The rapid growth in electric vehicle (EV) adoption, particularly in densely populated urban areas, together with the global aim of reducing greenhouse gas emissions, is placing increasing stress on existing power distribution infrastructure. Bipolar DC microgrids present a robust and flexible solution for integrating daily DC loads such as lighting networks and EV chargers, offering higher efficiency due to fewer power conversion stages compared to the AC grid system. This project focuses on developing a cost-effective, reliable and easily deployable EV charger that enables seamless integration of DC microgrids into today’s AC-based urban systems, leveraging the existing Dutch public lighting network. By utilising the already-installed AC grid combi cables with 6mm2 auxiliary copper conductors, the proposed converter operating at ±350V (700V bipolar DC) and 15A with rated power of 11 kW can deliver power directly to dual street-side parking spots while preserving sufficient current capacity for lighting loads. The goal is to enable practical low-power charging in locations where vehicles remain parked for extended periods, such as overnight or during working hours. High reliability and minimal maintenance needed are key requirements to support the large-scale deployment of DC-based EV charging in urban environments.
A comprehensive review and comparison of wide-bandgap semiconductor technologies and isolated DC-DC converter topologies for dual-output, bidirectional operation led to the selection of a SiC-based Triple Active Bridge (TAB) as the most balanced solution in terms of performance, reliability, complexity and cost. The TAB converter is an evolution of the conventional Dual Active Bridge (DAB) topology, enabling direct power transfer between three ports. The inclusion of a third port, however, increases the complexity of power flow management as a single core transformer allocates the three windings. A detailed theoretical analysis, supported by open-loop simulations, guided the parameter design of the converter to ensure zero-voltage switching (ZVS) across all charging scenarios. The full mathematical expressions of the transformer’s AC currents, obtained through Fourier series decomposition of the full-bridge voltages, allowed comparing different current measurement approaches for closed-loop DC current control. Implementing the control strategies under real operating conditions required investigating scenarios such as the sudden disconnection of one EV and single-vehicle charging. These cases deviate from the typical three-port operation and are critical to analyze in order to ensure safe and efficient performance. Building on these results, a passively cooled hardware prototype was developed, integrating the power semiconductors, high-frequency transformer, filters, protections, and thermal management. Experimental validation confirmed the converter’s functionality, demonstrating a complete workflow from concept to prototype for an EV charger designed to be integrated in the emerging DC microgrid infrastructure.

The growing complexity of electric vehicles asks for new battery management system (BMS) designs that are simpler, more reliable, and cost-efficient. This thesis presents the development of compact cell monitoring units (CMUs) that are mounted directly onto battery modules, eliminating bulky harnesses, reducing wiring complexity, and maintaining measurement accuracy. The CMUs combine redundant voltage and temperature sensing, passive balancing, and galvanic isolation in a custom four-layer printed circuit board optimized for thermal management and validated through simulation and experiments. Since these CMUs will be integrated into a future electrical/electronic architecture where the BMS master functions reside in the vehicle control unit, this design reduces component count and wiring complexity while maintaining functional safety. In parallel, a model-based state-of-charge (SoC) estimator was implemented as a redundant method to conventional Coulomb counting (CC), which suffers from drift, initial offset, and dependence on usable capacity. Through estimating the open-circuit voltage (OCV) during dynamic driving conditions with Kalman and H-infinity filters, a redundant SoC estimation method is demonstrated that compensates for the known drawbacks of CC. To prove the concept under realistic conditions, the model was validated not only on laboratory drive cycles but also on a real-life drive cycle containing measurement noise. Together, these innovations provide a cost-effective and scalable pathway towards robust battery monitoring and reliable SoC estimation in future electric vehicles.

The integration of renewable energy resources has seen a marked increase in recent decades, driven by the need to address the growing severity of the global energy crisis. Distributed generators, which incorporate renewable energy sources alongside energy storage systems, present a viable pathway toward achieving substantial economic and environmental benefits.
In the context of microgrids, maintaining frequency and voltage amplitude within prescribed limits is essential for stable operation. Furthermore, the proper distribution of power—including active, reactive, and harmonic components—among interconnected converters is critical to achieving balanced performance under steady-state conditions. During dynamic transitions, it is equally important for voltage and power levels to evolve smoothly, ensuring a seamless adjustment to the steady-state operating point....

