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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.

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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]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department 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.)

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]

In EV/HEV application, the maximum internal temperature allowed for film capacitor should be less than 105 ℃, which leaves especial limited temperature margin as the capacitor works in high ambient temperature of 85 ℃. However, temperature rising of capacitor is strongly related to the load condition. And it is difficult to define the temperature allowance of capacitor accurately in the early design. For this purpose, a consolidated electrothermal simulation method based Foster thermal network model is presented in this paper to predict the transient temperature inside the capacitor. To set up a complete simulation model, the parameters of five-order Foster resistor-capacitor thermal network model are extracted by the method of capacitor temperature rise experiment. The temperature rising of film capacitor in the conditions of NEDC (New European Driving Cycle) & USA highway driving cycle is calculated by the complete simulation model. Simulation results show that a good correspondence is presented between capacitor temperature rising curve vs ripple current under driving cycle, and the maximum temperature rise can be clearly assessed by this temperature prediction method.

• 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]