Investigation and validation of methods to implement a two-quadrant battery emulator for power Hardware-in-the-Loop Simulation

When new hardware is developed, it is often convenient to test the prototype in a Hardware-in-the-Loop Simulation (HILS). In this technique, the critical parts of the system including the hardware-under-test (HUT) are physically present while the rest of the system is emulated in real time. In this paper, a battery emulator (BE) is implemented to replicate the behaviour of a battery pack in a HILS experiment. For this purpose, a remotely controlled DC power supply is used, combined with external passive elements to allow two-quadrant operation. The emulation fidelity is validated through experimental comparison with a real battery pack under constant and pulsed current loads. These experiments show the importance of the impedance connecting the BE to the HUT and how a poor selection can cause oscillations that would not exist in an experiment with a real battery pack.</p

Control of power converter in modern power systems

A la portada consta el nom del programa interuniversitari: Joint Doctoral Programme in Electric Energy Systems [by the] Universidad de Málaga, Universidad de Sevilla, Universidad del País Vasco/Euskal Erriko Unibertsitatea i Universitat Politècnica de CatalunyaPower system is undergoing an unpreceded paradigm shift: from centralized to distributed generation. As the renewable-based generations and battery storage systems are increasingly displacing conventional generations, it becomes more and. more difficult to maintain the stability and reliability of the grid by using only conventional generations. The main reason for the degradation of grid stability is the rapid penetration of nonconventional sources. These new generations interface with the grids through power electronics converters which are conventionally designed to maximize conversion efficiency and resource utilization. Indeed, these power converters only focus on their internal operation despite the grid conditions, which often worsens the grid operation. To overcome such a drawback, the grid-forming concept has been proposed for power converters, aiming to redesign the control of the power converters to enforce more grid-friendly behaviours such as inertia response and power oscillation damping to name a few. Despite the rich literature, actual adaptation of grid-forming controller in real-world applications is still rare because incentives for renewable power plants to provide services based on such advanced grid-forming functions were at best scarce. In the last years, however, several system operators have imposed new requirements and markets for grid-supporting services. In addition, the existing grid-forming controllers require modification to low-level control firmware of a power converter, which is often unrealistic due to the control hardware limitations as well as necessary testing and certifications. To ensure a stable operation of a grid-forming converter under adverse operating conditions, a robust voltage sensorless current controller is developed in this PhD thesis. The proposed controller is able to handle most of the possible abnormal conditions of the grid such as impedance variations, unbalanced voltage; harmonics distortion. These abnormalities of the grid are mathematically represented using equivalent linear models such that they can be used for calculating the controller gains. Linear matrix inequality techniques are also used to facilitate parameter tuning. In fact, the performance and stability of the current control loop can be determined through only two tuning parameters instead of eight parameters for a controller of a similar structure. The existing grid-forming implementations are designed considering that the control firmware of the power converter can be upgraded at will. However, modifications of the control firmware are not straightforward and cost-effective at mass scale. To overcome such a limitation, an external synchronous controller is presented in this PhD thesis. The external synchronous controller uses measurements, which are either provided by the power converter or a dedicated measurement unit, to calculate the actual active and reactive power that should be injected by the power converters in a way that the power plant acts as an aggregated grid­forming converter. As a result, any conventional power converters can be utilized for providing grid-supporting services with minimal modification to the existing infrastructure. Power converters can provide even better performance than a synchronous generator if a proper control scheme is used. In this regard, the final chapter of this PhD thesis presents the multi-rotor virtual machine implementation for