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Advances in flexible electronics are driving dielectric capacitors with high energy storage density toward flexibility and miniaturization. In the present work, an all-inorganic thin film dielectric capacitor with the coexistence of ferroelectric (FE) and antiferroelectric (AFE) phases based on Pb0.96La0.04(Zr0.95Ti0.05)O3 (PLZT) was prepared on a 2D fluorophlogopite mica substrate via a simple one-step process. The flexible capacitor exhibits a high recoverable energy density (Urec) of ≈ 44.2 J/cm3, a large electric breakdown strength (EBDS) of 3011 kV/cm, excellent frequency stability (500 Hz-20 kHz) and high thermal stability over 30–190 °C. It also demonstrates an outstanding bending endurance, which can maintain a high energy storage performance under various bending radii (R = 2–10 mm) or 103 repeated bends at 4 mm. The FE phase is stable near the film surface and the interface with the bottom electrode. The AFE phase with multi-domains has incommensurate modulation structures with super-periodicity of 6.5, 6.9 and 5.2. It indicates that the PLZT/LNO/F-Mica capacitor has high potential for energy storage application and may provide great opportunities for exploring new energy storage materials.

As the fundamental energy storage components in electronic systems, dielectric capacitors with high power densities were demanded. In this work, the anti-ferroelectric Pb0.89La0.06Sr0.05(Zr0.95Ti0.05)O3 (PLSZT) ceramics and thin film capacitor were successfully fabricated by a solid-state reaction route and pulsed laser deposition method, respectively. The ferroelectric, dielectric, energy-storage properties, and temperature stability of anti-ferroelectric PLSZT capacitor were investigated in detail. By compared with the PLSZT ceramic (energy storage density is 1.29 J/cm3 with an efficiency of 78.7% under 75 kV/cm), the anti-ferroelectric PLSZT thin film capacitors exhibited the enhanced energy storage density of 52.6 J/cm3 with efficiency of 67.7% under an electric field as high as 2068.9 kV/cm, and the enhanced energy-storage temperature stabilities from room temperature (RT) to more than 200 °C were demonstrated, and the oxygen defects mechanism and size effect were discussed. Moreover, the fast charging (∼0.05 μs) and discharging (∼0.15 μs) time were certified for the anti-ferroelectric PLSZT film capacitor. These findings broaden the horizon for PLSZT anti-ferroelectrics in high energy storage properties and show promising for manufacturing pulse power capacitor.

The motion of domain walls is a crucial factor in piezoelectric properties and is usually related to the irreversible and hysteretic behaviors. Herein, we report on the investigation of inverse and transverse piezoelectric coefficients of capacitor-based and microcantilever-based Pb(Zr0.52Ti0.48)O3 films with a change in the DC bias and the AC applied voltage. A large inverse piezoelectric strain coefficient of about 350 p.m./V, and a low strain hysteresis of about 7.1%, are achieved in the film capacitors under a low applied voltage of 2 V (20 kV/cm) which can benefit the actuators for motion control in high-precision systems. The field-dependences of the transverse piezoelectric coefficients, obtained from four-point bending and microcantilever displacement, are in good agreement with each other. The results also reveal that the irreversible domain-wall motion is attributed to the nonlinearity in the field-dependent piezoelectric strain and cantilever displacement.

Polymer film capacitors are usually limited to relatively low working temperatures due to the large conduction loss of polymer dielectrics under high thermal stress. Here, a polymer dielectric sandwiched by medium-dielectric-constant nanoscale deposition layers is reported, which exhibits significantly suppressed conduction loss and outstanding capacitive performance at high temperatures. A series of deposition materials with distinct band structures and dielectric properties are investigated. It is found that well-balanced bandgap, dielectric constant and electrical conductivity of the nanoscale deposition layer is desirable for suppressing charge injection. The substantial performance improvements are demonstrated to result from the slow decay of barrier height with increasing electric field and the reduced electric field in the deposition layers. The optimized design using a polyetherimide film sandwiched by 150-nm-thick Al2O3 deposition layers gives rise to a concurrent high discharged energy density (2.8 J cm−3) and charge-discharge efficiency (90%) up to 200 °C, which are significantly higher than those of previously reported surface-coated polymer dielectrics, and are even comparable to the maximum values achieved with expensive, less productive solution-based composite approaches. Moreover, the nanoscale coating layer can be fabricated through evaporation deposition techniques, which is accessible with industrial equipment for fast surface deposition of capacitor films

Active power decoupling in single-phase conversion systems reduces the required capacitance for twice-line frequency power ripple buffering by operating the energy buffering capacitors with high energy utilization ratios. The bipolar active buffer is the buffer topology that can achieve 100% energy utilization ratio. Yet, the conventional two-level full-bridge designs suffer from high switching and conduction loss and large filter inductor size due to the direct connection of the buffer across the high voltage dc-bus. Moreover, the high voltage swings across the buffer capacitor impose challenges for the control to regulate harmonics in the system. This article improves the power density and the efficiency of the bipolar active buffer through a buffer architecture incorporating the flying capacitor multilevel topology. Moreover, control techniques to regulate harmonics in the buffer are proposed to maintain low ripple in the dc-side current. The use of two common types of capacitors, the metal film capacitor and the X6S multilayer ceramic capacitor (MLCC) as buffer capacitors, is addressed with different harmonic control schemes. With MLCCs, we have also achieved a total passive component volume that is almost three times smaller than state-of-the-art solutions. The proposed approach is validated using a compact hardware for a 2-kW, 400-V dc-bus, 60-Hz single-phase inverter application.

