The growing number of software vulnerabilities being disclosed is posing a challenge to many organisations. With limited patching resources and only a fraction of the vulnerabilities posing a real threat, prioritization is key. Current prioritization methods, such as CVSS, are failing and are sometimes no better than random guessing. Exploit Prediction Systems (EPS) try to fill this gap leveraging a data-driven approach. Related works in the exploit prediction domain make EPS design decisions based on different methodological assumptions. Some of these assumptions are unrealistic or faulty, yielding models that fail to represent a real world situation.
The first contribution of this thesis is the identification of critical methodological assumptions in EPS design and the magnitude of their effects. Then, as second contribution, EPS performance is optimized under restricting yet realistic circumstances, by exploring different techniques to handle class-imbalance, creating richer textual features and/or leveraging different prediction algorithms. The third contribution of this thesis is the implementation of an open-source framework that enables easy experimentation with different machine learning techniques for exploit prediction.

Six critical methodological assumptions have been identified in the area of realistic data collection, correct processing of data, and proper model evaluation. Experiments show that when adhering to the most realistic assumptions, only a fraction of the predictive power of the evaluated EPS is sustained. Almost all prior works fall victim to at least one faulty or unrealistic assumption, and thereby report overoptimistic results.

Substantial improvements are achieved in the optimization step of this thesis. With an optimized EPS with a F1-score of 0.366, performance is insufficient to justify its deployment in a production environment. With the current level of maturity, exploit prediction could have value as a complementary measure to existing vulnerability prioritization systems. Further improvements and more transparent systems are essential for EPS to be suitable for practical usage.

Wind energy is a growing energy resource in the current energy transition. Massive new amounts are planned to be built in the face of the climate and energy crisis. The current state-of-the-art type-4 Wind Turbines (WT) uses a Fully Rated Converter (FRC) to decouple the rotor speed from the grid frequency. In recent years this type of WT has been involved in so-called sub-synchronous events. The Grid Side Converter (GSC) of the FRC is very similar to other Inverter Based Generation (IBG) such as: Photovoltaics (PV), Battery Energy Storage Systems (BESS) and HVDC-links. As this research is focused on the GSC, it is very relevant to the integration of other Renewable Energy Resources (RES) as well.
This thesis investigates Sub-Synchronous Control Interaction (SSCI), a relatively new phenomenon. The GSC interacts with the grid, which can cause a Sub-Synchronous Oscillation SSO, an oscillation below the system's fundamental frequency. This oscillation can lead to damage, increased components wear or triggering protection systems. After different facets of SSCI are discussed, a new solution is put forward in this thesis. By feeding wide area Phasor Measurement Unit (PMU)-based measurements into the control system of the WT, an algorithm is constructed to mitigate SSCI. This algorithm is tested on the ability to mitigate sub-synchronous event risks.

First, a WT model is selected in the DIgSILENT PowerFactory software to recreate sub-synchronous behaviour. This model is tested in the weak radial grid. The influence of the different control parameters on the sub-synchronous behaviour is investigated and comped to literature studies. Different tools are used for this research. PowerFactory is used for small signal analysis to obtain a linear dynamic model of the system. RMS-time simulations are used to test the oscillatory behaviour of the system. These results are further analysed using eigen-analysis on the linear model and Fourier and Prony analysis on the time simulations.
Then, the same WT-model is implemented in a modified IEEE-39 bus system to see the behaviour of SSO propagation in a transmission network. The results are compared to an analytical method to determine voltage oscillations based on mode shapes. However, as SSCI has a fundamentally different driving force, this method is not valid in this case. In the same transmission network, the influence of grid operations is tested. Different variations are tested: the connection point, power output of the WT, grid loading and disconnection of nearby connections. As all these features can vary during normal operation, it is vital to understand better which circumstances increase the risk of SSO event.

At last, using the knowledge obtained, a new control algorithm is proposed. This algorithm uses wide-area voltage angle measurements. These measurements can be provided by PMUs. A remote signal is fed into the control system. Minimal modifications are made to the control system for this. Additional damping is performed on the local voltage reference angle depending on the movement of the remote signal. This prevents the initialisation of SSCI. This implementation of a WAMC is tested using eigen-analysis and time simulations and shows promising results.

The results of this thesis research are also modelled in the NextGen GridOps Framework of DNV. The framework aims to stimulate a fast deployment of the finding of this thesis research in the field. This is accomplished by sharing knowledge in an accessible, structured environment. This allows taking the findings into consideration for solving the complex problems encountered by transmission and distribution system operators.

