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Abstract This study extensively investigated the ageing characteristics and lifetime model of oil–paper insulation for oil‐immersed paper condenser bushing. The accelerated thermal and electrothermal ageing experiments of oil‐immersed paper condenser bushing were conducted respectively. The properties of oil–paper insulation during the ageing process were investigated. Results showed that descending speed of degree of polymerization of the innermost and the outermost layer paper was higher than that of middle layer paper, the difference in water content on different paper layers caused varying deterioration speeds. The aluminium foil contributed to a surge in aluminium dissolution in oil, further accelerating the ageing of insulation. Based on the obtained degree of polymerization data under thermal ageing at 90°C, 100°C and 130°C, the lifetime model of oil–paper insulation for condenser bushing model was established. In addition, the surface breakdown of the scale model of bushing occurred after 133 days ageing, the properties of bushing decreased gradually during the ageing process and sharply after the breakdown. Degree of polymerization deviation of different paper layers in bushing between calculated value according to the above lifetime model and actual value of bushing after the breakdown was less than 6%, further verifying the validity of lifetime model.

This paper describes a flow control of the dye in the paper mill with the quasi-Z-source indirect matrix converter (QZSIMC) fed induction motor drive. More than a decade the voltage-source inverter (VSI) and current-source inverter (CSI) have been used to control the speed of the induction motor, which in turns controls the flow of dye. Recently, the matrix converter (MC) has been an excellent competitor for the VSI or CSI for its compactness. The voltage transfer ratio of the VSI, CSI, and MC has been limited to 0.866. Thus, the efficiency of these converters is less. To improve the voltage transfer ratio the quasi-Z-source network (QZSN) is to be used between voltage source and indirect MC (IMC). The modification in the shoot-through duty ratio of the QZSN varies the voltage transfer ratio greater than 0.866. Different voltage transfer ratios are needed for different voltage sag conditions. For a variation of the duty ratio of the QZSN, the fuzzy logic controller has been presented. To control the IMC vector control with space vector modulation has been presented. This paper proposes the implementation of QZSIMC adjustable speed drive for the flow control of dye in paper mill during different voltage sag conditions. A 4-kW prototype has been built and the effectiveness of the proposed system is verified with simulation results and experimental setup. Simulation is done in MATLAB, Simulink platform. Experimental setup is done with the aid of a TMS320F2812 (Texas Instrument) processor. The experimental results validate the maintenance of the speed of an induction motor at the set condition, thus controlling the perfect flow of dye in paper manufacturing technology. [ABSTRACT FROM AUTHOR]

Lengthened ion pathway in porous carbon cathode, especially under high mass loading and packing state, severely impeded the ion transport, thus leading to a far unsatisfactory energy/power out of Zn//C capacitors. Here, we report a novel kapok-derived quasi-2D thin-walled porous carbon tile (CT) with proper curvature and rich doping used as stacked bricks. Together with high conductivity single-walled carbon nanotubes, a porous yet relatively packed self-standing carbon cathode was constructed, which features a hierarchical ion path including short ion pathways inside thin-walled porous CTs and adequate channels "highways" caused by rational sub-micron interlayer spacing, thus leading to an excellent combination of rate and gravimetric/volumetric/areal performance at practical mass loading (12 mg cm−2). [Display omitted] • A porous thin-walled layered carbon tile with proper curvature was prepared as bricks. • Porous yet packed cathode feathers hierarchical paths for fast ion/charge transfer. • High rate and gravimetric/volumetric capacity remain in high loading cathode. • The areal capacity increases linearly with the mass loading of cathode. Long ion pathway inside large-sized carbon particle or stacked 2D assembly greatly limit the electrochemical performance of practical carbon cathode (>10 mg cm−2) in Zn//C capacitors. Highly porous activated carbon and holy graphene can alleviate such ion-transport issue, but usually suffer from a far lower packing density and severe restacking, respectively. Herein, a kapok-derived quasi-2D thin-walled microporous carbon tile (CT) with optimized curvature and rich doping was developed and used as bricks. Assisted with single-walled carbon nanotubes (SWNTs), a porous yet relatively packed paper cathode was constructed. The unique doped thin wall (∼700 nm) can effectively shorten the ion-penetration pathways from electrolyte deep into pore structure inside CTs, and thus enlarge ion-accessible surface areas. Combined with rational sub-micron interlayer spacing among proper-curved CTs and bridged-like SWNTs, the continuous ion/charge transport "highways" are fabricated. As a result, such self-standing carbon cathode delivers outstanding rate and gravimetric/areal performance (114 mAh g−1/1.37 mAh cm−2) without sacrificing volumetric capacity even at high mass loading (12 mg cm−2). [ABSTRACT FROM AUTHOR]

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To effectively improve the power density and rate capability of layered double hydroxide (LDH) based supercapacitors, a hybrid supercapacitor (HSC) comprising of hierarchical ultrathin NiAl-LDH nanosheet arrays on carbon nanotube paper (CNP-LDH) is developed with porous graphene nanosheets as the negative electrode for the first time. SEM image shows that hierarchical NiAl LDH nanosheet arrays are assembled by numerous ultrathin nanosheets with thickness of a few to tens of nanometers. Remarkably, with an operating voltage of 1.6 V, the HSC possesses a high energy density of 50.0 Wh kg −1 at an average power density of 467 W kg −1 . Even at a fast discharging time of 3.9 s, a high energy density (23.3 Wh kg −1 ) could also be retained at a power density of 21.5 kW kg −1 . Moreover, the HSC exhibits cycling stability with a retention rate of 78% after 5000-cycle charge-discharge test at 5 A g −1 . The results inspire us to propose our high-performance CNP-LDH as a promising electrode for energy storage applications. [ABSTRACT FROM AUTHOR]

