As the European grid transitions towards renewable energy targets, new system stability phenomena are being observed through the electrical power system. The share of renewable generation is growing quickly as synchronous machine-based power plants are phased out. Unlike traditional synchronous machine plants, these Inverter-Based Resources (IBRs) do not provide inherent synchronous mechanical inertia. Consequently, the overall system inertia is decreasing, posing a threat to the frequency stability of the system. This trend is observed worldwide and addressed by organisations such as ENTSO-E through the introduction of future minimum inertia thresholds.

Grid-forming (GFM) technologies have emerged as a solution, providing an immediate active power support after a disturbance, via control methods. These technologies enable IBRs to contribute to frequency stability and mitigate the Rate of Change of Frequency (RoCoF).
The share of distributed energy resources has also grown, with utility-scale renewable Power Park Modules (PPMs) connected to the Medium Voltage (MV) network. These PPMs could help unlock further active power frequency support from the MV network. However, whether this support effectively supports the transmission system remains insufficiently explored.

This thesis assesses the effectiveness of synthetic inertia provided to the transmission network by GFM-controlled IBRs connected at the MV level. The study explores the metrics to assess the effectiveness of the synthetic inertia at the MV-HV interface, investigates the technical constraints of the provision from the distribution-connected resources and offers mitigation measures. Additionally, the comparison of the synthetic inertia support from the HV and MV-connected GFM assets is done.

Firstly, using DIgSILENT PowerFactory, a test benchmark is developed, where the response of a storage PPM with grid-forming controls is evaluated under different disturbances, in order to tune the GFM dynamic models and ensure compliance with grid code requirements. To test the synthetic inertia support of PPMs in a realistic model, a combined transmission and distribution system model is developed from an initial model, which has been adjusted to represent the Dutch grid characteristics. Multiple scenarios and disturbances are simulated with the GFM PPM connected at various locations within the MV network to explore the limits of synthetic inertia support.

The results demonstrate that for a frequency disturbance, the RoCoF and the frequency nadir/zenith improve regardless of the PPM connection point. However, the magnitude of the improvement is dependent on the available active power headroom and the current capabilities of the PPM. A critical limitation was observed regarding the parallel provision of active and reactive power when the PPM is connected to the MV grid. For connection points far from the point of interconnection, voltage stability became more important, as MV buses are more sensitive to active/reactive power injection. During large frequency disturbances, the PPM's active power and reactive power demand grew, which led to current limits being hit, as the PPM sustains the active and reactive current. This suggested a need to enhance voltage and reactive power control or alternative voltage stability methods to support the voltage during frequency disturbances for distribution-connected grid-forming units. ... Read more

The increasing penetration of converter-interfaced renewable energy sources (RES) in modern power systems has significantly reduced synchronous inertia, posing challenges to short-term frequency stability. As a result, fast active power response (FAPR) from power electronic converters, such as modular multilevel converters (MMCs) connected to offshore wind power plants (WPPs), has become increasingly important. However, transmission system operators (TSOs) often lack access to proprietary converter control settings, making it difficult to assess the available frequency support capability of these resources in real time.
This thesis proposes a signal-record-based estimation method using an artificial neural network (ANN) to quantify the fast active power response of a mixed generation system consisting of synchronous generators and MMC-interfaced wind power plants. The method relies exclusively on measurable system signals, such as system frequency, rate of change of frequency (RoCoF), and pre-disturbance operating conditions, without requiring explicit knowledge of converter control strategies.
A comprehensive synthetic dataset is generated using detailed RSCAD-RTDS simulations of a multi-terminal offshore HVDC network connected to a reduced onshore AC system. The dataset captures a wide range of operating conditions by systematically varying key system parameters, including
Synchronous generator inertia, initial loading levels, and wind speeds at multiple offshore WPPs. Controlled load-step disturbances are applied to excite system frequency dynamics and corresponding fast active power responses. An ANN is trained to estimate the active power response trajectories of both the MMC and the synchronous generator following a disturbance. The results demonstrate that the proposed approach can accurately infer fast active power response characteristics from frequency measurements alone. This work provides a practical estimation tool that supports TSOs in assessing frequency support capability in converter-dominated power systems under uncertain and time-varying conditions. ... Read more

