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.

In this master thesis, the design and implementation of a high-voltage switch using series-connected Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) is discussed. A high-voltage switch is needed for applications such as high-voltage DC converters. Multilevel modular converters (MMCs) can also aid in the voltage-blocking capabilities of converters. MMCs use multiple submodules to block the full voltage. Every submodule thus only blocks a part of the full voltage. Each submodule needs multiple components that can be expensive, like voltage sensors and gate drive circuitry. By having the submodules block a higher voltage, fewer components are needed. By implementing a higher voltage blocking switch into such a submodule, cost and components can be spared by having a lower total amount of submodules. Current technologies of high-voltage switches are MOSFETs, insulated gate bipolar transistors, thyristors or electro-mechanical switches. MOSFETs have the advantage of being faster and have lower losses than the other technologies. The downside of using MOSFETs is that the voltage-blocking capability is lower than the other technologies. This could be solved by connecting multiple MOSFETs in series for a higher blocking voltage. To do this, care has to be taken that the MOSFETs turn on- and off at the same time. They also need to share the voltage equally to take full advantage of the blocking voltage of each MOSFET. A cost-effective way to implement a high-voltage switch using series-connected MOSFETs is to use capacitive coupling. In this method, the gate charge needed to turn the MOSFETs on is stored in capacitors. When the first MOSFET is turned on, the other series-connected MOSFETs will also turn on. This method has the downside that the switch can only be turned on for a limited amount of time (a few microseconds) and that the voltage balancing is dependent on the load, the switching frequency and the parasitics of the circuit. For this reason, a single high-voltage MOSFET was used in this project, even though it can be slower and more lossy than the series-connected switch. An MMC submodule was made using a full-bridge configuration. Additionally required components such as a gate signal generator, power supply, voltage- and current sensors, and fault protection were also designed, built and tested. In this way, a functioning MMC submodule was created that can be used with a capacitor or an isolated transformer as its source.

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.

In 2019 the European Aviation Environmental Report stated showed a relative increase in CO2 emissions of 16% compared to 2005 to 2017. It also stated that an increase of 42% is expected according to current models. Aviation is thus a big sector of the global warming problem. The solution to this is to go full electric. There are already more electric aircraft who decline the use of fuel for aircraft. This project thus attempts to design an electrical architecture for one of these airplanes. This thesis in particular shows the power demand for most the loads on the plane using mostly linear extrapolations, and voltage to current ratio on the system. It also talk about a state of the art electrical motor, and its characteristics, estimated to be available by the year 2038

Electret transducers utilize the electric field generated by an electret, a dielectric with a quasi-permanent embedded charge, to induce charge on an electrode. When the electret is moved relative to the electrode, the induced charge magnitude on the electrode changes, generating a current that can be used to convert mechanical energy into electrical energy. Micro-electret transducers are promising alternatives to conventional electromagnetic transducers for small-scale energy harvesting as they can achieve a high voltage output at low frequencies, can be miniaturized effectively, and can be manufactured using microfabrication methods.

One-dimensional electrostatic models have been developed to predict the power output of electret transducers. However, for micro-electret transducers, fringing fields play a large role in the electrostatic domain. To be able to more accurately predict the output characteristics of micro-electret transducers, a two-dimensional (2D) electrostatic model is proposed. To verify the 2D model, a novel micro-electret transducer is designed. The novel electret design allows the micro-electret transducer to embed charges of only one polarity, increasing the power output of the electret transducer.

The novel 2D model more accurately predicts the power output characteristics of the micro-electret transducer with the voltage output deviating 57%, compared with 317% by the conventional model predictions. Furthermore, the novel unipolar micro-electret transducer achieves double the power output and better charge stability compared with conventional electret transducers.

In 2018 it was estimated that the aviation industry produced approximately 1.04 billion tons of CO2. This was an estimated 2.5% of the total CO2 emitted that year. In order to slow down global warming, big changes need to be made to the transportation industry. This change has already begun with commercialization of electric cars. The next step is clear: fully electric, zero emission air crafts. This projects goal is design a high power propulsion system for an electric aircraft set to launch in the year 2040. This project attempts at predicting how this propulsion system might look like, specifically the electrical architecture. This thesis looks at the battery energy storage system, the wiring system and how to deal with high-voltage phenomena at low pressure. Several simulations are performed to justify design choices and give a visual representation of the different design options.

