Search

Operating conditions of film capacitors are complex, and the problem of film insulation failure caused by repetitively pulsed voltage is becoming ever serious. Degradation of the film under repetitively pulsed voltage cannot be accurately evaluated by the average breakdown electric field. In this paper, the effects of pulsed electric field and pulse repetition frequency on the breakdown in biaxially oriented polypropylene (BOPP) films are investigated. Three phases of BOPP degradation are proposed based on the voltage amplitude, i.e., maintenance (M), decline (D), and near-zero (N). Evolution of the BOPP film from degradation to breakdown at different frequencies is presented. Meanwhile, transition of discharge mode and elemental composition of the film are analyzed. Experimental results show continuous heat generation under repetitive microsecond pulses is the dominant factor for degradation of BOPP film. The number of applied pulses and the repetitive stressing time decrease exponentially with increase of frequency. This research can be contributed to the safe and reliable operation of capacitors.

Highlights A bilayer dielectric film is prepared via coating boron nitride nanosheets (BNNSs) by solution casting on the surface of polyethylene terephthalate (PET) film. The BNNS layer acts as the efficient barrier layer to suppress the charge injection, thereby making the surface-modified PET films exhibit excellent breakdown strength and electrostatic energy storage performance. The surface coating methods are accessible and suitable for large-scale roll-to-roll process production of dielectric films.

This paper explores some efforts to suppress the voltage surge appearing during the operation of a SiC-MOSFET-based half-bridge circuit in an inverter topology. The study is important to carry out, as the voltage surge problem does not come up when a Si-IGBT is used as the switching component in the half-bridge; however, some applications demand certain properties like what is found in a SiC-MOSFET. Compared to Si-IGBT with rise-time/fall-time larger than 100 ns in general, the use of SiC-MOSFET is preferable due to its much shorter switching time, less than 50 ns, which brings about a much lower switching loss and lower operating temperature. However, the choice of the usual electrolytic capacitor in the dc-link would produce an undesired voltage surge during the half-bridge operation. The origin of the surge is sometimes assigned to the inductance parasitic effect of the SiC-MOSFET high frequency. This research proves the benefit of a film capacitor to suppress the surge due to its lower equivalent series resistance (ESR) than that of the electrolytic capacitor. The results contribute to the consideration to take during the circuit realization in various applications, as there are not many papers yet found discussing the use of film capacitor in the dc-link of a SiC-MOSFET half-bridge inverter. This study also reveals the importance of the film capacitor placement during the design stage of SiC-MOSFET applications; moreover, motor controllers being equipped with an inverter such as described in this study have not been found yet in the market. The efforts investigated in this work would help to control the undesirable voltage spikes that frequently occur when applying a SiC-MOSFET to a half-bridge inverter design. [ABSTRACT FROM AUTHOR]

Highlights: A bilayer dielectric film is prepared via coating boron nitride nanosheets (BNNSs) by solution casting on the surface of polyethylene terephthalate (PET) film. The BNNS layer acts as the efficient barrier layer to suppress the charge injection, thereby making the surface-modified PET films exhibit excellent breakdown strength and electrostatic energy storage performance. The surface coating methods are accessible and suitable for large-scale roll-to-roll process production of dielectric films. The further electrification of various fields in production and daily life makes it a topic worthy of exploration to improve the performance of capacitors for a long time, including thin-film capacitors. The discharge energy density of thin-film capacitors that serves as one of the important types directly depends on electric field strength and the dielectric constant of the insulation material. However, it has long been a great challenge to improve the breakdown strength and dielectric constant simultaneously. Considering that boron nitride nanosheets (BNNS) possess superior insulation and thermal conductivity owing to wide band gap and 2-dimensional structure, a bilayer polymer film is prepared via coating BNNS by solution casting on surface of polyethylene terephthalate (PET) films. By revealing the bandgap and insulating behavior with UV absorption spectrum, leakage current, and finite element calculation, it is manifested that nanocoating contributes to enhance the bandgap of polymer films, thereby suppressing the charge injection by redirecting their transport from electrodes. Worthy to note that an ultrahigh breakdown field strength (~ 736 MV m−1), an excellent discharge energy density (~ 8.77 J cm−3) and a prominent charge–discharge efficiency (~ 96.51%) are achieved concurrently, which is ascribed to the contribution of BNNS ultrathin layer. In addition, the modified PET films also have superior comprehensive performance at high temperatures (~ 120 °C). The materials and methods here selected are easily accessible and facile, which are suitable for large-scale roll-to-roll process production, and are of certain significance to explore the methods about film modification suitable for commercial promotion. [ABSTRACT FROM AUTHOR]