The operation of the buck converter can be in continuous mode or discontinuous mode. In a power electronic circuit, the semiconductors are one of the most significant sources of loss. For a given device, this loss has two components: the conduction loss associated with the forward voltage drop, which occurs as a part of conducting current, and the switching loss, which occurs when a device turns on or off. Switching losses are proportional to the voltage that the semiconductor must block in the off state and the value of current that was or will be conducted following the change in switching state. The chapter considers a passive air‐cooled scenario in which the transistor and diode are each mounted on their own heat sink. It focuses on polypropylene film capacitors, which are very commonly used in power electronics applications. The chapter considers the electrothermal analysis of an operating point.

Single-phase ac to three-phase ac converters are needed in numerous applications, including motor drives used for residential applications. These converters, however, suffer from an inherent problem of mismatch between instantaneous input and output powers. Specifically, the instantaneous input power has a dc component along with an alternating component with double-line frequency, while the three-phase instantaneous output power is only dc. Conventional single-phase ac to three-phase ac converters use large electrolytic capacitors to handle this mismatch of power. However, these electrolytic capacitors may have high failure rates, which contribute to reduced lifetime of the converters. Moreover, these capacitors can be bulky and heavy. This article introduces a new single-phase ac to three-phase ac converter that uses a small film capacitor instead of large electrolytic capacitors. Despite using a small film capacitor, the double-line frequency harmonic does not appear at the input or output currents/voltages. The principles of the operation of the proposed topology are presented in this article, and its performance is evaluated through both simulations and experiments.

This paper focuses on the effects of the nano Polyhedral oligomericsilsesquioxanes (POSS) with three similar molecular structures on the thermal and electrical properties of polypropylene (PP) films, aiming to propose a comprehensive modification method. After doping with micro amount of nano POSS, the crystallinity and regularity of films are elevated. Correspondingly, PP with optimized microstructure has the lowest conductivity, due to the interaction between the nanoparticles and the matrix, as well as the strong binding force of the crystal region to the carriers. The loss of the sample is restricted, especially in the low frequency region, since the combined effect of polarization and conduction. The DC breakdown strength of the modified PP is higher than that of the PP, with an increase of above 20% at 25–85 °C. Based on quantum chemical calculations, the energy level distributions are analyzed. By selecting appropriate additives, deep trap sites can be introduced to catch carriers, preventing the breaks of polymer molecular chains. This modification of PP films shows huge potential in the improvement of dielectric properties in the field of DC capacitors.

The demand for high-temperature energy storage capacitors arises to meet the noticeable increase in integration density of electronic devices. In pursuit of optimized energy storage performance at elevated temperatures, 0.85BaTiO3–0.15Bi(Mg0.5Zr0.5)O3 (BT-BMZ) thin film capacitors were prepared on graphene/silicon substrate in this work. Taking advantage of remarkable lateral heat dissipation ability of graphene, the dielectric breakdown strength has been promoted from 7.14 MV $\cdot $ cm−1 to 7.97 MV $\cdot $ cm−1 by inserting a graphene buffer layer at room temperature. Thus, an enhancement in energy storage density is also observed. Notably, the improvement is more significant with temperature increase. The energy storage density of BT-BMZ/graphene/Si is gained 150% to 34.84 $\text{J}\cdot $ cm−3 in comparison to BT-BMZ/Si (13.96 $\text{J}\cdot $ cm−3) at 125 °C. The results reveal that thermal management is an effective way to improve high-temperature energy storage performance of dielectric film capacitors and prove that transferred monolayer graphene is a promising material for heat dissipation of silicon integrated devices.

Well-crystallized perovskite ferroelectric films usually display a bulk-like polarization response (P) under an external electric field (E), i.e., a large P-E hysteresis loop featuring a sizable remnant polarization and an early polarization saturation. Such characteristics are undesirable for capacitive energy storage applications. In this work, we demonstrate an optimal P-E behavior, i.e., a small remnant polarization and a delayed polarization saturation, in perovskite BaTiO3 films consisting of superfine columnar nanograins. In a low-temperature, nucleation-dominated sputtering deposition, an in-situ grown conductive buffer layer promotes the formation of these nanograins, which display a controllable diameter down to ~10 nm and extend throughout the film thickness. The deterioration of the remnant polarization and its delayed saturation under an electric field, can be attributed to a strong polarization-constraining effect from the densely-packed, non-ferroelectric grain boundaries, which is supported by a phase field modeling simulation. The resulted BaTiO3 film capacitors integrated on Si at 350°C display a high recyclable energy density (Wrec~135±10 J/cm3) and efficiency (η~80%±4%) which are thickness-scalable. An intrinsically high power density, a simple and stable chemical composition, and good thermal (-150°C ~ 170°C) and cycling stabilities (up to ~ 2 × 108 charge-discharge cycles) warrant a broad range of applications for these film capacitors.

Considering the full utilization of energy and pursuing thin-film capacitors with high energy-storage density, the grain size engineering is used to adjust domain size, in order to enhance the energy-storage efficiency and energy-storage density of thin-film capacitors. Therefore, in this work, lead-free Bi0.5Na0.5TiO3 (BNT) films with designed grain size were grown on Nb-doped SrTiO3 (Nb:STO) (001) single-crystalline substrates by modulating the mineralizer concentrations via hydrothermal synthesis. The nature of epitaxial growth near the single-crystalline substrates was proved by transmission electron microscopy (TEM). In addition, the phenomenon of the decrease of grain size and the increase of [100] in-plane orientation with the decline of mineralizer concentrations were clarified by grazing-angle incidence X-ray diffraction (GIXRD) and field emission scanning electron microscope (FESEM). By reducing the grain size, an ultrahigh energy-storage efficiency (η) of 75.56% and superior the recoverable energy-storage density (Wrec) of 16.47 J/cm3 were acquired in pure Bi0.5Na0.5TiO3 films. Furthermore, the fine-grained film exhibits weak dependence on the frequency and has excellent anti-fatigue property. Therefore, hydrothermal synthesis is an efficient, inexpensive, and easy method, which is the most promising way to adjust grain size and energy storage of the film capacitor.