grid-forming converter to boost their damping performance to power oscillations. The multi-rotor virtual machine-controller implements several virtual rotors instead of only one rotor as in typical grid-forming strategies. Since each of the virtual rotors is tuned to target a specific critical mode, the damping participation to such a mode can be increased and adjusted individually. The controllers presented in this PhD thesis are validated through simulators and experiments in the framework of the H2020 FlexiTranstore project. The results are throughout analysed to assess the control performance as well as to highlight possible implications.A medida que las generaciones basadas en energías renovables y los sistemas de almacenamiento de baterías desplazan la generación convencional, se vuelve cada vez más difícil mantener la estabilidad y confiabilidad de la red. Estas nuevas generaciones interactúan con las redes a través de convertidores de electrónica de potencia que están diseñados tradicionalmente para maximizar la eficiencia de conversión y la utilización de recursos. Estos convertidores centran su funcionamiento interno independientemente de las condiciones de la red, lo que a menudo empeora el funcionamiento de la red. Para esto, se ha propuesto el concepto de convertidores de potencia formadores de red (grid-forming), con el objetivo de rediseñar el control de los convertidores de potencia para imponer comportamientos más favorables a la red, por ejemplo, la respuesta inercial y la amortiguación de oscilaciones de potencia. No en tanto, la adaptación real del controlador grid-forming en aplicaciones del mundo real todavía es escasa debido a los pocos incentivos para que las plantas de energía renovable proporcionen servicios basados en funciones de formación de red tan avanzadas. Aunque en los últimos años, operadores de sistemas han impuesto nuevos requisitos y mercados para servicios auxiliares, los controladores grid-forming existentes requieren cambios en el firmware de control de bajo nivel de un convertidor de potencia, algo poco realista debido a las limitaciones del hardware de control, así como a las pruebas y certificaciones necesarias. En esta tesis se desarrolla un controlador de corriente robusto, sin sensor de tensión, para garantizar el funcionamiento estable de un convertidor grid-forming en condiciones de operación adversas. Este controlador es capaz de manejar la mayoría de las condiciones anormales de red, como variaciones de impedancia, tensión desequilibrada y distorsión de armónicos. Estas anomalías de la red se representan matemáticamente mediante modelos lineales equivalentes, utilizados para calcular las ganancias del controlador. También, usando técnicas de desigualdad matricial lineal para facilitar el ajuste de parámetros. De hecho, el rendimiento y la estabilidad del bucle de control de la corriente pueden determinarse mediante sólo dos parámetros de sintonización. Las implementaciones de formación de red existentes están diseñadas considerando que el firmware de control del convertidor de potencia puede actualizarse a voluntad. Sin embargo, las modificaciones del firmware de control no son sencillas ni rentables a gran escala. Por tanto, esta tesis presenta un controlador síncrono externo que utiliza las mediciones proporcionadas por el convertidor de potencia o por una unidad de medición dedicada para calcular la potencia activa y reactiva real que deben inyectar los convertidores de potencia, de forma que la central eléctrica actúe como un convertidor grid-forming agregado. Como resultado, cualquier convertidor de potencia convencional puede utilizarse para proporcionar servicios de apoyo a la red con una modificación mínima de la infraestructura existente. Los convertidores de potencia pueden ofrecer mejor rendimiento que un generador síncrono utilizando un esquema de control adecuado. El último capítulo de esta tesis presenta la implementación de una máquina virtual multirrotor para que los convertidores de red aumenten su rendimiento de amortiguación de las oscilaciones de potencia. El controlador de la máquina virtual multirrotor implementa varios rotores virtuales en lugar de un solo rotor como en las estrategias típicas de grid-forming. Dado que cada uno de los rotores virtuales está sintonizado para dirigirse a un modo crítico específico, la participación de la amortiguación a dicho modo puede aumentarse y ajustarse individualmente. Los controladores presentados en esta tesis doctoral han sido validados mediante simulaciones y experimentos en el marco del proyecto H2020 FlexiTranstore.Postprint (published version

Development of a Converter-Based Testing Platform and Battery Energy Storage System (BESS) Emulator for Microgrid Controller Function Evaluation

