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Metallized film capacitor (MFC) is one of the key components in power electronic converters, accounting for a large proportion of failures. However, the time-varying external stress in long-term mission profile and time-varying internal stress due to the degradation of MFC are not well described by the conventional reliability evaluation method, which leads to a large deviation between the evaluation results and the engineering practices. Therefore, an improved reliability evaluation method considering time-varying stress mission profile and aging process for MFC is proposed. First, this article analyzes the influence of harmonics and provides a more accurate lifetime model under constant stress condition, compared with the conventional method. Second, the subsection integral accumulated damage model is proposed to transform the long-term time-varying stress mission profile to the short-term ideal constant stress condition, solving the reliability evaluation under time-varying external stress condition. And then, an improved aging model is proposed to describe the nonlinear variation of equivalent series resistance (ESR) and internal temperature rise due to the degradation process of MFC. Furthermore, Monte Carlo simulation is applied to analyze the difference of individual capacitor, obtaining lifetime distribution. Finally, a practical application example of modular multilevel converter (MMC) system is implemented to verify the superiority of the improved method.

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.

Single-phase matrix converters (MCs) are undergoing rapid developments due to their bipolar voltage gain (as required in dynamic voltage restorers) and step-changed frequency operation (used in high step-up ac–dc rectifiers, and to provide medium frequency isolation in traction and wind turbine converters, etc.). However, existing buck–boost MCs require high-voltage/current rating devices, and suffer from large component voltage/current stresses and ripples, significantly degrading their efficiency. This article proposes a highly efficient single-phase buck–boost MC; consisting of eight IGBTs (implemented using two full-bridge IGBT modules), second-order input and output filters, and a small value film capacitor. Efficient discrete inverting and noninverting buck and boost operations are proposed (same as that of sixteen-switch cascaded buck–boost MC) with significantly lower component voltage/current stresses and ripples. In addition, flexible inverting and noninverting buck–boost operations are proposed with independent control of buck and boost duty ratios. All of the proposed operations are free of commutation issues, compatible with reactive loads, and provide smooth input and output currents. Furthermore, all the switches have same voltage stresses, and all four switches in a full-bridge module experience the same current stresses. A comprehensive description of circuit operation is presented based on a number of proposed switch modulation strategies with a nonunity power factor load, followed by design guidelines, and comparative evaluations with existing topologies. Finally, experimental verification results are presented, using a 400-VA laboratory prototype converter.

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.

DC-link capacitors are one kind of reliability-critical component in traction inverters. As such, it is essential to evaluate the degradation characteristics of dc-link capacitors. Accelerated life testing is an effective and standard method to evaluate the capacitors’ lifetime and degradation mechanisms. Therefore, an accelerated life testing method for dc-link capacitors in three-phase inverter applications is proposed in this article. In order to reproduce the same encountered stress, exactly reflecting the real condition for the capacitor under test, a three-phase inverter with the capacitor under test and a three-phase balanced inductor load are used as the evaluation circuit. Due to the employment of the inductor load, the power consumption of the inverter can be reduced, while the full-scale current rating can be maintained so that the capacitor under test is subjected to the practical ripple current stress. In order to estimate a capacitor’s capacitance with high accuracy, an effective and direct condition monitoring method, which is based on the proposed evaluation circuit, is also proposed in this article. By injecting an ac voltage into the dc link, the ac current and voltage components in the dc-link capacitor are generated. Then, the capacitance mathematical model can be developed by analyzing the injected voltage component and the resultant current component. As the proposed method only requires estimating the parameters from the input voltage and current, there is no need to install additional capacitor current sensors, which are usually difficult to install. Moreover, the amount of monitored and processed data can be reduced. Thus, the proposed method is easy to implement for accelerated life testing in practice. In addition, experiments are carried out to verify the analysis and effectiveness of the proposed solution.

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.

Metallized film capacitors are an important part of the electromagnetic rail launch system. It is of great significance to predict its failure. In engineering, the failure law of capacitor is obtained by cyclic pulse accelerated life test of capacitor module with a small number of samples, and is used to predict the actual failure of capacitor in electromagnetic launch (EML) system. This method has the following problems: first, there are few samples of capacitor in life test at affordable cost, which cannot include all capacitor characteristics; second, the time interval of actual EML missions and the voltage of the capacitors are both changing and inconsistent with the conditions used in the life test; third, the statistical law is affected by the measurement and other errors. For these reasons, the prediction accuracy of the existing methods is limited. In this article, a new combined time series prediction method is proposed by using the high-order fuzzy time series prediction theory. Based on the capacitor used in the prototype of an electromagnetic railgun, the life test data of 20 pulse capacitors are used as the prior knowledge input, and the prediction model is obtained. Five groups of capacitor life test data simulating real launch conditions are used as test data to verify that the prediction accuracy of the proposed method is better than that of the traditional method, and the prediction accuracy of capacitor capacitance, which made by different processes, is much higher than that of the traditional method.