Heavy industry is responsible for about a third of global emissions but lags behind in its effort to become carbon neutral. The electrification of industrial processes is a necessary step to achieve this goal. The asphalt industry is a good candidate for decarbonisation, as it currently relies on burning fossil fuels to heat and dry the aggregate used in asphalt production. Instead, aggregates could be heated electrically by using induction heating.

This thesis will investigate the design of an aggregate induction drum heater. A COMSOL model will be developed to aid the design process and predict the heater behaviour. The heater will be powered by a resonant converter, which is modelled in Simulink. A test setup is built to serve as a proof-of-concept for the design and to experimentally verify the models.

The analysis of the simulation and test results show that the model quality is dependent on the description of the material properties. The COMSOL model predicts the temperature of the middle of the heater with reasonable accuracy while the Simulink model is able to simulate the coil current and converter voltage waveforms with little error. The design of the aggregate induction heater could be improved by thermally insulating the outside surface and increasing the contact area between the aggregate and the heater.

Energy arbitrage is a key activity in privately-owned energy storage system portfolios. However, the profitability of battery energy storage systems in this domain is limited by two primary challenges: the high cost of battery manufacturing and the insufficient temporal volatility of electricity prices within individual bidding area.

In this context, this study explores the economic viability of relocating the utility-scale battery energy storage systems. To enhance profitability, the proposed portable energy storage system integrates a semi-empirical battery degradation model to accurately account for degradation costs, while its mobility
allows for travel between different bidding zones to exploit inter-zonal electricity price differences.

A mixed-integer linear programming model is built to optimize the system’s daily charging/discharging and transportation scheduling. The system’s daily operations within the Norwegian day-ahead market are simulated using a Python model.

The investigation includes comparative analyses to assess how battery location, chemistry, and degradation models influence system profitability. The study compares stationary and portable battery energy storage systems: in the stationary case, it evaluates profitability with different battery chemistries (lithium ferrophosphate and lithium manganese) in different locations, while the portable case explores the impact of different battery chemistries and degradation models (semi-empirical vs. conventional energy throughput).

The findings reveal that none of the stationary energy storage systems can achieve break-even through conventional temporal arbitrage in the Norwegian day-ahead market. In contrast, relocating the battery proves profitable for all four portable energy storage systems.

Additionally, the application of the depth-of-discharge-aware semi-empirical model enhances profitability of portable systems with both battery chemistries, with the lithium manganese system showing a more than 15% increase in investment return rate. This makes lithium manganese a more attractive option than the lithium ferrophosphate battery due to its lower investment cost, shorter payback period, and higher return on investment.

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.

This master’s thesis investigates the design, challenges, and protection mechanisms of electrical power distribution systems on ships with a particular emphasis on DC distribution systems. A key focus is on the challenges of DC systems, including protection difficulties and unique characteristics, as well as their environmental benefits and contribution to sustainability. The thesis dedicates a significant portion to the technical analysis of short-circuit currents in DC grids, offering methodologies for their calculation and protection devices like fuses and circuit breakers. Relevant standards such as IEC 61660 and IEC 60269-1 ground these discussions, ensuring their practical relevance. The thesis includes a detailed simulation model of the DC grid of a vessel, developed using MATLAB-Simulink. The simulation analyses several scenarios, including short circuits and different operational modes, by examining crucial system components such as generators, IGBTs, batteries, drives, and link capacitors. The simulations  showcase the efficacy of protective measures by examining the performance of fuses and circuit breakers in different scenarios. The simulation results of the DC grid's performance under different short circuit scenarios, with and without protective measures, provide valuable information for optimising these systems for maritime applications. The thesis concludes with an improved Simulink model incorporating enhanced battery protection, demonstrating the potential for increased safety and reliability in shipboard DC power distribution systems.

The increasing penetration of renewable energy sources, such as wind and solar power, introduces significant uncertainties and challenges to conventional power grids. These challenges primarily arise from system frequency instability and voltage fluctuations due to the lack of inertia typically provided by conventional synchronous generators (SG). To enhance grid resilience and mitigate potential power quality issues, synthetic inertia is emulated by Grid-Forming (GFM) inverters, imitating the dynamics of conventional synchronous generators.

