Showing papers on "Equivalent series resistance published in 2010"

Thermally evaporated Cu2ZnSnS4 solar cells

Abstract: High efficiency Cu2ZnSnS4 solar cells have been fabricated on glass substrates by thermal evaporation of Cu, Zn, Sn, and S. Solar cells with up to 6.8% efficiency were obtained with absorber layer thicknesses less than 1 μm and annealing times in the minutes. Detailed electrical analysis of the devices indicate that the performance of the devices is limited by high series resistance, a “double diode” behavior of the current voltage characteristics, and an open circuit voltage that is limited by a carrier recombination process with an activation energy below the band gap of the material.

A Real-Time Predictive-Maintenance System of Aluminum Electrolytic Capacitors Used in Uninterrupted Power Supplies

Abstract: This paper presents a low-cost method to realize a real-time condition monitoring and a predictive-maintenance system of an electrolytic capacitor used in uninterruptible power supplies (UPSs). This method consists in detecting the changes in real time of the equivalent series resistance and the capacitance C values of the electrolytic capacitors. Simulation and experimental results are presented to illustrate the proposed monitoring technique. The proposed method can be used in UPS where waveforms are continuously varying in amplitude, frequency, and temperature. The proposed online failure prediction method has the merits of using only the existent resources in UPS and with the use of known algorithms.

Spatially resolved determination of dark saturation current and series resistance of silicon solar cells

Abstract: Luminescence images of silicon solar cells contain information about local recombination properties and local series resistance. It is difficult to separate the information and interpret single images correctly and quantitatively though, which greatly limits the use of single luminescence images, in particular for the application as an in-production characterization tool. We therefore developed a fast method based on photoluminescence imaging for a spatially resolved coupled determination of the dark saturation current and series resistance (C-DCR). (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An Online and Noninvasive Technique for the Condition Monitoring of Capacitors in Boost Converters

Abstract: Capacitors usually determine the overall lifetime of power converters since they are mainly responsible for breakdowns. Their failure results from the deterioration of their dielectric, the production of gases, and, eventually, their explosion. This process leads to an increase in the capacitor equivalent series resistance (ESR) and a decrease in its capacitance value for both electrolytic and metalized polypropylene film (MPPF) capacitors. In this paper, a novel noninvasive technique for capacitor diagnostic in Boost converters is presented. It can easily be applied online and even in real time, and it is suitable for the operation in both continuous current mode (CCM) and discontinuous current mode (DCM). The technique is based on the double estimations of the ESR and the capacitance, improving the diagnostic reliability. This way, predictive maintenance is provided, and it is possible to alarm for capacitor replacement, avoiding downtime. As the method is intended for railway high-power applications, it has been conceived neither to add any additional hardware in the power stage nor to even slightly modify it. To demonstrate and validate the effectiveness and accuracy of the proposed technique, several simulations and experimental results are discussed in a small prototype. In this prototype, the software for real-time estimation is programmed in a low-cost digital signal processor (DSP).

Evaluating luminescence based voltage images of silicon solar cells

Abstract: In this paper we give a mathematical derivation of how luminescence images of silicon solar cells can be calibrated to local junction voltage. We compare two different models to extract spatially resolved physical cell parameters from voltage images. The first model is the terminal connected diode model, where each pixel is regarded as a diode with a certain dark saturation current, which is connected via a series resistance with the terminal. This model is frequently used to evaluate measurement data of several measurement techniques with respect to local series resistance. The second model is the interconnected diode model, where the diode on one pixel is connected with the neighbor diodes via a sheet resistance. For each model parameter at least one image is required for a coupled determination of the parameters. We elaborate how also the voltage calibration can be added as an unknown parameter into the models, and how the resulting system of equations can be solved analytically. Finally the application of the models and the different ways of voltage calibration are compared experimentally.

Quantitative evaluation of electroluminescence images of solar cells

Abstract: A fast converging iterative procedure is proposed to calculate series resistance (Rs) and saturation current (j0) images from two electroluminescence (EL) images taken at two biases. It is not necessary here that for one bias the influence of the series resistance is negligible. Moreover, voltage series of EL images have been evaluated for calculating images of Rs, j0, and the parallel conductance Gp separately. However, it has been found that Rs variations cannot uniquely be separated from Gp variations. The reason for this is discussed. Thus, for quantitatively detecting weak ohmic shunts, EL imaging cannot replace lock-in thermography. For strong ohmic shunts a formula for converting EL images into shunt images is given. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Extraction of poly (3-hexylthiophene) (P3HT) properties from dark current voltage characteristics in a P3HT/n-crystalline-silicon solar cell

Abstract: The dark current-voltage characteristics of poly (3-hexylthiophene) (P3HT)/n-type crystalline silicon solar cells were analyzed using an electrical equivalent circuit. We found that without illumination transport occurs due to hopping between localized states at the P3HT/silicon interface not only at low voltages, through multitunneling capture emission, but also at medium voltages, through tunneling-enhanced recombination. At high voltages the current is limited by series resistance and space-charge limited mechanisms. At low reverse voltages the current is limited by shunt resistance. From the temperature dependence of the equivalent circuit’s fitting parameters, we were able to estimate some physical parameters of the P3HT layer, namely the electron affinity, the charge carrier concentration and the characteristic temperature of the exponential trap distribution. The extracted P3HT values are in good agreement with previously reported values obtained using different methods but our approach takes into ...

