Showing papers on "Equivalent series resistance published in 2019"

A VEN Condition Monitoring Method of DC-Link Capacitors for Power Converters

Abstract: The dc-link capacitors are important components that tend to be one of the weakest part of power converters. Thus, it is necessary to monitor the aging parameters of dc-link capacitors in valuable power electronic systems. This paper proposes a simple yet effective variable electrical network (VEN) condition monitoring method for dc-link capacitors in three-phase pulsewidth modulation (PWM) ac–dc–ac power converters. The capacitance ( C ) and equivalent series resistance of dc-link capacitors are estimated through the designed VEN unit during the discharging process. This VEN method does not need the current sensor or injecting signals into the control loop. The above property is favorable for the hardware and controller design. Besides, the designed monitoring circuit can be an external unit or a built-in unit which offers a flexible solution for electrical devices. When the designed VEN is used as an external unit, neither the hardware design nor the programs in the controller needs to change, which is practical and economic for electrical devices in use. Experiments are carried out in a 55 kW ac–dc–ac inverter with different capacitors. The experiment results prove the method to be effective and accurate.

An Online ESR Estimation Method for Output Capacitor of Boost Converter

Abstract: Aluminum electrolytic capacitor (AEC) is one of the most age-affected components in power electronic converters and its reliability has been a major concern. As the growth of service life, the equivalent series resistance (ESR) of AEC increases due to the loss of electrolyte. Therefore, online ESR estimation is critical for condition monitoring of AEC. This paper proposes an online ESR estimation method for output capacitor of boost converter. By analyzing the output voltage ripple, an ESR calculation model is derived. Based on the model, only output voltage and inductor current need to be measured, which can be obtained directly from double closed-loops converter. To implement this proposed method, a detailed extraction scheme based on wavelet transform denoising is presented. Non-ideal factors (noise and voltage spikes) are analyzed and the superiority of the proposed parameter identification scheme is verified. The proposed estimation method can obtain ESR for the converter operating at different working conditions such as resistive loads and converter loads. Effect of temperature on ESR is incorporated for accurate determination of the health of capacitor. Simulation and experimental results are provided to verify the effectiveness of the method.

From Dye Sensitized to Perovskite Solar Cells, The Missing Link

Abstract: Fundamental working mechanisms of perovskite solar cells remain an elusive topic of research. Impedance Spectroscopy (IS) application to perovskite-based devices generates uncommon features and misleading outputs, mainly due to the lack of a stablished model for the interpretation of the results. In this work we control the perovskite precursor concentration to fabricate a series of perovskite-based solar cells with different amounts of perovskite absorber. Low concentration devices present the well-known dye sensitized solar cell (DSSCs) impedance pattern. As the amount of perovskite is increased, the characteristic impedance spectra of thin-film perovskite solar cells (PSCs) arises. This transition is characterized by a change in the working principles, determined by an evolution of the dominant capacitance: from the intermediate frequency chemical capacitance of TiO2 in devices with isolated perovskite domains, to a large low-frequency capacitance signal which divides the spectra in two sections, yet with no direct influence in final device performance. This study allows to link experimentally, in terms of impedance behavior, PSCs with the rest of solar cell devices via DSSCs. We observe that it is not possible to assign a single physical origin to the different resistances determined in the impedance spectra except for the series resistance. In contrast, resistive element present contributions from different physical processes, observing a transport-recombination coupling. Based on this analysis we provide an equivalent circuit model to evaluate the impedance pattern of PSCs in terms of the processes directly affecting the final performance (i.e. considering transport-related and recombination-related losses), a crucial tool for further development of perovskite photovoltaics.