The microgrid has attracted increasing research attention in the last two decades. Due to the development of renewable energy resources and power electronics technologies, the future microgrid will trend to be smarter and more complicated. The microgrid controller performs a critical role in the microgrid operation, which will also become more and more sophisticated to support the future microgrid. Before final field deployment and test, the evaluation and testing of the controller is an indispensable step in the controller development, which requires a proper testing platform. However, existing simulation-based platforms have issues with potential numerical oscillation and may require huge computation resources for complex microgrid controllers. Meanwhile, field test-based controller evaluation is limited to the test conditions. Existing digital simulation-based platforms and field test-based platforms have limitations for microgrid controller testing. To provide a practical and flexible controller evaluation, a converter-based microgrid hardware testbed is designed and implemented considering the actual microgrid architecture and topology information. Compared with the digital simulation-based platforms, the developed microgrid testing platform can provide a more practical testing environment. Compared to the direct field test, the developed platform is more flexible to emulate different microgrids. As one of the key components, a converter-based battery energy storage system (BESS) emulator is proposed to complete the developed testing platform based on the testing requirements of microgrid controller functions. Meanwhile, the microgrid controller testing under different microgrid conditions is also considered. Two controllers for the microgrid with dynamic boundaries are tested to demonstrate the capability of the developed platform as well as the BESS emulator. Different testing cases are designed and tested to evaluate the controller performance under different microgrid conditions

A fast remotely operable digital twin of a generic electric powertrain for geographically distributed hardware-in-the-loop simulation testbed

The automotive industry today is seeing far-reaching and portentous changes that will change the face of it in the foreseeable future. Digitalisation and Electrification are two of the key megatrends that is changing the way vehicles are developed and produced. A recent development in R&D process is the Hardware-in-the-Loop (HIL) method that uses a hybrid approach of testing a physical prototype immersed in a virtual environment, which is nowadays being creatively re-applied towards geographically separated multi-centre testing strategies, that suits the horizontally integrated and supply-chain driven industry very well. Geographical separation entails the deployment of a “Digital Twin” in remote centre(s) participating in multi-centre testing. This PhD aims to produce a highly robust, efficient, and rapidly computable Digital Twin of a generic electric powertrain using the multi-frequency averaging (MFA) technique that has been extended for variable frequency operation. This PhD also aims to commission a local HIL simulation testbed for a generic electric power inverter testing. The greater goal is to co-simulate the local HIL centre testing a prototype inverter, and its Digital Twin in a different location “twinning” the prototype inverter as best as possible. A novel approach for the Digital Twin has been proposed that employs Dynamic Phasors to solve the system in the frequency domain. An original method of multiplication of two signals in the frequency domain has been proposed. The resultant model has been verified against an equivalent time domain switching model and shown to outperform appreciably. A distinctive advantage the MFA Digital Twin offers is the “fidelity customisability”; based on application, the Twin can be set to compute a low (or high)-fi model at different computational cost. Finally, a novel method of communicating high-speed motor shaft position information using a low-speed processing system has been developed and validated. This has been applied to run real-life HIL simulation cycles on a test inverter and effects studied. The two ends of a multi-HIL testbed, i.e., local HIL environment for an inverter, and its Digital Twin, has been developed and validated. The last piece of the puzzle, i.e., employing a State Convergence algorithm to ensure the Digital Twin is accurate duplicating the performance of its “master”, is required to close the loop. Several ideas and process plans have been proposed to do the same

Integration of Flywheel Energy Storage Systems in Low Voltage Distribution Grids

A Flywheel Energy Storage System (FESS) can rapidly inject or absorb high amounts of active power in order to support the grid, following abrupt changes in the generation or in the demand, with no concern over its lifetime. The work presented in this book studies the grid integration of a high-speed FESS in low voltage distribution grids from several perspectives, including optimal allocation, sizing, modeling, real-time simulation, and Power Hardware-in-the-Loop testing

