Equivalent series resistance

Abstract: DC-link capacitors are an important part in the majority of power electronic converters which contribute to cost, size and failure rate on a considerable scale. From capacitor users' viewpoint, this paper presents a review on the improvement of reliability of dc link in power electronic converters from two aspects: 1) reliability-oriented dc-link design solutions; 2) conditioning monitoring of dc-link capacitors during operation. Failure mechanisms, failure modes and lifetime models of capacitors suitable for the applications are also discussed as a basis to understand the physics-of-failure. This review serves to provide a clear picture of the state-of-the-art research in this area and to identify the corresponding challenges and future research directions for capacitors and their dc-link applications.

Abstract: Current-voltage characteristics of photovoltaic solar energy converter cells are obtainable by three methods, which yield different results due to the effects of the cell internal series resistance. The three resultant characteristics are: (1) the photovoltaic output characteristic, (2) the p-n junction characteristic, and (3) the rectifier forward characteristic. Choice of the proper method is necessary for obtaining the correct information for the individual application. Most frequently used, e.g. for the determination of solar converter performance, is the photovoltaic output characteristic. A quick way is described for deriving such a characteristic for any light level from a corresponding characteristic obtained at a different light level. This method involves two translations of the coordinate system and requires only the knowledge of the series resistance and the difference in light intensities or short circuit currents. An inversion of this method permits an easy determination of the series resistance, involving measurements at two arbitrary light levels of unknown magnitude. The effects of series resistance consist at high light levels in a flattening of the photovoltaic output characteristic and a related drop in the maximum power point voltage. The resultant decrease in efficiency has to be overcome by series resistance reduction for solar cell applications with optical concentrators or for space missions in closer sun-proximity. In cell portions progressively further distant from the contact strip increasing cell voltages develop, approaching open circuit condition at very high light intensities. This yields a reduction of current contribution from those portions of the cell and a deviation from the normal proportionality between short circuit current and light intensity. The direct measurability of the p-n junction characteristic at high current densities without series resistance effects by the second method provides a powerful tool to the device development engineer, besides yielding a second method for the determination of the series resistance. Results from the application of this method indicate that, in the current density range as used in solar energy conversion, the silicon solar cell characteristic is much more closely described by the diffusion theory for p-n junctions than was previously believed.

Abstract: A power conversion efficiency record of 10.1% was achieved for kesterite absorbers, using a Cu2ZnSn(Se,S)4 thin-film solar cell made by hydrazine-based solution processing. Key device characteristics were compiled, including light/dark J–V, quantum efficiency, temperature dependence of Voc and series resistance, photoluminescence, and capacitance spectroscopy, providing important insight into how the devices compare with high-performance Cu(In,Ga)Se2. The record kesterite device was shown to be primarily limited by interface recombination, minority carrier lifetime, and series resistance. The new level of device performance points to the significant promise of the kesterites as an emerging and commercially interesting thin-film technology. Copyright © 2011 John Wiley & Sons, Ltd.

Abstract: This paper describes the electrochemical performance of carbon onions, nanodiamonds, carbon black and multiwalled nanotubes as electrodes in electrical double layer capacitors with organic electrolyte. Onions were formed by vacuum annealing of 5 nm nanodiamond (ND) powder at 1200–2000 °C with the goal to investigate the effect of carbon microstructure on specific capacitance and ion transport. In contrast to micro- or mesoporous activated carbons, the outer surface of carbon onions is fully accessible to electrolyte ions and the size of pores between carbon onions or nanotubes does not depend on the annealing temperature. Charge-discharge measurements revealed a two times decrease in the specific capacitance of onions and nanotubes upon graphitization and formation of polyhedral particles after annealing at 1800 °C and above. However, the capacitance became less current dependant. The carbon onion cells are able to deliver the stored energy under a high current density with a capacitance twice than the one obtained with MWCNT. Electrical measurements and impedance spectroscopy showed about two orders of magnitude increase in conductivity of electrodes and twofold decrease in the equivalent series resistance of the assembled cells after heat treatments of ND. The time constant extracted from the impedance data is around 10 times smaller for ND annealed at above 1800 °C than for activated carbons and is closely approaching the one for MWCNT. This shows that the open structure of carbon onions leads to an increased ability to quickly deliver the stored energy.

Abstract: Internal resistance in a dye-sensitized solar cell (DSC) was investigated using electrochemical impedance spectroscopy measurements. Four resistance elements were observed in the impedance spectra, and their dependencies on the applied bias voltage were characterized. It is found that the resistance element related to charge transport at the TiO2/dye/electrolyte interface displays behavior like that of a diode, and the series resistance elements largely correspond to the sum of the other resistance elements. An equivalent circuit for DSCs is proposed based on these results.