1,721,171 research outputs found
Peculiar role of holes and electrons in the degradation of CdTe thin films
No full textFor the first time, the degradation rate of the electrical parameters in thin-film solar cells based on CdS/CdTe materials is simulated numerically using the Analysis of Micro- electronics and Photonic Structures (AMPS-1D) program. This time-dependent approach attributes the defect generation rate to the excess carrier concentration profile. The degradation rate is ana- lyzed for the devices stressed under the open-circuit, short-circuit, illumination, and dark conditions. Illuminated open-circuited devices showed a faster degradation rate than the short-circuited and dark-rested ones. This instability was mostly driven by the loss in the fill factor relevant to the increased series resistance. A separate analysis of the degradation behavior arisen from the holes and electrons indicates that the holes degrade the device slightly stronger than the electrons. In the CdTe thin films, the drift mobility of the holes is an order of magnitude lower than that of the electrons, which allows a longer interaction of the holes with the semiconductor lattice. Starting from the simplest device structure, e.g., Gloeckler model, the calculations are extended to the defect increment at the very thin layers placed at the front and back regions of the device. Both layers caused an almost similar degradation trend but a slightly faster rate when the thin defective layer was placed at the junction. This time-dependent approach can be extended to simulate the degradation behavior of the electrical parameters in other thin-film devices, such as CIGS and CZTS materials, under the different stress conditions leading to the different defect distribution across the device thickness
Variability caused by Setup and Operating Conditions for Conducted EMI of Switched Mode Power Supplies over the 2-1000 kHz Interval
Full text linkThe measurement of conducted emissions of Switched Mode Power Supplies (SMPSs) is discussed for the 2-1000 kHz frequency range, analyzing variability caused by setup elements and test conditions. The tested SMPSs have 12 VDC output and about 20 W nominal power. They are fed by a controlled AC power supply, instead of mains, through a Line Impedance Stabilization Network and various loading levels are applied. Identified causes of variability (supply volt- age and frequency variations, thermal stabilization influencing internal mechanisms of emissions) indicate a relevant impact on the spread of measured conducted emissions, ranging from a fraction of dB to about 10 dB (sample standard deviation). Such phenomena represent a cause first of all of systematic error, but also of increased uncertainty. No EMC standards are known to take them into account, nor the scientific literature reports extensive quantification, as in the present case. The shift of the line spectrum of emission consequential to a mains frequency change revealed to be exploitable also for better identification of internal sources of emission
Aggregation of Low-Frequency Conducted Emissions in DC Grids with Wireless Power Transfer Chargers
No full textThis work considers the aggregation of conducted emissions in the supraharmonic range below 150 kHz originating from a set of wireless power transfer (WPT) converters for electric vehicle (EV) charging. Such converters are all fed by a common DC grid, representing a promising architecture to allow the increase of EV penetration while better controlling distortion and stability. A network of three WPT converters is analysed under varying alignment, load, and synchronization conditions. The analysis demonstrates that the aggregation of emissions from multiple converters can be effectively managed through careful design of the DC grid, minimizing interference and maintaining overall system stability. Additionally, the results emphasize the significance of accounting for both the coupling coefficient and load conditions to reduce distortion and enhance the performance of the system
Numerical analysis of degradation kinetics in CdTe thin films
No full textA time-dependent approach is introduced to numerically analyze the degradation of CdS/CdTe thin film photovoltaics under different stress conditions using the SCAPS-1D program. Under the stress conditions of light, temperature or bias, the excess charge carriers (holes/electrons) are created/accumulated within the CdTe layer which leads to a defect generation/increment mostly at the interface. The defect increment specially around the midgap level leads to the degradation of device parameters. Since the excess charge carriers and defect increment are coupled we examine several carrier kinetics such as the linear n- or p-model, bilinear np-model and quadratic n2-model. This comprehensive simulation is consistent with the polycrystalline nature of CdTe materials and their ambiguous degrada- tion mechanism. Simulations are performed for short-circuited and open-circuited devices that are assumed to be also under stress con- ditions of temperature, dark and light. The degradation rate in the device parameters, variations in band diagrams and current–voltage characteristics are analyzed and compared with the relevant experimental reports in literature. As a novelty, our analyses indicate that the degradation rate caused by the linear kinetics of the holes competes with the nonlinear kinetics of the electrons. Thus, holes can lead to a stronger degradation than that of electrons because of their smaller mobility in CdTe materials. Dividing the CdTe layer into several thinner sublayers in the SCAPS platform allows us to analyze the effect of the defect increment position on the device degradation. It is shown that the junction is critically sensitive to defects and charge carrier accumulation. These simulations reveal that the location of carrier/defect accumulation can be just as important as the carrier type and concentration. This simulation approach can be extended to other thin film materials, dye cells and perovskite materials and also to photodetectors and CMOS devices
