Equivalent Series Capacitance Research Articles

Identifying the parameters of ultracapacitors based on variable forgetting factor recursive least square

PurposeUltracapacitors find extensive applications in various fields because of their high energy density and long cycling periods. However, due to the movement of ions and the arrangement patterns on rough/irregular electrode surfaces during the charge and discharge process of ultracapacitors, the parameters of ultracapacitors usually change with the variation of operating conditions. The purpose of this study is to accurately and quickly identify the parameters of ultracapacitors.Design/methodology/approachA variable forgetting factor recursive least square (VFFRLS) algorithm is proposed in this paper for online identifying the equivalent series resistance and capacitance C of ultracapacitors. In this work, a real-time error-based strategy is developed to adaptively regulate the value of the forgetting factor of traditional forgetting factor recursive least square (FFRLS) algorithm. The strategy uses the square of the average time autocorrelation estimation of the prior error and the posterior error between the predicted output and the actual output as the adjustment basis of forgetting factors.FindingsExperiments were conducted using the proposed scheme, and the results were compared with the estimation results obtained by the recursive least squares (RLS) algorithm and the traditional FFRLS algorithm. The maximum root mean square error between the estimated values and actual values for VFFRLS is 3.63%, whereas for FFRLS it is 9.61%, and for RLS it is 19.33%.Originality/valueBy using the proposed VFFRLS algorithm, a relatively high precision can be achieved for the online parameter estimation of ultracapacitors. Besides, the dynamic balance between parameter stability and tracking performance can be validated by dynamically adjusting the forgetting factor.

Online condition monitoring for DC-link capacitors of three-level NPC converters using noninvasive signal injection

This paper introduces an online method for monitoring the health condition of the DC-link in three-level NPC converters. This method does not require hardware changes or modifications to the control algorithm. It involves injecting a zero-sequence signal, added to the system reference voltages to generate a neutral-point current injection. A square waveform with an interharmonic cycle frequency is used for the signal injection to minimize estimation errors caused by existing signals. This combined signal allows for the simultaneous estimation of the capacitor equivalent series resistance (ESR) and capacitance (C) at different frequency components using wavelet decomposition. Additionally, a balance between the magnitudes of the system reference voltage and the signal injection is established to prevent power quality issues. Besides, the capacitor parameters are estimated in the time-frequency domain, enabling tracking of capacitor degradation and wear-out failure. A comparison with a Fourier-based approach shows that this method provides highly accurate capacitor parameter estimation with less than 2% errors, instilling confidence in its results. Experimental results from a three-level NPC converter’s laboratory setup demonstrate the proposed method’s effectiveness.

Local outlier factor based condition monitoring for sub-module capacitors in modular multilevel converters

Modular multilevel converters (MMC) as a key technology for future power grids is rapidly developing. The failure rate of sub-module (SM) capacitors is only lower than that of power devices in MMC, so accurate evaluation of the reliability of capacitors is crucial for the safe operation of MMC. Both the increase of equivalent series resistance (ESR) and decrease of equivalent series capacitance (ESC) are features for capacitor deteriorating. ESC or ESR of the capacitor reaching to limited values indicates that the end of its lifespan and it must be replaced. Most of contemporary researches only focus on ESC or ESR. This article considering the characteristics of both ESC and ESR, proposes a method for monitoring the status of SM capacitors based on machine learning algorithm: local outlier factor (LOF). By utilizing the existing SM switching function and capacitor voltage signals within a fundamental frequency cycle in the control system of MMC, the proposed strategy can not only monitor the faulty capacitors, but also can sort the degrees of abnormal states of capacitors, and the strategy is applicable to MMC with single and multiple types of SM topologies. The proposed method is verified by the hybrid MMC model on Matlab/Simulink.