Dielectric material is an important material for film capacitors. However, the progress of this material is either impeded by its low dielectric constant, high loss tangent, or insufficient flexibility. In this work, PVA/GO film with alternating layer structure was fabricated by Spin-Coating-Assembly (SCA) method. This alternating layer structure not only benefits forming numerous microscale capacitors which improve e value a lot, but also helps eliminate perpendicular contact of GO and prevents the formation of conductive pathways. Thus, compared with pure PVA, significantly increased dielectric permittivity and a low loss tangent were simultaneously observed for the PVA/GO film. The ratio of dielectric permittivity to loss tangent increased from 68 to 165. These films might be potential flexible dielectric materials for advanced electrical devices such as embedded capacitors.

In this article, we present the theoretical models on self-healing (SH) processes in metallized film capacitors (MFCs) in overload modes. Based on the proposed dynamic model of capacitor’s SH resistance, the current and voltage of MFC in SH process and the value of dissipated energy, $W_{\text {SH}}$ , can be calculated. Theoretical model of MFC degradation due to SH processes approves that in the vicinity of the breakdown places of polymer dielectric, a high SH energy leads to their carbonization. The numerous SH events result in the decreasing of the equivalent parallel resistance (EPR). An analysis of MFC electrothermal state shows that at critical values of applied voltage at 4–5 of nominal values, the dangerous local heating of the polymer dielectric can occur. Computer simulation describes the behavior of the EPR of the polymer film capacitor, which is determined by the number and intensity of SH acts. Finally, the numerical model for evaluation of the thermal state of the capacitor is offered. Numerous SH acts (especially of high SH energy level) cause the local heating of MFC section. The surface temperature of the capacitor may seem normal, though the local heating reaches the level dangerous for polymer. The analytic estimations and simulation results are in quite good agreement with experimental data.

In this paper, a novel modification method of polypropylene (PP) films is proposed in the field of metallized film capacitors for converter valves. An organic crystallization accelerator with good dispersion improves the micromorphology of PP films. The doping content of the organic crystallization accelerator is optimized based on breakdown experiments under DC voltage. The DC breakdown strength is 584.8 kV/mm, an increase of 19.6%, compared with that of the original film. Under DC, DC superimposed harmonics, and DC superimposed pulse voltages, the modified PP film has successfully withstood the tests, showing stable advantages in breakdown properties without increasing the conduction loss. Trap analysis and theoretical modeling were performed to clarify the mechanism of improving electrical performances based on crystallization control. The entanglement layer introduced by the organic crystallization accelerator helps to expand the crystal area, resulting in deep trap sites and limitation of carrier migration. This research can provide a reference for the PP performance optimization for metallized film capacitors of converter valves.

Capacitors are sources of EM field emissions whose characterization is crucial for electronic circuits EMC. This paper presents the modeling of equivalent radiating sources of rectangular film capacitors. It presents and analyses the magnetic near field measured above plastic and polyester capacitors. The measurements are then used by the inverse method to create a radiating source model for the capacitor. The results show a good agreement between the measured cartography and the one obtained when using radiating sources model. Finally, a generic radiating model is proposed for various types of rectangular film capacitors. The generic model is validated using the measurements on a rectangular capacitor. The suggested radiating model accelerates solving the inverse method. It can be used by circuit designers to optimize the placement of capacitors on the printed circuit board to reduce their coupling with other components of the studied system.

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 ...

BaTiO3-based ferroelectrics have been extensively studied due to their large dielectric constants and a high saturated polarization, which have the potential to store or supply electricity of very high energy and power densities. In order to further improve the energy efficiency η and the recyclable energy density Wrec, an A, B-site co-doped (Ba0.95,Sr0.05)(Zr0.2,Ti0.8)O3 ceramic target was used for sputter deposition of film capacitor structures on Si. This film composition reduces the remnant polarization Pr, while the choice of a low-temperature, templated sputtering process facilitates the formation of high-density arrays of columnar nanograins (average diameter d ∼20 nm) and grain boundary dead layers. This self-assembled nanostructure further delays the saturation of the electric polarization, leading to a high energy density Wrec of ∼148 J/cm3 and a high energy efficiency η of ∼90%. Moreover, the (Ba0.95,Sr0.05)(Zr0.2,Ti0.8)O3 film capacitors retain their high energy storage performance in a broad range of working temperature (-175-300 °C) and operating frequency (1 Hz-20 kHz). They are also fatigue-free after up to 2 × 109 switching cycles. Our work provides a new method and a cost-effective processing route for the creation and integration of high-performance dielectric capacitors for energy storage applications.

Metallized film capacitors (MFCs) are used in many applications requiring high volumetric energy characteristics. Along with an increase in the dielectric permittivity of the polymer film, operating in overload mode is a simple way to dramatically increase the energy density of capacitors for relatively short periods. The unique feature of MFC, a self-healing (SH) ability, makes this possible. However, the task is complicated by the lack of information on the energy characteristics of SH in real capacitors, especially when they are voltage overstressed. Part 1 of this article contains the results of experimental investigations of SH processes in overload modes under the soft-training test. At the level of voltage up to 8 of nominal values, three types of SH were discovered: single, repetitive, and multiple. The energy characteristics of SH processes obtained in real MFCs varied widely from those in the literature data. The cumulative SH energy characteristic was introduced and proposed for diagnostic purposes. The reasons for repetitive SH were investigated and analyzed. Equivalent parallel resistance as a sensitive diagnostic parameter of the overloaded MFC was chosen and applied.

For the metallized film capacitors (MFCs) designed to maximize the self-healing performance in the event of overvoltage, electrochemical corrosion is the major capacitance loss (CL) mechanism especially under high temperature and/or high humidity. In this paper, the electrode corrosion evolution is analyzed by dividing the process into anode and cathode reaction. In order to investigate the CL characteristics, three types of MFCs are stressed with 305 VAC under different temperature and humidity. Based on the corrosion mechanism and distribution analysis, a staged CL prediction method is proposed. The results indicate that the typical CL curve can be divided into 4 stages which are characterized by the reaction rate coefficient and the capacitance loss exponent derived from the experimental data.