• Internal micro-channel cold plates (IMCPs) were employed to electric vehicle film capacitor. • IMCPs were optimized using response surface methodology and genetic algorithms. • Capacitor with IMCPs exhibited temperature reductions of 45.50 °C and 48.45 °C. • Capacitor with IMCPs maintained normal functionality under ultra-high temperatures. The increasing voltage and power density demands of electric vehicles pose notable challenges to the high-temperature resistance performance of film capacitors within motor controllers. Existing methods primarily focus on material modifications and conventional thermal management designs, often tested at 85 °C, which fail to meet the escalating demands for high-temperature operations. This paper presents the design and optimization of a thermal management system for film capacitors through simulations and experiments under ultra-high temperatures. ANSYS electro-thermal coupled simulation was used to analyze the temperature distribution of the capacitor under different ripple currents, leading to the development of a thermal management system based on internal micro-channel cold plates (IMCPs). These IMCPs were optimized using response surface and genetic algorithms to enhance cooling performance. Experimental and simulation comparisons were made between standard capacitors and those with IMCPs under ripple currents of 120 A and 180 A at 85 °C. Further examinations were conducted at ultra-high temperatures of 125 °C and 140 °C with a ripple current of 180 A. The findings show that capacitors with IMCPs had average temperature reductions of 45.50 °C and 48.45 °C at 85 °C under 120 A and 180 A ripple currents, respectively. Additionally, standard capacitors developed cracks or exploded at 125 °C and 140 °C under 180 A ripple current, while capacitors with IMCPs maintained normal functionality. These results indicate that capacitors integrated with IMCPs meet the rigorous high-temperature operational standards required for motor controllers in high-voltage electric vehicles. [ABSTRACT FROM AUTHOR]

Polymer-based dielectric film capacitors are essential energy storage components in high-power energy storage devices benefiting from their high breakdown strength (E b) and ultra-fast charge storage/release capability. However, the state-of-the-art commercial capacitor, biaxially oriented polypropylene (BOPP), exhibits limited energy storage density primarily due to low dielectric constant, which hinders the advancement of the film capacitor industry. Introducing high-permittivity (high-k) nanofillers into PP matrix to improve polarization is a promising method but poor filler dispersion leads to a remarkable decrease of E b , while various strategies to enhance dispersion of fillers typically require sophisticated process involving toxic procedure and consuming significant time and cost. Herein, we show that a novel and scalable surface grafting method for high-k fillers can be achieved by a facile and short-period microwave irradiation with the assistance of silane coupling agent (KH560). As a demonstration, the KH560 is effectively grafted onto the surface of barium titanate (BT), achieving a high grafting ratio of 4.91 % at a yield of 85.1 % within a short time (40s). Furthermore, the surface modified BT nanofillers are introduced into PP matrix and then biaxially stretched. The as-prepared film exhibits excellent dispersion and superior compatibility, resulting in a remarkable enhancement of tensile strength (from 82 MPa to 115.4 MPa), breakdown strength (from 200 MV/m to 254 MV/m), and energy density (from 1.49 J/cm3 to 2.21 J/cm3). This work proposes a new strategy for constructing homogeneous polymer-based dielectric film by microwave activating high-k fillers and is crucial for the design of next-generation energy storage devices. [Display omitted] • A microwave assisted strategy is developed to prepare surface-grafted BT fillers. • The grafting method achieves high grafting ratio within a short time. • BT nanoparticles exhibit superior compatibility within the PP matrix. • The PP/BT composites show excellent dielectric properties and high energy density. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The development of polymer nanocomposites with superior dielectric performances is critical for flexible capacitive energy storage applications. However, the common approach to fabricate polymer composites with high-dielectric-constant ceramics as fillers always bring about exaggerate dielectric losses, hence low energy density and energy efficiency of polymer composites. In this work, BNNSs/AgNPs nanohybrids, where Ag nanoparticles were deposited on the surface of boron nitride nanosheets (BNNSs), are employed as fillers for poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) based nanocomposites. The contributions by enhanced interface polarisation and the internal barrier layer capacitor (IBLC) effect generated by the uniform distribution of conductive Ag nanoparticles on the insulative BNNSs, result in a large increase in dielectric constant and electric displacement meanwhile simultaneously suppressed dielectric losses. The BNNSs/AgNPs/PVDF-HFP nanocomposites exhibit much higher energy density and energy efficiency than the pristine PVDF-HFP and the BNNSs/PVDF-HFP composites counterparts, being great potential for dielectric energy storage applications. [ABSTRACT FROM AUTHOR]

In this article, polypropylene (PP), polyimide (PI), polyvinylidene difluoride (PVDF), and polyethylene (PE) dielectric materials are applied to analyze the performance degradation mechanism under magnetic field. The properties of the dielectrics are investigated under different magnetic fields. With the increase of magnetic field, the dielectric constant of materials is reduced and that of PVDF decreases the most. The conductivity of dielectric materials is all on the rise due to the magnetic field. Compared with under normal environment, the conductivity of the PVDF under 12-T magnetic field climbs to 574%, which is the largest increase in all dielectrics. The breakdown strength of PP and PE decreases by 17.2% and that of PVDF decreases by 22%. On the one hand, the magnetic field deflects the electric dipole in the opposite direction through Lorentz force, so as to limit the dipole steering and reduce the dielectric constant. On the other hand, the magnetic field increases the quantity of carriers by exciting electrons, which is the main reason for the decrease of breakdown strength. This article is of significance to the application of dielectric capacitors under harsh magnetic environment. [ABSTRACT FROM AUTHOR]