Supercapacitors have drawn numerous attentions in recent years since they can deliver relatively high power and energy densities. This article introduces an all-printed paper based surface mountable supercapacitor (SMS), which could withstand the reflow soldering process when integrated into microelectronic systems. The device was fabricated by screen printing and stencil printing processes, contributing to low cost and large-scale fabrication. Furthermore, building electronic devices on ubiquitous paper substrates had advantages of light weight, low cost, and eco-friendliness, etc. Based on activated carbon electrode material and ionic liquid electrolyte, the capacity of the supercapacitor could reach 14 mF at the device volume of 3.2 mm ? 2.5 mm ? 0.175 mm, besides, the specific volumetric capacity was superior than most of the commercial SMS devices. [ABSTRACT FROM PUBLISHER]

In this study, the multifunctionality of structural dielectric capacitor made by integrating graphene oxide paper into carbon fibre reinforced composite has been investigated. The study is based on an earlier work on the use of graphene oxide for dielectric material in the structural dielectric capacitor, in which electrical properties have been characterized. In this work, an in-depth study on electrical and mechanical properties of this kind of structural dielectric capacitor have been carried out. In addition, the multifunctional efficiency of structural dielectric capacitors were evaluated and compared with existing structural dielectric capacitors. Through experiments, it is revealed that both electrical and mechanical properties of the structural dielectric capacitors were significantly enhanced by interleaving a graphene oxide paper in the middle of composite. Therefore, the multifunctional efficiency of this kind of structural dielectric capacitors has been ultimately improved, indicating the excellent potential of graphene oxide paper in the development of multifunctional materials for energy storage, potentially for high-strength required applications, such as electric vehicles and unmanned aerial vehicles. [ABSTRACT FROM AUTHOR]

Electronic capacitors were constructed via hand-printing on paper using pencil graphite. Graphite traces were used to draw conductive connections and capacitor plates on opposing sides of a sheet of standard notebook paper. The paper served as the dielectric separating the plates. Capacitance of the devices was generally < 1000 pF and scaled with surface area of the plate electrodes. By combining a pencil-drawn capacitor with an additional resistive pencil trace, an RC low-pass filter was demonstrated. Further utility of the pencil-on-paper devices was demonstrated through description of a capacitive force transducer and reversible chemical sensing. The latter was achieved for water vapor when the hygroscopic cellulose matrix of the paper capacitor’s dielectric adsorbed water. The construction and demonstration of pencil-on-paper capacitive elements broadens the scope of paper-based electronic circuits while allowing new opportunities in the rapidly expanding field of paper-based sensors. [ABSTRACT FROM AUTHOR]

Measurements of capacitors made with paper sheets reveal a significant decrease in capacitance with increasing frequency from 10 to 100,000 Hz, offering a simple demonstration of complex dielectric phenomena using common equipment. [ABSTRACT FROM AUTHOR]

The work reported in this paper aims at developing an algorithm for system operators to solve a robust security-constrained AC optimal power flow (R-SC-ACOPF) problem, which also optimizes the settings of discrete controllers including load tap changers (LTCs) and shunt capacitor banks (SCBs). An iterative algorithm involving a master problem and a number of sub-problems is proposed. The master problem selects the optimal discrete controllers’ settings by taking into account primal SC-ACOPF constraints based on the single-component worst contingencies identified by the sub-problems. Each sub-problem is a bi-level max-min problem used to find the current worst contingency. The overall objective is to minimize the total cost, including generation and load shedding cost, while satisfying all relevant constraints. The master problem and sub-problems allow representing LTC tap positions, SCB status, and contingencies using binary variables. Two case studies are presented as applications of this novel technique. [ABSTRACT FROM AUTHOR]

Germination paper (GP) is used as a growth substrate in plant development studies. Current studies bear two limitations: (1) The actual GP water content and variations in GP water content are neglected. (2) Existing irrigation methods either maintain the GP water content at fully sufficient or at a constant deficit. Variation of the intensity of water deficit over time for plants grown on GP is not directly achievable using these methods. In this contribution, a new measurement and control approach was presented. As a first step, a more precise measurement of water content was realized by employing the discharging process of capacitors to determine the electrical resistance of GP, which is related to the water content. A Kalman filter using an evapotranspiration model in combination with experimental data was used to refine the measurements, serving as the input for a model predictive controller (MPC). The MPC was used to improve the dynamics of the irrigation amount to more precisely achieve the required water content for regulated water uptake in plant studies. This is important in studies involving deficit irrigation. The novel method described was capable of increasing the accuracy of GP water content control. As a first step, the measurement system achieved an improved accuracy of 0.22 g/g. The application of a MPC for water content control based on the improved measurement results in an overall control accuracy was 0.09 g/g. This method offers a new approach, allowing the use of GP for studies with varying water content. This addressed the limitations of existing plant growth studies and allowed the prospection of dependencies between dynamic water deficit and plant development using GP as a growth substrate for research studies. [ABSTRACT FROM AUTHOR]

In recent years, there is an increased use of passive filters in both transmission and distribution systems due to the proliferation of power electronic devices. However, the problem of filter design has not been well addressed in the past and one example is the application of high-pass filters in a filter package. Three types of HP filters are widely used to mitigate multiple harmonics, i.e., 2nd HP filter, 3rd HP filter and C-type filter. There is still a lack of research to clearly reveal the characteristics of each filter, which makes it difficult for the designer to select the optimal filter topology under different circumstances. The main goal of this paper is to solve the problem of how to select a proper configuration among three HP filter candidates for a given harmonic problem. Unlike the conventional optimization-based filter studies, this paper investigates three HP filters in an analytical way. As a result, the paper provides a deep insight into the inherent characteristics of the filter and the conclusions drawn in the paper are universal; thus can be used in different applications, ranging from low voltage levels to high voltage levels. The research results lead to a recommended application scope of each HP filter, which is very useful to guide the design of filter packages and help designers to evaluate the design results. [ABSTRACT FROM AUTHOR]