Integration of Flywheel Energy Storage Systems in Low Voltage Distribution Grids

Mit dem Ziel, den Stromsektor zu dekarbonisieren und dem Klimawandel zu begegnen, steigt der Anteil erneuerbarer Energieressourcen in den Energiesystemen rund um den Globus kontinuierlich an. Aufgrund des intermittierenden Charakters dieser Ressourcen kann die Aufrechterhaltung des momentanen Gleichgewichts zwischen Erzeugung und Verbrauch und damit der Netzfrequenz ohne angemessene Maßnahmen jedoch eine Herausforderung darstellen. Da erneuerbare Energiequellen mit Umrichterschnittstellen dem System selbst keine Trägheit verleihen, nimmt gleichzeitig die kumulative Systemträgheit ab, was zu schnelleren Änderungen der Netzfrequenz und Bedenken hinsichtlich der Netzstabilität führt. Ein Schwungrad-Energiespeichersystem (Flywheel Energy Storage System, FESS) kann schnell große Leistungsmengen einspeisen oder aufnehmen, um das Netz nach einer abrupten Änderung der Erzeugung oder des Verbrauchs zu unterstützen. Neben der schnellen Reaktionszeit hat ein FESS den Vorteil einer hohen Leistungsdichte und einer großen Anzahl von Lade- und Entladezyklen ohne Kapazitätsverlust während seiner gesamten Lebensdauer. Diese Eigenschaften machen das FESS zu einem gut geeigneten Kandidaten für die Frequenzstabilisierung des Netzes oder die Glättung kurzfristiger Leistungsschwankungen auf lokaler Ebene. In dieser Dissertation wird die Netzintegration eines Hochgeschwindigkeits-FESS auf der Niederspannungsebene aus mehreren Perspektiven untersucht. Zunächst wird das Problem der Platzierung und Dimensionierung eines FESS in Niederspannungsverteilnetzen für Leistungsglättungsanwendungen behandelt. Um den am besten geeigneten Standort für ein FESS zu finden, wird eine datengetriebene Methode zur Abschätzung der relativen Spannungsempfindlichkeit vorgestellt, die auf dem Konzept der Transinformation basiert. Der Hauptvorteil der vorgeschlagenen Methode besteht darin, dass sie kein Netzmodell erfordert und nur Messwerte an den interessierenden Punkten verwendet. Messergebnisse aus einem realen Netz in Süddeutschland zeigen, dass mit dem vorgeschlagenen Ansatz die Netzanschlusspunkte mit einer höheren Spannungsempfindlichkeit gegenüber Wirkleistungsänderungen, welche am meisten von einem durch FESS ermöglichten, glatteren Leistungsprofil profitieren können, erfolgreich zugeordnet werden können. Darüber hinaus wird eine neue Methode zur Dimensionierung von Energiespeichersystemen unter Verwendung von Messdaten eingeführt. Der vorgeschlagene Ansatz erkennt wiederkehrende Verbrauchsmuster in aufgezeichneten Leistungsprofilen mit Hilfe des "Motif Discovery"-Algorithmus, die dann zur Dimensionierung verschiedener Speichertechnologien, einschließlich eines FESS, verwendet werden. Anhand von gesammelten Messdaten aus mehreren Niederspannungsnetzen in Deutschland wird gezeigt, dass die Speichersysteme mit den aus den detektierten Mustern abgeleiteten Charakteristika während der gesamten Messperiode effektiv für ihre Anwendungen genutzt werden können. Als nächstes wurde ein dynamisches Modell eines Hochgeschwindigkeits-FESS entwickelt und mit experimentellen Ergebnissen in mehreren Szenarien, unter Berücksichtigung der Verluste und des Hilfsenergiebedarfs des Systems, validiert. In den untersuchten Szenarien wurde eine maximale Differenz von nur 0,8 % zwischen dem Ladezustand des Modells und dem realen FESS beobachtet, was die Genauigkeit des entwickelten Modells beschreibt. Nach Festlegung des erforderlichen Aufbaus wurde die Leistungsfähigkeit eines 60 kW Hochgeschwindigkeits-FESS während mehrerer Frequenzabweichungsszenarien mit Hilfe von Power Hardware-in-the-Loop-Tests beurteilt. Die Ergebnisse der PHIL-Tests zeigen, dass das Hochgeschwindigkeits-FESS sehr schnell nach einer plötzlichen Frequenzabweichung reagiert und in knapp 60 ms die erforderliche Leistung erreicht, wobei die neuesten Anforderungen der Anwendungsregeln für die Frequenzunterstützung auf der Niederspannungsebene erfüllt werden. Um schließlich die Vorteile des schnellen Verhaltens des FESS für Energiesysteme mit geringer Trägheit zu demonstrieren, wurde ein neuartiger adaptiver Trägheits-Emulationsregler für das Hochgeschwindigkeits-FESS eingeführt und seine Leistung in einem Microgrid mit geringer Trägheit durch Simulationen und Experimente validiert. Die Simulationsergebnisse zeigen, dass die Verwendung des FESS mit dem vorgeschlagenen Trägheits-Emulationsregler die maximale Änderungsrate der Frequenz um 28 % und die maximale Frequenzabweichung um 44 % während der Inselbildung des untersuchten Microgrid reduzieren kann und mehrere zuvor vorgestellte adaptive Regelungskonzepte übertrifft. Der vorgeschlagene Regler wurde auch auf einem realen 60 kW FESS mit dem Konzept des Rapid Control Prototyping implementiert, und die Leistungsfähigkeit des FESS mit dem neuen Regelungsentwurf wurde mit Hilfe von PHIL-Tests des FESS validiert. Die PHIL-Ergebnisse, die die allererste experimentelle Validierung der Trägheitsemulation mit einem FESS darstellen, bestätigen die Simulationsergebnisse und zeigen die Vorteile des vorgeschlagenen Reglers

