This thesis investigates the effect of the ripple current on the output power of solar cells. A solar panel with several metal halide lamps is set up to emulate the photovoltaic power system, which is cascaded by a boost converter and a buck-boost converter to extract triangular and trapezoidal currents, respectively. All experiments are operated under the room temperature with different current ripples and frequencies. The measured current and voltage waveforms at the output powers indicate that the dynamic characteristics are very different from static ones obtained from the dc loads. It is found that the output voltage lags the current when the peak of the rippled current goes beyond the maximum power point (MPP), leading to a declination in the average output power. This phenomenon becomes more severe for a higher peak, lower frequency, and larger charge of the rippled current exceeding the MPP. In addition, the declination in the average power may cause a shift of the MPP.

Fuel cells are expected to play an important role in future power generation. However, significant technical challenges remain and the commercial breakthrough of fuel cells is hindered by the high price of fuel cell components. As is well known, the fuel cells do not provide the robust source characteristics required to effectively follow the load during significant load steps and they have limited overload-handling capability. Further, the performance of the fuel cell is significantly degraded when the CO (Carbon Monoxide) is contained in the hydrogen fuel. In this thesis several new approaches to improve the performance of PEM based fuel cell power systems are discussed. In the first section an impedance model of the Proton Exchange Membrane Fuel Cell Stack (PEMFCS) is first proposed. This equivalent circuit model of the fuel cell stack is derived by a frequency response analysis (FRA) technique to evaluate the effects of the ripple current generated by the power-conditioning unit. Experimental results are presented to show the effects of the ripple currents. In the second section, a fuel cell powered UPS (Uninterruptible Power Supply) system is proposed. In this approach, two PEM Fuel Cell modules along with suitable DC/DC and DC/AC power electronic converter modules are employed. A Supercapacitor module is also employed to compensate for instantaneous power fluctuations including overload and to overcome the slow dynamics of the fuel processor such as reformers. A complete design example for a 1-kVA system is presented. In the third section, an advanced power converter topology is proposed to significantly improve the CO tolerance on PEM based fuel cell power systems. An additional two-stage dc-dc converter with a supercapacitor module is connected to the fuel cell to draw a low frequency (0.5Hz) pulsating current of the specific amplitude (20-30[A]) from the fuel cell stack. CO on the catalyst surface can be electro-oxidized by using this technique, and thereby the CO tolerance of the system can be significantly improved. Simulation and experimental results show the validity and feasibility of the proposed scheme.

An investigation was conducted to determine and compare the effect of cell current pulsing and "self-oxidation" in increasing the CO tolerance of a PEM fuel cell. The most effective pulsing parameter values were also determined. Current pulsing involves periodically demanding positive current pulses from the fuel cell to create an anode over-potential, while "self-oxidation" or sustained potential oscillations is achieved when the anode catalyst becomes so saturated with CO that the anode over-potential increases to a value at which CO is oxidized from the catalyst surface. The CO tolerance of a fuel cell system with a Pt-Ru anode was tested using 50 and 496 ppm CO in the anode fuel. The performance of the system declined with an increase in CO concentration. Current pulses of various amplitude, frequency, and duty cycle were applied to the cell while CO was present in the anode fuel. With 50 ppm CO in the anode fuel, the most effective pulse in increasing CO tolerance while maintaining normal cell operation was 1.0 A/cm2, 0.25 Hz, and a 5% duty cycle. A pulse (120 Hz, 50% duty cycle) similar to the ripple current often generated when converting DC to single-phase 60 Hz AC had a positive effect on the CO tolerance of the system, but at frequencies that high, the pulse duration was not long enough to completely oxidize the CO from the catalyst surface. With 496 ppm CO in the anode fuel, a pulse of 1.0 A/cm2, 0.5 Hz, and a 20% duty cycle proved most effective. When the cell was exposed to 496 ppm CO, without employing pulsing, "self-oxidation" occurred and CO was periodically oxidized from the catalyst surface. However, pulsing allowed the cell to operate at the desired voltage and power a higher percentage of the time than "self-oxidation"; hence, pulsing was more effective.

This thesis deals with position control of movable solenoid core without using a distance sensor. There are several methods of sensorless position estimation presented in theoretical part. The method based on measurement of ripple current is chosen for experiments. Firstly, it is verified by simulations with mathematical model of solenoid. After that, the experiment is created. The goal is position control based on sensorless method.