Reliability evaluation of a novel metal oxide-aluminum glycerol film capacitor using nonlinear degradation modeling with dependency considerations

Capacitors are components predominantly used to stabilize voltage, store energy, and lower electrical ripples. To improve the flexibility and capacitance of capacitors, we were motivated to develop hybrid film capacitors using two emerging thin film techniques, atomic and molecular layer deposition (ALD and MLD). Validation of its operational reliability in a power module or an electrical system is critical to facilitate its adoption. Equivalent series resistance (ESR) and capacitance are key performance characteristics (PC) of a capacitor, whose degradation path and process are nonlinear and dependent. Few studies have implemented the Wiener process (WP), to capture the dependency between the PC, based on the assumption of a normally distributed performance loss, notwithstanding that the performance loss may not be normally distributed. To address this concern as well as improve the accuracy of reliability prediction, a reliability framework is proposed. The gamma distribution is found to better fit the incremental PC degradation used in this work. The derived reliability model captured the non-linearity in the PC degradation path as well as its dependency using a selected Copula function. Akaike information criterion (AIC) was used to determine the most suitable Copula. Reliability estimation based on dependency consideration shows the least mean square error (MSE) compared to reliability estimate using a model that considers only one PC or assumes independent PCs. In addition, the hybrid capacitor was compared with an aluminum oxide dielectric layer capacitor, and the result was discussed.

Concept of Condition Monitoring for AC-DC Converter Output Capacitors via Discriminative Features

This paper discusses recent research on the condition mon- itoring (CM) approach for aluminium electrolytic capacitors (AEC) used in power electronics equipment such as switched- mode power supplies (SMPS). Capacitors are identified as the most critical component with the highest percentage of failure in AEC. CM offers a better paradigm for AEC due to its long- lasting ability (endurance). This study proposes accelerated life testing through electrical stress and long-term frequency testing for the AEC component. An experiment test bench was set up to monitor the critical electrical parameters such as dissipation factor (D), equivalent series resistance (ESR), capacitance (Cp), and impedance (Z), which serve as health indicators (HI) for the evaluation of the AECs. Time-domain features were extracted from the measured data, and the best features were selected using the correlation-based technique. This research contributes to developing a cost-effective CM approach for AECs used in power electronics equipment, which can reduce downtime and maintenance costs.

Degradation indicators for power electronic converters

Power electronic converters are an important element in the interaction between source and load. In fact, failures in this system often lead to bigger problems. Therefore, it is necessary to monitor the converter components that have the most failures. In this work, we present the estimation of three parameters, which are, in turn, degradation indicators of components in the power electronic converters: equivalent series resistance, capacitance and on-state resistance. Using current and voltage measurements of the Boost converter.

Wavelet-based estimation method for online condition monitoring of dc-link capacitors of distributed energy resources

This paper proposes a novel capacitor condition monitoring for dc-link of power converters employed in distributed energy resources systems. It follows the active methodology, in which an intermittent noncharacteristic signal is injected into the dc-link to estimate the equivalent series resistance (ESR) and capacitance (C) of dc-link capacitors. A real-time stationary discrete wavelet packet transform (RT-SDWPT) performs the capacitor parameter estimations. In this scheme, an interharmonic is used as a noncharacteristic signal to prevent the influence of the system’s inherent harmonic components, mitigating estimation errors. Moreover, the interharmonic frequency is chosen in the region influenced by the ESR and C parameters to ensure capacitor degradation condition. Besides, to mitigate quality issues, the interharmonic’s amplitude, duration, and the time interval between two signal injections follow the recommendations defined by standards. Furthermore, a parameter deviation detection scheme is employed to adaptively adjust the time interval between two estimations, improving failure detection. Experimental results obtained from a microgrid laboratory setup demonstrate the effectiveness and feasibility of the proposed method.

Reliability evaluation of supercapacitors based on pseudo-failure calendar lifetime distribution

Supercapacitors are new types of electrical energy storage components with an electric double layer. Ageing characteristics, lifetime and reliability evaluation are of great significance for quality evaluation and rational use. This paper focused on the pseudo-failure calendar lifetime distribution and reliability evaluation of supercapacitors. High-temperature accelerated calendar ageing test of supercapacitors is carried out, and equivalent series resistance and capacitance were tested. Pseudo-lifetime is calculated and distribution is fitted. Fitting results showed that the pseudo-lifetime of supercapacitors is more in line with Weibull distribution. Finally, the reliability curve and its bounds with 95% confidence are made, as a result of the reliability evaluation of supercapacitors.