Induction motors have a significant role in every aspect of modern living. They are extensively used in every industry because of their robust construction, easy operation, controllable and adaptable features. Therefore, occurrence of faults in these machines are a major concern. The protection schemes implemented in a network plays an important role in the safe operation of the machine. The key component of common protection schemes is a relay that senses abnormalities in the network and separates the faulty section from the healthy network. Large faults such as phase faults, phase-to-phase faults are easily detected as they impact the whole network. However, commonly occurring faults such as stator winding faults, bearing faults, etc. are difficult to detect using the standardised protection schemes. Stator winding faults create localised heating that can rapidly incite phase faults. Thus, additional protection schemes are required to detect them in time. This thesis focuses on modelling and simulation of stator inter-turn faults in an induction motor using Electromagnetic Transient Program - Alternative Transients Program (EMTP-ATP) platform; dynamic testing of a chosen relay at various fault severities and fault resistances. Finally, optimised settings of the chosen relay are suggested for a given medium power induction motor and the results are discussed.

Fast charging technology has accelerated the growth of the electric vehicle(EV) market and attracted significant attention from the industry. Two-stage AC/DC converter system is one of the traditional fast-charging architectures consists of the front-end converter and back-end converter. Numerous researches have developed IGBT-based medium-voltage converter or MOSFET-based low-voltage applications. In this work, a two-stage IGBT-based converter system is proposed in consideration of power switch costs and magnetic component loss.

The Electric Vehicle (EV) charging market is very dynamic. The so-called AC-type chargers can be found confined within the vehicle or on-board. This must be able to withstand the harsh environment with an ambient temperature of above 75℃. Therefore, compact and high-efficiency power electronics and implementing electrolytic-less capacitors in the power range of 6 kW to 12 kW is desired. The operation of the grid-connected power stage with DC active power buffer has become standard in high compact systems. More importantly, this solution eliminates the requirement of high energy storage in the DC-link because the pulsating power is compensated leading to an electrolytic-less capacitor design. As the lifetime of the power converter in high-temperature environments is typically limited by the usage of the electrolytic capacitor technology, a more reliable system is finally obtained with the active pulsating power buffer.

With distributed energy sources becoming prominent, it is expected that new market mechanisms would become necessary to overcome the issues caused by the intermittency of those sources. This research determines the effect of certain market mechanisms, which have been proposed to either incentivize the distributed generation or to reduce their undesirable effects, on power flow of a prosumer household. The prosumer household was assumed to consist of PV generation system, an Electric Vehicle which was capable of V2G and a household battery. The market mechanisms used were Feed-in tariffs, Capacity Mechanism and Frequency Containment Reserve. An Energy Management System which determines both, the optimal system size and the optimal power flow by minimizing the operational costs was used to achieve this. It was observed that different level of feed in tariff affected the optimal system size and the power flow. At high feed-in tariff, the system size was the largest and high grid peak power was observed. Furthermore, the introduction of the capacity mechanism in the form of capacity tariffs per kW led to reduction in grid power consumption and feeding in. Finally, it was observed that the energy management system was able to reserve power for the frequency regulation market. Compared to an uncontrolled case, a reduction of 70.26% in total costs was achieved when the EMS control was introduced. A cost reduction of 52.02% compared to the uncontrolled case was achieved when an additional capacity tariff was also introduced to the control. Finally, introduction of the frequency regulation mechanism in the EMS control led to even further reduction in costs with a drop of 1205.07% compared to the uncontrolled case.

There is an increasing demand for compact onsite dielectric test systems of medium and high voltage equipment. Though there are commercially available mobile high voltage (HV) test sources, they have some important drawbacks such as limitation in voltage capability, complexity in building up the test setup and lack of versatility to test different equipment. Alternatively, the present challenges in these conventional test sources could be resolved by constructing a power electronics based test source. Amongst various converter topologies, Modular Multilevel Converter (MMC) is considered as a suitable topology for this application because of its high efficiency, modular structure, and reduced filter requirement. In order to achieve a compact solution, an oil immersed design of MMC, instead of the typical air insulated converter design is proposed in this master thesis. Oil can act both as a coolant and an effective insulating medium, thereby reducing the dimensions of the test system.
This master thesis demonstrates the feasibility of oil immersed MMC based HV test source, covering both system level and component level aspects. The extent of compactness of the test source in oil was estimated at a system level. It was found that for the given trailer dimensions, the voltage capability of test source is around 4 times higher in oil when compared to air, This shows the effectiveness of oil as an insulating medium. The feasibility of oil immersed converter design depends on the degree of compatibility of its components under oil. Hence, experimental investigation was conducted on Insulated Gate Bipolar Transistor modules (IGBT) under oil as they are considered to be a pivotal component in MMC. Preliminary results show the penetration of oil into the IGBT chip surface. Despite oil migration, the operation of IGBT was not hindered during the test. Based on the results obtained from experimental work, a road map of future tests is suggested that need to be performed to realize an oil immersed HV mobile test source.