In this article, the dielectric properties of polypropylene (PP) films are investigated under 0–12-T magnetic field. The modification method based on aromatic compound blending is proposed to improve the performance of PP in the strong electromagnetic environment. Under the 12-T magnetic field, the dielectric constant declines from 2.34 to 2.27 at 1 kHz, and the dielectric loss grows up from 0.40% to 0.64% at 1 kHz. The leakage conductivity increases from $0.56\times 10^{-{12}}$ to 1.85 $\times \,\,10^{-{12}}$ S/m. The breakdown strength drops from 546.1 kV/mm under 0 T to 454.2 kV/mm under 12 T. The energy density of PP decreases from 3.09 to 2.07 J/cm3 due to the magnetic field. After blending with 0.05 wt% aromatic compounds, the dielectric properties of PP films got enhanced. The energy storage density of the modified films reaches 3.63 (under 0 T) and 2.72 (under 12 T) J/cm3 with enhanced voltage resistance and enlarged dielectric constant. This article is of significance to the application of PP capacitors under strong electromagnetic environment. [ABSTRACT FROM AUTHOR]

This paper proposes a grid-connected single-phase micro-inverter (MI) with a rated power of 300 W and an appropriate control strategy for photovoltaic (PV) systems. The proposed MI is designed based on a two-stage topology. The first stage consists of a SEPIC DC-DC converter with high voltage gain to step up the voltage of the PV panel and harness the maximum power, while the second stage includes a full-bridge DC-AC converter. The advantages of the proposed MI are the use of fewer components to provide suitable output voltage level for connection to a single-phase grid, continuous input current, limited voltage stress on the switch, high efficiency, long operational lifetime, and high reliability. Lower input current ripple and the presence of film capacitors in the power decoupling circuit increase the lifetime and reliability of the proposed MI. In the proposed MI, the active power decoupling circuit, which is normally used in a typical single-stage SEPIC-based MI, is eliminated to achieve both a long lifetime and high efficiency. The operating principles of the proposed MI are analyzed under different conditions. The results of design and simulation confirm the advantages and proper performance of the proposed MI. [ABSTRACT FROM AUTHOR]

This review provides a detailed overview of the latest developments using nanoscale strategies in the field of polymeric and polymer nanocomposite materials for emerging dielectric capacitor-based energy storage applications. Among the various energy storage devices, solid-state dielectric capacitors possess the advantage of high-power density which makes them highly attractive for pulsed power applications. Polymers are particularly suitable for dielectric energy storage applications because of their high breakdown strength, low dielectric loss, formability, self-healing capability, flexibility, solvent processability, and graceful breakdown failure. Strategies to enhance the dielectric breakdown strength of polymeric dielectric capacitors are emphasized in this review. General background on breakdown mechanism, breakdown characteristics, and factors influencing polymer dielectrics breakdown are introduced. Given that polymers have low permittivity, strategies to substantially enhance dipole mobility and hence the permittivity, are highlighted. We discuss strategies to address permittivity contrast between nanofillers and the polymer matrix including the potential for developing gradient permittivity structured nanofillers. To improve the compatibility of nanofiller with polymer and minimize nanofiller aggregation, different routes to surface functionalize nanoparticles are presented. An outlook and future perspectives section are provided for the design of high energy density polymer film capacitors. [ABSTRACT FROM AUTHOR]

Dielectric film capacitors have aroused considerable attention on account of the fast development of pulsed power systems. However, enhanced energy density is always acquired at the cost of deteriorated charge/discharge efficiency. Herein, well balanced energy density and efficiency are achieved in a series of reasonably designed bilayer composites consisting of a ferroelectric layer and a paraelectric layer at the meantime. It is interesting to find that, when merely 1.6 wt% Zr(HPO4)2 nanosheets are introduced into the ferroelectric layer, a substantially improved energy density of 11.22 J cm−3, which is about 165% that of the bilayer composite without Zr(HPO4)2 nanosheets, is achieved at 650 kV mm−1. Meanwhile, a high charge/discharge efficiency of 89.8% and a low loss tangent of 0.024@10 kHz which is much lower than the pristine ferroelectric polymer layer (0.058@10 kHz) is maintained. Furthermore, finite element simulation reveals that the electric breakdown paths will develop along the macroscopical‐interfaces between adjoining layers and the microcosmic‐interfaces between the Zr(HPO4)2 nanosheets and polymer matrix, which can effectively increase the length of breakdown paths and contribute to improved breakdown strength. This work demonstrates that the Zr(HPO4)2 nanosheets can be promising fillers for other high‐performance dielectric composites. [ABSTRACT FROM AUTHOR]