This paper proposes a single-phase, transformer-less, seven-level inverter that utilizes eight switches, three capacitors, and two diodes to produce seven voltage levels with triple boosting ability. The availability of the common-ground point eliminates the leakage current in PV applications. The proposed Transformer-Less Triple-Boosting Seven-Level Inverter (TLTB7LI) has the ability to feed different types of loads from non-unity to unity power factors. The voltage balancing of capacitors takes place naturally without the need for auxiliary circuits and complicated control strategies. This paper investigates the appropriateness of the proposed TLTB7LI for grid-connected application. The Peak Current Controller (PCC) is employed to generate the switching pulses and regulate the active/reactive power transfer between the converter and the output, which guarantees the high quality of injected current to the output. Moreover, the operational principles, its control technique, as well as the design procedure of the key components of the proposed inverter have been presented. The superiority of the proposed inverter over existing counterparts has been verified through comparative analysis. The simulation and experimental analysis validated the proper operation of the proposed TLTB7LI. [ABSTRACT FROM AUTHOR]

A grid-forming wind generation system exhibits exceptional grid frequency support abilities. The DC capacitor of the grid-forming wind generation system, which is characterized by rapid response and high sensitivity to minor disturbances, can provide short-term inertia support for the power system. This paper proposes the capacitor virtual inertia control for the grid-forming wind generation system, coupling the DC capacitor voltage with the power system frequency, which enables the DC capacitor to participate in the system frequency response process and reduces the rate of change of the system frequency during the disturbance. To analyze the inertia of the wind power generation system, this paper establishes an equivalent Philips-Heffron model for the grid-forming wind generation system and uses the equivalent inertia constant to quantify the inertia of the wind power generation system. The effectiveness of the proposed control strategy and the reasonableness of the inertia assessment method are verified through simulations in the single-turbine system and the IEEE four-machine two-area system. [ABSTRACT FROM AUTHOR]

Single-phase rectifiers are one of the most practical instruments with various applications. Among them, active front-end (AFE) rectifiers are introduced with bidirectional power transfer capability for power factor correction and the elimination of current harmonics. This paper proposes an adaptive model predictive control (MPC) for a single-phase AFE rectifier. The AFE topology used in this paper is a half-bridge boost converter. This topology has higher efficiency than other single-phase AFEs due to the fewer number of active semiconductor devices. Considering the presence of one leg of capacitors in this topology, balancing the voltages of these capacitors is a challenge, along with other control objectives. Also, this paper benefits from an MPC approach by which the switching signal for every switching state is chosen such that the defined cost function is minimized in the operation state to achieve all control goals based on the predefined model of the rectifier. Furthermore, an adaptive algorithm for the inductor current estimation is presented to robustify the control system against any unwanted disturbance in the control system. As a demonstration of the superior performance of the proposed method, a 1kW rectifier setup with 700Vdc output voltage fed from a 230Vrms/50Hz grid is built in the laboratory. The applicability of the MPC controller is verified and all operation waveforms of the test setup are presented. The proposed method offers a high-quality input current with total harmonic distortion (THD) below 5% and a high-power factor (PF) close to one. Also, the efficiency is comparable with the available commercialized rectifiers. [ABSTRACT FROM AUTHOR]

In today's healthcare landscape, MRI (magnetic resonance imaging) plays a pivotal role in early diagnosis and treatment decisions. However, the quest for higher frequencies to achieve micron‐level resolutions poses technological challenges. This paper focuses on coils and capacitors, with special attention to air gap considerations for movable electrodes. The paper delves into the development of adjustable capacitors using high‐fired NP0 ceramic, tailored for 128‐MHz MRI systems. These capacitors boast impressive specs: a 3‐kV breakdown voltage (VBreakdown), a 3‐pF minimum capacitance (Cmin), a 30‐pF maximum capacitance (CMax), and a 1.5‐pF stepwise capacitance variation (Cvariation step). Notably, they enhance breakdown voltage while preserving frequency stability with MgTiCa ceramic between the fixed and mobile electrode, critical for adaptive blocks. Leveraging geometrical parameters analyzed through the ANSYS simulator, the authors meticulously designed an optimized 25–40 pF capacitor with a 15‐mm height and 1600 mm2 surface area. Post‐fabrication and sintering, extensive testing using a vector network analyzer across 10 MHz to 100 MHz validated performance against simulated expectations. [ABSTRACT FROM AUTHOR]

In photovoltaic grid-connected systems, the interaction between grid-connected inverters and the grid may cause harmonic oscillation, which severely affects the normal operation of the system. To improve the quality of the output electrical energy, photovoltaic grid-connected systems often use LCL filters as output filters to filter out high-frequency harmonics. Taking the three-phase LCL-type photovoltaic grid-connected inverter system as an example, this paper addresses the issue of harmonic resonance. Firstly, based on the harmonic linearization method and considering the impact of the coupling compensation term on the grid-side voltage, a modular positive and negative sequence impedance modeling method is proposed, which simplifies the secondary modeling process of the converter under feedback control. Then, the stability analysis is conducted using the Nyquist criterion, revealing the mechanism of high-frequency resonance in photovoltaic grid-connected systems. Furthermore, this paper delves into the impact of changes in system parameters on impedance characteristics and system stability. The results indicate that the proportional coefficient of the internal loop current controller has a significant influence on system impedance characteristics. Additionally, this paper proposes an active damping design method that combines lead correction and capacitor current feedback to impedance-reconstruct the easily oscillating frequency band. Finally, the effectiveness of this method is verified in the simulation platform. Simulation results confirm the effectiveness of this method in suppressing harmonic resonance while maintaining rapid dynamic response. [ABSTRACT FROM AUTHOR]

