Integrating renewable offshore wind generation into global power grids is a critical issue in the energy industry. Modular Multilevel Converter (MMC)-based High Voltage Direct Current (HVDC) grids are the most effective and promising technical solution for the new offshore wind energy power system connections. These grids offer scalability, controllability, and reliability advantages, but their stable and compliant operation requires implementing MMC control strategies and controllers. This thesis investigates the intricacies of HVDC technologies, focusing on MMC control strategies and controllers. The research explores grid following and grid forming converter control strategies, essential for ensuring stable and compliant operation of MMC-based HVDC grids. The research elaborates on the Model Predictive Control (MPC), which is a promising control strategy for MMC-based HVDC grids. The MPC controller makes the control strategies respond faster, emphasizing constraints and cost functions. Furthermore, a comparative analysis of Proportional Integral (PI)-based and MPC-based controllers is conducted across various scenarios, highlighting the advantages of MPC-based controllers over PI-based controllers regarding response time and stability. Lastly, a large stability analysis is conducted using the direct Lyapunov method to evaluate the effectiveness of the control strategies and controllers during transient events. This analysis provides insights into the stability and performance of MMC-based HVDC grids under different operating conditions and disturbances. This thesis illustrates the capabilities of grid-forming control strategy through Model Predictive controllers for FPGA-based MMC-MTDC networks on RSCAD/RTDS®. The outcomes of this thesis contribute to advancing HVDC technologies and control strategies, with implications for enhancing the stability and efficiency of MMC-based HVDC grids. The findings of this thesis have significant potential in the energy industry, particularly in integrating renewable offshore wind generation into global power grids.

LVDC Distribution systems are becoming popular due to the avenue of integrating renewable energy sources on a large scale. Predominant DC based power system architecture has been predicted to serve the needs of a sustainable society that holds the capability to self-generate, share, and trade power produced from renewable energy sources. Bottom - up approach beginning from development of products that run on DC till microgrids and integration of rural communities using LVDC distribution presents as a promising avenue for adoption of DC grids worldwide. Many areas in DC distribution system are yet to undergo rigorous study both theoretically and practically. Touch protection is one such area which is largely unexplored. Residual current devices (RCD) are traditionally implemented at the load side to trip at specific residual current levels ranging from few to hundreds of milli amperes. Current trip thresholds and time within which the fault must be isolated are different for DC. There is dearth of standards for DC RCD. In this thesis project we attempt to design a compact, reliable, and cost-effective RCD. The designed and developed prototype is tested at DC Low Voltage levels for various residual current magnitudes to determine important parameters like reaction time and accuracy.

This Master's Thesis is conducted in collaboration with Alewijnse, a leading maritime systems integrator in the Netherlands. The thesis aims to identify the optimal and cost-effective method of incorporating battery energy storage systems (BESS) into both new and existing DP-2 vessels, as well as DP-3 vessels. The objective is to determine the most efficient battery size and technology, establish the ideal time frame for return on investment, and design a power generation schedule that is ideal for the DP-2 cable laying vessel’s power system. The primary objectives of this research are to optimize the battery system, ensure effective energy system operation, and establish a strong business case. Specifically, the study explores the feasibility of retrofitting a DP-2 vessel that operates in the North Sea and Taiwan with a battery system to create a hybrid system. To determine the optimal sizing of the battery energy storage system, 12 different battery solutions from two European battery suppliers considering three different fuel price scenarios are analyzed. These solutions encompass a variety of battery technologies, such as High Power or High Energy Li-ion batteries or a combination of both. The integration of BESS into vessels offers several operational benefits to operators, including the ability to operate diesel engines at higher or more efficient points of operation to maximize their performance. Battery systems can also act as ”virtual generators” during dynamic positioning (DP) mode for DP-2 vessels, reducing fuel consumption, lowering diesel engine ON-time, and decreasing maintenance costs. However, hybridizing vessels involves more than just integrating an optimally sized battery system.The existing power management system (PMS) and energy management system (EMS) must also undergo upgrades to ensure effective operation. To address these challenges, the BOOSTER (Battery Optimization for Optimal Sizing and Throughput Energy Regulation) methodology is proposed, which incorporates the operation of an optimized management system based on fuel prices and the throughput energy cost of the battery system.