CaBi2Nb2O9 thin film capacitors were fabricated on SrRuO3-buffered Pt(111)/Ti/Si(100) substrates by adopting a two-step fabrication process. This process combines a low-temperature sputtering deposition with a rapid thermal annealing (RTA) to inhibit the grain growth, for the purposes of delaying the polarization saturation and reducing the ferroelectric hysteresis. By using this method, CaBi2Nb2O9 thin films with uniformly distributed nanograins were obtained, which display a large recyclable energy density Wrec ≈ 69 J/cm3 and a high energy efficiency η ≈ 82.4%. A superior fatigue-resistance (negligible energy performance degradation after 109 charge-discharge cycles) and a good thermal stability (from −170 to 150 °C) have also been achieved. This two-step method can be used to prepare other bismuth layer-structured ferroelectric film capacitors with enhanced energy storage performances.

In this work, polypropylene (PP) film samples doped with an organic phosphorus nucleating agent under three cooling processes are examined for the effects of regulating the crystallization. The conductivity and DC breakdown strength of the film samples were tested at 25, 55 and 85 °C. The average breakdown strength with 0.01 wt% nucleating agent increased by approximately 25% compared to un-nucleating samples and the DC conductivity decreased slightly. For the three cooling methods in these tests, the slow process increased the crystallinity of the film samples and stabilized the electrical properties of the PP samples. It is concluded that improving the insulation performance through crystallization control is feasible, and this method shows great potential for the modification of PP films.

Polymer film capacitors are widely used in modern power equipment, because of excellent volumetric characteristics in combination with high-voltage application ability. Using segmented electrodes of nanometer thickness increased the capacitor’s performance and reliability because of the self-healing feature. In this paper, we present the results of the experimental investigation and numerical simulation of electrothermal destruction of the metallized film capacitors segmented electrodes during the self-healing process. The destruction processes were investigated for both a single gate and single segment, comprising four parallel gates connected to the segment. The numerical simulation was conducted by means of COMSOL Multiphysics software. The model takes into account the heat flow from metal layer to polymer film since it has significant influence on the destruction process. Based on a good agreement of experimental and numerical results, the simulation model was proposed for the real metallized film capacitor segmented electrodes design. The model allows evaluating the single segment isolating time during self-healing, the energy required for the isolating, effective value of segmented electrodes surface resistance.

Single-stage utility-scale photovoltaic (PV) systems are usually interfaced with the host grid via a centralized voltage-source converter (VSC). Recently, and due to their reliability, the dc-link film capacitors are favored over electrolytic types in grid-connected applications. However, the capacitance per unit volume of film capacitors is significantly smaller than electrolytic capacitors. The overall system stability might be compromised by the reduction of the dc-link capacitance, particularly in PV systems that have a dynamic resistance that varies with operating conditions. Using a detailed small-signal model of the grid-connected PV system, it is shown in this paper that the reduction of the dc-link capacitance interferes with the dynamic resistance of the PV array, which eventually leads to instabilities. The minimum dc-link capacitance that preserves the overall system stability is determined. A simple and effective active compensator is developed to mitigate the instabilities with the reduced dc-link capacitance. Detailed time-domain simulations are presented to validate the analytical results and show the proposed compensator’s effectiveness in preserving the system stability.

Polymer film capacitors for energy storage applications at high temperature have shown great potential in modern electronic and electrical systems such as those used in aerospace, automotive, and oil exploration industries. The crosslinking strategy has been regarded as one of the most feasible approaches for polymer dielectrics to meet the high temperature requirements. This article presents recent progress in the field of crosslinked polymer-based materials as high-performance dielectrics at elevated temperature. Self-crosslinking polymers, polymers crosslinked by agents and crosslinked polymer nanocomposites are the focus of materials reviewed. We identify the critical relationships between the crosslinking construction methods and the capacitive energy storage properties of dielectric materials on the molecular scale. An in-depth analysis of challenges and future prospects in this field is also provided. The understanding of the crosslinking strategy enables the rational design of polymer-based materials for high-temperature capacitive energy storage.

Silicon integrated lead-free oxide thin film capacitors with high energy storage density (Wre), high efficiency (η) and good thermal stability have great application potential in modern communication fields. Here, 1 mol% SiO2-doped Ba(Zr0.35Ti0.65)O3 (BZTS) thin film capacitors are integrated on Si and HfO2 buffered Si substrates by using a radio-frequency magnetron sputtering system. It is found that the energy storage performances are significantly improved by inserting an HfO2 buffer layer (about 13.5 nm) between the BZTS layer and the Si substrate. The improved Wre of the BZTS/HfO2 thin film capacitors can be up to 93.48 J cm−3 at room temperature, which is about 65% higher than that of the film without the HfO2 buffer layer, and the η is ∼ 71.44%. Moreover, the introduction of the HfO2 buffer layer leads to a superior thermal stability in a wide temperature range from −100 °C to 200 °C with a very small change rate of ∼3.39%. Under different irradiations with doses of He+ from 1 × 1012 ions per cm2 to 7 × 1015 ions per cm2 and neutrons from 5 × 1012 ions per cm2 to 1 × 1014 ions per cm2, the BZTS thin film capacitors with the HfO2 buffer layer show ultra-stable energy storage performance. Our research provides an effective strategy for the integration of high performance BZTS thin film capacitors on Si substrates, and our results demonstrate potential of the Si integrated thin film capacitors for the application in nuclear technology, space stations, satellites, radiation centers and other harsh environments.