This thesis addresses these challenges by investigating the integration of supercapacitors (SC) and the implementation of advanced GFM control strategies, such as Virtual Synchronous Generator (VSG) control, within solar power generators. The primary objective is to ensure power quality and enhance system stability, particularly in scenarios involving high penetration of renewable energy, where the absence of conventional inertia can lead to significant voltage and frequency deviations. In this research, a comprehensive solar power generation system is designed, integrating a 200kW photovoltaic (PV) system with a 100kW SC storage system on the DC bus. The design aims to mitigate the adverse effects of frequency and voltage fluctuations while providing synthetic inertia through the integration of the SC energy storage system and the implementation of VSG control. These strategies are crucial for maintaining system stability and ensuring a rapid response to grid disturbances.

Extensive simulations and analyses are conducted to evaluate the performance of the proposed system under various operational scenarios. Case studies are performed under different assumptions. The results demonstrate that the synthetic virtual inertia significantly enhances the system’s ability to manage voltage and frequency deviations, providing a robust and reliable solution to maintain grid stability in the GFM solar power generator.

This thesis implements the proposed design of a solar power generator that can effectively ensure system stability in power systems with high levels of renewable energy penetration.

In the last decade, the market for Electric Vehicles (EV) has expanded at an unprecedented rate. Concurrently, there has been a surge in the demand for public Direct Current (DC) EV charging stations. To accommodate a diverse array of EVs, these charging stations are required to support a broad operational voltage and power spectrum. However, this necessity introduces a trade-off between the operational range and the efficiency and utilization of the installed power within the charging infrastructure. The core of the issue lies in the fact that the charging stations, designed to cater to a wide range of operational conditions, often do not operate at their peak efficiency outside their designated optimal performance region.
To address this challenge, this thesis investigates the advantageous DC/DC power electronics solutions that can maintain high efficiency across a wider operational range while optimizing the utilization of installed power. The research topics include the suitable DC/DC converters for the back-end power modules of the charging system, the multi-objective design process of the power modules, and the advanced operation of the power modules.

Electric vehicle (EV) charging plays a crucial role in paving the way for zero-emission vehicle markets, which require massive installations of EV chargers. However, that causes degraded power quality of the power grid, which may lead to non-compliance issues. To prepare for massive installations, a comprehensive understanding of EV chargers’ potential power quality impacts is essential. Furthermore, mitigation measures for potential power quality issues should be prepared beforehand to prevent catastrophic power quality issues from happening. Therefore, the thesis aims to clarify the potential power quality issues caused by EV chargers, prepare modelling methods to understand the root cause of the power quality issues and develop mitigation measures to alleviate chargers’ power quality impacts.

One of the main technical challenges in the energy transition is the seamless integration of renewable energies into the grid ensuring, among others, system stability and acceptable power quality levels. This thesis explores the effect that voltage imbalance has on the small-signal stability and harmonic performance of the grid-side converter in grid-following type 4 wind turbine generators (full converter). Within the scope of this thesis is voltage imbalance that appears in steady-state (typically, a low value limited by grid codes and international power quality standards) and also voltage imbalance that appears during transient situations (typically, a higher value due to temporary conditions like faults).

The integration of renewable energy systems into the grid brings new and unique propositions involving the integration of power electronic inverter based solutions into the High Voltage (HV) grid. Thus a need arises to test the HV components with unconventional waveforms which can be satisfied by the Arbitrary Waveshape Generator (AWG). Two such topologies have been shortlisted for the AWG, ie: Modular Multilevel Converter (MMC) & Cascaded H Bridge (CHB). The MMC requires a single insulated DC source while the CHB requires multiple insulated DC sources with isolation.

Developing insulated DC sources using traditional transformers requires oil, epoxy or other complex insulation materials. The insulation requirements are further exacerbated when HV > 5 kV is required at power levels greater than 1 kW. For this reason, Wireless Power Transfer methods are studied in this thesis to develop a DC Power Supply based on Inductive Power Transfer (IPT). The developed supply is capable of conducting DC breakdown tests and high frequency (>100 kHz) AC discharge tests on dielectrics.

The key requirements for developing such a system are Load Invariant Voltage, High Voltage Gain and Soft Switching. Considering these requirements the Series Parallel (S-P) topology is chosen to deliver 1.5 kW at a DC voltage of 5 kV from a 350 V input, with a diode rectifier. Using the Greinacher rectifier, 10 kV DC output is obtained. Different parameters of the developed resonant converter such as coupling coefficient, switching frequency, deadtime and overcurrent protection are analysed to find a suitable configuration for the DC Power Supply. An efficiency of 88% at rated load and load regulation of 18% is achieved for the developed power supply.