Zero emission fuels and reducing emissions are important topics in all transport sectors and hybrid systems play a key role in the transition towards full decarbonization. This thesis studies the components that are found in hybrid maritime electrical power systems and their influence on power quality, short-circuit currents and protection & coordination. In order to help system integrators such as Alewijnse in the design of these hybrid systems, two typical models of actual vessels are created in simulation software ETAP. Both systems are low-voltage, high-power systems, based on either an AC or DC busbar. Rules and standards related to power quality and short-circuit currents are studied as well as practical protection strategies. For the AC model, various studies have been successfully simulated including a load flow study, transient stability study including peak shaving and virtual generator simulations for the battery, a protection & coordination study and a harmonic study. Some challenges with ETAP regarding DC grid simulations are discussed, but is also demonstrated how to use the formulas and standard approximation function from the IEC 61660 to calculate short-circuit currents and I2t values and how to use these results in the protection & coordination study.

As the electricity sector transitions towards a low-carbon future, an increasing proportion of synchronous generation in the power system is replaced with inverter-based resources (IBRs). The result is a reduction in the available rotational inertia in the grid, depleting its ability to withstand and arrest frequency changes following disturbances. Consequently, disturbances such as a loss of generation or load have an increasingly larger impact on the system, resulting in higher frequency deviations and increased rate of change of frequency (RoCoF). On two occasions in 2021, the Continental Europe Synchronous Area (CESA) experienced system splitting events caused by cascading trips of several transmission system elements. In both cases, system defence plans were activated in order to preserve the integrity of the overall system. The amount of disconnected load was limited on both occasions, however, should similar events occur in the future with even lower rotational inertia in the grid, the impact could be more severe. This raises the question of whether the existing defence measures are sufficient to maintain system integrity and stable system operation. Currently in CESA, containment of system frequency excursions following a severe loss of generation is achieved through low-frequency demand disconnection (LFDD) at a frequency below 49Hz. Due to the reduction in traditional synchronous generation and system inertia, the frequency stability of the system is expected to deteriorate, leading to an elevated impact of major disturbances, a rising probability of forced disconnections at frequencies below 49 Hz, and the potential for cascading loss of generation and blackout events. The objective of this research is to explore the potential impact of reduced system inertia and increased penetration of renewable generation on the performance of the traditional LFDD scheme. In conjunction, additional proactive measures are proposed and investigated with the aim to reduce the probability of LFDD disconnections, by taking actions at frequency thresholds between 50 and 49Hz, as well as to improve the performance of the LFDD scheme in the event that disconnections are required. As a test case, the LFDD scheme as currently applied by one of the distribution system operators in the Netherlands is considered. This project is therefore categorised in two primary research directions: (i) improving selection criteria for LFDD load shedding locations, and (ii) improving LFDD performance using alternative load shedding schemes. Key topics explored in this research include: (i) the use of system strength and real-time DER generation as input parameters to load bus selection criteria for LFDD, and (ii) proactive RoCoF-based disconnection of pre-determined consumers above 49Hz. The findings of this study indicate that adapting the current LFDD implementation based on the local system strength and the level of active DER generation at LFDD buses can improve frequency response and reduce instability following LFDD switching operations. Furthermore, proactive RoCoF-based demand side load management techniques above 49Hz prove effective in reducing frequency deviation during the most severe events while avoiding LFDD over-shedding for smaller contingencies.

Using the energy system is part of our daily routine but the complexity of power systems and its understanding have both been confined to the experts in the field. Furthermore, the advent of the Information and Communication Technology (ICT) and the Internet of Things (IoT), power system integration is becoming even more complex for the system planners and operators. Various clean energy technologies like solar power, massive offshore wind, Electric vehicle as well as the increasing dependency of the Prosumers to move towards a future decentralized and transactive energy market. There is hence a need to educate the general public about the important problems encountered during the energy transition as well as to provide a demystifying version of the existing power system to exhibit its complexity and its benefits of intelligent multi-energy systems. Energy System Integration Development (ESID) kit could solve this issue. This project concerns the design and development of a Middleware software system based IOT application, which runs on Raspberry PIs (RasPi), contribute to the layered bottom-top approach of the Illuminator - Energy System Integration Development Tool Kit and has the main goal to help in assisting the application layer to simulate energy system integration scenarios and will be prototyping simple proofs-of-concept for validation purpose. It’s realized as part of the master thesis curriculum of the author. On the completion of this project, there will be a generic middleware system that can be used by the end users/application layer to demonstrate energy system integration scenarios, which is scalable, reconfigurable, inter portable. Illuminator - Energy System Integration Development Tool Kit aimed to become an open-source platform depicting energy integration problems, an education tool kit, and research to prototype control algorithms for counteracting the energy transition challenges. The general public and system integrators would benefit as well as the stakeholders as it can help them analyze the energy integration challenges in a user-centric fashion.vii