In hydrogen production, AC‐DC rectifiers must provide a high current and low voltage to the production load. This paper focuses on the efficient performance and elimination of the output ripple in these AC‐DC rectifiers. Unfortunately, efforts to reduce the current ripple often lead to lower efficiency, causing a contradiction. To address this issue, a low‐ripple high‐efficiency AC‐DC rectifier with an auxiliary compensator is proposed in this paper. The proposed rectifier can maximise efficiency while eliminating the current ripple, including the switching ripple and low‐frequency ripple. By incorporating a rectifier‐chopper and a buck circuit with a series‐connected capacitor, the auxiliary compensator, the solution provides an additional flow path for the current ripple at the rectifier output, successfully preventing the ripple from being output to the load. This paper offers a thorough exposition regarding the causative factors and sources of the switching and low‐frequency ripple. Furthermore, a detailed explication of the operating principle of the proposed rectifier system is provided. The losses and costs associated with auxiliary compensators are then analysed for persuasive purposes. Finally, simulation and experimental results verify the feasibility and superiority of the proposed rectifier. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to reveal the landscape and trends of graphene research in the world by using data from Chemical Abstracts Service (CAS). Design/methodology/approach: Index data from CAS have been retrieved on 78,756 papers and 23,057 patents on graphene from 1985 to March 2016, and scientometric methods were used to analyze the growth and distribution of R&D output, topic distribution and evolution, and distribution and evolution of substance properties and roles. Findings: In recent years R&D in graphene keeps in rapid growth, while China, South Korea and United States are the largest producers in research but China is relatively weak in patent applications in other countries. Research topics in graphene are continuously expanding from mechanical, material, and electrical properties to a diverse range of application areas such as batteries, capacitors, semiconductors, and sensors devices. The roles of emerging substances are increasing in Preparation and Biological Study. More techniques have been included to improve the preparation processes and applications of graphene in various fields. Research limitations: Only data from CAS is used and some R&D activities solely reported through other channels may be missed. Also more detailed analysis need to be done to reveal the impact of research on development or vice verse, development dynamics among the players, and impact of emerging terms or substance roles on research and technology development. Practical implications: This will provide a valuable reference for scientists and developers, R&D managers, R&D policy makers, industrial and business investers to understand the landscape and trends of graphene research. Its methodologies can be applied to other fields or with data from other similar sources. Originality/value: The integrative use of indexing data on papers and patents of CAS and the systematic exploration of the distribution trends in output, topics, substance roles are distinctive and insightful. [ABSTRACT FROM AUTHOR]

This paper presents a foreground calibration algorithm combination with a background calibration algorithm for successive approximation register analog-to-digital converters (ADC). The foreground calibration for capacitor mismatch is capacitor recombination algorithm and the background calibration for capacitor mismatch is single-channel least mean square (LMS) algorithm. The capacitor recombination algorithm can initially calibrate the capacitor array mismatch and provide an environment conducive to convergence for LMS algorithm. After running the capacitor recombination algorithm, the convergence speed of LMS algorithm can be improved. The results of 100 times of Monte Carlo simulation show that LMS algorithm can converge within 1500 cycles, the ADC signal-to-noise and distortion ratio is improved from 71.63 to 97.47 dB, the spurious-free dynamic range is improved from 84.98 to 125.28 dB, the effective number of bits is improved from 12.85 to 15.90 bits, the differential nonlinearity is reduced from 2.09 to 0.90 LSBs, and the integer nonlinear is reduced from 7.14 to 0.68 LSBs. [ABSTRACT FROM AUTHOR]

Extensive research on the multi-bridge extension of cascaded rectifier stages is deemed important to meet the requirements of high-voltage and high-power applications. Two control structures for capacitor voltage balancing in cascaded rectifier stages are analyzed in this paper. On this basis, the balance strategy for the multi-bridge extension of single-phase cascaded rectifiers is explored. The balance method of ultra-fast balance modulation trajectories is introduced into single-phase multi-bridge cascaded rectification, and the optimal control strategy is selected through simulation verification and comparative analysis. During the actual experiments, some disturbance factors were introduced into the system, causing an instantaneous unbalanced state. However, through the control strategy proposed in this paper, the system can quickly regain balance. Through simulation validation and analysis of the experimental results, the reliability and innovation of this control strategy have been demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents a novel topology for Z-source inverters (ZSI). The new Z-Source network is based on the coupled-inductors and active switched boost. Features of the topology include high voltage boost ability, single magnetic-core, low voltage stress on the active switch, and capacitors. The principles of operation, analysis, voltage and current equations of each component, and the converter voltage gain in the steady-state are presented. A comparison with other topologies has also been performed to determine the advantages and disadvantages of the proposed ZSI. Finally, experimental results of the laboratory prototype are presented to confirm the performance of the proposed topology. [ABSTRACT FROM AUTHOR]

Grid-forming (GFM) wind storage systems (WSSs) possess the capability of actively building frequency and phase, enabling faster frequency response. The frequency regulation power of GFM WSSs is provided by both the rotor of wind turbine and the battery storage (BS) in parallel with DC capacitor. However, with existing control strategies, the energy storage immediately responds to both small and large grid disturbances. The frequent responses significantly decrease the lifespan of energy storage. To address this issue, a cooperative strategy between rotor and energy storage is necessary. This paper proposes an advanced strategy of GFM WSSs for cooperative DC power support. The cooperative principle is that for small disturbances, the BS is disabled and total frequency regulation power is provided by the rotor, while for large disturbances, the BS is enabled to cooperatively provide power support with the rotor. The proposed cooperative strategy can decrease the charging and discharging times of BS with a small range of rotor speed fluctuation, and then the service life of BS can be significantly extended. Simulation results validate the effectiveness and superiority of the proposed strategy. [ABSTRACT FROM AUTHOR]