This thesis presents an implementation method for optimizing the external geometric dimensions of an existing wireless power transfer (WPT) coil through multi-objective optimization. Wireless charging systems have been widely applied in daily electrical devices, and the trade-off between the geometric dimensions of the charging system, its charging efficiency, and power transfer capability is a key challenge faced by designers and manufacturers. During the design process, the evaluation methods for the power, losses, weight, and size of wireless charging coils significantly influence the product design cycle as well as the labor and time expenses associated with the design process. Based on an existing WPT coil sketch, this thesis designs and verifies the feasibility of implementing a multi-objective optimization method. The proposed optimization method is developed based on given power transfer requirements and external dimension constraints. A 3D geometric model is reconstructed using the SALOME open-source modeling platform, where meshing is performed to prepare the geometry for finite element analysis (FEA). The ElmerFEM open-source finite element solver is then employed to evaluate the coil's performance from multiple perspectives. To achieve large-scale iterative optimization for a single performance evaluation, a multi-objective constrained optimization framework is formulated in a Python environment, where constraint equations are defined and deployed using Pymoo. To address the challenges encountered in the implementation of this design method, this thesis primarily considers two key aspects. The first is the automated performance evaluation of a given coil geometry using Python. Given a set of geometric parameters, SALOME can be automated using Python scripts to generate the geometric model and perform mesh generation through a descriptive approach. The generated mesh files are then processed by the ElmerFEM solver, which, supported by SIF configuration files, computes the required physical quantities for performance evaluation. The obtained physical quantities are refined through a proposed computational method to extract the objective data necessary for multi-objective optimization. The second aspect is the multi-objective optimization of coil dimensions using Pymoo. Pymoo is a well-established open-source multi-objective optimization framework. It enables designers to define problems, establish constraints, and formulate quantitative equations, thereby integrating and binding optimization cases with real-world applications. By leveraging this framework, the desired optimization design is effectively achieved. ... Read more

The research is conducted via collaboration betweenthe Delft University of Technology, Netherlands and Alewijnse Netherlands B.V. The objective of this work is to verify the techno-economic feasibility, of a proposed hybrid marine vessel configuration. This proposed hybrid solution now requires an upgraded Energy Management System, to efficiently make use of the distributed energy resources on the grid. Verification of these results are conducted in real time using the Typhoon Hardware - in - Loop (HIL) platform, to create a Digital Twin of the proposed hybrid marine vessel. The designed digital twin, with modified EMS control, is specifically aimed to optimize vessel operations in the DP2 mode. The designed EMS control ensures the vessel operates it's diesel generators at their optimal loading points, in combination with the battery energy storage system. This operation effectively reduces fuel consumption, reduces maintenance costs for generators and green house gas emissions. The findings of this research contributes to the field of green ships and marine industry decarbonization. ... Read more