Thermionic-enhanced near-field thermophotovoltaics for medium-grade heat sources

Abstract: Conversion of medium-grade heat (temperature from 500 to 1000 K) into electricity is important in applications such as waste heat recovery or power generation in solar thermal and co-generation systems. At such temperatures, current solid-state devices lack either high conversion efficiency (thermoelectrics) or high-power density capacity (thermophotovoltaics and thermionics). Near-field thermophotovoltaics (nTPV) theoretically enables high-power density and conversion efficiency by exploiting the enhancement of thermal radiation between a hot emitter and a photovoltaic cell separated by nanometric vacuum gaps. However, significant improvements are possible only at very small gap distances (<100 nm) and when ohmic losses in the photovoltaic cell are negligible. Both requirements are very challenging for current device designs. In this work, we present a thermionic-enhanced near-field thermophotovoltaic (nTiPV) converter consisting of a thermionic emitter (graphite) and a narrow bandgap photovoltaic cell (InAs) coated with low-workfunction nanodiamond films. Thermionic emission through the vacuum gap electrically interconnects the emitter with the front side of the photovoltaic cell and generates an additional thermionic voltage. This avoids the use of metal grids at the front of the cell and virtually eliminates the ohmic losses, which are unavoidable in realistic nTPV devices. We show that nTiPV operating at 1000 K and with a realizable vacuum gap distance of 100 nm enables a 10.7-fold enhancement of electrical power (6.73 W/cm2) and a 2.8-fold enhancement of conversion efficiency (18%) in comparison with a realistic nTPV device having a series resistance of 10 mΩ·cm2.

The study on negative dielectric properties of Al/PVA (Zn-doped)/p-Si (MPS) capacitors

Abstract: In this research, PVA (doped with 7% Zn) was sandwiched between Al and p-Si as a polymer interfacial layer. Voltage and frequency effect on the real and imaginary components of complex dielectric constant (e′ and e″), electric modulus (M′ and M″), loss tangent (tan δ) and electrical conductivity (σ) of the MPS-type capacitor has been studied. Impedance spectroscopy method was used between 5 and 5000 kHz at room temperature. Almost all frequency-related parameters were found as quite susceptible, especially in the accumulation and depletion regions. These changes in real and imaginary components of dielectric properties in depletion region were attributed to the interface layer and dipole polarization, the existence of surface states (Nss) and their relaxation time (τ), especially at low frequencies. But these changes in the accumulation region were attributed to the existence of interfacial layer and series resistance (Rs) of the capacitor owing to the voltage divided between them and capacitor. As a result, frequency, applied biases, interfacial polymer layer, polarization processes, Nss and Rs of the capacitor are more effective on the values of e′, e″, tan δ, M′, M″ and σ. Therefore, the effects of them must be considered in determining the dielectric parameters, electric modulus, conductivity and conduction mechanisms in the capacitors with and without an interfacial layer such as insulator/oxide, polymer, ferroelectric materials.

ON-Resistance in Vertical Power FinFETs

Abstract: This paper presents the first analytical model for the ON-resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON}}$ ) in vertical power FinFETs. The model allows to extract the channel mobility and series resistance and to separate the current conduction through the bulk fin channel and the accumulation-mode metal–oxide–semiconductor (MOS) channel. The model was validated by experiments and simulations. The extracted series resistance was verified by measuring a diode fabricated in the same wafer with the FinFETs. At the same time, simulations using the extracted channel mobility and series resistance agreed well with the experiments. The model was then used to analyze a 1200 V GaN vertical power FinFET. The main ${R}_{ \mathrm{\scriptscriptstyle ON}}$ component was identified to be from the drift layer and the substrate, while the gate-modulated channel resistance only accounts for ~13% of the total device ${R}_{ \mathrm{\scriptscriptstyle ON}}$ . Our model enables parameter extraction from the dc characteristics of a single device, and therefore, provides a fast and easy way to understand, analyze, and design vertical power FinFETs. Our model can also be adjusted to allow for fast and accurate parameter extraction in other power transistors with a vertical gate-modulated channel, such as trench MOSFETs.

Frequency, voltage and illumination interaction with the electrical characteristics of the CdZnO interlayered Schottky structure

Abstract: cadmium–zincoxide (CdZnO) interlayered metal–semiconductor structure was examined by capacitance and conductance versus voltage data in dark and under 250 W illumination at 100 kHz, 500 kHz and 1 MHz frequencies, respectively. The effectuality of the frequency, applied voltage, illumination, and series resistance on the electrical parameters was discussed in detail. The increase in the frequency led to the decrement in capacitance and conductance and the increment in the illumination generally led to the increment in capacitance and conductance. An abnormal behavior was detected in the accumulation region of the C–V plots at 500 kHz and 1 MHz due to the inductive phenomenon of device. The effect of illumination intensity reduces the Ri values in the inversion region while enhances them in the depletion and accumulation region for 1 MHz. Additionally, the series resistance values decrease with increasing frequency due to the specific dispersion of localized interface states. As a consequence of the experimental results, a remarkable interaction was realized between the electrical parameters and the illumination, frequency and applied biases.