A three‐level neutral point clamped (3L‐NPC) voltage source inverter (VSI) topology can be advantageous in electric vehicles with a high DC‐link voltage and a high switching frequency. A bulky DC‐link capacitor is not an option; thus, the DC‐link capacitor's sizing considering the traction system characteristics is an important design step. This paper investigates how the DC‐link capacitor size of a 3L‐NPC VSI gets affected by the combination of the interdependent characteristics of an electric drive, such as its power factor, modulation index, current, and fundamental frequency, with the effects of the modulation methods. Five pulse width modulation (PWM) methods, of which three of them have an active neutral point potential control, are compared in terms of their neutral point potential (NPP) oscillations. Then, the size of the DC‐link capacitor is determined for each PWM method so that the NPP ripple is kept under desired limits at all operating conditions. It is shown that both the modulation technique and the electric machine characteristics influence the capacitor size. For example, electric machine design modifications can introduce more than a 30% reduction in capacitor size. Finally, DC‐link and NPP oscillations with different PWM methods are experimentally validated in a scaled‐down 3L‐NPC inverter. [ABSTRACT FROM AUTHOR]

The present paper is concerned with a magnetorheological (MR)-damper-based vibration-reduction system with energy harvesting capability considering sprung mass changes. The system represents a mechanical harmonic oscillator with electrical coupling, set in motion by kinematic excitation. The authors examine the system performance in the case when the MR damper control coil (damper control coil) is powered directly by the alternating current resulting from the voltage generated in an electromagnetic harvester in the assumed frequency range of sine excitation. Such a system is able to attenuate vibration in the near-resonance frequency range when the current in the damper control coil increases; however, its drawback is vibration amplification at higher frequencies. To eliminate this negative feature, it is proposed to connect shunt capacitors in parallel with the damper control coil. Then, the system can be tested experimentally in terms of current in the damper control coil, sprung mass, and the capacity of shunt capacitors in order to evaluate system performance according to the assumed performance index. The obtained results demonstrate significant improvement in system performance at higher frequencies of excitation. [ABSTRACT FROM AUTHOR]

In order to cope with the failure of existing fault analysis schemes for AC/DC distribution networks with a high proportion of distributed generations, this paper proposes a fault characteristic analysis method for AC/DC distribution networks that considers the influence of distributed generation control strategies. Firstly, a transient model for the AC/DC distribution network connected to distributed generations is built. Then, the fault characteristics of the AC/DC distribution network in different stages, such as the capacitor discharge stage, inductive renewal stage, and steady state stage, is analyzed. Finally, detailed simulation analysis is conducted using PSCAD/EMTDC to validate the effectiveness of the developed scheme by the superior approximation performance between simulated curves and calculated curves. [ABSTRACT FROM AUTHOR]

This paper focuses on the influence of the fractional-order (FO) resonant capacitor on the zero-voltage-switching quasi-resonant converter (ZVS QRC). The FO impedance model of the capacitor is introduced to the circuit model of the ZVS QRC; hence, a piecewise smooth FO model is developed for the converter. Numerical solutions of the converter are obtained by using both the fractional Adams–Bashforth–Moulton (F-ABM) method and Oustaloup's rational approximation method. In addition, the analytical solution of the converter is obtained by the Grünwald–Letnikov (GL) definition, which reveals the influence of the FO resonant capacitor on the zero-crossing point (ZCP) and resonant state of the converter. An experimental platform was built to verify the results of the theoretical analysis and numerical calculation. [ABSTRACT FROM AUTHOR]

Capacitors are crucial components in power electronic converters, responsible for harmonic elimination, energy buffering, and voltage stabilization. However, they are also the most susceptible to damage due to their operational environment. Accurate temperature estimation of capacitors is essential for monitoring their condition and ensuring the reliability of the converter system. This paper presents a novel method for estimating the core temperature of capacitors using a long short-term memory (LSTM) algorithm. The approach incorporates a continued training mechanism to adapt to variable load conditions in converters. Experimental results demonstrate the proposed method's high accuracy and robustness, making it suitable for real-time capacitor temperature monitoring in practical applications. [ABSTRACT FROM AUTHOR]

Conventional 5-level active neutral-point-clamped (5L-ANPC) topology and state-of-the-art 5-level hybrid active neutral-point-clamped (5L-HANPC) topology are popular for inverter applications. However, their dc-link voltage utilization is limited to only 50%. With the maximum voltage level generated by only half dc-link voltage, these inverters are not capable of boosting voltage in their ac output. To resolve these drawbacks, this paper proposes a family of four novel 5-level boost-active neutral-point-clamped (5L-BANPC) inverters. Without requiring any flying capacitors, the proposed topologies can generate five voltage levels by effectively using the dc-link capacitors. The dc-link voltage utilization of the proposed 5L-BANPC inverters is twice that of the 5L-ANPC and 5L-HANPC topologies. While generating the five-level ac output voltage, natural voltage balancing of both dc-link capacitors and voltage boosting are achieved. Ease of implementation is another noteworthy merit of the proposed 5L-BANPC inverters because they can be implemented using six widely available commercial half-bridge modules without requiring a dedicated circuit design. The operation of the proposed topologies is analyzed. Experimental results are presented for verification. [ABSTRACT FROM AUTHOR]

This paper proposes a single-stage direct AC to high-frequency (HF) AC resonant converter based on LLC configuration for induction heating (IH) systems or HF applications. Unlike conventional converters for IH systems, the proposed topology converts the utility frequency to HF AC in a single stage without using a DC link inductor and capacitors and takes the advantages of LLC configuration. Additionally, it improves the power factor to 0.9–1, lowers the THD (3.2% experimentally), and protects against the high-frequency components. An embedded control scheme was designed to keep the HF current oscillating at a resonant frequency, ensuring zero-voltage switching. The operating principle of the proposed topology was investigated using mathematical equations and equivalent circuits. Finally, it was verified using computer simulation, and an experimental prototype of 1.1 kW was developed to demonstrate the proposed topology's uniqueness. [ABSTRACT FROM AUTHOR]