The world is going through an energy transition towards decentralized electricity generation like photovoltaic systems and new loads like electric vehicles, which contribute to the variability of the operation state of distribution systems. To ensure future operation under safe and efficient conditions, it becomes increasingly important to have precise knowledge of the state of the grid. For this, Distribution System State Estimation (DSSE) has extensively been discussed in the literature. However, distribution networks at present are not only characterized by sparse measurement locations, which makes application of DSSE difficult due to un-observability, but also the anticipated highly stochastic load profiles will affect the accuracy of the system state estimate. Therefore, it is now necessary to assess how the DSSE accuracy is affected by different factors that result from continuous changes in the consumption pattern and measurement scheme. For this purpose, an improved measurement scheme is proposed in this thesis, that not only considers the meter placement, but also the required measurement intervals, to establish a minimum required accuracy level of the state estimator under stochastic conditions. The work presented in this thesis starts with a sensitivity analysis of the Weighted Least Square (WLS) DSSE algorithm applied on a synthetic model of an existing 10kV distribution network in the Netherlands, with respect to the stochasticity of the load profiles applied. Based on this analysis, an algorithm is developed to determine the measurement configuration that satisfies a predefined maximum DSSE error. The effects of the following parameters on the state estimation accuracy are assessed: i) Percentage of pseudo measurements ii) Stochasticity of the applied load profiles iii) Interval of measurements The analysis can be used to recognize the conditions at which the DSSE results become unacceptable. From here, a novel algorithm for determining a proper measurement scheme is presented, considering the existing meter placement and the required interval of measurements to compensate for the uncertainty in the load profiles. The focus is on determining intervals of measurement to establish a minimum predefined DSSE accuracy level, more than placing additional meters. The method first establishes the meter locations to achieve observability. Then, the algorithm uses the SE error resulting from Monte Carlo simulations to improve the accuracy. The measurement intervals are determined based on the analysis of sensitivity to the interval of measurements. This results in a measurement configuration that maintains the SE error within the acceptable range at every instant of time. It is tested on the 10kV distribution network model, in the future scenario with high stochasticity in load profiles resulting from the projections of the energy transition for the year 2040. The results will show the effectiveness of the proposed algorithm for the determination of measurement scheme. This is important for the network operators who would use the results of the SE algorithm to make decisions on the grid operation.

Access to electricity is a key actuator in order to tackle poverty in areas of limited resources. While the population without access to electricity has a decreasing tendency, still almost 1 billion people continue to live without this basic amenity. This thesis has been carried out at the company DC Opportunities as part of the rural electrification project. On this field, the main activity focuses on developing cost-effective DC solutions in the form of a solar home system which consists of a total of 4 devices including low-power LED lights, a solar charging station, a high-power rate power bank and a power hub. The report analyses various existing electrification projects identifying the characteristics of their approaches in order to recognize the shortcomings of market available products and to build a design criterion. Given that the main target application is aimed at rural areas, a modular approach has been the base of the design criterion with the purpose of tailoring the SHS to developing countries with limited resources. The project analyses each step within this modular process together with the power electronics involved in every stage. The main objective of the project is to perform direct charging between the charging station and the power bank, which consists in feeding power directly from the bus voltage of the charging station into the battery cells with only one active converter. This feature is implemented as a result of the introduction of the power delivery protocol released together with the USB type C connector . This offers a wide variety of possibilities which includes negotiable voltage levels ranging from 5 to 20V. The first element taking part in the direct charging is the charging station .This thesis addresses the challenge of designing and building a circuit with dynamic adjustment of voltage and current in a cost-effective and reliable manner. By adding a digital to analogue converter and 2 operational amplifiers, it is possible to add this feature to a wide range of standard voltage converters available in the market. The report analyses this circuit in 3 steps: first with circuit theory, secondly by simulation and eventually by including the results obtained in an empirical test implemented in one of the prototypes. The power delivery protocol is also beneficial for a power-bank application, which is the second element of the direct charging. It is one of the purposes of the thesis to evaluate the performance of direct charging. Eventually, the report presents the main conclusions derived from the analysis of the aforementioned elements and also covers future lines which include improvements to be implemented within the components of the solar home systems.