The purpose of this thesis is to evaluate a selection of power quality parameters (harmonic distortion and voltage variations) in the microgrid on Arholma Island in the Stockholm archipelago, Sweden. Measurements of harmonic distortion, total harmonic distortion, and voltage magnitudes is evaluated and compared prior to and after the installation of the microgrid. Furthermore, a comparison is made between grid-connected mode and island operation mode where also the frequency is analysed. The measured values are compared against regulatory limits.  The microgrid is owned and managed by the company Vattenfall, who provides the data used for the evaluation. The microgrid consists of two battery energy storage systems and a small photovoltaic system. The central energy management system has different use cases, for example peak shaving and voltage regulation. At the time when this thesis is conducted, the microgrid has been up and running continuously for approximately 8 months, from September, 2023 to April, 2024. A power quality meter has been collecting data at the point of common coupling (connection to the mainland) for a period of two years, i.e., from April, 2022, which is one year prior to the installation of the microgrid in mid-April, 2023. The microgrid is also operated in island operation mode for three short periods on April 18, 2024.  The data analysis is executed in Excel and Matlab. The results show that all measured harmonics (2nd to 25th), and total harmonic distortion stays well within regulatory limits throughout the whole measuring period. The microgrid does not seem to make the harmonic magnitude increase in general, although there is a slight increase during island operation mode for certain harmonics. Only on one occasion (with the exception of a planned maintenance outage) does the voltage drop below the levels of what is considered as good voltage quality during the two-year measurement period. Also, during island operation mode, the frequency show less variations than during grid-connected mode. / Syftet med detta examensarbete är att utvärdera ett urval av elkvalitetsparametrar (spänningsdistorsion/övertoner och spänningsvariationer) i mikronätet på ön Arholma i Stockholms skärgård, Sverige. Mätdata för övertoner, total övertonsdistorsion och spänningsamplitud utvärderas och jämförs före och efter installationen av mikronätet. Dessutom görs en jämförelse mellan nätanslutet läge och ö-driftläge, där även frekvensen analyseras. De uppmätta värdena jämförs med föreskrivna gränsvärden. Mikronätet ägs och förvaltas av företaget Vattenfall, och tillhandahåller den data som används för utvärderingen. Mikronätet består av två batterilagringssystem och ett litet solcellssystem. Det centrala kontrollsystemet har olika funktioner, till exempel ”peak shaving” och spänningsreglering. Vid t idpunkten då detta examensarbete genomförs har mikronätet varit i drift kontinuerligt i cirka 8 månader, från september 2023 till april 2024. En elkvalitetsmätare har samlat in data vid sammankopplingspunkten mot fastlandet under en period av två år, dvs. från april 2022, vilket är ett år före installationen av mikronätet i mitten av april 2023. Mikronätet körs i ö-drift under tre korta perioder den 18 april 2024. Dataanalysen utförs i Excel och Matlab. Resultaten visar att alla uppmätta övertoner (2:a till och med 25:e) och total övertonsdistorsion håller sig väl inom regulatoriska gränser genom hela mätperioden. Mikronätet verkar inte bidra till att övertonernas magnitud ökar i allmänhet, men en liten ökning för vissa övertoner kan ses i samband med att mikronätet körs i ö-drift. Endast vid ett tillfälle (med undantag för ett planerat underhållsavbrott) under den tvååriga mätperioden sjunker spänningen under nivåerna för vad som anses vara god spänningskvalitet. Resultaten visar även att frekvensen varierar mindre vid ö-drift än när mikronätet är sammankopplat med fastlandsnätet.

The electrification of societies and the decarbonisation of electricity production are changing energy systems worldwide. A fast transition towards the replacement of fossil fuels by intermittent renewable energy sources is expected in the next decades to combat climate change. A significant share of the produced electricity is likely to be generated from offshore wind farms, due to the abundant wind resources in the offshore regions and the lack of available onshore sites. However, increased electricity dependence in combination with expanded offshore wind power generation introduce new vulnerabilities to the society. Specifically, the effects of high impact low probability (HILP) events are considered as potential threats to the power system, not least because of the increasing number of extreme weather events. Therefore, research on power grid vulnerability and power system resilience to HILP events are of significant interest. This thesis presents results of studies investigating power grid vulnerability from a topological perspective, and resilience to storm conditions of power systems with varying dependencies on offshore wind. To achieve this, methods based on complex network theory and AC power flow analysis have been developed, tested, and evaluated. Further, geospatial wind data from historical extreme storm events have been used to generate realistic power production profiles from hypothetical offshore wind farms. The results strengthen that complex network concepts can be used successfully in the context of power grid vulnerability analysis. Further, the results show that the resilience of power systems with large dependencies on offshore wind differ vastly depending on the grid properties and control strategies, which are further discussed in this thesis.