Investigation of supercapacitor cyclic degradation through impedance spectroscopy and Randles circuit model

AbstractHigh power density and long cyclic stability are important characteristics that make supercapacitor suitable for many industrial applications. Measurement of equivalent series resistance and capacitance, is a general way to investigate performance of the Electric Double Layer Capacitor (EDLC). In this work, a Panasonic EDLC (10F) was investigated under cyclic degradation and monitored using electrochemical impedance spectroscopy (EIS) characterisation and Randles circuit model. After fitting, it was observed that series resistance was increased up to 80% and parallel capacitance was decreased up to 22%. The EIS data were validated using Kramers‐Kronig Transformation to check causality, linearity, and stability in the system.

Online ESR Monitoring of DC-Link Capacitor in Voltage-Source-Converter Using Damping Characteristic of Switching Ringings

Online monitoring of dc-link capacitor's equivalent series resistance (ESR) could provide valuable and timely information for power converter failure prognosis and predictive maintenance. The conventional ESR estimation methods are mainly based on pulsewidth modulation (PWM) voltage and current ripples (ESR≈Δu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> /Δi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ), but the performance is affected by operating conditions (especially at light-load), quasi-resonance effect and sensor amplitude error. To overcome these difficulties, an online ESR monitoring method is proposed using the damping characteristic of dc capacitor switching ringings. The intrinsic high-frequency (HF) resonance incidents between the power device fast switching and converter parasitic parameters are utilized in this article. First, the mechanism of dc capacitor switching ringing is analyzed by the HF resonance equivalent circuit. The analytic relationship between the damping characteristic and the ESR is established. Then, the condition monitoring (CM) scheme, noncontact HF sensor, and half-power bandwidth algorithm for ESR estimation are presented. Finally, an experimental study is carried out to validate the feasibility and effectiveness. The damping of switching ringing is inherently sensitive to the ESR of dc capacitor under the condition of resonance. Both theoretical analysis and experimental results confirm that the proposed method can achieve mΩ-level accuracy and good robustness under different conditions.

An Online Monitoring Scheme of Output Capacitor's Equivalent Series Resistance for Buck Converters Without Current Sensors

Aluminum electrolytic capacitors are widely used in switching mode power supply as smoothing capacitor, but they are the weakest among power components in dc–dc converter. It is very important to monitor its electrical parameters, mainly the equivalent series resistance (ESR). A monitoring method of capacitor's ESR for buck converters is proposed in this article. Based on the calculation model of ESR, the target parameter is monitored by sampling output ripple voltage. The proposed method needs no current sensor. Whether the circuit is in continuous conduction mode or discontinuous conduction mode, it is convenient to monitor the capacitor. Implementation of the monitoring system is presented. The experimental results validate the effectiveness of the method.

Online Monitoring of Aluminum Electrolytic Capacitors in Photovoltaic Systems by Magnetoresistive Sensors

Due to the environmental concerns and new energy policies, worldwide expectations for energy production utilizing photovoltaic (PV) systems are increasing significantly. The aluminum electrolytic capacitor (AEC) is extensively used in filtering application for power electronic converters in PV systems since they can achieve the highest energy density with the lowest cost. However, the lifetime of an AEC is limited due to the electrolyte vaporization. The degradation of AECs challenges the efficiency and reliability of a PV system. Therefore, the health-monitoring of AECs is indispensable for the PV systems to operate reliably. In this paper, an online AEC-monitoring scheme based on magnetic-field sensing is proposed for PV systems under various working conditions. The AEC-monitoring technique using the equivalent series resistance (ESR) and capacitance (C) as the health indicators were developed for the power electronic converters in PV systems. The proposed methodology considering the voltage drops on C can improve the accuracy in ESR-estimation and achieve the estimation of C. The simulation results with Simulink verified that the proposed method was capable of estimating the health indicators accurately over various levels of solar irradiance and ambient temperature. The tunneling magnetoresistive (TMR) sensors were pre-calibrated from −25 to 100° C for implementation in PV systems. The experimental results proved that TMR sensors could measure the current of AECs effectively to achieve the precise estimations of the health indicators using the proposed technique. This technique is non-invasive, compact, and cost-effective since it can be realized with the TMR sensors or other MR sensors.

