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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.

Investigates interaction of harmonics with capacitors. First the main applications of capacitors in power systems are outlined: power factor correction, definitions of displacement power factor and total power factor which includes harmonics. Thereafter, the power quality issues associated with capacitors are discussed, including series and parallel harmonic resonances, and transients due to capacitor switching. Frequency and capacitance scanning techniques including harmonic voltage, current and reactive-power constraints for capacitors are addressed next. Feasible exemplary operating regions for safe operation of capacitors in the presence of voltage, current and reactive-power harmonic components are investigated. Equivalent circuits of capacitors in terms of inductance, resistance, and capacitance are reviewed. 9 application examples with solutions and 10 application-oriented problems are listed.

Modular converters with stackable cells are widely used in high-power applications, where the voltages and/or currents are beyond the ratings of the commercially available switches. Majority of existing modular converter topologies are based on dc-link converters that require several electrolytic capacitors with large capacitances, which reduce the lifetime of the power converter and increase size and volume. This article proposes an input-series output-parallel modular three-phase ac–ac universal power converter, which is formed by three identical and stackable capacitive-link modules that do not require electrolytic capacitors for power conversion. Exclusion of the electrolytic capacitors is achieved by operating the modules in discontinuous capacitor voltage mode. Each module requires two film capacitors with very small capacitances for transferring the power and provides galvanic isolation through high-frequency transformers. Utilization of film capacitors with small capacitances enhances the reliability. Furthermore, the proposed stackable capacitive-link modules enable a scalable and modular design. In this article, power cells are connected in series at the input and in parallel at the output to form a modular universal power converter that can share voltage/current among the power cells in an ac–ac power conversion system. Frequency transformation and voltage step-up/-down are among the other features of the proposed converter. The details of the operation principles along with design considerations are discussed in this article. Moreover, the proposed modular power converter with two power cells is evaluated through simulations and experiments.

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.

Metallized Film Capacitors (MFC) are vital devices in many important fields such as energy, transportation, and aviation, whilst Digital Twin (DT) technology opens a new channel to leverage existing data resources of metallized film capacitors. This paper review current knowledge about metallized film capacitors and digital twin, list the key issues, propose frameworks, and provide the outlook to clarify the potential of digital twin’s application in metallized film capacitors. First, based on the development history and research status of metallized film capacitors, this review sorts out the key research issues of data utilization. Then, the connotation and typical characteristics of the digital twin definition are combed and refined, and the typical architecture of digital twin implementation is presented. Furthermore, the overall application architecture of digital twin in metallized film capacitors is constructed, and the technology system of each application scenario and the role of digital twin are analyzed. Finally, the main challenges in the application of the digital twin in metallized film capacitors and the future development directions are discussed. This review promotes the performance improvement, cost reduction and application expansion of metallized film capacitors, which can be used as a guide for the application of digital twin in other power equipment of energy system.

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.

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.

Unlike voltage-source inverters (VSI), the power decoupling element in current-source inverters (CSI) is inductor. Inductor has a long lifetime and makes the CSI more reliable. However, the traditional CSIs suffer from open-circuit problem and dangerous voltage spikes are generated if the input inductor current is intermitted. Therefore, to avoid the voltage spikes, overlap-time should be inserted in the gate signals. But these intervals distort the output currents and reduce the current source utilization. To address these issues, a novel three-phase CSI is proposed in this article. The proposed inverter is originated from the conventional seven-switch CSI named CSI7 by adding only two small film capacitors. The film capacitors along with the pre-existing diodes of the CSI7 ensure that there is always a path for the inductor current, and thus the open-circuit issue is resolved. The elimination of open-circuit issue enhances the reliability and allows to minimize the overlap-time. This will improve the quality of output currents as well. Moreover, simulation and experimental results are provided at the output power of 950 W to verify the effectiveness of the proposed inverter.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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%.

Single-phase microinverters used in household applications draw pulsating power from its input dc source while delivering ac power output to loads. While this introduces double line frequency harmonics into the dc bus of the microinverters, which lead to poor operational efficiencies of input energy sources (like solar arrays and fuel-cells etc.), it also deteriorates the quality of power fed to ac loads. Traditionally, large electrolytic capacitors or auxiliary decoupling circuits are used to mitigate the above-mentioned problems, making the converter system heavy, bulky, and thus increases the cost. In this letter, a new approach based on a simple pulsewidth modulation is proposed for single-phase microinverter system, aimed at mitigating the ill effects of double line frequency harmonics on both the dc side and ac side of the inverter. It is shown that by allowing a voltage swing of about 20% on the dc bus can significantly bring down the capacitance requirement by a factor of 3 to 5. Thus enabling, smaller and more durable film capacitors to be deployed instead of the bulky electrolytic capacitors. The envisaged approach is simulated and experimentally validated to support the claims on a laboratory setup.