To ensure that wave power reaches its full potential it is important to optimise all aspects of the technology. The optimisation process requires us to consider computationally heavy simulations and several objective functions, so one should carefully choose which optimisation algorithm is most suitable. This study has reviewed three different multi-objective optimisation algorithms: NSGA-II, MO-CMA-ES and MOPSO. The algorithms will optimise a wave park in respect to its generated power, power fluctuation, cost and park area. Multi-objective optimisation results in a so-called Pareto front of many optimal solutions, and this study has investigated how to choose one preferred solution from the Pareto front to best satisfy the user's requirements. The results show that NSGA-II and MOPSO are fast algorithms that can reliably converge towards non-dominated solutions, although NSGA-II may miss essential parts of the solution space and MOPSO is reliant on uncertain parameters. MO-CMA-ES also converges reliably, but computationally heavy parameters make it unsuitable for high-dimensional problems. The preferred solution depends on how all objective functions are weighed against each other, and the results show that the values of the weights will change depending on the specific problem setup. In the end, the identification of the preferred solution from the Pareto front depends on subjective decisions made by human decision makers.

Given the importance of diagnosing internal combustion engines and their expandingmarket, it is crucial to investigate the complex dynamics of these engines and developa model to detect and localize component and sensor faults, independent of operatingconditions. This master’s thesis explores capturing dynamic relationships in engine signalsto detect faults. Internal combustion engines have highly nonlinear dynamics that arenot easy to capture with basic system identification methods. Consequently, some newlydeveloped methods, such as Sparse Identification of Nonlinear Dynamics (SINDy) andAuto Regressive (AR) models, have been implemented to address the governing equations.Following previous research in this field, some analytical relations between the sensorswere known. Additionally, these equations provide the sensitivity of residuals based onthe input sensor fault. By implementing the mentioned methods and using informationfrom the analytical equations, some relationships between the sensor values and the inputfault have been identified.After finding these dynamic relationships between the sensor values, a classificationalgorithm was selected to classify the sensor faults. Additionally, to estimate the faultseverities (sensor inaccuracies), some regression models have been implemented. Further-more, it was desired to evaluate the isolability of the faults, and in this regard, some newconstraints have been considered to reconstruct the relations with the desired isolability.Finally, through several evaluations, it was shown that the proposed method is not af-fected by the driving cycle. However, this research established these methods based on aspecific case study, which is a specific turbocharged internal combustion engine.

Measuring low electrical currents with high precision is critical across various fields, particularly in applications like microfluidic biosensing. Traditional digital multimeters (DMMs) are inadequate for low current measurements due to their high input burden and limited resolution. Therefore, more sensitive instruments like electrometers and picoammeters are often required but are typically expensive. This thesis explores the design and construction of a cost-effective, portable, and user-friendly picoammeter based on a transimpedance amplifier (TIA), capable of measuring currents in the picoampere (pA) range with a resolution of 1-5 pA and minimal noise. The constructed picoammeter has a maximum input current range of ±1.5 nA.  A prototype was built on a soldering board to validate the design, which was then translated into a practical printed circuit board (PCB) layout. The device is powered by batteries to ensure low noise levels and enable isolated operation. An Arduino microcontroller was used to interface with the circuit, manage data acquisition, and enable real-time visualisation of the measured current data on a computer.  Simulation results confirmed the theoretical performance of the circuit, and experimental validation showed RMS noise levels of less than 0.3 pA under controlled conditions and up to 3 pA when measuring streaming currents from a microchip. Despite a slight underestimation of input currents due to resistor tolerances, calibration adjustments successfully corrected these discrepancies.  The total cost of the materials used in constructing the picoammeter was significantly less than the cost of commercially available devices. While commercial devices offer higher precision and additional functionalities, the developed picoammeter demonstrates how application-focused solutions can provide comparable accuracy and noise characteristics to commercial devices for a fraction of the price.