Three LED drivers which can be used for illumination, but whose main task is the transmission of information (data) via the light of the LEDs, are explored in this paper. The converter circuits need no capacitors for the energy transformation and avoid an inrush current. The lack of necessity of electrolytic capacitors reduces cost and space. Dimming the illumination is also easy to achieve. The control concept of the converters and the generation of pulsing of the LEDs for transmitting the information (data) are explained. The converters can also be expanded to more stages to drive more LEDs with different types of information. All three converters are explained in detail; all presented circuits are built up and simulated with LTSpice. Several data transmission concepts are applied and demonstrated through simulations. [ABSTRACT FROM AUTHOR]

The recently proposed novel unidirectional multilevel rectifier, a three single-phase star-connected multilevel rectifier, has the characteristic of having a large number of DC-side capacitors and a complex capacitor voltage balancing control structure under conventional carrier-based phase-shift sine wave pulse-width modulation (SPWM). Hence, a space vector pulse-width modulation (SVPWM) algorithm for the novel multilevel rectifier is proposed in this paper, which can quickly balance the capacitor voltage without an additional voltage balancing control structure. Firstly, it divides the space vectors of the rectifier, then it determines the two basis voltage vectors that synthesize the output reference voltage. After that, based on the analysis of the relationship between switching states and the charge–discharge of capacitors, the final action sequences of redundant vectors are determined according to the principle of keeping the capacitor charge–discharge time consistent. Thus, the capacitor voltages can be automatically balanced without an additional voltage balancing control structure. Finally, simulation and experimental results validated the feasibility and effectiveness of the proposed SVPWM algorithm. The results also show improvements in current quality, capacitor voltage balance and the fluctuation of the neutral point voltage on the DC-link, allowing for further reduction in the overall volume and cost of the rectifier. [ABSTRACT FROM AUTHOR]

This paper presents a measurement-based method for real-time determination of the wind farms or wind turbines that contribute most significantly to a subsynchronous resonance (SSR) event. The method is based on the concept of subsynchronous power (SSP). This paper has shown that it is the SSP that drives the SSR. By monitoring the direction and amount of SSPs produced by different wind farms or turbines, the most critical wind farms or turbines can be identified and quantified. A dq0 transform-based algorithm is developed to calculate the SSP in real time. The method overcomes the interference of fundamental frequency components and non-steady-state SSR components on the extraction of the SSP component. Several test cases have demonstrated the usefulness of the proposed concept and method. [ABSTRACT FROM AUTHOR]

With their high-energy density, high-power density, long life, and low self-discharge, lithium-ion capacitors are a novel form of electrochemical energy storage devices which are extensively utilized in electric vehicles, energy storage systems, and portable electronic gadgets. Li-ion capacitor aging mechanisms and life prediction techniques, however, continue to be active research areas. This paper examines the aging process for Li-ion batteries, covering the alterations in cell composition, the effect of the electrode charge state, temperature effects, and electrolyte deterioration. Additionally, this research offers approaches for predicting the lifespan of lithium-ion batteries, including those based on physical models, machine learning, and artificial intelligence. In this work, cycle life testing techniques are also discussed, including accelerated aging experiments for lithium-ion capacitors. The paper concludes by discussing future directions for the creation of aging mechanisms and lithium-ion capacitor life prediction techniques. [ABSTRACT FROM AUTHOR]

This paper presents capacitor dimensioning to increase a system's power density while the converter performance for the delta-connected cascaded H-bridge (CHB) active power filter (APF) is not impaired. After comparing aluminum electrolytic capacitors with film capacitors, this paper proposes capacitance design requirements for film capacitors. With the help of trigonometric transformation for periodic time-varying variables, including capacitor voltages and branch voltages, the capacitance design requirements can be represented as positive univariate polynomials, the coefficients of which are with regard to the capacitance value. The optimization solver SeDuMi is then applied to determine whether a capacitance value is feasible by checking the positiveness of the polynomials. This research has very appealing theoretical and practical properties: the time-domain analysis capability for periodic variables is improved, therefore, enabling a fast computation and a broad application. Both the simulations and experimental results validate the proposed strategy. Compared with the previous work, the proposed method can result in a lower capacitance value without degrading the performance, which is beneficial for a low-cost and low-volume system. [ABSTRACT FROM AUTHOR]

The paper discusses in detail the inability of a circuit designer to design a single input single element-controlled universal memelement emulator. A Single input Single element-controlled universal memelement emulator would be such a configuration that can provide the realization of any of the three memelements (Memristor/Memcapacitor/Meminductor) by taking a circuit element as inductor (L), Capacitor (C) or Resistor (R) with the same input port. The analysis shows that no such circuit configuration can be built to realize such a highly flexible universal memelement emulator. It is found that by using such structures, only two ideal memelements can be realized at maximum. If these circuit structures are used to realize the remaining third memelement, then, the resulting element comes out to be a non-ideal memelement. Two circuit configurations to demonstrate this theory are also included for both charge-controlled and flux-controlled memelement emulation based on the approaches shown in this paper. [ABSTRACT FROM AUTHOR]

This paper deals with the stability analysis and enhancement in the AC‐microgrid system comprising parallel‐operated voltage‐source inverters (VSIs) supplying an active‐load. The active‐load behaves such as a constant power load from the AC‐side. In the paper, two models for the active‐load modeling in the AC microgrid are considered: (i) simple model in which the active‐load is modeled as an ideal current source, (ii) detailed model in which all dynamics of the active‐load converter and related controllers are taken into account. The main findings and contribution of this paper are as follows. (a) All linearized state equations of the study system are extracted and transferred into a unified common dq‐reference frame, and then, small‐signal stability of the study system is carried out in the common reference frame by using the simple and detailed models of the active‐load. (b) It is shown that the simple model of the active‐load, as a current source, leads to more pessimistic results in comparison to the active‐load detailed model. (c) Impacts of the active‐load power and bandwidth of the active‐load voltage control loop on the system stability are examined. (d) Control of the generation‐side VSIs is modified and a stabilizing approach, called generation‐side virtual capacitor, is proposed for stabilizing the system under high active‐load penetration. Next, modal analysis and time‐domain simulations are used to investigate the study system responses with and without the proposed stabilizing approach. [ABSTRACT FROM AUTHOR]