High-power and reliable GaN-based vertical light-emitting diodes on 4-inch silicon substrate

Abstract: High-power and reliable GaN-based vertical light-emitting diodes (V-LEDs) on 4-inch silicon substrate were fabricated and characterized in this article. The metallization scheme reliability was improved by depositing the Pt/Ti films that surround the compressed Ag/TiW films to protect it from environmental humidity. We demonstrated that although current crowding in V-LEDs was not as severe as that in lateral light-emitting diodes (L-LEDs), high current density around the opaque metal n-electrode in V-LEDs remained a problem. A SiO2 current blocking layer (CBL) was incorporated in V-LEDs to modify the current distribution. Roughening the emitting surface of V-LEDs with KOH and H3PO4 etchant was compared and the influence of surface roughening on the emission property of V-LEDs was studied. The high-power V-LEDs showed low forward voltage with small series resistance and high light output power (LOP) without saturation up to 1300 mA. Under 350 mA injection current, V-LEDs achieved an excellent light output power (LOP) of 501 mW with the peak emission wavelength at 453 nm. The prominent output performance of V-LEDs demonstrated in this work confirmed that integrating the optimized metallization scheme, SiO2 CBL and surface texturing by KOH wet etching is an effective approach to higher performance V-LEDs.

Determining Series Resistance for Equivalent Circuit Models of a PV Module

Abstract: Literature describes various methods for determining a series resistance for a photovoltaic device from measured IV curves. We investigate use of these techniques to estimate the series resistance parameter for a single diode equivalent circuit model. With simulated IV curves we demonstrate that the series resistance values obtained by these techniques differ systematically from the known series resistance parameter values used to generate the curves, indicating that these methods are not suitable for determining the series resistance parameter for the single diode model equation. We present an alternative method to determine the series resistance parameter jointly with the other parameters for the single diode model equation, and demonstrate the accuracy and reliability of this technique in the presence of measurement errors.

Condition Monitoring of Electrolytic Capacitors in Boost Converters by Magnetic Sensors

Abstract: The aluminum electrolytic capacitors (AEC) are important in filtering and energy storage applications since they are of high energy density and low cost. However, the AECs suffer from low reliability and limited lifetime due to the electrolyte vaporization. The degradation of AECs challenges the reliability and efficiency of the power electronic systems. Therefore, it is essential to monitor the condition of AECs for system reliability and efficiency. In this paper, a real-time condition monitoring technique for input and output AECs based on the estimation of equivalent series resistance (ESR) was developed for the boost converter. The ESRs were estimated by using the capacitor and inductor current obtained through the magnetic-field sensing by magnetic sensors. The influences of the load, duty cycle, inductance, ESR, and capacitance on the ESR estimation were investigated to develop the proposed methodology. The proposed methodology can largely improve the accuracy of the estimated ESR of output AEC in the boost converter. The higher accuracy enables predictive maintenance of AECs and contributes to the reliability and efficiency of power electronic systems. The simulation and experimental results from −25 °C to 100 °C verified that the proposed methodology could be used to estimate the ESR of input and output AECs accurately. The experimental results showed that the compact tunnel magnetoresistance (TMR) sensors were capable of measuring the capacitor and inductor current for the estimation of ESR. This technique is cost-effective and non-invasive since it can be implemented with TMR magnetic sensors and does not require the Hall-effect current transducers with magnetic concentrators of larger volume, higher cost, and limited bandwidth or invasive shunt resistors.

Modeling and Simulation of the Photovoltaic Cells for Different Values of Physical and Environmental Parameters

Abstract: Both research and technological development in the area of renewable energy sources are necessary to account for the increase in energy demand and environment problems in the world. The photovoltaic (PV) cell has been described by non-linear outputs characteristics in current-voltage and power-voltage. This outputs is affected by various effects such as; series resistance ( ), shunt resistance ( ), solar irradiance and temperature. In this paper the effect of variation of parameters has been studied such as series resistance ( ) and shunt resistance ( ) of the diode in the photovoltaic cell and these effects could be seen in the Current-Voltage (I-V) and Power-Voltage (P-V) characteristic curves. In this paper also has been studied the effect of variation of the environmental parameters such as solar irradiance and temperature. Results show that a higher temperature at constant solar irradiance produces a decrease power. So the voltage and the photovoltaic cell output power tend to decrease at higher temperatures, but there is no noticeable effect on the photovoltaic cell current. Thus, it is important to keep the cell temperature as low as possible, because higher temperatures have negative effect on output power of photovoltaic cell. On the other hand, the effect of solar irradiance on photovoltaic cell, it reveals that higher solar irradiance gives higher current and higher power. Shunt resistance has significant effect on the operating characteristic curves of PV cells as low power output is recorded if the value of shunt resistance varies from 0.07 ohms to 1700 ohms. Finally, I have presented power-voltage characteristic curves and current voltage characteristic curves of photovoltaic cell for different solar irradiance in Shkoder, Tirana and Vlore.

