power plants, which are the classical actuators of the grid. In addition, this development results in a decreasing system inertia, which is expected to yield faster frequency dynamics. Therefore power-electronics-interfaced units have to take over system control tasks and, in particular, frequency control. For this purpose, accurate and fast estimation algorithms for time-varying frequency signals are needed. Motivated by this fact, we propose a time-varying parameter estimator and a tuning criterion, which for sufficiently small initial estimation errors allows to reconstruct the time-varying frequency signal of a symmetric three-phase waveform in finite time. The proposed estimator is derived by using a time-varying version of the super twisting algorithm and its performance is illustrated via numerical examples.}, subject = {Distributed power generation; Frequency control; Parameter estimation; Power plants; Power system control; Frequenzsignale; Massentr{\"a}gheit; Systemsteuerung; Transformation; Frequenzdynamik; Energieversorgung; Frequenzstabilit{\"a}t}, language = {en} }