The paper presents a synthesis of the author contributions in developing a new class of DC-DC hybrid converters (HDC) with large voltage conversion ratio. The HDC structures are obtained by introducing commutated inductive and capacitive cells in the classical DC-DC converters. With these topologies, the voltage conversion ratio is larger, at the same duty cycle, compared with the classical converters. The paper presents some of the developed configurations, with unidirectional and bidirectional power flow, and some corresponding applications in renewable energy conversion and automotive industries. [ABSTRACT FROM AUTHOR]

This paper proposes a novel approach for low-power applications for the fast estimation of filter capacitor value and the output performance parameters such as average, and Root Mean Square (RMS) values for the voltage and current considering single-phase full-wave, three-phase half-wave and three-phase full-wave rectifier circuits. For this aim, the novel equations in this work are derived for the average output voltage and rms ripple voltage separately for each of the above-mentioned three rectifier types. Then % ripple factors for each rectifier type are calculated using newly derived equations and plotted versus the newly introduced Normalized Time Constant (NTC). Besides, considering the peak supply voltage as the base voltage, the Per Unit (p.u.) output average voltage and rms ripple voltage for each of the rectifier circuits are computed and plotted versus NTC. These graphs will be normalized graphs since the output values of these graphs have turned into independent of both supply voltage amplitude and supply frequency. Normalized graphs are set up only once for each type of the rectifier circuit. Then, and for a pre-selected ripple factor value, the corresponding NTC value is obtained by straightforward reading from the graphs set up between the % ripple factor and NTC. Once the NTC value has been acquired, using the formula of NTC leads to finding the capacitor value required for the pre-selected ripple factor with one simple step calculation. Furthermore, the p.u. values of the average output voltage and rms ripple voltage values that correspond to the same NTC value are obtained by reading them from the set-up graphs directly. Finally, the efficiency of the proposed method is demonstrated through design examples for each type of rectifier circuit. The three design examples highlight how the output performance values can be obtained easily, accurately and swiftly. Furthermore, the viability of the graphical approach is verified by the experimental results which demonstrate the suitability of the derived equations in the proposed method. [ABSTRACT FROM AUTHOR]

Frequency Domain Spectroscopy (FDS) is mainly used to determine the moisture in the paper-oil insulation systems in power transformers and Oil-Impregnated-Paper (OIP) bushings. Another application of this method is detection of puncture developing in the paper layer between the adjacent conductive foils in the condenser core. The paper presents theoretical calculations of tan? frequency response in the case of short circuit of conductive layers in bushing's condenser core and their experimental verification, with the help of paper-oil insulation capacitor. Furthermore, examples of measurements of real bushings in operation that agree with the proposed idea are described. [ABSTRACT FROM AUTHOR]

With the massive expansion of decentralised renewable energy in electricity grid networks, the power supply system has been changed from centralised to decentralised one and from directional to bi-directional one. However, due to the regional energy structure difference in the power imbalance between electricity generation and consumption is becoming more and more serious. A grid-scale energy storage system (ESS) can be one solution to balance the local difference. In this paper, two charging/discharging strategies for the grid-scale ESS were proposed to decide when and with how much power to charge/discharge the ESS. In order to realise the two strategies, this paper focuses on the application of fuzzy logic control system. The proposed strategies aim to reduce the peak power generation, consumption and the grid fluctuation. In particular, this paper analysis the ratio between energy-capacity and rated power of ESS. The performance of the proposed strategies is evaluated from two aspects, the normalised power of ESS itself and the influence on the power grid. Simulation studies were carried out on the rule-based control systems with different energy-to-power (e2p) ratios, and the results show that the proposed charging strategy with combination of extreme situation of power imbalance and the rest capacity of ESS provides a smooth load curve for the regional power grid system while the external power exchange is reduced effectively. [ABSTRACT FROM AUTHOR]

A capacitance multiplier is an active circuit designed specifically to increase the capacitance of a passive capacitor to a significantly higher capacitance level. In this paper, the use of a voltage differencing differential difference amplifier (VDDDA), an electronically controllable active device for designing grounded and floating capacitance multipliers, is proposed. The capacitance multipliers proposed in this study are extremely simple and consist of a VDDDA, a resistor, and a capacitor. The multiplication factor ( K c ) can be electronically controlled by adjusting the external bias current ( I B ). It offers an easy way of controlling it by utilizing a microcontroller for modern analog signal processing systems. The multiplication factor has the potential to be adjusted to a value that is either less than or greater than one, hence widening the variety of uses. The grounded capacitance multiplier can be easily transformed into a floating one by utilizing Zc-VDDDA. PSpice simulation and experimentation with a VDDDA realized from commercially available integrated circuits were used to test the performance of the proposed capacitance multipliers. The multiplication factor is electronically adjustable, ranging in approximation from 0.56 to 13.94. The operating frequency range is approximately three frequency decades. The realization of the lagging and leading phase shifters using the proposed capacitance multiplier is also examined and proven. The results reveal that the lagging and leading phase shifts are electronically tuned via the multiplication factor of the proposed capacitance multipliers. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) has many advantages of low switching losses, good harmonic performance and high modularity structure in state-of-the-art HVDC applications. The full-bridge submodules (FBSMs) of the hybrid MMC can inherently output negative voltage to absorb fault currents, and consequently the hybrid MMC can ride through severe DC faults without blocking. During the DC fault-ride-through process, the submodule capacitor voltage and arm current of the MMC will be temporarily increased. These characteristics limit the proportion of the FBSMs, which should not be too low and thus increase the cost and operating losses of the hybrid MMC. In this paper, an improved sorting algorithm of SM capacitor voltage is established, and a novel virtual damping control strategy is proposed that can effectively suppress the increase in submodule capacitor voltage and arm current of the hybrid MMC during the DC fault-ride-through process. By adopting this optimization control, the proportion of FBSMs can be reduced significantly without deteriorating the fault-ride-through capability or safety of the MMC. The effectiveness of the proposed control is verified by careful theoretical analysis and detailed simulation results. [ABSTRACT FROM AUTHOR]