This letter proposes a safe operating area (SOA) concept for film capacitors in dc-link applications. The SOA is presented by capacitor voltage and ripple current, considering the impact of ambient temperature, degradation, and parameter variance. The theoretical derivations and proof-of-concept experimental verifications are given. [ABSTRACT FROM AUTHOR]

A large number of electrolytic capacitors are applied in DC link of EAST vertical stabilization control power supply (VSPS), which become the reliability weak links of the power supply. An appropriate film capacitor is selected to take place of electrolytic capacitor applied in DC link. The criteria for calculation of capacitance according to energy storage and ripple current absorption for sizing the DC link are given. The feasibility of the selection of the capacitor is proven in MATLAB simulation in various operation conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel positively charged nanoparticle/polymer composite for high temperature capacitors. • The positively charged CSO effectively addresses the agglomeration issue in the composite film. • The introduction of CSO synergistically enhances the ε r and BDS of the PI film. • The PI-3 wt% CSO composite possesses a U e of 7.33 J/cm3 and a BDS of 616.5 MV/m @150 °C. The issue of inorganic nanoparticle aggregation has impeded the development of nanocomposite applications. In this study, calcium silicate colloidal nanoparticles (CSO) with positively charged surfaces were prepared using triethylamine (TEA) as a capping agent. Owing to the electrostatic repulsion, the CSO colloidal particles are distributed evenly throughout the polyimide (PI), thus preventing the accumulation of electric fields and enhancing breakdown strength (BDS). Furthermore, the positively charged colloidal nanoparticles enhance the resistivity of the PI composite by absorbing electrons produced under high electric fields and reducing electron transit. The beneficial impact of CSO introduction on BDS is confirmed by the electrical breakdown simulation of PI composite films based on a Multiphysics finite element model. Besides, the positively charged colloidal particles promote the improvement of dielectric performance, resulting in the excellent high-temperature energy storage properties of the PI/CSO composite (BDS = 616.5 MV/m, U e = 7.33 J/cm3, and η = 70 % @ 150 °C). Even in a high-temperature environment of 200 °C, the PI/CSO film still possesses rapid charge–discharge capability (t 0.9 = 0.0554 μs) and an ultra-high power density (P D = 130.9 MW/cm3), positioning it as a highly promising material for high-temperature film capacitors. [ABSTRACT FROM AUTHOR]

Film capacitors have shown great potential in high-power energy storage devices due to their high breakdown strength and low dielectric loss. However, the state-of-the-art commercial capacitor dielectric, biaxially oriented polypropylene (BOPP), exhibits limited energy storage density below 2 J cm−3 because of its low dielectric constant (approximately 2.2 at 103 Hz). In this work, we present a novel PP-based nanocomposites by incorporating nonpolar sub-10 nm sized TiO 2 nanoparticles into the PP matrix for the first time. The nonpolar TiO 2 nanoparticles are functionalized with Trioctylphosphine oxide (TOPO) ligands, ensuring excellent compatibility and dispersion of the TiO 2 fillers in the PP matrix, resulting in a homogeneous dielectric PP nanocomposite. Moreover, the TOPO ligand, with lower LUMO energy level and higher HOMO level than that of PP matrix, serves as an energy trap to capture carriers upon their occurrence. Furthermore, the well-dispersed sub-10 nm sized TiO 2 nanoparticles enlarges the interfacial area, thereby increasing the interfacial polarization and the dielectric constant. The resultant PP nanocomposites exhibit a high discharged energy density of 4.19 J cm−3 at 600 MV m−1, representing a remarkable 74.9% increase compared to that of the pure PP films. This work provides a brand-new strategy for constructing homogeneous PP nanocomposite dielectrics by incorporating nonpolar sub-10 nm sized TiO 2 nanoparticles as fillers. And this approach is critical for the design of high energy density PP-based nanocomposites. [Display omitted] • Nonpolar sub-10 nm TiO 2 nanoparticles were incorporated into polypropylene (PP) to form a homogeneous PP nanocomposite. • The nonpolar TiO 2 , with TOPO ligand on the surface, exhibited excellent compatibility and dispersion within PP matrix. • The TOPO ligands on the TiO 2 filler surface acted as effective energy traps for free carriers upon they occur. • The sub-10 nm TiO 2 fillers enlarge the interfacial area, attributing to enhanced interfacial polarization. • The resultant PP nanocomposites exhibit an increased discharged energy density of 4.19 J cm-3 at 600 MV m-1. [ABSTRACT FROM AUTHOR]