This thesis investigates the formation of hotspots in single junction amorphous silicon thin film solar modules through experimental methods. Employing electroluminescence (EL) imaging and infrared (IR) imaging, the study aims at identifying and classifying defects that can be used to predict hotspot formation and assesses the endurance of different sized modules.
To predict hotspot formation on small 30 by 30 cm monolithically interconnected modules, the research first categorises shunts into four different classes based on their severity and localization (Mode A, Mode AB, Mode B and Mode C). Mode A defects are severe and cover a large area, Mode B defects are severe and localized, Mode AB defects are severe and rather localized and Mode C defects are weak and localized. It was found that only shunts that are severe and localized lead to the formation of hotspots (Mode B and rather localized Mode AB). Since no hotspots formed at locations without predictors EL based shunt classification has proven to be an effective predictor with high predictive accuracy for hotspots.
Industrial modules with a dimension of 190cm by 30 cm exhibit similar defect behavior, however the interaction between multiple hotspots within one cell leads to some exceptions. When multiple defects are located within the same cell, the most severe and localized defect forms a strong hotspot, while the other defects either form weaker hotspots or no hotspots at all. Due to a higher current level also Mode C defects can lead to hotspot formation when they are the most severe defect within a cell. Furthermore locations that show defect cluster or current crowding also experience strong hotspot formation. Lastly, shunts that were found to be originating from scribe defects are prone to form strong hotspots.
EL based shunt classification has therefore proven to be a reliable predictor for hotspot formation on modules of different sizes. Furthermore this procedure did not induce any performance losses on the modules. However the EL imaging procedure itself is quite time intensive and therefore not suitable as a quality test that could be implemented at the end of a production line.
Using IR imaging in reverse bias, hotspots can reliably be identified on small and large modules. Due to higher current levels, hotspots can easier be identified on large modules. However high reverse currents can lead to significant damage and loss of performance of the modules. IR imaging in reverse has proven to be a faster alternative for hotspot detection, suitable for production line integration.
The findings contribute to improved defect identification and hotspot prediction techniques, enhancing the reliability of solar module manufacturing and maintenance processes. Future work should focus on refining defect classification and exploring the behaviour of hotspot formation and impacts on reliability in field applications. ... Read more

To utilize electronic power converters for water electrolysis in industrial electrical networks, reliable testing methods are required to ensure safe control operation as malfunctions can instigate hydrogen explosion and fierce electrical hazards. In this thesis, Digital Twin modeling via OPAL-RT software and hardware is compared to Simulink and PLECS simulation methods by creating the same power-to-power hydrogen network for all three with a Dual Active Bridge, a Medium Voltage DC grid, and an Alkaline electrolyzer whilst utilizing PI control via single phase shift modulation.

The Digital Twin model showed great control tuneability, while the PLECS model showed superior control performance, modeling complexity, error occurrence, and time-based performance for the designed specifications. It was concluded that the Digital Twin model needs to be developed further or reassessed
to outperform the other modeling methods. The recommendations made included re-evaluating the OPAL-RT Digital Twin results for different signal measurement methods and validating the OPAL-RT Digital Twin’s performance by comparing the results with other Digital Twin brands. Future work suggestions included creating a hardware-in-the-loop system and expanding on the current network design to include all components of a power-to-power hydrogen network. ... Read more

Board-level reliability (BLR) looks at the reliability problem in the package and PCB interconnection, which is an important topic in microelectronics. The current criterion in the BLR test is to look if the connection is open, which can only detect the failure and there is no available method that can detect the degradation of the solder joints. This project mainly focuses on the degradation process of solder joints in board-level vibration tests and thermal cycle tests.

Special methods and test programs are developed tailored for two test vehicles, and some of the test results are collected and analyzed. Assisted by the failure analysis technique, the physical change of solder joints can be observed.

Findings in this study show the parameter shift during the solder joint degradation and also the mathematic model that describes the relationship between the crack of the solder joints and resistance increment.
... Read more

Remotely operated vehicles (ROV) are used for the inspection, maintenance and repair of submarine and offshore cables, subsea exploration, and rescue operations. ROVs are powered by umbilical cables, which have to withstand electrical, mechanical, and thermal stresses. This thesis investigates the effect of repetitive bending on the insulation properties of ROV umbilical cables for medium voltage.

Umbilical cables with XLPE, polypropylene, and HDPE insulation were mechanically aged using a cyclic bend-over-sheave setup, after which the dielectric properties were analysed using electrical breakdown tests and several diagnostic tests, such as partial discharge analysis.