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Sjöfarten är idag dominerad av förbränningsmotorer som är beroende av fossila drivmedel. Elektrifiering är en av huvudstrategierna för att möjliggöra fossilfri energiförsörjning inom internationell sjöfart. Polymerelektrolytbränslecellen (PEMFC) omvandlar vätgas till elektricitet med hög verkningsgrad och är för närvarande kommersiellt tillgängligt upp till MW-skala för ett fartyg. Vätgas är en utmärkt energibärare för att tillgodose hög energidensitet hos ett fraktfartyg. Rippelströmmar från elkraftskomponenter påstås accelerera åldring av materialen i PEMFC och kan därför skapa negativa effekter över tid som påverkar livslängden av systemet.  De tillgängliga studier som utvärderar rippelströmmars påverkan på åldring i PEMFC är begränsade. Resultaten i dessa studier är tvetydiga och saknar tydliga kopplingar mellan rippelströmmarnas inverkan på åldringsfenomen, som på sikt kan påverka den tekniska livslängden. Målet med examensarbetet var att identifiera effekten av rippelströmmar på åldring av bränslecellen vid typiska körförhållanden för ett fraktfartyg. Tester genomfördes på en PEMFC genom att applicera en sinusformad (70 Hz, 50 % amplitud) rippelström på en dynamisk last som simulerar ett fraktfartyg. En konstant lastcykling vid 0.4 A/cm2 utfördes som ett komplement för att verifiera den dynamiska lastens inverkan på bränslecellen.  Alla tester resulterade i prestandaförluster både under den konstanta och dynamiska lasten, med eller utan rippelström. Men resultaten indikerade att effekten av en sinusformad rippelström inte orsakade någon signifikant åldring varken vid konstant respektive dynamisk lastcykel. / The marine shipping industry is dominated by fossil fuel driven propulsion. Electrification of marine vessels is one of the main strategies to enable emission-free propulsion. Hydrogen is an excellent energy carrier to meet the power demand of a marine vessel. Proton exchange membrane fuel cells (PEMFC) is a commercially available alternative for converting hydrogen into electricity. However, durability issues of the PEMFC is a constraint with the technology which limits technical lifetime. Research around ripple currents impact on degradation of PEMFC is scarce and the reported results are ambiguous and lack clear correlation between the effects of the ripple current on the lifetime of a PEMFC. This master thesis evaluates the impact on degradation of a single cell PEMFC by imposing a sinusoidal (70 Hz, 50 % amplitude) AC ripple to a dynamic load cycle. The dynamic load cycle is designed to simulate typical operating conditions of a marine vessel. Constant load cycling at 0.4 A/cm2 with the same ripple characteristics was also conducted to verify the dynamic load cycling impact on the performance losses of the PEMFC. The in-situ characterization showed performance losses both during the dynamic and constant load cycling, for the ripple current and reference tests. To conclude, no significant effects on degradation by the sinusoidal ripple current of 70 Hz and 50% amplitude is found when applied to a single cell PEMFC despite of performance losses for all cases.

In recent years, the demand for Li-ion-type batteries has been increasing significantly in various fields of applications including portable electronics, electric vehicles, and also in renewable energy support. These applications ask for a highly efficient charging strategy in order to maintain a long life cycle of the batteries. Recently, a new charging technique referred as sinusoidal ripple current-constant voltage charging (SRC-CV) technique has been proposed and is in certain publications claimed to realize an improved charging per-formance on Li-ion batteries than conventional constant-current constant-voltage charg-ing (CC-CV) techniques. In this thesis, the charging performance of the SRC-CV charging method applied to a prismatic Li-ion cell for an automotive traction application is inves-tigated. An existing experimental setup is upgraded to realize charging of the Li-ion cells using the SRC-CV charging method. Electrochemical impedance spectrums of three Li-ion cells have been obtained using electrochemical impedance spectroscopy (EIS). These spectrums were used to determine the charging ripple-current frequency where the mag-nitudes of the ac impedance of the cell are minimized. Key parameters like charging time, discharging time, and energy efficiency are calculated in order to compare the charg-ing performance of the CC-CV and SRC-CV charging techniques. The results reported from the experimental results obtained in this thesis indicate that there is no significant improvement with the SRC-CV charging method (implemented using a constant ripple-current frequency) compared to the CC-CV method in terms of charging time and energy efficiency. / På senare tid har behovet av batterier av Li-jontyp ökat kraftigt inom ett flertal applikationsområden inkluderande portabel elektronik, elfordon och miljövänlig elenergiproduktion. I dessa applikationsområden behövs en högeffektiv laddstrategi för att möjliggöra ett stort antal cyklingar av batterierna. Nyligen har en new laddmetod, benämnd sinusoidal ripple current-constant voltage-laddning (SRC-CV-laddning) föreslagits och har i vissa publikationer demonsterat en förbättring av laddprestanda hos Li-jonbatterier jämfört med konventionell constant-current constant-voltage-laddning (CC-CV-laddning). I detta examensarbete undersöks laddprestandan hos SRC-CV och CC-CV-laddning när de appliceras på prismatiska Li-jonceller avsedda för traktionsdrift. En existerande experimentuppsättning har uppgraderats för att realisera laddcykling med SRC-CV-laddning. Med hjälp av elektrokemisk impedansspektroskopi på tre Li-jonceller har den frekvens vid vilken magnituden på cellernas impedans är minimerad identifierats. Nyckelparametrar såsom laddtid, urladdningstid och energieffektivitet har uppmätts för både SRC-CV- och CC-CV-laddning. De experimentella resultaten visar ingen signifikant förbättring mellan SRC-CV-laddning (implementerat med en konstant rippelströmfrekvens) och konventionell CC-CV-laddning.