This paper proposes a grid-connected single-phase micro-inverter (MI) with a rated power of 300 W and an appropriate control strategy for photovoltaic (PV) systems. The proposed MI is designed based on a two-stage topology. The first stage consists of a SEPIC DC-DC converter with high voltage gain to step up the voltage of the PV panel and harness the maximum power, while the second stage includes a full-bridge DC-AC converter. The advantages of the proposed MI are the use of fewer components to provide suitable output voltage level for connection to a single-phase grid, continuous input current, limited voltage stress on the switch, high efficiency, long operational lifetime, and high reliability. Lower input current ripple and the presence of film capacitors in the power decoupling circuit increase the lifetime and reliability of the proposed MI. In the proposed MI, the active power decoupling circuit, which is normally used in a typical single-stage SEPIC-based MI, is eliminated to achieve both a long lifetime and high efficiency. The operating principles of the proposed MI are analyzed under different conditions. The results of design and simulation confirm the advantages and proper performance of the proposed MI.

In this paper, current-mode boundary conduction mode (BCM) of a high-efficiency LED driver with high power factor, utilizing low-voltage film capacitors, is presented, and its theoretical design and considerations are discussed. The 1.5-stage driver consists of a forward-flyback and buck converter. Higher efficiency was reached using the reduced redundant power processing approach. Most of the processed energy is transferred to the output through flyback, while the rest removes the low harmonic ripple in the output current through the forward-buck path. An acceptable amount of odd harmonics is injected into the input current by using current-mode BCM control method, further reducing bus capacitance. To validate these principles, a laboratory prototype has been built and experimental results of a high-current 85 W (29.5 V/2.9 A) lamp with 50 Hz, 185–255 V power supply are provided. The results show that output current ripple is low, and the input current harmonics are within the standard regulations. [ABSTRACT FROM AUTHOR]

Performance of electromagnetic interference (EMI) filters in power-electronics applications is limited by the parasitic coupling between the components of the filters and the self-parasitic of each component. While these parasitic effects can be partially taken into account on the circuit level, it is difficult to estimate their values. In this article, a full-wave modeling methodology is proposed to predict the performance of a complete EMI filter up to 1 GHz. Following the proposed methodology, the mutual couplings among the EMI filter components are taken into account as well as the self-parasitics of each individual component. Experiments and simulations are carried out to validate the modeling methodology. A self-parasitic cancellation technique is also applied to demonstrate the benefits of three-dimensional modeling methodology in EMI filter design. [ABSTRACT FROM AUTHOR]

Polymer dielectrics are the key component in film capacitors, which are one of the most fundamental elements in modern electronics and power systems [1–3]. Film capacitors are capable of storing energy when voltage is applied, in the form of electric charges separated by a dielectric material sandwiched by a pair of metal electrodes. Film capacitors possess the advantages of high breakdown strength, low power loss and processing flexibility compared with their counterparts in competition such as electrolytic capacitors and ceramic capacitors [4], meaning they can sustain high voltage, have great efficiency in electrical energy storage and can be manufactured in low-cost and efficient methods. Moreover, the unique self-clearing (sometimes referred to as self-healing) characteristic of polymer dielectrics ensures reliable operation of film capacitors [5], which is of paramount significance since capacitors storing a large amount of electrical energy can explode when catastrophic failure occurs. To be specific, the self-clearing is a process that when localized breakdown occurs at a spot of metallized film capacitors (i.e., a film capacitor using dielectric polymer films with metallic electrodes deposited on the surface [5], [6]), the energy released in the breakdown process can "clear" the breakdown-site, forming an open circuit. This process protects the capacitor from catastrophic failure (Figure 1) [7]. Serving as a device for charge storage and control, film capacitors are commonly used in many types of circuits such as snubbers, phase shifters, filters and AC/DC converters/inverters. In particular, film capacitors are capable of releasing the stored energy in an extremely short period of time to supply a high power density [8–10], which is desirable for the pulsed power application [1]. However, sizeable energy storage has not yet been achievable with film capacitors due to the limited volumetric energy density (usually measured in Joule per cubic centimeter at the material level). This shortcoming has caused a major issue in the electrical apparatus and electrified systems where capacitors constitute a large volume and weight fraction, i.e., a bulky, and sometimes even cumbersome size. For instance, in the 800 kV voltage source converter-based high voltage direct current transmission system, each converter tower has a volume of approximately 480 m3, where capacitors are ∼60% of the converter weight, and ∼50% of the volume. [ABSTRACT FROM AUTHOR]

Ferroelectric thin film capacitors have triggered great interest in pulsed power systems because of their high-power density and ultrafast charge–discharge speed, but less attention has been paid to the realization of flexible capacitors for wearable electronics and power systems. In this work, a flexible Ba0.5Sr0.5TiO3/0.4BiFeO3-0.6SrTiO3 thin film capacitor is synthesized on mica substrate. It possesses an energy storage density of Wrec ~ 62 J cm−3, combined with an efficiency of η ~ 74% due to the moderate breakdown strength (3000 kV cm−1) and the strong relaxor behavior. The energy storage performances for the film capacitor are also very stable over a broad temperature range (−50–200 °C) and frequency range (500 Hz–20 kHz). Moreover, the Wrec and η are stabilized after 108 fatigue cycles. Additionally, the superior energy storage capability can be well maintained under a small bending radius (r = 2 mm), or after 104 mechanical bending cycles. These results reveal that the Ba0.5Sr0.5TiO3/0.4BiFeO3-0.6SrTiO3 film capacitors in this work have great potential for use in flexible microenergy storage systems.