Integration of Flywheel Energy Storage Systems in Low Voltage Distribution Grids

A Flywheel Energy Storage System (FESS) can rapidly inject or absorb high amounts of active power in order to support the grid, following abrupt changes in the generation or in the demand, with no concern over its lifetime. The work presented in this book studies the grid integration of a high-speed FESS in low voltage distribution grids from several perspectives, including optimal allocation, sizing, modeling, real-time simulation, and Power Hardware-in-the-Loop testing

Nonlinear Modeling of Power Electronics-based Power Systems for Control Design and Harmonic Studies

The massive integration of power electronics devices in the modern electric grid marked a turning point in the concept of stability, power quality and control in power systems. The evolution of the grid toward a converter-dominated network motivates a deep renovation of the classical power system theory developed for machine-dominated networks. The high degree of controllability of power electronics converters, furthermore, paves the way to the investigation of advanced control strategies to enhance the grid stability, resiliency and sustainability. This doctoral dissertation explores four cardinal topics in the field of power electronics-based power systems: dynamic modeling, stability analysis, converters control, and power quality with particular focus on harmonic distortion. In all four research areas, a particular attention is given to the implications of the nonlinearity of the converter models on the power system

DALILA - Design architectures in a Living Lab

Real-time testing of a Multi-Microgrid system emulated in Matlab Simulink. The experimental tests were undercarried on real hardware components through a analog/digital converter (Power Harware in The Loop).This thesis provides an overview of Microgrids and Multi-Microgrids control architectures and validates control functionalities through the combined efforts of numerical simulation and practical tests in a real laboratory by using Power Hardware In the Loop (PHIL) technology. The thesis is divided in five major topics. The first topic is related with Microgrids, Multi-Microgrids and Smartgrids. It starts by describing the context of such concepts and their implications on power systems: the operational challenges they brought along are laid out in order to make sense out of the proposed solutions. Afterwards it details what characterizes these concepts and the essential components behind them. The devices that enable main functionalities such as autonomous operation, active demand response, voltage/var control, blackstart, etc. This involves explaining the models of microgeneration units, storage devices, electric vehicles and system coordinators. Lastly, there is mentioning to some international reference projects.The second topic is related with Living Labs. In order to conduct experiments regarding Microgrids/Smartgrids, it is necessary to identify key laboratory infrastructures and their main experimental objectives. Therefore, a brief outlook of the most notorious international laboratories and their topics of research is presented.The third topic revolves around the simulation mechanics and the software utilized to study power systems behaviour, which in this case was \textit{Matlab Simulink}. A base case of a Multi-Microgrid system scenario was built based on an existing rural grid and is presented. The MicroSource modelling and the control strategy implemented are described and test results are driven and analysed. The fourth topic details the theory associated with the PHIL converter and describes the series of steps to be followed that allow interaction with \textit{Simulink} and proper operation. Finally, the last topic describes the experimental tests that were under carried in the laboratory and their respective results. These results will serve to validate the ones obtained in the simulation environment. This serves the purpose of demonstrating microgrid operation and testing