This BSc Thesis is about the construction and control elements of the airplane group of the Solar Drone project. The project aims to improve the flight time of aerial vehicles, using solar energy. This document is delves into the possibility of applying solar cells to small model aircrafts. It outlines the challenges and solutions involved in building and controlling such a system. A ready-available airframe and fitting components will be used, in combination with a custom photo-voltaic and energy system, to create a prototype. The prototype takes the form of an unmanned aerial vehicle, making it capable of extended flights without requiring extensive monitoring. It will serve as a testing platform for the performance of the PV modifications done to the aircraft. Included in this document are simulations for calculating optimal solar panel placement inside a transparent wing with opaque ribs, in addition to software and hardware modifications that were required to make the other systems work well in combination with the custom energy system.

Multi-junction solar cells with Si alloys have true potential for high conversion efficiency, because of the spectrum splitting capability. For optimal spectral utilization, a multi-junction silicon based device needs a silicon alloy with a bandgap between that of nc-Si (1.1 eV) and a-Si (1.8 eV). a-SiGe:H has a tunable bandgap between 1.4-1.6 eV by varying the GeH4 flow rate in the layer. An investigation of deposition parameters on PECVD processed a-SiGe:H films showed that variation of the GeH4/SiH4 flow rate is the most influential deposition parameter to achieve bandgap tuning. It influences the optical-, electrical- and material properties due to the fact that it directly changes the GeH4 flow rate in the material. Subsequently, a n-i-p substrate single junction a-SiGe:H solar cell is fabricated. This is the reversed p-i-n superstrate a-SiGe:H solar cell, fabricated by the PVMD group. It has a Voc of 508 mV, a FF of 0.39, a Jsc of 9.9 mA/cm2 and a final efficiency of 2.9%. Due to the low performance, manipulation techniques were introduced. The different proposed shapes consist of bandgap grading in the absorber through GeH4 flow rate profiling. A study on buffer type and thickness, different profiling schemes, grading widths and total absorber thickness strongly improved the device performance. The overall champion single junction a-SiGe:H solar cell has a 3.2 nm n/i i-a-Si buffer combined with a 5 nm n/i i-a-SiGe:H buffer, a V-shape GeH4 peak flow rate of 2.4 sccm, a 134 nm n/i grading width, a 36 nm i/p grading width and a total absorber thickness of 170 nm. This cell generates a Voc of 735 mV, a FF of 0.64, a Jsc of 13.23 mA/cm2 and a final efficiency of 6.18%. This is a relative increase of 113.8% in efficiency. The single junction solar cell fabrication is followed by demonstration of a two-junction device. The overall champion tandem solar cell consists of a 200 nm a-Si:H top cell and a 170 nm a-SiGe:H bottom cell with a V-shape GeH4 peak flow rate of 5.3 sccm. This champion tandem solar cell generates a Voc of 1395 mV, a FF of 0.69, a current limiting Jsc of 8.34 mA/cm2 and a final efficiency of 7.99%. Finally, research proved that the change in top and bottom cell thickness, the maximum GeH4 flow rate and the U- and V-shape profiles are interesting manipulation techniques in a multi-junction device due to their flexibility to increase the current limiting Jsc and improve current matching.

Although the idea of electric vehicles fell out of favour in the 1930s, it seems this phenomenon is now reversing and that many companies are willing to invest again on this technology. The advantages are clear: no emissions and the possibility to power vehicles by means of sustainable sources. On the other hand, a high number of simultaneously active charging stations would likely lead to severe problems in the electrical network, e.g. grid congestions and voltage issues. One of the main goals of this work is to estimate the impact that a higher EV penetration has on the power loading of the lines and transformers in a distribution grid. Once these effects are clear, the focus can move towards the investigation of possible strategies to limit it. Excluding an equipment reinforcement, the only possible way to keep a grid operating when the general working conditions approach the technical limits, is to improve the power management. In this regard, five control strategies were tested in different combinations. Among these, three were implemented on a single charging station level to control the charging operations of the single vehicles. These are the uncontrolled charging (the most commonly used strategy worldwide), the average power charging, where a constant low power is provided during the whole parking time, and the local optimisation charging, where a completely local optimisation analysis is carried out to calculate the cheapest operation possible. The other two strategies instead were implemented at central level, to curtail power in case of necessity. These are the Equal Curtailment Method, that prioritises an equal division of the curtailment among the chargers, and the Flexible Curtailment Method, that optimises the curtailment considering the flexibility of the charging stations. Several tests were run by means of simulations on real Dutch distribution grid models and they showed that simple charging strategies - such as the average power charging – can lead to both low charging prices and low loading percentages. It seemed hardly possible, though, to make the charging stations take greater advantage of the low prices at night, without causing overloading issues. However, this could be achieved if a curtailment scheme was also included by means of a central coordination unit. Therefore, it is clear that different levels of complexity may bring benefits to the network, but they may also present drawbacks. The purpose of this work is to shed some light on the different possibilities and to provide hints on how to choose the most appropriate strategy for each situation.