AC–DC light-emitting diode (LED) drivers suffer from short lifetime because of the low-lifetime electrolytic capacitors used for dc bus decoupling. In this paper, a primary-side peak current control method applied for driving a two-stage multichannel LED driver is proposed. The LED driver consists of an ac–dc boost power factor correction stage and an isolated dc–dc nonresonant stage. A long-lifetime and small film capacitor is used for implementing the intermediate dc bus. The proposed method, which controls the peak value of the primary-side current of the transformers, is applied to the dc–dc stage to ensure constant dc current output of LEDs in spite of the widely varying dc bus voltage due to low bus capacitance. The proposed method compensates the effect of the large dc bus voltage ripple by varying the switching frequency of the primary-side switches. Detailed design procedure, theoretical analysis, and experimental results of the LED driver operating at 180 W with the proposed method are provided. The LED driver with the proposed control method is proved to have high overall efficiency.

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

Series capacitive-link universal converters are a relatively new class of single-stage power converters that offer numerous advantages including high reliability, high power density, and high efficiency. One of the limitations of these converters is high current stress of the switches, which lowers their efficiency in high current applications. In this paper, a new class of soft-/hard-switched parallel capacitive-link converters is introduced to address this limitation of the series capacitive-link universal converter while keeping its advantages. A small film capacitor, which is placed in parallel with the input and output switch bridges, is responsible for transferring the power from input towards output. A small inductor can be placed in series with the link capacitor to minimize switching losses and reduce EMI. The proposed parallel capacitive-link converter is expected to offer an enhanced efficiency and reduced current stress compared to the series capacitive-link universal converters. In this paper, principles of the operation of the proposed converter will be presented and its performance and advantages will be verified by simulation.

Capacitors are usually utilized at the DC-link of a power conversion system. Generally low parasitic inductance capacitors such as ceramic capacitors and film capacitors can reduce overshoot voltage during switching and DC bulk capacitors can address the low-frequency ripple. Due to the parasitic inductance, the energy swinging between the two types of caps via parasitic inductance leads to the oscillation which is typically at Mega-Hertz level and increases the voltage stress and power loss of the power devices. This phenomenon has been discovered repeatedly in the power converters with bus bar, integrated power module, and device characterization setup. To investigate and address this oscillation, the mechanism behind this oscillation is analyzed in details via a frequency-domain model in this paper. The impact of various electrical parameters are summarized. The proposed analytical model is validated via SPICE simulation and experimental study.

An integrated on-board charger uses the motor drive and its voltage source converter for battery charging when the vehicle is not running. This charger in AC-DC conversion stage has an inherent tendency to produce low frequency voltage ripple in both DC-link and split DC-link capacitor voltages. Therefore, bulky high valued electrolytic capacitors are adopted to absorb these low frequency capacitor ripples. Replacing these electrolytic capacitors with low valued film capacitors, results in poor input power quality. Therefore, this paper presents a control strategy based on modified unit-template control with reduced DC-link capacitance value to achieve improved input power quality without using any additional active/passive components. In modified unit-template control, the harmonics information of the grid current is feed-forwarded into the unit template to achieve unity power factor operation and reduced grid current THD. Furthermore, to reduce the influence of double frequency component on EV current/voltage, a DC-link feedforward control is implemented in DC-DC stage. Finally, the effectiveness of the solution presented in this paper, is verified by simulation and experimental results.

High-performance dielectric capacitors are in high demand for advanced electronics and electric power systems. They possess high power density (on the order of Megawatt) and exhibit ultrafast charge/discharge capability (on a microsecond scale) and long-term storage lifetime1-5, and thus they are particularly demanded in pulse power systems such as high-power microwaves, hybrid electric vehicles, and high-frequency inverters. However, their relatively low operating temperature limits their widespread applications6-9. Here, guided by phase-field simulations, we synthesized capacitors with an energy storage density of 55.4 joules per cubic centimeter, energy efficiency of over 82%, and superior thermal stability and fatigue properties at record high operating temperature of 400°C. These ultrahigh-temperature performances are achieved through a relatively simple method of introduction and engineering of interfaces within the capacitors, which greatly improve their high-temperature stability, relaxation behavior, and breakdown strength. Our work not only successfully fabricated capacitors with potential applications in high-temperature electric power systems and electronic technologies but also opens up a promising and general route for designing high-performance electrostatic capacitors through interface engineering.