Study of the Conducted Emissions of an SMPS Power Converter from 2 to 150 kHz
No full textIn this paper the electromagnetic interference generated by an SMPS power converter in the 2-150 kHz frequency range is studied. Measurement and evaluation of the conducted emissions are carried out in the time domain and transformed into the frequency domain by means of the Short-Time Fourier transform. In the absence of current coordinate electromagnetic compatibility regulations for this frequency range, the aim is to find out whether measurement and processing settings of the time-domain electromagnetic interference may have an impact on the conducted emission results in the frequency domain. A prototype of an SMPS battery charger power converter for electric vehicles is used in the experiments. The results show that both measurement and processing settings may affect the conducted emissions
Magnetic near field from an inductive power transfer system using an array of coupled resonators
No full textIn this paper the magnetic near field from a wireless power transfer (WPT) system that employs an array of magnetically coupled resonators is assessed with the aim of examining the relation between the termination impedance of the system and the magnetic near field generated. The electromotive force at the terminals of a circular probe produced by the time-varying magnetic near field generated by the WPT system is measured and the corresponding magnetic flux density is calculated. The measurements are compared with the results obtained using a finite-element software. It is found that, despite the fact that the field at a small distance is much higher than that at a higher distance from the array, not all the field is confined into to the array of resonators. Furthermore, by analysing the measurements and simulations it can be observed that, when the system is matched, in no case the obtained peak values for the magnetic flux density are the highest ones
Extension of Random Walk Modelling of CM Current Harmonics in Multi-converter Setups
No full textThis paper presents an extension of a Pearson's Random Walk (PRW) discussed in our previous papers as a modelling tool for predicting the common mode (CM) current in multi-converter setups, based on the CM current of a single converter. Our earlier work was limited by the assumption that CM current could only be modeled as a sinusoidal damped oscillation. Here, we introduce a more general approach where the PRW modelling can be applied to any periodic signal with an existing Fourier Transform. Beyond theoretical discussion, we validate our extended methodology through multiple test cases using signals commonly found in power electronic (PE), electromagnetic compatibility (EMC), and other electrical circuit applications - including damped sinusoids, exponential decays, chirps, Lorentzian pulses, half-sine pulses, Gaussian pulses, and sawtooth waves. Our test results confirm our theoretical derivations, demonstrating that the PRW can be effectively extended to model diverse classes of periodic signals. We also address limitations associated with test signal post-processing
Measurement and Evaluation of the Conducted Emissions of a DC/DC Power Converter in the Frequency Range 2-150 kHz
No full textIn this paper the conducted emissions generated by a DC/DC power converter system in the 2-150 kHz frequency range are studied in both time and frequency domains. Measurement and evaluation of the conducted emissions are carried out to assess the level of the emissions of the system with reference to the existing standards and to point out which measurement settings may have an impact on the measurement results. A prototype of a DC/DC battery charger for electric vehicles was used in the experiments. The results show that the DC/DC power converter system may not result in being compliant to some of the existing standards in the frequency range 2-150 kHz and that measurement settings may affect significantly the evaluation of the conducted emissions
Circuit model of a resonator array for a WPT system by means of a continued fraction
No full textThis paper presents the circuit model of an array of magnetically coupled identical resonators, which is represented with an equivalent impedance expressed as a continued fraction. By solving this continued fraction with the theory of linear homogeneous difference equations, it is possible to determine the equivalent impedance of an array of identical resonators terminated in a given load as well as the equivalent impedance in the case of one or more receivers above the resonator line. The equivalent impedance is used afterwards to analyse the behaviour of the input impedance of the resonator array as seen from the voltage source, when series or parallel resonance configurations are considered. Additionally, some numerical examples are made considering an array of resonators with two receivers over the line. Finally, using the software Simulink as circuit simulator, the theoretical results presented in this work are numerically validated for different conditions of the system
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