The cables with XLPE and HDPE insulation showed delamination of the conductor–insulation interface, which resulted in increased partial discharge activity, a reduced breakdown voltage, and a significantly decreased lifetime. For HDPE, the lifetime power law exponent 𝑛 dropped from 18 to 9 after 23,000 cycles of mechanical ageing. Polypropylene, on the other hand, did not show delamination but an increase in dielectric-bounded cavities with mechanical ageing. ... Read more

Lightweight PV modules offer a solution to the constructional weight limitations of rooftops. PV modules made by Solarge are considered as one the lightweight PV module solutions. The aim of this thesis project is to analyse and compare the thermal- and electrical behaviour of the polymer modules with glass modules. Also, the thermal- and electrical behaviour of polymer modules with a white backsheet are compared with polymer module containing a black backsheet. First, an experimental setup was designed and installed. The PV modules selected for the installation were polymer and glass PV modules both containing half-cut cells. The white- and black backsheet polymer modules contained full PV cells. All PV modules had a pre-installation check with separate electroluminescence and indoor I-V measurements to determine the performance values under standard test condtions.
The first thermal- and electrical behaviour comparison was performed for the polymer- and glass modules over the period of 1 June till 30 September. It was found that increasing wind speed affects the cell temperature of glass modules most compared to the polymer modules. On the other hand, the level of irradiance affects most the cell temperatures of the polymer modules. Overall, it was found that the solar weighted average cell temperature was higher for the polymer modules, 39.1 - 39.3∘𝐶, compared to the glass modules, 36.9 - 37.2∘𝐶. Regarding the electrical behaviour, it was found that the mean energy yield of the polymer modules was 4.69% lower compared to the mean energy yield of the glass modules. Also the the glass modules had a higher daily performance ratio, 91.5 - 92.2%, compared to the polymer modules, 87.5 - 87.7%. Part of the difference in energy yield and performance ratio origins in the higher cell temperature for the polymer modules. However, a normalised current difference was found as well, that root in optical losses.
The second thermal- and electrical behaviour comparison was performed for the white backsheet and
black backsheet polymer modules over the period of 1 June till 30 September. It was found that
increasing wind speed affects the cell temperature of black backsheet polymer modules most compared to the white backsheet polymer modules. On the other hand, the level of irradiance affects the cell temperatures of the white backsheet- and black backsheet polymer modules with a comparable heating slope. Overall, it was found that the solar weighted average cell temperature was comparable with 8.3 - 38.7∘𝐶 for the white backsheet polymer modules and 38.1 - 38.7∘𝐶 for the black backsheet polymer modules. Regarding the electrical behaviour, it was found that the mean energy yield of the white backsheet polymer modules was 1.54% higher compared to the mean energy yield of the black backsheet polymer modules. Also, the white backsheet polymer modules had a higher daily PR, 87.7 - 89.1%, compared to the black backsheet polymer modules, 86.8 - 87.8%. The small difference in performance was not directly found in the normalised current and voltage. Measurement uncertainties are therefore seen as a possible root for this difference.
... Read more

Thin-film solar cells are second-generation solar cells and they are gaining more traction than the first-generation c-Si solar cells. This is due to the advantages they have over conventional solar cells. The advantages are that they are lightweight, flexible, cheaper and also have better aesthetics than conventional solar cells. Thin-film cells are being processed on a flexible aluminium substrate at HyET Solar which is a Netherlands based company. Their processing technique involves depositing thin-film silicon solar cells on a temporary flexible aluminium substrate. The cells are laminated on a plastic carrier foil and the Al substrate is etched away. HyET solar produces tandem and amorphous single-junction solar cells. For their tandem solar cells, the bottom layer is crystalline. Hence, single-junction crystalline silicon cells are developed at TU Delft to incorporate them into the tandem modules at HyET solar. The crystalline silicon cells deposited at TU Delft are characterized using SEM and raman. The cells deposited at Delft are processed at HyET solar and characterized. Upon characterization, the crystalline fraction and deposition rates increase with an increase in deposition power in the intrinsic layer. The crystalline fraction and deposition rate of a cell does not change by changing the cell thickness of the i-layer. The cell characteristics also change with a change in the silane flow rate in the i-layer. The optimal deposition power with an optimal crystalline fraction was 40W and the corresponding silane flow rate was 3.3 sccm. The deposition rate for a 40W deposition power was 0.41 nm/s. Cells deposited using these parameters were then processed at HyET solar. The cells developed at HyET Solar was shunted. The cause of the shunts was critically analyzed and depositing an amorphous n-layer with a thickness of 80nm seemed to get rid of the shunts. The JV characteristics of the cell were not significant under illumination but the cells displayed diode behaviour when measured in the dark (dark JV). All the deposition parameters except for the deposition time (thickness of deposition) have been optimized for an nc-Si single-junction cell. Further dedicated research on thin-film silicon cells can be performed to improve the electrical characteristics of the cell. ... Read more