The market for wireless portable devices has grown signicantly over the recent years.Wireless devices with ever-increased functionality require high rate data transmissionand reduced costs. High data rate is achieved through communication standards such asLTE and WLAN, which generate signals with high peak-to-average-power ratio (PAPR),hence requiring a power amplier (PA) that can handle a large dynamic range signal. Tokeep the costs low, modern CMOS processes allow the integration of the digital, analogand radio functions on to a single chip. However, the design of PAs with large dynamicrange and high eciency is challenging due to the low voltage headroom. To prolong the battery life, the PAs have to be power-ecient as they consume a sizablepercentage of the total power. For LTE and WLAN, traditional transmitters operatethe PA at back-o power, below their peak efficiency, whereas pulse-width modulation(PWM) transmitters use the PA at their peak power, resulting in a higher efficiency.PWM transmitters can use both linear and SMPAs where the latter are more power efficient and easy to implement in nanometer CMOS. The PWM transmitters have a higher efficiency but suffer from image and aliasing distortion, resulting in a lower dynamic range,amplitude and phase resolution. This thesis studies several new transmitter architectures to improve the dynamicrange, amplitude and phase resolution of PWM transmitters with relaxed filtering requirements.The architectures are suited for fully integrated CMOS solutions, in particular forportable applications. The first transmitter (MAF-PWMT) eliminates aliasing and image distortions whileallowing the use of SMPAs by combining RF-PWM and band-limited PWM. The transmittercan be implemented using all-digital techniques and exhibits an improved linearity and spectral performance. The approach is validated using a Class-D PA based transmitter where an improvement of 10.2 dB in the dynamic range compared to a PWM transmitter for a 1.4 MHz of LTE signal is achieved. The second transmitter (AC-PWMT) compensates for aliasing distortion by combining PWM and outphasing. It can be used with switch-mode PAs (SMPAs) or linear PAs at peak power. The proposed transmitter shows better linearity, improved spectral performanceand increased dynamic range as it does not suffer from AM-AM distortion of the PAs and aliasing distortion due to digital PWM. The idea is validated using push-pull PAs and the proposed transmitter shows an improvement of 9 dB in the dynamic rangeas compared to a PWM transmitter using digital pulse-width modulation for a 1.4 MHzLTE signal. The third transmitter (MD-PWMT) is an all-digital implementation of the second transmitter. The PWM is implemented using a Field Programmable Gate Array(FPGA) core, and outphasing is implemented as pulse-position modulation using FPGA transceivers, which drive two class-D PAs. The digital implementation offers the exibility to adapt the transmitter for multi-standard and multi-band signals. From the measurement results, an improvement of 5 dB in the dynamic range is observed as compared to an all-digital PWM transmitter for a 1.4 MHz LTE signal. The fourth transmitter (EP-PWMT) improves the phase linearity of an all-digital PWM transmitter using PWM and asymmetric outphasing. The transmitter uses PWM to encode the amplitude, and outphasing for enhanced phase control thus doubling the phase resolution. The measurement setup uses Class-D PAs to amplify a 1.4 MHz LTEup-link signal. An improvement of 2.8 dB in the adjacent channel leakage ratio is observed whereas the EVM is reduced by 3.3 % as compared to an all-digital PWM transmitter. The fifth transmitter (CRF-ML-PWMT) combines multilevel and RF-PWM, whereas the sixth transmitter (CRF-MP-PMWT) combines multiphase PWM and RF-PWM. Both transmitters have smaller chip area as compared to the conventional multiphase and multilevel PWM transmitters, as a combiner is not required. The proposed transmitters also show better dynamic range and improved amplitude resolution as compared to conventional RF-PWM transmitters. The solutions presented in this thesis aims to enhance the performance and simplify the digital implementation of PWM-based RF transmitters.

This thesis demonstrates a method for transformer core diagnostics. The method uses the no-load current of the transformer as an indicator, and gives different characteristic signatures for different types of faults or defects. Using the no-load current for the diagnostic gives high sensitivity. The method is therefore able to detect defects that are too small to have an impact on the losses. In addition to different types of fault, the method can in some cases also distinguish between faults in different locations within the core. Both single-phase and three-phase transformers can be diagnosed using this method, and the measurements can be easily performed at any facility capable of measuring the no-load loss. There are, however, some phenomena that occur in large transformers, and in transformers with high rated voltages. Examples include capacitive resonance and magnetic remanence. This thesis proposes and demonstrates techniques for compensating for these phenomena. With these compensating techniques, the repeatability of the measurements is high. It is shown that units with the same core steel tend to have very similar no-load behavior. The diagnostics can then be performed either by comparing the transformer to another unit, or to simulations. The thesis presents one possible simulation method, and demonstrates the agreement with measurements. This topological simulation method includes both the electric circuit and an accurate model of the magnetic hysteresis. It is therefore also suitable for other, related, studies in addition to core diagnostics. Possible subjects include ferroresonance, inrush, DC magnetization of transformers, and transformer core optimization. The thesis also demonstrates that, for three-phase transformers, it is possible to compare the phases to each other. This technique makes it possible to diagnose a transformer even without a previous measurement to compare to, and without the data required to make a simulation. / <p>QC 20170607</p>