A series of high dielectric composite films based on low-cost and eco-friendly titanium dioxide (TiO2) and cellulose nanofibril (CNF) was prepared under a facile condition. The relative dielectric constants (εr) and dielectric loss ( tan δ ) were studied as the function of frequency and filler content. The εr of CNF/TiO2 composite film was 19.51 (at 1 kHz) with a relatively low dielectric loss. Compared with pure CNF films (εr = 6.92 at 1 kHz), the εr of the composite film was improved about three times with the dielectric loss increased slightly. The effects of TiO2 addition and hot-press treatment on microstructure, thermal stability, and dynamic mechanical properties of the composite films were also analyzed. It was found that the addition of TiO2 particles reduces the cellulose–cellulose bonding so generates more pores in the films, which has significant impacts on both dielectric and physical strength properties. [ABSTRACT FROM AUTHOR]

Abstract Metallized film capacitors are used to reduce electromagnetic interference (EMI) in electric power mains due to their high voltage capability and their open circuit failure mode, which aids in safe operation. This paper presents a comprehensive review of metallized film capacitors used for EMI filtering and their failure modes and mechanisms. One of the major failure mechanisms discussed is the corrosion of the metallized film due to moisture ingress into the package. Safety, quality, and reliability standards for metallized film capacitors are also discussed. The paper concludes with recommendations for film capacitor selection and the proper qualification and accelerated life testing to ensure long-term reliable operation. [ABSTRACT FROM AUTHOR]

The primary objective of Maximum Power Point Tracking (MPPT) for PV systems connected to a low-voltage DC grid is to extract the maximum possible power output from the PV array. Normally high-frequency switched mode power converters are employed to track the maximum power. These converters, however, impose switching frequency voltage ripple on the PV output. This causes fluctuation around the Maximum Power Point (MPP) and results in power loss. These losses can be reduced using electrolytic capacitors, however, the electrolytic capacitors' lifespan is relatively shorter than that of a PV panel. In this paper, an interleaved boost converter is used to reduce high-frequency voltage ripple introduced on panel. Hence, smaller values of longer lifespan capacitors such as film capacitors will be sufficient to curtail the smaller ripple. Moreover, film capacitors are selected based on voltage ripple. Analysis was carried out for calculating voltage ripple imposed on PV module to select input filter more precisely. In addition, reduction in the voltage ripple is calculated quantitatively and is compared with that of a conventional boost converter. Enhanced power output from the PV panel is mathematically proven and experimentally demonstrated. [ABSTRACT FROM AUTHOR]

The amount of light flicker in an AC–DC light-emitting diode (LED) driver is dependent on the size of filter capacitors. In this study, a study is conducted on reducing the size of filter capacitor in an AC–DC buck–boost/flyback LED driver using flicker index and per cent flicker light measures. Using this approach, a procedure for minimising the filter capacitance is presented. It is then concluded that relatively small filter capacitors such as film or ceramic capacitors can be chosen while meeting light flicker requirements. Hence, an LED drive with a longer lifetime can be achieved when compared with a driver using electrolytic capacitors. Experimental studies are presented for a 20 W AC–DC buck–boost/flyback LED driver prototype which utilises ceramic capacitors for driving Cree CR22-32L and XLamp XP-G LED strings.

The objective of this paper is to propose a novel photovoltaic (PV) micro-inverter with PV current decoupling (PVCD) strategy to achieve maximum power point tracking (MPPT) performance without using large electrolytic capacitors. Conventionally, the grid-connected PV micro-inverter needs a large PV-side electrolytic capacitor to suppress the double-line frequency voltage ripple, which is caused by the injected ac grid power, to achieve the desired MPPT performance. However, the short lifetime electrolytic capacitor will reduce the PV micro-inverter's reliability dramatically. Therefore, different active power decoupling circuits (APDCs) have been proposed in published papers to reduce the required input capacitance so that the long lifetime film capacitor can be used to replace the electrolytic capacitor. Unlike the conventional APDC with charging and discharging modes operation, a novel PVCD strategy, which is based on the concept of current decoupling instead of power decoupling, is proposed to simplify the control mechanism of the PV micro-inverter. Furthermore, to accomplish the proposed current decoupling concept, a novel circuit topology for the PV micro-inverter is also proposed. With the proposed PVCD strategy, the current decoupling tank (CDT) inside the proposed PV micro-inverter can buffer the current difference between the constant current from the PV panel and the rectified sinusoidal current of the ac grid current. Therefore, the input capacitance on the PV-side can be reduced dramatically and the long lifetime film capacitor can be used to replace the electrolytic capacitor. The reliability of the PV micro-inverter with good MPPT performance can be increased. In this paper, the operation principle and the component design of the proposed PV micro-inverter with PVCD strategy will be presented. Simulation results and experimental results of a prototype 240 W PV micro-inverter is shown to verify the performance of the PV micro-inverter with PVCD strategy. [ABSTRACT FROM AUTHOR]