Modelling of the Bearing Breakdown Resistance in Bearing Currents Problem of AC Motors

Abstract: With the wide application of pulse width modulation (PWM) technology in motor driving, the bearing current problem has become more and more severe. The most complicated problem in analyzing bearing currents is modeling the equivalent circuit of the bearing and determination of the equivalent parameters of the model. During the process of bearing current breakdown, the bearing undergoes a transition from the capacitor state to the resistor state. The previously used equivalent model, which only consists of a capacitor parallel with a constant resistor, cannot reveal the real breakdown process. In this paper, an improved equivalent bearing model is derived from the waveform analysis of the experiment. The variable breakdown resistance model of the bearing is put forward and the calculation method of the breakdown resistance is given. The circuit simulation results from the variable resistance bearing model were much closer to the results of the experiment than those from the constant resistance model.

A Constant On-Time Control With Internal Active Ripple Compensation Strategy for Buck Converter With Ceramic Capacitors

Abstract: Constant on-time control has been widely used due to its advantages of fast transient response and light load efficiency. However, the control scheme is intrinsically unstable if the output capacitor's equivalent series resistance (ESR) is not large enough, which needs ripple injection techniques to enhance loop stability. The traditional passive ripple compensation technique uses only passive component networks to realize this function, which exhibits some inherent shortcomings, including difficulties in high-speed current sensing amplifier design and large chip area consumption. This paper proposes an internal active ripple compensation strategy that senses the low-side power mosfet current and extracts relevant ac information for feedback-ripple enhancement. Output-voltage dc offset does not occur and subharmonic instability is significantly improved even with ceramic capacitors. The circuit architecture has been realized in a synchronous buck regulator with a 0.5 μm 40 V bipolar-CMOS-DMOS (BCD) process. The programmable switching frequency is up to 1 MHz and the maximum load current is 4 A. Simulation and experimental results are given to prove the proposed high performance.

Vertical InGaAs Nanowire Array Photodiodes on Si

Abstract: We demonstrated vertical InGaAs nanowire (NW) array photodiodes on Si that were optically responsive to visible light (635 nm) and near-infrared light (∼1.55 μm). The vertical NWs were directly grown on Si by selective-area growth. Implementation of a heavily Sn-doped contact layer in the InGaAs NWs improved the diode characteristic because of a lower series resistance, and as a result, a photoresponsivity of 0.25 A/W was obtained at 635 nm, which was twice that before the improvement. Moreover, the photocurrent density of InGaAs–InP core–shell NWs was about 20-fold higher under illumination with light in the 1.55 μm wavelength band as a result of suppression of surface recombination. These findings are expected to be useful for NW-based photovoltaic applications for optical interconnection and Si platforms.

Quasi-Online Low-Frequency Impedance Monitoring Scheme for Submodule Capacitors in Modular Multilevel Converters

Abstract: Despite being the most fragile component, aluminum electrolytic capacitors (AECs) are preferred in modular multilevel converters (MMC) due to their high volumetric efficiency and low price. Due to the ageing of AECs, its capacitance decreases and equivalent series resistance (ESR) increases. This can result in an increased voltage ripple, power loss, and could damage the operation of the MMC. Therefore, condition monitoring of submodule (SM) capacitors in an MMC is indispensable to enhance system reliability. This paper presents a new condition monitoring technique for SM capacitors based on the measurement of its low-frequency impedance. The low-frequency impedance is evaluated based on the information of the second harmonic component in the SM capacitor voltage and current. In this scheme, a low-frequency voltage signal is injected in the control loop of the MMC with available hardware and controller for converter control. The proposed scheme has been validated through PLECS simulations on a three-phase half-bridge submodule (HB-SM) based MMC. This technique is also verified experimentally on a single-phase MMC with a four HB-SMs per arm.