With the rise of various renewable energy sources, comes the possibility for combining the different type of sources together to balance their shortcomings. The goal is to find a renewable energy system that can be reliable year-round and be accessible for everyone. This research tries to model such a system. A model of a grid-tied PV-battery-electrolyser-fuel cell power system, which is based on a continuation of a series of master thesis projects, was expanded to include a neighbourhood with a fully electrical load or a combination of electrical and hydrogen loads. This model was developed to answer the following question. What is the techno-economic feasibility of a grid-tied PV-battery-electrolyser-fuel cell power system for a household area in the Netherlands which is either fully electrical or hydrogen integrated? This hybrid system is simulated by using the graphical interface program TRNSYS. The system size of the PV, batteries, electrolyser, fuel cell and hydrogen gas storage tank are optimised by the GenOpt, an add-on for TRNSYS. The optimisation algorithm will try to find the lowest levelised cost of energy(LCOE) while keeping the system self-sufficiency ratio(SSR) around 1 [%]. This will mean that only 1 [%] of the load is allowed to be extracted from the grid. The simulation is based on a neighbourhood that consists of 630 houses located in Pijnacker Netherlands. All houses will be equipped with a roof mounted solar PV system with centralised batteries, electrolyser, fuel cell and a hydrogen storage tank. If needed the model can be extended to include a small solar park next to the neighbourhood. The model will simulate two scenarios for a simulation time of one year, the first being that the neighbourhood is fully electrical and the second for a neighbourhood with integrated hydrogen gas in its consumption. The first one is the base, with only the electrical load demand of houses. Then the load profile will be extended by adding vehicle to the neighbourhood, including the heat demand of the house. These additional load profiles will either be electrical energy based for the fully electrical scenario or hydrogen gas based for the integrated hydrogen scenario. To estimate the economic development of this hybrid system, a price projection of PV, battery, electrolyser, fuel cell, hydrogen heating, heat pumps and inverters components were determined for the years 2020, 2030, 2040 and 2050. a, the cases will all be simulated for these years. The economic analysis will be over the systems lifetime, which is 25 years. Before the cases were simulated the model undertook a sensitivity analysis. From this resulted that the simulation start time can be moved from the 1st of January to the 2nd of March to relief the storage tank of getting depleted at the start of the simulation. A battery discharge constraint was lifted and this led the batteries to provide more energy. A forecasting method was applied to the system that effectively reduced the electrolyser on/off cycles by 60 [%], which increased the lifetime of the electrolyser component. From a technical feasibility analysis of the cases, it resulted that the integrated hydrogen scenario was not technical feasible with the PV system (roof mounted with the PV park) of this model. All the integrated hydrogen scenario cases resulted in a depleted hydrogen storage tank, which forced the system to buy the hydrogen demand externally. The system will rely on an external source more than the allowed 1 [%] (hydrogen gas SSR >> 1 [%]) of the load demand. From the fully electrical scenario the 2020 C-E-(V+H) case resulted not be technical feasible with a SSR value of 2.1 [%]. All the other cases were technical feasible. From an economic and cost perspective, the cases resulted that the LCOE reduced with the years. The lowest LCOE value found was for the C-E-(Base) case, which reduced from 0.44 [€/KWh] in 2020 to 0.21[€/KWh] in 2050. The cost breakdown of the cases resulted in the PV system and the storage tank to be the most expensive components of this system. Due to the fact that the C-H2-(H) case had to buy a significant amount of hydrogen from an external source, this became a significant expensive cost of the system. Comparing the two scenarios resulted that the integrated hydrogen scenario system sizes were smaller, but this is an effect of the system being more eager to buy hydrogen gas then to expand the hydrogen production components. As both scenarios had different SSR values of their respected energy demands, a conclusion of which scenario is more beneficial will be inadequate. ... Read more