Polymer-based dielectrics have been attracted much attention to flexible energy storage devices due to their rapid charge–discharge rate, flexibility, lightness and compactness. Nevertheless, the energy storage performance of these dielectric polymers was limited by the weak dielectric breakdown properties. Crosslinked structure has been proven efficient to enhance breakdown strength (Eb) and charge–discharge efficiency (η) of polymer film capacitors. However, crosslinked networks usually lead to low electric displacement of dielectric capacitors, which greatly restrict their energy storage density (Ud). In this work, we present a tri-layered composite via layer-by-layer casting technology, where crosslinked polyvinylidene fluoride (c-PVDF) was used as the inter-layer to offer high breakdown strength, and the outer ternary fluoropolymer layers with high dielectric constant could provide high electric displacement. The optimal tri-layered composites exhibit an ultrahigh discharge energy density of 18.3 J cm−3 and a discharge efficiency of 60.6% at 550 kV mm−1. This energy density is much higher than that of the PVDF terpolymer and commercially biaxially oriented polypropylene (BOPP, 1–2 J cm−3). The simulation results prove that the enhanced energy density originates from the effectively depressed charge transport in crosslinked structure at high applied electric field. Moreover, this work provides a feasible method for developing flexible all-organic high-energy-density composites for polymer capacitors.

Dielectric capacitors, which have the characteristics of greater power density, have received extensive research attention due to their application prospects in pulsed power devices. Film capacitors are easier to integrate into circuits due to their smaller size and higher energy storage density compared to other dielectric capacitor devices. Recently, film capacitors have achieved excellent energy storage performance through a variety of methods and the preparation of multilayer films has become the main way to improve its energy storage performance. In this review, we have summarized several control optimization mechanisms, such as heterojunction effect, interfacial ‘dead-layer’ and space-charges effect, modulating the distribution of electric field and polarization, multilayer film interface design and interface blocking effects, and interlayer coupling, for multilayer films by recalling previous studies on multilayer films. The outlook and future research direction of multilayer films are also discussed in this article.

Capacitors are widely used in electronic systems and have a key function in electromagnetic compatibility (EMC) compliance. However, the aging of capacitors results in an alteration of their parameters, which could pose a threat on the normal operation of systems as well as their EMC compliance. Normally, accelerated aging is employed to shorten the experiment time. After the aging, the capacitance and equivalent series resistance (ESR) are measured to evaluate the aging process. In this article, a new continuous characterization measurement setup is implemented in which the accelerated aging of the capacitors under test (CUTs) is continuously monitored during the overall accelerated aging process. It significantly improves the continuity of the measurement and eliminates the errors attributed to the interrupting of the aging process. This method is validated by comparing measurement results from the new measurement method with the results of the conventional method. This was done by subjecting two types of film capacitors to thermal and electrical stress in order to evaluate the accelerated aging effects. Furthermore, a conditional deep neural network with a dropout technique is proposed to predict the accelerated aging conditions of the capacitors. Instead of only forecasting the failure threshold, the proposed network is able to dynamically predict the accelerated aging conditions at different elevated temperatures and voltages. This leads to a serious reduction in the total measurement time from 1000 to 200 h.

A rapid method based on activation energy values for the lifetime assessment of PP films used as dielectrics for capacitors is proposed. The activation energy is determined from a nonisothermal measurement made by differential scanning calorimetry and an aging test at a single elevated temperature. The use of the onset temperature of the exothermal peak is proposed to evaluate the activation energy of the degradation of the PP film. Four types of PP film capacitors were thermally aged at 100 °C for different aging times. For each aging time, the capacitance was measured at different frequencies. According to the standards, two end-of-life criteria (2% and 5%) were imposed for the reduction in the capacitance. The parameters of the lifetime line $a$ and $b$ were determined, and finally, the lifetime values were calculated. The novel proposed method is effective in terms of both energy and manpower costs compared with the current method, which uses three aging temperatures.

A polyvinylidene fluoride (PVDF)-based composite film embedded with plate-like fillers was investigated as a novel dielectric composite material that can serve as a candidate film capacitor. Plate-like particles of the dielectric Ca2Na3Nb6O19 (CNN6) filler material were prepared through liquid-phase exfoliation of KCa2Na3Nb6O19 synthesized by a conventional solid-state reaction method. CNN6 fillers with an average aspect ratio of 2.0 were successfully dispersed in a PVDF matrix without large aggregation using a solution blending and casting method. The resultant CNN6/PVDF composite film exhibited higher breakdown strength than a dielectric PVDF-based composite embedded with spherical BaTiO3 fillers. The superiority of the plate-like filler particles over spherical filler particles was qualitatively confirmed by finite element simulation using a simplified filler/matrix model. A CNN6/PVDF composite film with a thickness of 3.8 µm exhibited a high capacitance density of 10.1 F m−3, which was three times higher than that of a biaxially oriented polypropylene film currently used for film capacitors in the power control units of hybrid vehicles.

In power electronics for electrical drivetrains, DC-link film capacitors are exposed to high ripple voltages. These voltages lead to electromechanical forces inside the dielectric of the capacitor which may result in acoustical noise emission. Therefore, an analytical model for calculating the electrostrictive deformation of polypropylene including intermediate layer polarization is presented. Numerical finite-element simulations are further accomplished and are validated with laser vibrometer and atomic force microscopy measurements.

Polymer-based dielectric energy storage materials have been playing critical roles in high-performance energy storage capacitors due to their high breakdown electric fields and facile processability. However, the low energy density and efficiency of polymer-based film capacitors limit their widespread application in various electronics products. In this contribution, we synthesized the SrBi4Ti4O15 (SBT) nanosheets with large aspect ratio by using the molten salt method and introduced them into the PVDF matrix to prepare a multilayer nanocomposite film, of which the discharge energy density and discharge efficiency were much improved. Finite element simulation results show that the addition of 2D SBT nanosheets can significantly improve the local electric field distribution of nanocomposite films. Finally, a high discharge energy density of 11.69 J cm−3 and an excellent discharge efficiency of 78.95% were simultaneously achieved in the 0/5/0 sample. This work provides a reference for polymer-based dielectrics with excellent comprehensive energy storage performance.