Recent Developments in Fault Detection and Power Loss Estimation of Electrolytic Capacitors

Abstract: This paper proposes a comparative study of current-controlled hysteresis and pulsewidth modulation (PWM) techniques, and their influence upon power loss dissipation in a power-factor controller (PFC) output filtering capacitors. First, theoretical calculation of low-frequency and high-frequency components of the capacitor current is presented in the two cases, as well as the total harmonic distortion of the source current. Second, we prove that the methods already used to determine the capacitor power losses are not accurate because of the capacitor model chosen. In fact, a new electric equivalent scheme of electrolytic capacitors is determined using genetic algorithms. This model, characterized by frequency-independent parameters, redraws with accuracy the capacitor behavior for large frequency and temperature ranges. Thereby, the new capacitor model is integrated into the converter, and then, software simulation is carried out to determine the power losses for both control techniques. Due to this model, the equivalent series resistance (ESR) increase at high frequencies due to the skin effect is taken into account. Finally, for hysteresis and PWM controls, we suggest a method to determine the value of the series resistance and the remaining time to failure, based on the measurement of the output ripple voltage at steady-state and transient-state converter working.

Process for producing electrolytic capacitors with a polymeric outer layer

Abstract: The invention relates to a process for producing electrolytic capacitors with low equivalent series resistance, low residual current and high thermal stability, which consist of a solid electrolyte and an outer layer comprising conjugated polymers, to electrolytic capacitors produced by this process and to the use of such electrolytic capacitors.

Integrated diagnostic/prognostic experimental setup for capacitor degradation and health monitoring

Abstract: This paper proposes the experiments and setups for studying diagnosis and prognosis of electrolytic capacitors in DC-DC power converters. Electrolytic capacitors and power MOS-FET's have higher failure rates than other components in DC-DC converter systems. Currently, our work focuses on experimental analysis and modeling electrolytic capacitors degradation and its effects on the output of DC-DC converter systems. The output degradation is typically measured by the increase in Equivalent series resistance and decrease in capacitance leading to output ripple currents. Typically, the ripple current effects dominate, and they can have adverse effects on downstream components. A model based approach to studying degradation phenomena enables us to combine the physics based modeling of the DC-DC converter with physics of failure models of capacitor degradation, and predict using stochastic simulation methods how system performance deteriorates with time. Degradation experiments were conducted where electrolytic capacitors were subjected to electrical and thermal stress to accelerate the aging of the system. This more systematic analysis may provide a more general and accurate method for computing the remaining useful life (RUL) of the component and the converter system.

Investigation of the electrical properties of a surface-type Al/NiPc/Ag Schottky diode using I- V and C- V characteristics

Abstract: Electrical properties of Al/NiPc/Ag surface type Schottky diode fabricated by vacuum thermal evaporation have been investigated. The current–voltage (I–V) and capacitance–voltage (C–V) characteristics are measured at room temperature in dark. The electronic parameters such as ideality factor, barrier height, series resistance and shunt resistance of the Schottky diode are calculated from the current–voltage and capacitance–voltage characteristics. The charge carrier concentration and built in potential values of 9.1×1015 cm−3 and 1.6 V, respectively, are obtained from the C–V plot. The value of conductivity and mobility has also been calculated. In addition, the values of ideality factor and series resistance are also verified by using Cheung's function. Frequency-dependent measurements on this Schottky barrier diode show that the capacitance is reduced at high frequency.

Simple Experimental Techniques to Characterize Capacitors in a Wide Range of Frequencies and Temperatures

Abstract: The aim of this paper is to present two very simple, cheap, and practical experimental techniques that are able to estimate the capacitor equivalent circuit for a wide range of frequencies and temperatures. The capacitor equivalent circuit considerably changes with temperature, aging, and frequency. Therefore, knowledge of their equivalent circuit at their operating conditions can lead to better design proposals. In addition, knowledge of the evolution of the equivalent series resistance (ESR) with temperature is essential for the development of reliable online fault diagnosis techniques. This issue is particularly important for aluminum electrolytic capacitors, since they are the preferred capacitor type in power electronics applications and simultaneously one of the most critical components in such applications. To implement the first technique, it is necessary to put the capacitor under test in series with a resistor and connect it to a sinusoidal voltage. The second technique requires a simple charge-discharge circuit. After acquiring both capacitors' current and voltage through an oscilloscope, which is connected to a PC with Matlab software, it is possible to compute both capacitor capacitance and resistance using the least mean square (LMS) algorithm. To simulate the variation of capacitor case temperature, a very simple prototype was used. Several experimental results were obtained to evaluate the accuracy and precision of the two experimental techniques.