Shading on photovoltaic modules is practically inevitable, especially in urban environments. The shadows cast by neighbouring objects on the solar panel force shaded solar cells to operate under reverse bias. In this case, instead of generating power, the shaded solar cell dissipates power, which is converted into heat and may induce the formation of hot-spots. Many attempts have been made to improve the shade tolerance photovoltaic modules. In this work, we focus on solar cells with low breakdown characteristics to build shade tolerant photovoltaic modules. These types of solar cells allow the current flow at low reverse bias voltages (around −4 V). The main design challenge is to maintain high conversion efficiencies while achieving low breakdown voltages.
In order to design shade tolerant photovoltaic modules, the carrier transport mechanisms in the solar cell under reverse bias conditions are firstly investigated. A robust simulation template is created in Sentaurus TCAD to perform a parametric evaluation, including both the structural and operating parameters, of the device I-V characteristics. The silicon heterojunction interdigitated back contact solar cell with a silicon oxide passivation layer is among the most promising cell structures to achieve both the low breakdown voltage and the high efficiency. Band-to-band tunneling happens between the heavily doped p+ and n+ regions at the rear side, which allow charge carriers to recombine without entering the bulk of the solar cell. We analyze the effect of the tunneling mass, the gap distance and the dopants penetration length on the forward and reverse I-V curves. Simulations suggest that it is possible to design high efficiency solar cells with breakdown voltages as low as −1.2 V. In addition, device performances under different temperature and irradiance conditions are analysed for the purpose of further investigations on the system level.
While this research study is mainly focused on the performance of solar cells, the results presented in this thesis facilitate comprehensive system level energy yield analyses of shade tolerant photovoltaic modules with low breakdown voltage solar cells.
... Read more

We are on the verge of a global energy system revolution. By signing and ratifying global treaties, the groundwork for this revolution is laid. The objective is to limit global warming to two degrees Celsius above pre-industrial levels and stabilise greenhouse gas concentrations at a level that would prevent dangerous anthropogenic interference with the climate system, before 2050. This requires a carbon-free electricity system, which implicates that existing fossil sources of electricity need to be replaced by renewable sources. Most of these sources are weather-dependent and follow seasonal patterns. This leads to a variable, uncertain, and uncontrollable electricity supply. Energy system integration is posed as a key concept to provide the much-needed flexibility to the electricity grid and has been the subject of extensive research. However, there still is a considerable need for further research in the field of energy system integration. Part of the research gap is validation and substantiation of the proposed energy system integration policies and investment decisions. An indispensable component for filling the research gap is a numerical model of the energy system.

In this context, the author of this thesis developed a numerical model of the Dutch high-voltage electricity grid. The model can be used to analyse proposed energy system integration policies, optimise the electricity system investment decisions, and prioritise the bottlenecks in the electricity system. The model is used to analyse the effects of several power and heating sector integration scenarios for 2050.

The model is constructed in the pandapower framework. The framework is coded in the Python programming language. The model parameters are based on open data and the model input is derived from national sector outlooks and the Energy Transition Model from Quintel Intelligence. Due to the unavailability of operational data from the reference system, the accuracy of the model is determined by evaluating the underlying assumptions and performing a sensitivity analysis. Once the model is validated, the effects of power and heating sector integration on the Dutch high-voltage electricity grid are analysed and the bottlenecks are identified. The results show a substantial increase in grid loading. The highest grid loading occurs when a large portion of the heating demand is electrified, and a large portion of the electricity supply is generated by variable renewable energy sources.

The bottleneck analysis of power and heating sector integration scenarios presents one of the use cases of the created representative model of the Dutch high-voltage electricity grid. As the model is based on open data, it is the intention of the author to make the model publicly available as well. This allows other entities to perform a broad range of analysis on the electricity system. ... Read more

The development in solar cells began with wafer based cells, also called the first generation photovoltaic technology. Most of these wafer based cells were made of crystalline silicon. As a crystalline silicon cell must be relatively thick to absorb most of the incoming energy, the second generation (thin film solar cells) was introduced. In the third generation the focus is more on achieving high efficiencies at low production costs. A way to achieve higher efficiencies is by the use of multi-junction devices. In such devices, different sub cells are stacked onto each other and in this way a larger part of the solar spectrum can be utilized. Moreover, the fabrication costs of multi-junction devices can significantly be reduced by using a cheap processing technique, like plasma enhanced chemical vapor deposition (PECVD).