For the CHB, a multi-receiver IPT system is desirable to provide multiple isolated DC outputs. A 2-receiver and a 3-receiver IPT system is constructed and their coupling behaviour is studied. A conclusion is drawn that an ”n” receiver system has a coupling coefficient 𝑘𝑛 = √𝑛𝑘1 and accordingly a S-P IPT system can be developed to obtain multiple (n) isolated DC voltage sources.

Global average temperatures are setting new records compared to the previous decade, primarily due to the accumulation of greenhouse gases such as CO₂. The growth potential in emerging economies worsens the current global situation. These CO₂ emissions are needed to be curtained and efforts are underway. The emissions target set by the International Maritime Organization seems far-fetched given the forecast for the growth of the shipping sector. Although electrification has proven to reduce emissions, the energy efficiency metrics (EEDI, EEXI) are incapable of providing the quantitative benefits that can be realized by switching to a bipolar DC (BiDC) grid when compared with the AC grid.
This thesis aims to evaluate the feasibility of BiDC grids over the complete operating profile of the ship by comparing ten arrangements, five for AC and five for DC, with the Key Performance Indicators (KPIs). The arrangements are two diesel generators (AC1 & DC1), two diesel generators and battery (AC2 & DC2), two diesel generators, battery, and shore power (AC3 & DC3), one diesel generator and battery (AC4 & DC4), one diesel generator, battery, and shore power (AC5 & DC5). The comparison is made for key performance indicators like CO₂ emissions, fuel consumption, electrical power requirement, propulsion power cable losses, capital costs, operating costs, propulsion system weight, and load carrying capacity of the ship. In this study, a ferry is chosen to compare the two grid architectures.
To establish the required background knowledge for the reader of this thesis, the literature on the current emission regulations, the different propulsion systems, and the differences in AC and DC grids are presented. The ship’s propulsion and auxiliary power demand are not freely available and are in the possession of the ship operator. Therefore, first, a preliminary methodology was developed for estimating the ship’s mechanical power requirements. Second, the ship’s electrical power requirements are estimated from the understanding of the literature. The cable power losses are also calculated for the AC and BiDC grid topology. Third, the diesel generator model was developed from the data points of a marine diesel generator for the AC and BiDC grid operation, i.e., the fixed speed and variable speed operation. Finally, an optimization problem was formulated for all the ten arrangements for minimising the CO₂ emissions over the complete operational profile of the ship.
Overall, it was observed that the minimum emissions achieved by BiDC grids, when compared with AC grids for all the arrangements, the emissions from the former were lower. Furthermore, these results depend on the operating profile of the ship, the shore infrastructure, the diesel generator and battery configuration and their technical parameters. However, these findings demonstrate the possible potential of BiDC grids in emission reduction from the shipping sector.

An isolated bidirectional DC-DC converter is designed for a dual-output EV charger. Various DC-DC converter topologies are compared, including single-output converters and dual-output converters. Then one suitable topology is selected between the multiport CLLC converter and triple active bridge converter based on the simulation performances for the dual-output EV charger. Meanwhile, an investigation into the voltage regulation for a wide output voltage range is conducted with the research of interleaved buck converters. Finally, the system-level control of the EV charger is designed for different operation modes and the converter is modelled in PLEVS and simulated under different scenarios.

This master's thesis presents the design and analysis of the inverter stage and controller architecture for a modular Solid-State Transformer (SST) to interconnect DC microgrids and a 10kV AC grid for bidirectional power flow. The research focuses on inverter topologies, modulation techniques, and modular controller architecture.

The inverter stage, a crucial stage of the modular SST, converts DC power from microgrids to AC power suitable for the 10kV AC grid. The most popular inverter topologies for modular converters are researched and investigated based on their compatibility with the specific application. Factors such as efficiency, power quality, harmonic distortion, number of components, control complexity, and scalability are considered for this process. Along with the topology, modulation techniques are important in producing high-quality output waveforms and efficient power transfer. Different modulation strategies, including pulse width modulation (PWM) techniques and space vector modulation schemes specifically for multilevel converter applications, are reviewed and discussed in terms of how they affect the system's performance.