Rise in distributed energy resources has prompted a shift in the way electricity market operators function. Traditionally, centralized optimization techniques are used by such operators to plan for economic dispatches of power tominimize the overall operational costs and increase system social welfare. Due to the dispersed nature of renewable energy sources as scattered nodes in a system, it can get difficult to accommodate them in a centralized optimization problem. Also, sharing of complete information for such nodes can create privacy issues. This motivates research in the field of distributed optimization techniques. This thesis aims to develop a distributed optimization algorithm for a DC distribution system which would take into account network congestion and line losses and ultimately provide a more precise optimal solution. Based on past research for distributed optimization approaches for AC systems, the Consensus and Innovations approach was used to model an algorithm and provide nodal optimization for a DC system with minimal data exchange. The developed model was implemented on various DC network topologies like meshed grids, single line networks, T Shaped networks, etc. and a converged output of system variables was accomplished. The results were also compared with a centralized optimization approach to check for deviations. The decision variables for the developed approach were found to be well within the deviation range of 2 percent. The algorithm managed to provide distributed optimization within a DC system while minimizing power generator operational costs and cost associated with network losses.

The vast size of a modern interconnected power grid precludes controlling and operating it as a single object. Subdividing a power grid into a number of internally coherent areas allows to cope with its inherent complexity and to enable more efficient control structures. This thesis focuses on discovering the power system structure to facilitate the definition of control areas for wide-area monitoring, protection and control (WAMPAC) applications. Graph partitioning is a well-developed discipline whose potential is not fully recognized in the power system domain. Particularly, spectral graph partitioning methods are shown to be very promising. Their efficiency is first demonstrated by accurately selecting the number and extent of control zones for secondary voltage control (SVC). Next, it is shown that grouping generators with similar slow rotor angle dynamics can also be efficiently tackled through spectral graph partitioning. The final topic is constrained graph partitioning subject to node grouping constraints, which is related to intentional controlled islanding (ICI). As both solution time and accuracy are critical for ICI, a new polynomial-time heuristic algorithm is proposed that is more accurate than comparable state-of-the-art methods. @en

In recent decades, the electrical power system has evolved into a new phase, in which the renewable energy resources are massively integrated into the grid. This change is mainly inspired by global policies that intend to reduce greenhouse gas emissions and decrease the society’s reliance on fossil fuels by replacing them with sustainable energy sources. The good examples are the European Network of Transmission System Operators for Electricity (ENTSO-E) that intends to integrate a high degree of renewables in Europe’s energy system, and the West-East Electricity Transmission Project that delivers wind energy from the northwest to the southeast of China. One important technology used to connect renewable energy resources is the high voltage direct current (HVDC) system based on the voltage source converter (VSC). Aside from the simple point-to-point HVDC link, the multi-terminal HVDC (MTDC) system is another option to connect these remote energy resources. In the MTDC system, the generation units are usually unsynchronized turbines that are interfaced with powerelectronic- based converters. As such, the responses of theMTDC system after faults occur are drastically different fromthe conventional AC systems that are based on synchronized generators. Since the development of an MTDC system is an important process, the research on the matter must be carried out. In an electrical power system, the transient events refer to a system’s response shortly after disturbances occur, such as the generation loss, the load shedding, the transmission line tripping, and the fault. This thesis focuses on the MTDC system’s protection based on the system’s transient events after faults. Due to the low impedance of the DC system and the low inertia of the HVDC converter, a fault in the DC system can spread quickly throughout both the DC and AC sides. Usually, the transient behavior of the HVDC system must be observed within severalmilliseconds, and it is a challenge to simulate the transient phenomena of a large HVDC system. The reason is that the accuracy of the electromagnetic transient (EMT) simulation heavily depends on how detailed the modeling system is: an extremely detailed system, such as one based on physical features of the semiconductor, cannot be modeled smoothly in the EMT application, while a too much simplified system cannot ensure accurate simulation results. Therefore, it means that a compromise must be made between modeling efficiency and accuracy. Consequently, this thesis implements an efficient method that ensures the efficient simulation of large-scaleMTDC system and its accurate transient phenomena. By using this method, the responses of an HVDC link after faults occur can be determined. More importantly, they can be classified into different stages, and the thesis explains themechanism of each stage. Furthermore, the thesis discusses the impact of grounding methods on the HVDC converter’s post-fault responses. @en