Temperature dependent capacitance and conductance-voltage characteristics of Au/polyvinyl alcohol(Co,Zn)/n-Si Schottky diodes

Abstract: The temperature dependence of capacitance-voltage (C-V) and conductance-voltage (G/w-V) characteristics of Au/polyvinyl alcohol (Co,Zn-doped)/n-Si Schottky diodes (SDs) was investigated by considering series resistance effect in the temperature range of 80–400 K. The C-V and G/w-V characteristics confirm that the series resistance (Rs) and interface state density (Nss) of the diode are important parameters that strongly influence the electric parameters of SDs. The crossing of the G/w-V curves appears as an abnormality compared to the conventional behavior of ideal SDs. It is thought that the presence of series resistance keeps this intersection hidden and unobservable in homogeneous SDs but it appears in the case of inhomogeneous SDs. In addition, the high frequency Cm and Gm/w values measured under both reverse and forward bias were corrected for the effect of series resistance to obtain the real diode capacitance and conductance.

Determination of diode parameters of a silicon solar cell from variation of slopes of the I–V curve at open circuit and short circuit conditions with the intensity of illumination

Abstract: An analytical method of determination of all the four diode parameters of the single exponential model of a silicon solar cell, namely shunt resistance Rsh, series resistance Rs, diode ideality factor n and reverse saturation current I0 from the variation of slopes of the I–V curve of the cell near short circuit and open circuit conditions with intensity of illumination in a small range of intensity, is presented for the first time. In a suitable range of intensity the variation of dI/dV at short circuit enables determination of Rsh, whereas the variation of dI/dV at open circuit enables determination of Rs, n and I0. The diode parameters of a silicon solar cell were determined with this method using I–V characteristics of the cell in 40–125 mW cm−2 intensity range of a simulated AM1.5 solar radiation. Theoretical I–V curves generated using so determined values of the diode parameters matched well with the experimental I–V curves of the cell obtained under various intensities of illumination in the above range.

Large-area organic solar cells with metal subelectrode on indium tin oxide anode

Abstract: This study examined the effects of the electrode geometry combined with the cell area on the device performance. We systematically investigated the effects of cell area in organic solar cells (OSCs) by introducing of metal subelectrodes to reduce the resistive loss of indium tin oxide. The subelectrode defines the active area and works as the conducting electrode at the same time with very low resistance. The series resistance could be reduced significantly by using the subelectrode, yielding a power conversion efficiency of 2.6±0.3% up to the cell area of 4.08 cm2. This suggests that OSCs with subelectrode geometry can be used for evaluating new materials and processes with accurate measurements on the centimeter scale.

Overview of laminar dielectric capacitors

Abstract: Laminar dielectric capacitors tend to be used in high voltage, precision, high power density, and high energy density applications. Such capacitors are near ideal in their discharge characteristics.

Lifetime analysis of aluminum electrolytic capacitor subject to voltage fluctuations

Abstract: This paper evaluates the changes in the ripple current for an electrolytic capacitor used in the dc-side of a single-phase rectifier circuit when subjected to input voltage fluctuations. The study has been undertaken in order to analyse the potential impact on capacitor lifetime. The key effect is that the capacitor ripple current, as a consequence of voltage fluctuations, increases dramatically and this phenomenon keeps deteriorating as the frequency of the voltage fluctuations increases. Simulations and experimental work confirm this phenomenon. Since the power loss and temperature rise are dependent on the capacitor equivalent series resistance (ESR) and ripple current components, an increase in ripple current under voltage fluctuation conditions is likely to accelerate this process, resulting in a reduced lifetime.

Voltage-dependent capacitors in power electronic multi-domain simulations

Abstract: We discuss multi-domain simulation of power electronic systems where non-linear capacitors have a significant impact on the system behaviour, e.g. employing the MOSFET output capacitor Coss for soft switching or employing nonlinear thermal models in coupled electrical-thermal simulations. It is shown which errors can result from approximating non-linear capacitors with simple linear ones as proposed e.g. for Coss in datasheets. Furthermore a highly efficient implementation of non-linear capacitors in numerical circuit simulators is proposed.