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.

Single-phase zero-voltage-switching (ZVS) inverter with wide bandgap devices has higher efficiency and power density. However, the dc-side capacitor of the inverter will suffer double line frequency ripple and reduces the lifetime of the dc bus capacitor. Active power decoupling (APD) is an effective method to replace the short lifetime electrolytic capacitor with a smaller film capacitor. In order to help achieving the ZVS condition for ZVS inverter and the additional APD circuit, this article presents a ZVS topology for single-phase full-bridge inverter with APD circuit by adding an auxiliary branch between the dc source and the bridge legs. The auxiliary branch is composed of a clamping capacitor, an auxiliary switch, and a resonant inductor. A ZVS pulsewidth modulation scheme is proposed for a single-phase inverter with APD. The gate drive pulses are designed to realize the ZVS turn- on for the main switches of both APD circuit and single-phase full-bridge inverter. Circuit operation stages are analyzed and ZVS conditions are given. Finally, the proposed ZVS inverter with APD circuit is verified on a 1.5-kW inverter prototype.

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.

Active capacitors with long lifetime film capacitors can be adopted to replace short lifetime electrolytic capacitors to improve the reliability of the power converter. However, the conventional active capacitor suffers from the complicated control method or the need for an expensive current sensor. Based on the derived mathematical equations, a novel Ripple Cancellation Control (RCC) method for the active capacitor is proposed. The proposed RCC method is simple and can be easily realized by using analog circuits. Also, it can be applied to active capacitors implemented by different circuit topologies. Besides, a new approach for developing the mathematical model of the active capacitors implemented by different circuit topologies are also proposed. The energy storage capability and the impedance analysis by using the developed mathematical model are presented to verify the performance of the active capacitors with the proposed RCC method. Computer simulations and the hardware results are presented to validate the accuracy of the mathematical model as well as the performance of the proposed RCC method.

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.

For the conventional configuration of the single-phase electric springs, the electrolytic capacitor (E-cap) is required for buffering the double-line-frequency dc-link power. This demands large capacitance and constant average dc-link voltage for achieving sufficiently low-voltage ripples of the E-cap, which renders low efficiency and poor reliability of the ES. To address these issues, a cascaded voltage control scheme is proposed in this article. The proposed control scheme enables large fluctuations of the dc-link voltage so that the film capacitor (F-cap), which is of smaller capacitance and higher reliability, can be applied. In addition, the proposed control scheme can adaptively adjust the average dc-link voltage for achieving the minimum power loss of the ES. The quasi-steady-state and steady-state models of the electric-spring-based smart load are developed. The optimum average dc-link voltage for achieving the minimum power loss is analytically derived. The functionality and loss reduction capability of the proposed controller are verified through hardware experiments and simulations.

The EMI filter is a critical component for power electronics to conform with the electromagnetic interference (EMI) standards, ensuring electromagnetic compatibility (EMC) and a safe operating environment. Yet, its attenuation capability can be shifted during the long-term operating period due to the passive components' degradation. A poorly designed EMI filter may fail to meet the standards' specifications and affect the robustness, leading to the converter's fault and even failure. This paper proposes a robustness assessment procedure of an EMI filter for a three-level active neutral-point-clamped (3L-ANPC) inverter. The mission profile is used to emulate the operating environment. The nonlinear degradations of film capacitors and nanocrystalline core chokes are modeled. Further, the Monte-Carlo-Based robustness assessment procedure is presented. It considers the uncertainties of model parameters and uses the filter attenuation capability as the failure criteria. Finally, an EMI filter for a 15 kW 3L-ANPC inverter is used as the demonstration and experimental verification of the evaluation procedure. The B10 lifetime of the EMI filter is obtained, which serves as a first step of the inverter-system-level EMI robustness evaluation and feedback for the robustness-oriented EMI filter design.

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.