The report is a study of error management and localization in underground cable network with very little overhead line. Error management is treated with the theoretical troubleshooting model and theoretical model with practical feedback. The work relates to the fact that troubleshooting has been complicated when the supply safety in the electricity grid increases. Difficult troubleshooting is followed by a difficult reset work in case of malfunctioning in the network and it leads to longer interruptions.The grid is built with main feed and radial feeds. In the cable stretches, an interval of the short-circuit current occurs with a minimum and a maximum current below the distance. Depending on how the network is built, multiples of same error current is created, that create harder error-handling. The analysis examines which locations in the grid, which help increase the number of alternative malfunctions and if there is any alternative method to solve the problem. The report deals with the connection between currents in main feed and in radial feeds along the line. There appears to be a connection between the emergences of currents with similar current values in several places. A network consisting of a main feed and a plurality of radial feeds, the occurrence of streams in several places is a disadvantage in the troubleshooting task and the work is adversely affected and the troubleshooting work becomes more difficult. / Rapporten är en studie om felhantering och fellokalisering i ett markbelagt kabelnät med en väldigt liten del friledning. Felhanteringen be-handlas med både dataprogramvara och teoretiska beräkningar. Arbetet relaterar till att felsökningen försvåras när leveranssäkerheten i elnätet ökar. Svårare felsökning är följt av ett försvårat återställningsar-bete vid fel i nätet som leder till längre avbrottstider. Elnätsområdet är uppbyggt med huvudmatning samt radiella matning-ar. I kabelsträckorna uppkommer ett intervall på kortslutningsström-men med en minsta och en högsta ström under sträckan. Beroende på hur nätet är uppbyggt skapas multiplar av felställen som skapar svårare felhantering. Analysen undersöker vilka ställen i elnätet som bidrar till att antalet alternativa felställen ökar och om det finns någon alternativ metod att lösa problemet. Rapporten behandlar sammanbandet mellan strömmar i huvudmatning och i radiella matningar längs ledningens sträcka. Det visar sig vara ett samband mellan uppkomsten av strömmar med liknande strömvärden på ett flertal ställen. Ett nät som består av en huvudmatning och ett flertal radiella matningar är uppkomsten av samma kortslutningsströmmar på flera ställen. Det är en nackdel i felsökningsarbetet och arbetet påverkas negativt och fel-sökningsarbetet blir svårare.

The grid code, FIKS, from the Norwegian transmission system operator (TSO), Statnett, states that synchronous generators &gt; 25MVA, must have a static excitation system. However, an improved brushless excitation system is in operation on some commercial power plants (36MVA, 93.75rpm &amp; 52MVA, 166.67rpm) with grid-assisting performance beyond the conventional static system. The convenional diode bridge is replaced with a remote-controlled thyristor bridge on the shaft. If wireless communication is not allowed, a control signal through brushes should be employed instead. The thesis explores the expected new era for large brushless hydrogenerators. The proposed brushless system have benefits of reduced regular maintenance due to elimination of brushes and reduced unscheduled maintenance due to redundancy; causing a redused cost-of-energy. A six-phase exciter design with a hybrid-mode thyristor bridge interface leads to improved fault-tolerance, better controllability, minimized torque pulsations and reduced armature currents of the exciter. Excitation boosting (EB) capability is included in the brushless system without additional components or circuitry, contrary to the static excitation system. The brushless excitation system is made insensitive to voltage dips in the interconnected grid, causing improved fault ride-through (FRT) capability and power system stabilizer (PSS) actions.

I en traditionellt konservativ bransch rör det sig nu snabbt. En snabb ökning av andelen förnybar elproduktion gör att det uppstår en rad nya utmaningar som måste lösas. Den här studien är en undersökning av framtidens distributionsnät och har ett fokus på nätstationerna. Studien visar att en ökad mängd distribuerad generering kan göra att dagens skydd inte fungerar som tänkt. Samtidigt ökar kraven på våra elnät. Detta medför att nya skydd kan behövas. Man ser också att automation ökar vilket minskar avbrottstiderna. Det undersöks också vilka elenergilagringssystem som finns och kan vara aktuellt i distributionsnätet. Studien visar att ett Li-Jon batterilager kan fylla flera olika viktiga funktioner åt olika aktörer, detta öppnar för flera olika inkomstkällor samtidigt som kostnaderna sjunker. Detta gör att det kan bli möjligt att energilager blir en vanligt förekommande komponent i distributionsnätet.