When germanium and germanium-tin are passivated by hydrogen atoms, Ge:H has its theoretical bandgap in the 0.9-1.1eV range and GeSn:H its bandgap in the 0.6-1.0eV range. The use of such low bandgap materials facilitates absorption of photons in the infrared spectrum, what reduces the non-absorption losses. Their low bandgaps make them perfect candidates to act as the absorber material in a bottom cell in a multi-junction device. Both materials can also be processed by PECVD.

In this thesis about 100 Ge(Sn):H films were PECVD processed in the CASCADE reactor located in the Else Kooi Lab. The objective was optimizing the plasma conditions to obtain device quality thin films. A device quality bottom cell material must fulfil some requirements, like having a low bandgap, being intrinsic and having a high photo response. The influence of various deposition parameters was investigated to characterize their effect on the material properties.

It was found that a densification of Ge(Sn):H generally lead to lower bandgap energies. Densification of these materials can be caused by increasing the substrate temperature (in the 250-300°C range). Next to this, a decrease in hydrogen dilution (in the 100-400 range) also leads to lower bandgap energies for the amorphous Ge(Sn):H films. By combining a substrate temperature of 290°C with a hydrogen dilution of 100, promising a-Ge:H films were processed containing refractive indexes above 5.3, optical bandgap energies below 1.1eV, activation energies above 330meV and dark conductivities below 5∙10-4 Ω-1cm-1. The material properties of the processed a-GeSn:H films were even closer to a device quality bottom cell material. Nevertheless, processing device quality GeSn:H layers remains challenging. Adding relatively large amounts of tetramethyltin (TMT) into the plasma chamber led to clusters of tin and significant oxygen and carbon concentrations throughout the layer. Managing the atomic carbon, oxygen, germanium and tin fractions could be crucial in obtaining device quality bottom cell absorber layers based on GeSn:H in the future. ... Read more

TU Delft and KEMA laboratories are collaborating to create a Programmable high voltage test source by employing Modular Multilevel Converter MMC which can generate output voltage waveforms of any arbitrary shape. To produce an Impulse waveform of magnitude 250 kV across a capacitive load of 10 nF with a rise time of 1.2 µs as output voltage, each Power Electronic device incorporated into each Sub-Module of the MMC has to conduct pulse currents as high as 850 Amperes. Moreover, the Impulse Waveform has a very short time duration. Hence the Power Electronic devices need to conduct such high current magnitude only for a very short duration of time. This motivates this Master thesis to find out how many multiples of its rated current a Power Electronic device is able to conduct within such short time and what factor limits the peak current capability of the Power Electronic device. However, to produce an output voltage of any other waveshape each Power Electronic device of each Sub-Module of the MMC has to conduct only a few amperes of continuous current. Employing Power Electronic devices of current rating as high as pulse currents of Impulse waveform is not only uneconomical since other waveforms do not require such high continuous currents, but also such Power Electronic devices of high current rating would make the MMC bulkier.
To identify the Power Electronic device technology that is capable of conducting such high pulse currents, a literature review is conducted among IGBT, MOSFET and their types. Each device of IGBT and MOSFET is compared to one another. Finally, the most promising switching technology is chosen among MOSFET and IGBT based on three criteria namely, high peak current capability, high voltage blocking capability and high switching frequency.
A prototype of Pulse Current Test circuit is built to test the peak pulse current of the chosen switching technology. Then, the factors that can be utilized to achieve the peak pulse current are identified. Based on results of the pulse current test, the multiplication factor of the rated current of the Power Electronic device is identified. Switch technology for the MMC specifically for Impulse waveform is suggested. ... Read more