Transient pulse‐based impedance characterisation of DC‐link capacitor for EV systems

In this study, a method for impedance characterisation of DC-link capacitors based on transient pulse analysis is proposed. The fundamentals of the concept are presented and design considerations are discussed. The functionality of the proposed approach is supported by SPICE simulation with two different commercial capacitors from different manufacturers and validated with experimental results. Experimental results for equivalent series resistance, equivalent series inductance (ESL) and capacitance estimation are presented for commercial DC-link capacitors and compared with component analyser results. The simulation and experimental results show that the proposed method is a promising candidate for capacitance and ESL estimation of capacitors in EV traction systems.

Continuously Tunable True-Time-Delay Phase Shifter Based on Transmission Lines With Simultaneously Reconfigurable Impedance and Phase Constant

This article reports on the design of continuously tunable true-time-delay (TTD) phase shifter using transmission lines with simultaneously reconfigurable impedance and phase constant. The reconfigurable transmission lines are designed with an independent control of equivalent series inductance and capacitance, which thus can achieve tunable phase constant (i.e., phase shift) while maintaining constant characteristic impedance. With the perfect matching property for all tuning states of phase constant, the proposed reconfigurable transmission-line units are cascaded to construct a tunable TTD phase shifter. For the proof-of-concept demonstration, three TTD phase shifters based on the proposed reconfigurable transmission lines with phase shifts of 45°, 90°, and 180° at center frequency of 1 GHz ( $f_{0}$ ) are designed and fabricated. The measured 2-unit phase shifter is tuned from −128° to −175° at $f_{0}$ while the insertion loss is better than 0.8 dB. The return loss is better than 15 dB from dc to $1.28f_{0}$ . For the 4-unit phase shifter, the phase shift tuning range is 93° at $f_{0}$ with insertion loss better than 1.4 dB. The return loss is better than 15 dB from dc to $1.03f_{0}$ for all states. The 8-unit phase shifter shows a measured tuning range of 183° at $f_{0}$ with insertion loss better than 2.0 dB. The return loss is better than 15 dB from dc to $1.03~ f_{0}$ for all states. The measured continuously tunable delay time is 507 ps. The measured 1-dB compression point is better than 12 dBm at $f_{0}$ for all states. As compared with the state-of-the-arts, the main merits of the proposed phase shifter are large phase shift/unit and wide matching bandwidth.

High-Accuracy Capacitance Monitoring of DC-Link Capacitor in VSI Systems by LC Resonance

Monitoring the condition of a dc-link capacitor is important for the reliability-critical voltage source inverter (VSI) systems. With the ever increasing application of a metalized poly propylene film (MPPF) capacitor, a new challenge for dc-link capacitor condition monitoring (CM) is presented due to the very small equivalent series resistance and capacitance end-of-life criterion (typically 2%–5%) of an MPPF capacitor. To improve the accuracy of capacitance estimation, a novel quasi-online CM method is proposed in this paper, which introduces an LC resonance intentionally when system is not in operation. Experimental work is carried out to validate the method and the results show that 1% capacitance estimation accuracy can be achieved in a 3-kW induction machine variable frequency drive system. Because of the signal measurement at large amplitude (e.g., nominal current) and the time-based multi-parameters identification algorithm, the method is accurate and inherently insensitive to the system parameters variation, measurement noise, and effect of temperature drift. In practice, the method can be implemented using the system available sensors with no need of hardware modification. Moreover, since the resonance current is limited and decays shortly, the condition of a dc-link capacitor can be monitored safely and frequently on-site in a VSI system.

Analysis of the DC-Link Current for the Single-Phase H-Bridge Inverter Under Harmonic Output Currents

This paper investigates the dc-link current to facilitate the dc-link capacitor sizing for the single-phase H-bridge inverter under harmonic ac currents. As the capacitor equivalent series resistance varies significantly until the frequency is higher than 1 kHz, the expressions of the dc-link current individual low-order harmonics (LOHs) and the switching harmonic currents (SHCs) root-mean-square (rms) value are derived, respectively, to accurately evaluate the dc capacitor losses. The dc-link LOH expressions reveal that each harmonic ac current induces two harmonic currents in the dc-link. When the ac current has multiple combinations of LOHs, the dc-link current envelopes take infinite possible unusual forms, so after somewhat complicated derivation, the SHCs rms equations are successfully derived and further simplified into one equation for easy worst case design as demonstrated by the actual case study. A single-phase H-bridge inverter lab prototype is developed to inject arbitrary combinations of harmonic currents of different orders, amplitudes, and angles into the grid. The good match between the computational, simulation, and experimental results validate the effectiveness of the proposed method. In particular, the worst case analysis is verified by the experiment and the differences between the experimental and computational results are formulated and explained definitely.