In addition to the inverter stage, the thesis focuses on designing a modular controller architecture for the SST. The controller design prioritizes maintaining flawless data flow and synchronization between all controllers for converter and AC grid coordination. The central controller and distributed control architectures are studied and evaluated for scalability, modularity, and flexibility. The distributed architecture enhances the system's overall flexibility but is subject to synchronization issues and limitations in communication bandwidth. These issues are addressed in the developed design.

To evaluate the performance of the proposed inverter stage and controller architecture, extensive simulations and experimental validations are carried out. The simulations consider various operating conditions, such as islanded and grid-connected modes, to assess the system's stability, control, harmonic content, and power quality in the output waveforms. The simulation results indicate that the chosen inverter design and modulation strategies successfully attain high efficiency and minimal harmonic distortion in the operation of the converter. The modular, distributed controller design demonstrates its ability to provide seamless operation and effective coordination between DC microgrids and the AC grid.

Overall, this master's thesis contributes to the advancement of solid-state transformer technology by delving into the design of the inverter stage and controller architecture for interconnecting DC microgrids and a 10kV AC grid and providing useful insights. The findings and recommendations can be a valuable framework for future research and development of modular SSTs for grid-connected applications.

As renewable energy sources and DC energy storage continue to increase in modern power systems, the power electronic converters required to interface them with existing power grids are also rapidly increasing. This is resulting in increasing amounts of the total power exchanged on the grids being converted between DC and AC. Additionally, the majority of today's grid loads ultimately convert their input power to some form of DC whether they are connected to an AC or DC grid. Therefore, the concept of DC grids is becoming more attractive for applications such as DC distribution systems and electric vehicle charging stations. However, the existing AC grids will continue to play a fundamental role in the power infrastructure. Therefore, it is, important to consider how LVDC distribution grids will be connected to, and exhange power with, the AC grid. A transformerless interface between LVDC distribution grids and the LV AC grid via a power electronic converter is an attractive option in terms of size and cost reduction. However, the challenge of ground leakage current is a major challenge for such an interface.

This thesis assesses the different possible three-phase DC-AC converter topologies for a transformerless interface between a bipolar DC microgrid and the LV AC grid. The DC-AC converter modulation is explored to understand the challenges of ground leakage current and determine the feasibility of a transformerless interface. A detailed analysis of the common-mode voltage, common-mode impedance and resulting circulating currents in a grid-tied DC-AC converter is performed. The effect of this circulating current on AC grid protection equipment is considered.

A survey of converter modulation methods for common-mode reduction and DC bus voltage balancing is conducted. Simulations are used to verify the performance of the different modulation methods in terms of common-mode reduction and DC balancing capabilities in the bipolar DC grid. A new modulation method is proposed for simultaneously mitigating ground leakage current and providing DC voltage balancing. The limitations of this method are analyzed and simulations are performed to evaluate its effectiveness. The developed modulation method is also shown to eliminate the low-frequency voltage ripple in the DC bus caused by the conventional modulation methods. An experimental hardware prototype DC-AC converter is designed and built for testing the different modulation methods. Finally, recommendations for future work are made.

Rural electrification remains a significant challenge for engineers, given its intricate relationship with multiple issues, including geographical constraints and underdeveloped infrastructural provisions. As a result, with the development of Solar Home Systems (SHS) and direct current (DC) microgrids, DC systems for energy access have emerged as a promising solution.

In this context, a bidirectional DC/DC converter serves as a bridge connecting the SHS and the grid. Thus, it is important to design a converter's control mechanism to ensure a smooth and efficient exchange of power in both directions. Beyond this aspect, the system perspective involves the coordination of photovoltaic (PV), battery storage, and grid power supply priorities within the SHS. Consequently, this thesis centers its attention on two objectives: the control of the bidirectional DC/DC converter and the system-level control of the DC microgrid.

To ensure high efficiency under variable loads and smooth transitions between two directional operations, this thesis proposes and evaluates a novel control methodology. Transfer functions are derived through mathematical modeling and PI parameters are determined by analyzing Bode-Plots. This work also shows the simulation and testing results. Both results demonstrate that the proposed control method achieves a high efficiency under light load conditions, maintaining a stable output voltage despite load power dramatic fluctuations.

Analysis of energy exchange between the DC microgrid and SHS involves a bipolar DC microgrid model based on an established grid in Matlab/Simulink. Employing droop control, which is a widely used decentralized strategy, for each converter within the grid. To ensure priority order of power supply in the system, a system-level decentralized control methodology is developed, assuming internal communication within the SHS. Through simulation, the priority order of PV, battery, and grid is verified, along with the impact of dynamic shifts between scenarios on the load. However, given the absence of communication devices in the existing SHS, an alternate decentralized coordinated control strategy is developed and simulated, without direct communication interfaces. Simulation results demonstrate that the SHS bus voltage remains stable even with power supply changes.