Materials offering high energy density are currently desired to meet the increasing demand for energy storage applications, such as pulsed power devices, electric vehicles, high-frequency inverters, and so on. Particularly, ceramic-based dielectric materials have received significant attention for energy storage capacitor applications due to their outstanding properties of high power density, fast charge–discharge capabilities, and excellent temperature stability relative to batteries, electrochemical capacitors, and dielectric polymers. In this paper, we present fundamental concepts for energy storage in dielectrics, key parameters, and influence factors to enhance the energy storage performance, and we also summarize the recent progress of dielectrics, such as bulk ceramics (linear dielectrics, ferroelectrics, relaxor ferroelectrics, and anti-ferroelectrics), ceramic films, and multilayer ceramic capacitors. In addition, various strategies, such as chemical modification, grain refinement/microstructure, defect engineering, phase, local structure, domain evolution, layer thickness, stability, and electrical homogeneity, are focused on the structure–property relationship on the multiscale, which has been thoroughly addressed. Moreover, this review addresses the challenges and opportunities for future dielectric materials in energy storage capacitor applications. Overall, this review provides readers with a deeper understanding of the chemical composition, physical properties, and energy storage performance in this field of energy storage ceramic materials. [ABSTRACT FROM AUTHOR]

Reactive power compensation (RPC) is a big problem during power system operation. Parenthetically, capacitor allocation and sizing may be the only convenient solution for RPC of power systems. The loss sensitivity factor (LSF) is applied here for finding the optimum capacitor position. This paper presents quasi-oppositional fast convergence evolutionary programming (QOFCEP), fast convergence evolutionary programming (FCEP), and evolutionary programming (EP) for the optimum location and sizing of shunt capacitors in the isolated microgrid (MG) for minimizing total real power loss throughout the day with and without the demand response program (DRP). The 33-node, 69-node, and 118- node isolated MGs have been studied to authenticate the efficacy of the suggested approach. Each MG includes small hydro power plants (SHPPs), solar PV plants (SPVPs), wind turbine generators (WTGs), diesel generators (DGs), and plug-in electric vehicles (PEVs). [ABSTRACT FROM AUTHOR]

A 16-bit 125 MS/s pipelined analog-to-digital converter (ADC) implemented in a 0.18 μ m CMOS process is presented in this paper. A sample-and-hold amplifier-less (SHA-less) modified 2.5-bit front-end is adopted, which splits the sampling capacitor in half to eliminate the common-mode voltage buffer. The multiplying-digital-to-analog converter (MDAC) in the first pipeline stage is modified by reusing the sampling capacitor in a foreground digital calibration for improving the ADC linearity. This design can circumvent a dedicated reference buffer to generate the calibration voltages at all comparator thresholds. By calibrating the ADC in the digital domain, the integral non-linearity (INL) is improved from −9.2/10 LSB to −3/2.2 LSB, and the spurious-free dynamic range (SFDR) is optimized by over 8dB. The ADC consumes 154mW (reference buffer and clock included) from a 1.8 V supply. [ABSTRACT FROM AUTHOR]

As electrochemical research undergoes rapid technological progression, the acquisition of substantial amounts of electrochemical impedance spectra (EIS) becomes increasingly feasible. Yet, this advancement introduces intricate challenges in data processing, automation, and interpretation. This paper delves into the sufficiency of unsupervised machine learning (ML) and in particular dimensionality reduction methods in decoding EIS complexities, examining its strengths, limitations, and potential pathways for optimization. As we navigated the intricacies of non‐linear dimensionality reduction, spotlighting t‐distributed stochastic neighbor embedding (t‐SNE) and uniform manifold approximation and projection (UMAP) algorithms, a pattern emerged: these techniques excel at categorizing divergent impedance spectra but show limitations when faced with analogous circuit configurations, especially those substituting a capacitor with a constant phase element. This observation not only underscores a limitation but also accentuates that unsupervised ML approaches, alone, may not fully unravel the nuances of EIS spectra. In the concluding section of our manuscript, we discuss the implications of this finding from a practical standpoint, particularly for electrochemists seeking to apply these methods in their work. [ABSTRACT FROM AUTHOR]

The paper deals with the capacitance of cylindrical two-dimensional capacitor which consists of Cartesian orthotropic dielectric material. The determination of the capacitance of capacitor with orthotropic dielectric material by a suitable coordinate transformation is reduced to the computation of capacitance of an isotropic capacitor. It is proven that the capacitance of a Cartesian orthotropic capacitor can be obtained in terms of an isotropic capacitor whose dielectric constant is the geometric mean of the dielectric constant of the orthotropic capacitor. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is a research hotspot in medium-voltage and high-voltage applications. The measurement offset error would cause an increase in the monitoring error of the submodule (SM) capacitance of the MMC, affecting the estimation accuracy of the SM capacitance monitoring. This paper proposes a capacitor monitoring strategy based on the offset error compensation, where two reasonable capacitor monitoring periods are selected in one fundamental period under the proposed voltage-balancing control (VBC) based on the virtual capacitor voltage (VCV) to compensate for the offset error impact on the capacitance monitoring. The proposed strategy can effectively eliminate the offset error impact on the capacitance monitoring, which ensures the accuracy of the SM capacitance monitoring in the MMCs. The effectiveness of the proposed monitoring strategy is confirmed by the simulations and experiments. [ABSTRACT FROM AUTHOR]