Flexible lead-free Na0.5Bi0.5TiO3–EuTiO3 solid solution film capacitors were fabricated. The recoverable energy storage density and energy storage efficiency reach 65.4 J/cm3 and 52%, respectively, due to the great insulation characteristic and relaxor behaviors. And the energy storage performances for the flexible solid solution films show excellent stabilities on temperature, frequency and bending endurance, especially, with bending endurance stability over 105 cycles. And the energy storage performances still remain great properties after delay of a month and another 105 cycles. This work provides a candidate for the flexible film capacitors with giant application potentials in wearable energy storage devices.

Hexagonal boron nitride nanosheets (BNNSs) are two-dimensional nanomaterials with graphitic-like layered nanostructures, high surface areas, and large aspect ratios. Owing to their excellent thermal conductivity, electrical and mechanical strengths, BNNSs are emerging as multifunctional fillers in polymer dielectrics. In this article, the authors review the recent progress in the BN-containing polymer nanocomposites designed for high-performance film capacitors. While general synthetic approaches to BNNSs and polymer/BNNS nanocomposites are summarized, particular attention is placed on structure-property correlation and rational structural design of the composites with optimized dielectric properties and capacitive performances. In stark contrast to the polymer composites employing high dielectric constant fillers to enhance the electric displacement, a new design concept based on the utilization of BNNSs with a wide bandgap to impede electrical conduction and consequently improve breakdown strength and charge-discharge efficiency of the polymer composites, is highlighted. The significance of developing dielectric capacitors with desirable thermal conductivity and thermal stability to ensure their robust and efficient operation is emphasized. The merits and challenges regarding the existing polymer dielectrics containing BNNSs for energy storage are identified. An outlook for future research opportunities and engineering applications is also presented in this review.

Polymer dielectric materials of film capacitors have been investigated widely for advanced electronics and energy storage systems, in which high discharge energy density and low loss are the key pa...

In order to apply power electronics systems to applications such as superconducting systems under cryogenic temperatures, it is necessary to investigate the characteristics of different parts in the power electronics system. This article reviews the influence of cryogenic temperature on power semiconductor devices including Si and wide bandgap switches, integrated circuits, passive components, interconnection and dielectric materials, and some typical cryogenic converter systems. Also, the basic theories and principles are given to explain the trends for different aspects of cryogenically cooled converters. Based on the review, Si active power devices, bulk Complementary metal-oxide-semiconductor (CMOS) based integrated circuits, nanocrystalline and amorphous magnetic cores, NP0 ceramic and film capacitors, thin/metal film and wirewound resistors are the components suitable for cryogenic operation. Pb-rich PbSn solder or In solder, classic printed circuit boards material, most insulation papers and epoxy encapsulant are good interconnection and dielectric parts for cryogenic temperatures.

Film capacitor, one typical type of electrostatic capacitors, exhibits its unique advantages in the high-power energy storage devices operating at a high electric field due to the high electrical breakdown strength (Eb) of the polymeric films. However, the development of film capacitor towards high energy storage density is severely hindered by the low dielectric constant (e) and low charge-discharge efficiency (η) of the polymeric films. The film of polypropylene (PP), the most used polymeric film with a market share of 50%, owns a high η due to its low inherent hysteresis loss. Yet the low e (2.2 ​at 103 ​Hz) impedes the increase of its energy storage density (1–2 ​J/cm3). Here we demonstrate that the discharged energy density (Ue) of PP film could be largely increased from 1.40 ​J/cm3 of pure PP film to 3.86 ​J/cm3 of PP nanocomposite film by incorporating a small loading of core-shell structured PMMA@BaTiO3 (PMMA@BT) nanoparticles (2.27 ​vol%) into PP matrix. The obtained Ue of 3.86 ​J/cm3, to the best of our knowledge, is the highest reported value for the PP based films using commercial PP resin. Meanwhile, the η merely undergoes a slight decrease from 99.5% to 94.1%. Similarly, the obtained η of 94.1%, to the best of our knowledge, is also the highest value for the polymeric films reported in the previous works. The significant increase of Ue (175.7%) and negligible decrease of η (5.4%) are mainly attributed to the increases of e from 2.2 to 3.7 and Eb from 361 ​MV/m to 448 ​MV/m. Compared with the films of raw BT/PP nanocomposites, the Ue exhibits a significant increase of 365.1% from 0.83 ​J/cm3 to 3.86 ​J/cm3 and the η also displays an increase of 7.4% from 87.6% to 94.1%. The significant improvement of energy storage performance achieved in the film of PMMA@BT/PP nanocomposite suggests that the organic PMMA shell plays an important role in the amelioration of compatibility of BT nanoparticles and PP matrix and the alleviation of local electric field concentration. Moreover, the PMMA shell could also provide a robust scaffold to hinder the early breakdown failure of nanocomposites due to its high Eb (425 ​MV/m). Thus, high e, low loss and high Eb are simultaneously achieved. Specifically, the high hot stretch ratio (1:4) of nanocomposite film indicates the strong feasibility of industrialized film processing. Apart from the experimental analysis, theoretical analysis using the simulation of finite element is also carried out to figure out the influence of organic PMMA shell on the dielectric performance of PP nanocomposites films. These findings enable the development of film capacitor using non-polar PP based film towards high energy storage density.

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.