EU carbon emission targets related to climate change has set in motion a process of transition towards an environmentally clean and sustainable power system. A central focus on this process is the transition from fossil fuel based energy sources to clean Renewable Energy Sources (RES). However, the intermittency of RES (e.g. solar and wind) presents a formidable challenge to achieve a stable and reliable supply-demand balance in grid oper- ations. To achieve high levels of RES deployment, increasing the power system flexibility will be central to accommodate large fluctuations in supply and to cope with peak demand. Prospects of electricity storage technologies have emerged as a potential key technology to manage high levels of RES in the power system.

Recent projections on the cost of electricity storage show a high decrease in the next five years ([1],[2], [3]). As the commercial maturity of batteries might become a reality within the next decade, many questions remain on the role of batteries in the power system, where batteries should be located? What capacity will be optimal? What kind of battery services are the most valuable? How do batteries contribute to the large deployment of distributed RES installations? Significant research has been done on estimating sizing and sitting of storage in power systems. Yet, most of this research treat storage capacity as continuous instead of discrete, i.e. allocating storage by percentages of a total allowed capacity, wherever necessary in the grid. Despite these previous studies have provided interesting contributions on the value of storage in the power system, many of them lack the modelling of power flows, technical limits, or voltage considerations.

This thesis focuses on battery flexibility in medium voltage grids. Specifically, how to define cost-effective strategies to deploy batteries in a medium voltage grid? What is the optimal battery location in a distribution grid? And how do the technical limits of the power grid influence the allocation of storage? To address these questions, an optimization model was developed to simulate half-hourly operational decisions for a distribution grid. The model is multi-period and includes: power flows, diverse technical consideration for different battery sizes, high RES penetration levels, time of use electricity prices (half-hour dynamic prices), load data of actual customers and battery costs. To decide on the battery location, the model employs binary variables to determine the investment and sitting of the battery in a distribution grid. That is, the model is a mixed integer linear program with multi-period features which provides an investment analysis for the cost-effective sitting of batteries in a time horizon of 10 years. The model is implemented to the IEEE 33 bus test system. Results show that in general battery location and size strategies are driven by multiple factors, which can be either fixed or dynamic, like thermal limits and power load consumption, respectively. Some relevant findings are: First, flexibility in terms of power arbitrage delivers costs reductions of around 4% when RES production is low, compared to a No-Batteries case. Moreover, when RES production is high, the reductions in total costs can ramp up to 12% below the No-Batteries case. Also, this model decides to al-

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locate batteries only if they are economically feasible for a 10-year time horizon. These results indicate a potential revenue up to 2.1 million pounds (GBP) based on the investment in batteries. And they are based on battery cost prices from 2008, together with several optimistic projections for the next decade. Furthermore, depending on battery size, RES penetration, RES generation and technical limits, batteries tend to be located for buses at the entrance of branches with high loads. Likewise, line limits and voltage limits proved to be decisive in the election of buses and the number of batteries placed.

On one hand, results show that optimal allocation strategies depend on grid topology features and technical limits, on the other hand, they also have a high dependency on time- varying and unsteady factors (e.g. power generation and loads). The optimal location strategies tend to change and adapt to the dynamics of the system. Moreover, with the exception of the slack bus, every bus in the system turned out to be an optimal location, at least once. These results indicate that batteries might be useful in every bus of the dis- tribution grid, but only if each battery is operated in coordination and cooperation with one another. These insights support the idea of designing local electricity markets. Based on a reflection of this work, we recommend a market design that retrieves day-ahead and intraday DSO-reports of the battery operations and the flexibility that is available in the distribution grid. And also a subsequent structure of market incentives and penalties that maximizes the value of flexibility while keeping non-optimal operations to a minimum.

In short, this thesis contributes with a novel modelling approach that can shed some lights on the optimal battery allocation problem for distribution grids. Moreover, it pro- vides insights on how location affects the value of storage, how optimal locations are affected by multiple technical factors. And finally, it also provide some reflections on the need to collectively, cooperatively and coordinately operate the storage resources in the grid by considering market-based solutions.