In this paper, a novel DHB power-decoupling control scheme without current sensor is proposed for single-phase inverters. As electrolyte capacitors are conventionally used; however, these capacitors limit ripple current capability and circuit reliability. Film capacitors improve the ripple current capability, size reduction, and circuit reliability. Conventionally, non-isolated topologies are used for power decoupling. The volume of the decoupling capacitor per unit energy in isolated bidirectional power decoupling topologies is reduced as compared to nonisolated due to unrestricted voltage across the decoupling capacitor. Voltage-fed Phase-Shift Dual Half-Bridge (DHB) is preferred with film capacitors as it has the least number of components in isolated bidirectional topologies. However, in DHB, power decoupling controller is a challenge as current control is conventionally required. The challenge has been overcome with novel current-sensorless dc link ripple rejection control. The controller has the advantage of current-sensorless configuration especially when it needs information from inverter phase-lock-loop (PLL). The proposed power decoupling control scheme is independent of the inverter control and universal. A new dynamic analysis has been carried out by taking into account the input-voltage dynamics. The advantage of the DHB is that it has single pole behavior and, hence, sufficient bandwidth can be obtained. Simulations and experiments have been performed to verify the analysis of the power decoupling control scheme and the capability of film-capacitor DHB for power decoupling. [ABSTRACT FROM AUTHOR]

Following the recently proposed $\theta$ -converter that reduces voltage ripples, leakage currents, and total capacitance required in a single-phase converter, this paper further improves the $\theta$ -converter by reducing the current stress of the neutral inductor, by relocating it to the dc side without affecting the other functions of the $\theta$-converter. Based on the average circuit model of the proposed converter, it is found that the current flowing through the neutral inductor can be reduced by at least three times, and hence, the size of the inductor can be reduced by at least nine times. How to operate the converter to achieve the reduction of the current stress is discussed in detail. Moreover, the selection criteria on the neutral inductor and other passive components used in the proposed converter are discussed in order to minimize their usage. Intensive experimental results are presented to demonstrate that the proposed converter can indeed reduce the current-stress while the other functions of the $\theta$-converter are not affected. [ABSTRACT FROM AUTHOR]

In this paper, a single-phase converter consisting of two legs with four switches, called the $\theta$-converter, is proposed. It has a common ac and dc ground, which reduces common mode currents and removes the need for an isolation transformer, and two capacitors: one across the whole dc bus and the other across the output. The dc bus capacitor provides a direct path for the double-frequency ripple current inherently existing in single-phase converters to return continuously so the output capacitor can be sized very small, only to filter out switching ripples. Moreover, the dc bus capacitor is intentionally designed to store the system ripple energy with large voltage ripples, which reduces its capacitance. Hence, the total capacitance needed and the output voltage ripples are reduced at the same time. This makes it cost-effective to use highly reliable film capacitors instead of bulky and vulnerable electrolytic capacitors. Because of the removed isolation transformers and bulky electrolytic capacitors, the power density and system reliability are improved. In order to properly operate the converter, two independent controllers are designed for the two legs, respectively, to achieve the desired functions and other normal objectives, such as the unity power factor. Experimental results are presented to demonstrate the high performance of the proposed converter. [ABSTRACT FROM AUTHOR]

We have investigated dielectric properties of aromatic polythiourea (ArPTU, a polar polymer containing high dipolar moments with very low defect levels) thin films that were developed on Pt/SiO2 substrate. The detected response is compared to the response of commercially available polymers, such as high density polyethylene (HDPE) and polypropylene (PP), which are at present used in foil capacitors. Stable values of the dielectric constant ε′≈5 (being twice higher than in HDPE and PP) over broad temperature and frequency ranges and dielectric losses as low as in commercial systems suggest ArPTU as a promising candidate for future use in a variety of applications.