Single-phase ac–dc converter for low-frequency pulse load normally requires high-capacitance electrolytic capacitors, which reduces the lifetime and may cause reliability problem. To meet the challenges of voltage ripple, this article introduces a power pulsation buffer (PPB) that smooths the output voltage and provides essential pulse power to the load simultaneously. The proposed PPB is realized by a discontinuous current mode (DCM) bidirectional buck/boost converter with real-time duty-cycle calculation (RDC) and peak voltage control. The proposed control method can relieve the capacitance requirement and achieve good dynamic response. The electrolytic capacitor is replaced with the film capacitor which has better reliability. SiC devices are adopted to further reduce the inductor volume of PPB. The core-less design is also proposed to design an integrated air-core inductor for further volume deduction. To meet the DCM requirement of PPB in various operating conditions, the phase shift between the line voltage and pulse load is taken into account. An electrolytic capacitor-less prototype with 1800-W peak power is built to verify the advantages of the proposed method.

As an essential energy-stored device, the inorganic dielectric film capacitor plays an irreplaceable role in high-energy pulse power technology area. In this work, propelled by the challenge of overcoming the bottlenecks of inflexibility and inferior energy storage density of the pure BiFeO3 films, the mica with high bendability and thermal stability is adopted as substrate, and the relaxor ferroelectric (Sr0.7Bi0.2)TiO3 is introduced to form solid solution to introduce relaxor behavior. The subsequently fabricated 0.3Bi(Fe0.95Mn0.05)O3-0.7(Sr0.7Bi0.2)TiO3 (BFMO-SBT) thin film capacitor exhibits a high recoverable energy storage density (Wrec = 61 J cm−3) and a high efficiency (η = 75%) combined with a fast discharging rate (23.5 μs) due to the large polarization difference (ΔP = 59.4 μC cm−2), high breakdown strength (Eb = 3000 kV cm−1), and the strong relaxor dispersion (γ = 1.78). Of particular importance is the capacitor presents excellent stability of energy storage performance, including a wide working temperature window of -50-200 °C, fatigue endurance of 108 cycles, and frequency range of 500 Hz-20 kHz. Furthermore, there are no obviously deteriorations on energy storage capability under various bending states and after 104 times of mechanical bending cycles. All these results indicate that BFMO-SBT on mica film capacitor has potential application in the future flexible electronics. Keywords: Flexible, BiFeO3 film, Energy storage performance, Wide temperature range, Bending-endurance

The present work reports for the first time, the employment of ferroelectric ZrO2 films as energy storage capacitors utilized in pulsed power systems. Furthermore, the effect of insertion of a low permittivity dielectric HfO2:Al2O3 (HAO) layer, with a thickness ranging from 2 to 8 nm, on the tunability of ferroelectric and energy storage characteristics of ZrO2 films is assessed. The increase in thickness of the HAO layer gave rise to distorted ferroelectric loops with decreased polarization, coercive field, and hysteresis loss of the films. These results are correlated with the depolarization field induced by the insertion of the dielectric HAO layer. An optimum combination of high energy density of 54.3 J cm−3 and good storage efficiency of 51.3% are obtained for the ZrO2 film capacitors with 2 nm-thick HAO insert layer. These values correspond to an increase of ∼55% and ∼92%, from the respective values of pure ZrO2 film capacitors. In addition, the HAO/ZrO2 films showed a good fatigue endurance of energy storage performance over 109 electric field cycles. The energy storage density obtained from HAO(2 nm)/ZrO2 film capacitor is found to be higher than that reported for several Pb-based as well as Pb-free ferroelectric ceramic films with complex compositions. The present study demonstrates that simple binary oxides such as ZrO2 with ferroelectric behavior could be potential candidates for developing high performance energy storage capacitors., This work was supported by: (i) the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contracts UIDB/04650/2020 and the Scientific and Technological Cooperation Program between Portugal (FCT) and Morocco (CNRST) – 2019/2020; (ii) DST-SERB, Govt. of India through Grant No. ECR/2017/00006. C. I., R. N. and C. G. acknowledge the financial support from the Romanian Ministry of Education and Research within the project PN3– PCCF PN-III-P4-ID-PCCF2016-0047, contract no. 16/2018. The authors acknowledge the CERIC-ERIC Consortium for access to experimental facilities and financial support under proposal 20192055.

For metallized film capacitors (MFCs), the pulsed current would lead to the electrode fracture, the process might be accelerated under the repetitive pulsed current, and finally leading to the failure of MFCs. In order to study the mechanism of electrode fracture and its influencing factors, an experiment platform based on metallized film is established to observe electrode fracture by using a microscope. The experimental results show that for electrode fracture of metallized film, the threshold current density (TCD) is $2.20 \times 10^{10}$ A/m2 when the period is 310 $\mu \text{s}$ and the reverse factor is 10%. Theoretical results are also derived based on the analysis of electromagnetic force and Joule heat. The results indicate that, the fracture development is caused by the melting process of the electrode, together with the liquid metal flow driving by the electromagnetic force under the effect of multiple current pulses. Neither the electromagnetic force individually nor the direct vaporization would cause the fracture to develop. With respect to current distortion and heat conversion efficiency, the calculated peak current density is $j_{\mathrm {max}} = 2.17 \times 10^{10}$ A/m2, which agrees with the TCD in the experiment. Thinner electrode has a larger TCD, when $d_{m}$ decreases from 20 to 4 nm; TCD increases from $1.07 \times 10^{10}$ to $2.25 \times 10^{10}$ A/m2.

Polymer dielectric composites are of considerable interest for film capacitors that are widely used in modern electric devices and electric power systems. However, the adverse coupling between dielectric permittivity (er) and breakdown strength (Eb) makes it difficult to obtain high energy densities in natural materials. With the aim of achieving concurrently improved er and Eb, a class of rationally designed layer-structured composites consisting of pure poly(vinylidene fluoride–hexafluoropropylene) (P(VDF–HFP)) layers and barium titanate/P(VDF–HFP) (BT/P(VDF–HFP)) composite layers were prepared. Interestingly, the layer-structured composites exhibit a concurrent improvement of er and Eb. The 4-layer composite with 15 vol% BT exhibits substantially enhanced er and Eb which are nearly ∼186% and ∼248% of those for its 1-layer counterpart, respectively. Consequently, a high energy density of ∼4 J cm−3 along with a satisfactory efficiency of 71% at 240 kV mm−1 is achieved. Meanwhile, a low loss tangent of ∼0.05 at 10 kHz which is comparable to that of pure P(VDF–HFP) is maintained. This work shows that the adverse coupling between er and Eb in dielectric materials could be well addressed by constructing nanocomposites with layered rather than random distribution of fillers.