Condition Monitoring of DC-Link Capacitors Using Goertzel Algorithm for Failure Precursor Parameter and Temperature Estimation

Aluminum electrolytic capacitors are some of the weakest components in a power converter system. Therefore, condition monitoring of capacitors can prevent unexpected system downtime due to capacitor failures. This article proposes a condition monitoring system for electrolytic capacitors used as dc-link capacitors in front-end rectifier-fed three-phase inverters. The proposed methodology is based on equivalent series resistance (ESR) and capacitance estimation using the Goertzel algorithm. The ESR is used as the degradation indicator, whereas the capacitance value is used as both degradation indicator and temperature-sensitive electrical parameter to estimate core or hotspot temperature. Even though the use of capacitance to estimate hotspot temperature has already been proposed, this article tackles the practical difficulties associated with capacitor core-temperature estimation using the capacitance and demonstrates a successful implementation strategy for applying this method in power converters to estimate core temperature online. It also introduces a self-calibration procedure to mitigate ageing-related errors in temperature estimation. An experimental setup is used to verify the proposed conditioning monitoring system. The experimental results prove the effectiveness and accuracy of the proposed technique.

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

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.

High‐efficiency leaky‐wave antenna with continuous wide‐angle scanning using hybrid composite right/left handed structure

A hybrid composite right/left handed (CRLH) structure based leaky-wave antenna with continuous wide beam scanning is proposed in this article. Six series-wound periodic units, combining spoof surface plasmon polariton (SSPP) with CRLH, form the radiating portion of proposed antenna. The unit is connected to the ground with metal hole, which provides the equivalent parallel inductance, and the unit is separated from its adjacent unit at prescheduled intervals, which provides the equivalent series capacitance. Additionally, the unit operates at balanced state and the open stopband is obviously suppressed. Dispersion diagram is also used to analyze this continuous scanning. A prototype of proposed antenna is fabricated and measured. The main beam of the antenna scans continuously from −70° to +40° in the range from 5.2 to 8.8 GHz. The antenna radiation efficiency reaches a maximum of 92% in the working band. Measurement results agree quite well with the simulation, which indicate this leaky wave antenna can find potential applications in communication systems and radars.

Mathematical correlations between selected quality attributes and electrical parameters of apple juice

This study aimed at determining mathematical correlations between total soluble solids (TSS) content, content of organic acids (OA), pH value (pH), and density (D) of apple juice and their electrical conductance and capacitance using the RCC equivalent model of food products (resistance and capacitance). Linear correlations were determined between total soluble solids content, organic acids content, and density of aqueous solutions of the apple juice concentrate and values of their impedance (Z) and admittance (Y) in a frequency from 100 to 100,000 Hz; and their equivalent parallel capacitance (Cp) at frequencies of 100, 120, and 1,000 Hz; as well as their equivalent series capacitance (Cs) at frequency of 100,000 Hz. It was concluded that the correlations obtained from grounds for future studies on the development of a method for detecting adulterations (through watering) of apple juices based on measurements of electrical parameters, including the impedance or admittance. Practical applications Due to increasing requirements for the food quality and safety, as well as an increased demand for apple juice, many research works on the development of modern techniques for identification, detection of adulteration, and predicting its quality have been undertaken. Taking this into account, the research was undertaken to determine the mathematical relationships between selected quality attributes of apple juice (TSS, organic acids, pH, density) and their electrical parameters. The obtained significant mathematical correlations (r > 0.87 and p ≤ 0.01), indicate that the quality of apple juices can be predicted on the basis of simple impedance and admittance measurements at f = 100 Hz. These dependencies also justify the use of the RCC electric model for predicting the basic attributes of the apple juice quality, which in the future will make possible the development of a method for detecting its adulteration with water. On this basis, a relevant patent has been yet obtained.