Recently, there have been numerous DC microgrids coming up in every sector. Some of these microgrids operate as independent entities with their own renewable energy sources, active loads, distribution networks and energy storage units. However, they are not highly reliable as the renewable energy sources are location and climate dependent. Having a large energy storage unit can be one possible solution, but that involves high expenditure and occupies a large amount of space. Thus, an alternative is to connect the independent DC microgrid to an established AC grid. With the advancements in power electronic technologies, such a connection can be established by a multi-stage converter known as Solid state transformer (SST).

Numerous studies have been conducted on SSTs for low-voltage levels, and there is a wide scope for research in the area of medium and high-voltage converters. Also, the scope of using Planar transformer (PT) as high-frequency transformers in DC-DC converters for medium and high-voltage applications is yet to be extensively explored. Hence, the main focus of this thesis would be to develop an isolated bidirectional DC-DC converter with a planar transformer that can be used in an SST which can potentially connect a low-voltage DC microgrid comprising a solar-based car parking system, to a medium-voltage AC grid.

Firstly, various DC-DC converter topologies have been investigated, and the single phase Dual active full bridge (DAFB) is chosen as the best suitable topology for this application. Secondly, various control strategies have been investigated, and single-phase shift control has been implemented due to its simple control techniques and low data transfer requirement across high isolation. Thereafter, a script is developed to identify the optimal parameters for the Dual active bridge (DAB) and PT design. Further, the planar transformer with high isolation is realized by considering various factors like shielding and termination into account. Finally, a single-cell prototype is developed and tested for DAB operation and isolation requirement of the designed planar transformer.

The result of the presented work is a single-cell isolated bidirectional DC-DC converter rated for 12 kW designed and developed with a PT rated for 16.3 kV isolation.

With an increase in higher power (ultra) fast EV charging stations and a new EU law for mandatory deployments of EV charging stations, an optimal MVAC grid connection for these charging stations is desired. Considering this connection, the use of a solid-state transformer (SST) performs better in terms of weight, size and efficiency with a similar cost, compared to the conventional low-frequency transformer (LFT) for MVAC to LVDC conversions. This study compares three MMC-based SST topologies where a DAB is connected to each submodule: Double-Star, Single-Star and Single-Delta. The cost of an MMC mainly depends upon the required energy storage and the switch stress. The topologies are therefore mainly compared based on these parameters, but other parameters are considered as well. With the goal of minimising the required energy storage, an 80% MMC energy storage reduction compared to the theoretical minimum requirement has been achieved by control.

A novel mathematical model has been proposed for each SST; this uses an MMC model based on the switching function and a DAB model based on the single phase-shift control. The model has been implemented in simulation and proven to accurately determine the average behaviour of the SST while significantly reducing the simulation complexity and time. This model helps to understand the SST's behaviour and furthermore allows for control system tuning both manually and automatically using the Genetic Algorithm.

Three different control systems have been designed. Control system A, where the MMC current is controlled by the average submodule voltage and the DAB controls the LVDC bus voltage. Control system B, where the DAB controls each individual submodule voltage and the MMC current is controlled by the LVDC bus voltage. Control system C, which is similar to control system B, but uses a stable DC voltage source on the LVDC bus and a set MMC current. An improved DAB control has been designed for control systems B and C, resulting in control systems B* and C*. This control is based on the use of a current feedforward and a PI controller combined with the inverted equations of the DAB model. The three topologies have been successfully simulated with this improved DAB control system using an 80% MMC energy storage reduction compared to the theoretical minimum requirement. This improves the general behaviour and significantly reduces the cost of the SST. The improved DAB control system has been tested using a hardware DAB with a current step input, which has shown that the new control system performs better in voltage peak reduction compared to PI control.

Out of the three topologies, the Single-Star topology performs the best. It has the lowest energy storage requirement and switch stress. Furthermore, its behaviour lies the closest to the ideal model. The best result for the Single-Star SST is achieved with the proposed improved DAB control, which leads to the lowest energy storage requirement, switch stress, THD, submodule voltage deviations and settling time. Out of these two control systems, C* performs the best.