With the renewable energy application fields of film capacitors gradually expanding, mining film capacitors' data is an important issue. When the aging mechanism and environment are unfamiliar, it will be hard to extract the capacitance's variation law and predict its changes. At the same time, the parallel operation of film capacitor components also brings practical needs and data basis for collaborative prediction. In this work, the capacitance of five film capacitors at room temperature and humidity for 70 days was measured and the characteristics of capacitance variation were analyzed. Then, the capacitance law extraction, single prediction, and collaborative prediction methods for film capacitors were proposed based on the smoothing splines theory. Finally, the effectiveness and application potential of the single prediction and collaborative prediction methods were verified by actual data. The performance of the single prediction and collaborative prediction methods is evaluated by error analysis. The single prediction and collaborative prediction methods proposed in this work can also provide a reference for the prediction and evaluation of other parameters like equivalent series resistance of film capacitors, and help to effectively and accurately explore the aging mechanism. • We measured the capacitance for 70 days at room temperature and humidity and analyzed the characteristics. • Based on smooth splines theory, the law extraction, single prediction, and collaborative prediction methods were constructed. • This work will provide a reference for predicting and evaluating other parameter such as the equivalent series resistance of film capacitors, helping to monitor the state and explore the aging mechanism effectively and accurately. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENGs) is one of the promising energy harvesting methods, and is expected to serve as primary power source. Nevertheless, previous TENGs were only able to generate low-current outputs. Even when energy management systems (EMSs) are used for TENGs, electrical losses occurred owing to complicated EMS circuits. Accordingly, high-mechanical inputs were still necessary to match power levels for existing electronics. Therefore, film capacitor-based charge-carrier TENGs (FCC-TENGs) are fabricated herein. These can be easily utilized for various circuits owing to their ultrahigh output with low input. As film capacitor-covered charge-carrier cylinders are rolling, FCC-TENGs can produce high voltage and current outputs of about 5000 V and 10 A, respectively, and can effectively reduce friction and wear. By loading external load, the root mean square power of FCC-TENG is measured up to 720 mW. Given the generated outputs, FCC-TENG can be used as primary power source for several power supply circuits that can turn on 12 commercial 5 W light-emitting diodes, power electric device, and charge lithium-ion battery. [Display omitted] • Can produce ultrahigh electrical outputs of about 5000 V and 10 A and generate RMS power of 720 mW with external load. • Easily optimized by using a simple energy management system circuit. • Effectively reduce friction and wear by rolling film capacitor covered charge-carrier cylinders. • Hand-operatable device that can turn on LEDs, power electric device, and charge lithium-ion battery. [ABSTRACT FROM AUTHOR]

This paper presents a robust vision inspection system for detecting the surface defects of film capacitors. In particular, we use a novel Non-subsampled Contourlet Transform (NSCT) based algorithm to detect the surface defects. Then, the detection results are sent to the mechanical separation system via a serial port. The defective capacitors are peeled off from the production line by motor. The proposed system can improve the detection efficiency. It thus can improve the product quality and reduce production costs. Experimental results have demonstrated that the system achieves superior performance over other state-of-the-art solutions. Moreover, with the system, large-scale vision data of capacitor surfaces can be collected and used to supervise capacitor manufacturing process. [ABSTRACT FROM AUTHOR]

Single-phase ac/dc or dc/ac systems are inherently subject to the harmonic disturbance that is caused by the well-known double-line frequency ripple power. This issue can be eased through the installation of bulky electrolytic capacitors in the dc link. Unfortunately, such passive filtering approach may inevitably lead to low power density and limited system lifetime. An alternative approach is to use active power decoupling so that the ripple power can be diverted into other energy storage devices to gain an improved system performance. Nevertheless, all existing active methods have to introduce extra energy storage elements, either inductors or film capacitors in the system to store the ripple power, and this again leads to increased component costs. In view of this, this paper presents a symmetrical half-bridge circuit which utilizes the dc-link capacitors to absorb the ripple power, and the only additional components are a pair of switches and a small filtering inductor. A design example is presented and the proposed circuit concept is also verified with simulation and experimental results. It shows that at least ten times capacitance reduction can be achieved with the proposed active power decoupling method, and both the input current and output voltage of the converter can be well regulated even when very small dc-link capacitors are employed. [ABSTRACT FROM AUTHOR]

Light emitting diode (LED) lamps with ac-input (50 or 60 Hz) usually require an electrolytic capacitor as the dc-link capacitor in the driver circuit to: 1) balance the energy between the input and output power, and 2) to minimize the low-frequency component of the output ripple across the LEDs. The lifetime of this capacitor, however, is much shorter than that of a LED. To maximize the potential lifetime of the LED lighting system, a new pulsating current driving LED driver that does not require any electrolytic capacitors or complicated control circuits to minimize the low-frequency (i.e., 100 or 120 Hz) output ripple is proposed in this paper. The proposed circuit is simple and a single-switch topology is designed to simplify the controller design. The proposed circuit is able to reduce the energy storage capacitance to a few microfarads range, so that film capacitor can be used to replace the unreliable electrolytic capacitor. The circuit operating principles and its theoretical analysis are provided in this paper. Simulation and experimental results are given on a 9-W LED lamp to highlight the merits of the proposed circuit. [ABSTRACT FROM AUTHOR]