High-performance lead-free film capacitors with simultaneously large energy storage density and high power density are strongly demanded in applications. Here, a novel relaxor-ferroelectric 0.88Ba0.55Sr0.45TiO3–0.12BiMg2/3Nb1/3O3 (BST–BMN) thin film capacitor was obtained with an ultrahigh recoverable energy storage density (Wrec) of ∼86 J cm−3 and high efficiency of ∼73% under the dielectric breakdown strength of 5 MV cm−1. In addition, the investigated thin film capacitor exhibited an excellent fatigue resistance property with the Wrec variation less than ∼2% after 107 cycles. More importantly, a considerable power density of ∼208 MW cm−3 was obtained in BST–BMN thin film capacitors, which is superior to many other thin film capacitors. These remarkable performances should be attributed to the simultaneously enhanced BDS and relaxor behavior through the incorporation of non-isovalent ions. These results qualify the environment-benign BST–BMN thin films as promising candidates for energy storage applications and promote the development of BST-based film capacitors with enhanced Wrec in the future.

High-temperature film capacitors have been widely used in numerous applications, such as energy storage components in hybrid electric vehicles, smart grids and pulsed power sources. The commercial film capacitors fabricated by biaxially oriented polypropylene (BOPP) possess high energy efficiency, but low energy density of 2.0–3.0 J cm−3, which restricts their applications. In this work, a poly(acrylonitrile butadiene styrene) (ABS) polymer was prepared by a solution cast method. A high room temperature discharged energy density was achieved, being on the order of 7.3 J cm−3 at 525 MV m−1, benefitting from the aromatic groups and high polar cyano group in the ABS polymer. Of particular significance is that high energy density (6.7 J cm−3) and efficiency (75%) were simultaneously achieved at an elevated temperature of 120 °C under 500 MV m−1. It is worth noting that the gravimetric energy density, being on the order of 6.3 J g−1 at 120 °C, is significantly higher than the values of other high-temperature energy storage dielectrics. Together with its excellent thermal stability and cycling reliability (105 cycles), the ABS polymer demonstrates that it is a promising candidate for high power energy storage capacitors at elevated temperatures.

Polymer dielectric composites are of great interest as film capacitors that are widely used in pulsed power systems. For a long time, huge efforts have been devoted to achieving energy densities as high as possible to satisfy the miniaturization and high integration of electronic devices. However, the discharge efficiency which is particularly crucial to practical applications has gained little attention. With the target of achieving concurrently improved energy density and efficiency, a class of rationally designed bilayer composites consisting of a pure polyetherimide layer and a BaTiO3/P(VDF-HFP) composite layer were prepared. Interestingly, the bilayer composites exhibit ultrahigh discharge efficiencies η (>95%) under external electric fields up to 400 kV mm−1 which are much higher than most of the so far reported results (η < 80%). Meanwhile, a low loss (tan δ < 0.05 @ 10 kHz) comparable to that of the pure polyetherimide is obtained. In addition, the bilayer composites show impressive improvements in breakdown strengths Eb, i.e., 285%, 363%, 366% and 567% for composites with 5 vol%, 10 vol%, 20 vol% and 40 vol% BaTiO3, compared to their single layer counterparts, resulting in obviously improved energy densities Ud. In particular, the bilayer composite with 10 vol% BaTiO3 displays the most prominent comprehensive energy storage performance, i.e., η ∼ 96.8% @ 450 kV mm−1, Ud ∼ 6 J cm−3 @ 450 kV mm−1, tan δ ∼ 0.025 @ 10 kHz, and Eb ∼ 483.18 kV mm−1. The ultrahigh discharge efficiencies and high energy densities, along with low loss and breakdown strengths, make these bilayer composites ideal candidates for high-performance dielectric energy-storage capacitors.

A two-stage power converter for PV applications is developed in this paper. In the first stage, a multiple-input high step-up dc/dc converter is proposed. The second stage is the five-level dc/dc inverter with boosting functionality. The proposed two-stage converter harnesses the superior features of WBG devices to build a converter with high efficiency and high-power density. The high switching speed of WBG power devices allow both stages operating at high switching frequency, hence, large size film capacitors can be replaced by small size multilayer ceramic capacitors, furthermore, the high operating temperature of WBG devices will help to shrink the cooling size. In additions, a zero current-switching technique is implemented in order to reduce the switching loss and electromagnetic interferences. Prototype with 300 W is built and experimental results are presented with a peak efficiency of 98.3%.

The current urgent desire of the renewable energy has imposed much challenge and inspiration for the design and development of the lead-free dielectric capacitors. High recoverable energy storage density (Wrec) and efficiency (η) associated with long-time stability are highly demanded for the pulsed power systems. Here, we present a significantly enhanced energy storage performance in (Ce,Mn) hybrid doped (Na0.8K0.2)0.5Bi0.5TiO3–BiFeO3 [(Ce,Mn):NKBT-BFO] ceramic film capacitor deposited on indium tin oxide (ITO)/glass substrate. Meanwhile, the pure NKBT-BFO, Ce doped NKBT-BFO and Mn doped NKBT-BFO are studied for comparison. A large Wrec of 58.3 J/cm3 together with a high η of 58.1% is realized in (Ce,Mn):NKBT-BFO at 2200 kV/cm, which is proposed by the formation of a slim loop with a large difference between the remanent polarization (Pr) and maximum polarization (Pmax) at a high dielectric breakdown field strength. Moreover, the energy storage property is weakly dependent on time with small variations of Wrec (