This thesis aims to provide insight into the necessary power system operation and control developments to facilitate a sustainable, safe and reliable electric power supply now and in the future. The primary objective is to enhance the interconnected power system situational awareness with the aim of reinforcing the reliability of power systems. First, the thesis elaborates on the existing and emerging operational challenges of modern power systems and identifies the required power system developments to overcome them. Next, it focuses on state-of-the-art Synchronised Measurement Technology (SMT) supported Wide-area Monitoring Protection and Control (WAMPAC) of power systems. In this context, a cyber-physical experimental testbed for online evaluation of the emerging WAMPAC applications under realistic conditions is developed. Following, to fill the scientific gap between the IEEE Std. C37.118-2005 (communication part) and IEEE Std. C37.118.2-2011 specifications and their implementation, the MATLAB supported Synchro-measurement Application Development Framework is developed. Next, to improve situational awareness of power systems, two SMT-supported algorithms are proposed. The first algorithm is suitable for online detection of disturbances, observed as excursions in SMT measurements, in AC and HVDC power grids. Whereas the second algorithm is suitable for online identification of grouping changes of slow coherent generators in an interconnected power system during quasi-steady-state and the electromechanical transient period following a disturbance. Finally, further research directions towards the Control Room of Future are presented. @en

The development of large offshore wind power generation in the North Sea has been significantly accelerated in the last years. The large distance from shore in combination with the need for large transmission capacity has raised the interest for the voltage source converter high voltage direct current technology (VSC-HVDC). Transmission system operators in order to ensure high degree of the power system security of supply, impose strict grid connection requirements to offshore wind power plants and their HVDC transmission. Based on these boundary conditions, the overall research objectives that have been assessed in the context of this thesis include the following. Assessment of the state of the art coordinated fault-ride through strategies for offshore wind power plants with VSC-HVDC transmission. Analysis of unbalanced grid faults for wind power plants with VSC-HVDC transmission. Investigation of the effect of negative sequence current control for onshore and offshore AC faults. Analysis of the effect of typical grid codes on the power system voltage and rotor angle stability. The developed methodologies, models and control schemes proposed within the context of this thesis could facilitate the analysis and stable operation of transmission systems with VSC-HVDC connected offshore wind power plants. @en

Submodules are the building blocks for MMC-type HVDC converters and therefore of utmost importance for converter reliability. In order to unlock smarter maintenance strategies for submodule semiconductors, the technical condition of the semiconductors needs to be estimated to form a health index. Besides the non-project-specific traditional health index methods, a complete practical implementable data-driven lifetime estimation approach for individual converters is needed to determine the exact remaining useful lifetime of all submodule semiconductors. The methodologies should finally explore a new research direction in the optimization of the converter lifetime considering maintenance intervals. This thesis presents a health index methodology applicable to submodule semiconductors in modern MMC-type HVDC converters. The ON-state collector-emitter voltage is used as a condition indicator and external influences are neglected with electrical and thermal models. These models are needed to estimate the junction temperature in the submodule semiconductors due to the temperature-dependent ON-state collector-emitter voltage. A novel lifetime optimization methodology is presented that determines the submodule that is near its end-of-lifetime and should be replaced in the next maintenance interval. In order to optimize the converter lifetime, the selected submodule is switched more frequently based on a selection window generated from the submodule insertion vector. Switching this submodule more frequently can ensure that it fails exactly at a determined time instant and allows other submodules to be switched less frequently extending their remaining useful lifetime. Finally, a complete data-driven lifetime estimation methodology has been described that uses available measurements in existing MMC-type HVDC converters. Based on the converter load profile and the semiconductor specifications, estimations are made on the submodule semiconductors’ lifetime. Simulations show the significant influence of the DC-pole current based on different voltage class semiconductors and their limitations considering the minimum required lifetime.