The large-scale integration of distributed photovoltaic generation causes several power quality issues in low voltage (LV) distribution networks. Network voltage profile variations severely affect the LV distribution networks. The four-leg unified power flow controller (4L-UPFC) has series and shunt converters that can address the power quality issues. However, instantaneous power theory shows that second-order harmonic voltage (2ωHV) appears at the dc-link capacitor of the 4L-UPFC during any unbalanced operations. This article proposes control strategies for series and shunt converters that will simultaneously regulate the load voltages of a distribution feeder while suppressing the 2ωHV term on the dc-link of the UPFC. A controlled negative sequence current from the shunt converter is used to suppress the 2ωHV term on the dc-link. The active suppression of the 2ωHV term allows electrolytic capacitors to be replaced with small long life ceramic or film capacitors, and this does not require additional passive compensation. Stability analysis of the control loops demonstrates the overall stability of the converter system. The proposed control methods have been implemented on a Texas DSP (F28377D). An experimental demonstration on a laboratory scale prototype shows that the proposed control methods can effectively regulate the load voltages at LV distribution feeders and suppress the 2ωHV on the dc-link of UPFC during unbalanced loads and supply conditions.

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.

Permanent magnet synchronous motor (PMSM) drives equipped with slim film capacitors have many advantages, including longer lifetime, smaller volume, and lower cost. However, improving the dc-link voltage utilization rate by the typical overmodulation strategy will cause the distortion of the stator voltage and current due to the dc-link voltage fluctuation. In this article, the influence of the dual-mode overmodulation strategy used in the small dc-link capacitor PMSM drive, including the stator voltage distortion and uncontrollable time for entering the six-step operation, is analyzed. A novel overmodulation strategy named as the optimized voltage boundary-based overmodulation strategy is proposed to reduce the distortion of the stator voltage and current. By switching between the actual dc-link voltage and the fixed dc-link voltage used for space vector pulse width modulation (SVPWM), the performance can be improved in the overmodulation region if the value of the dc-link voltage for SVPWM is selected appropriately. Experimental results on a PMSM drive platform are provided to verify the effectiveness of the proposed strategy.

In this article, a single-phase transformerless inverter for photovoltaic (PV) applications is introduced. The proposed inverter provides common ground between input and output terminals, which results in the elimination of the leakage current in the PV systems. Moreover, the voltage gain of the proposed inverter is higher than that of the single-phase quasi-Z-source and semi-Z-source inverters. Utilizing the film capacitors makes the proposed inverter more reliable and also increases its lifetime. The operation of the proposed inverter is analyzed in detail. Finally, the performance of the proposed inverter is verified through the experimental results both in off-grid and grid-tied operation modes.

This article proposes a single-phase bridge inverter with both voltage boosting and power decoupling capabilities. The proposed inverter topology diverts the second-order ripple power into a small film capacitor instead of using a bulky electrolytic capacitor at the dc side, thus eliminating the large electrolytic capacitor that has a short lifetime. The voltage across the decoupling capacitor is controlled as a dc-biased sine wave to cancel out the second-order ripple power originated from the single-phase grid power, and the dc offset in the decoupling capacitor is used to boost the dc-link voltage, as opposed to being under-utilized in previous dc voltage-reference power decoupling techniques. The proposed topology also maintains the advantages of the traditional bridge inverters with the unipolar sinusoidal pulsewidth modulation technique. Moreover, the output filter and power decoupling control method are designed for the proposed inverter. Finally, the simulation and experimental results verify the feasibility of the proposed topology and control algorithm, which show successful voltage boosting and power decoupling functions.

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.

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.

This paper proposes a novel method to reduce the DC-link capacitor in the single-phase onboard battery chargers. A low-voltage charging circuit is used as a two-parallel buck–boost converter to absorb ripple in the DC link. Thus, the required DC-link capacitance of the onboard battery charger can be reduced significantly without adding additional switches, heat sinks, and gated drivers. In addition, the voltage of the auxiliary capacitor can be controlled to be higher than the DC-link voltage. This allows for a further reduction of the capacitance of the auxiliary capacitor. As a result, small film capacitors can be used at the DC link instead of bulky capacitor banks or additional active power decoupling circuit. Therefore, the cost and volume of the onboard battery charger are reduced significantly. By experimental results for a 2-kW SiC-based prototype, the effectiveness of the proposed circuit has been verified.

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.

The active capacitor concept based on power electronic circuits has been proposed recently to exceed the physical limit of the passive capacitor. It retains the physical convenience of use as a passive capacitor and has the potential to increase either the power density or the lifetime depending on the applications. However, the cost of the existing design by using ceramic or film capacitors to achieve extreme performance increases a lot, which must be taken into account in the design from the industry aspect. This article proposes a cost-constrained design of an active capacitor used for dc-link applications. It is implemented based on high-current electrolytic capacitors instead of film capacitors or ceramic capacitors. A model-based optimization design procedure is discussed in terms of performance factors of interest. A case study of a 5.5-kW single-phase inverter demonstrates a 38% volume reduction of the dc link with the proposed active capacitor under specific constraints of cost, volume, power loss, and lifetime. The outcomes move one step further for the practical application of the active capacitor concept.

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.