This paper presents a novel DC/DC converter for hybrid energy storage system (HESS) in DC microgrids. The proposed converter contributes to significantly reduce the component ratings, cost and size of the conventional HESS converters by using the multi-level, interleaved structure. The multi-level structure helps decrease the ratings and cost of power semiconductor and inductor; whereas the interleaved structure enables the replacement of bulky electrolytic capacitors using film capacitors, which substantially enhances converter reliability. Furthermore, the proposed converter allows the independent control of battery and supercapacitor energy storage. Its performance is verified by simulation results.

Modular multilevel power electronic converters are considered an increasingly critical family of converters for myriad high voltage high power applications. With the ever-growing emphasis on electrification of the economy, they play a crucial role in serving energy sources and loads whose electrical ratings go beyond the ratings of the conventional power electronic building blocks. In particular, modular multilevel converter (MMC) topology enjoy its dominance in such applications due to modularity, scalability, performance and fault-tolerance capability. However, the MMC topology design imposes low-frequency ac components on the module capacitors and thus is inhibited by the capacitor size. Capacitor sizing plays a significant role in the overall system’s size, cost and reliability. This paper introduces a minimal capacitor module based topology for DC to three-phase AC conversion. The unique design feature of the module includes minimal capacitor requirement due to elimination of single-phase ac power processing requirements. Together with improved power density, reduction of capacitor size permits the use of only film capacitors thus eliminating the weakest link of the overall system. Along with the step-by-step analytical derivation of the proposed approach, the paper presents detailed simulation studies, comparative analysis and experimental results from a proof-of-concept laboratory-scale prototype.

The increasing utilization of electronic converters to interface distributed energy resources (energy storage units and renewable energies) with the grid, has decreased the inertial spinning reserves of the power system. In this context, an isolated and bidirectional two-stage DC-AC converter with grid-forming virtual inertia capability and film capacitor on the DC-Link is presented. The proposed converter allows to interface energy storage units (ESU) with the single-phase grid. The two-stage DC-AC converter is composed of a dual active bridge series resonant (DABSR) DC-DC converter cascaded with a single-phase voltage source inverter (VSI), linked by a film capacitor. In the proposed control strategy, the DABSR controls the DC-Link voltage allowing the power decoupling on the DC-side while the VSI is controlled to emulate a virtual synchronous machine (VSM) when the ESU are connected to the grid. Therefore, the proposed converter has the following advantages: (1) high durability with reduced volume due to film capacitor instead of electrolytic capacitor on the DC-Bus, (2) high efficiency due to ZVS in the DC-DC converter and, (3) virtual inertia provided by VSI controlled as a VSM, increasing inertial energy reserves in the grid. The converter functionality and control strategy are validated by simulation of a 3.3kW system.

This article presents an isolated single-stage Dual- Active-Bridge Series-Resonant (DABSR) DC-AC converter with series-power decoupling (SPD) to interface PV with the single-phase grid. A third port is added in the proposed DABSR DC-AC converter, which is series-connected on the AC side to power decoupling. Therefore, the electrolytic capacitors, typically used on the DC side, are replaced by film capacitors. The single-phase time-variant power is decoupled by controlling the time-variant voltage on the third port, which depends on the power amplitude, the filter capacitor and the grid frequency. A novel modulation is proposed where the grid and the third port voltages are modulated by unipolar PWM while the PV voltage is modulated by duty ratio. The power flow is controlled by phase-shift modulation. High efficiency is obtained due to soft-switching operation into all active bridges. Besides, low THD in the grid current is obtained. MPPT is performed with high accuracy. Finally, the proposed converter is compared with a similar DABSR DC-AC converter without SPD (WoSPD). The novel modulation, converter design and the control strategy are presented and validated by simulation.

Non-inverting buck-boost converter is a classical topology that can provide wide range of voltage conversion and bidirectional power transfer; thus, it is frequently used in industrial applications. However, the conventional hard-switching configuration can only reach a high voltage conversion ratio at the expense of low efficiency due to switching loss. In this paper, a soft switching non-inverting buck-boost converter is proposed. This converter uses a small film capacitor in parallel with the link inductor to provide zero voltage switching (ZVS) by allowing the link capacitor and link inductor resonate between power transfer states. This paper presents the principles of the operation of this converter and verifies its performance through simulation and experiment.

In this paper, the samples preparation, experimental details, and characterization of the Electrophoretic Deposition (EPD) of a thick film Barium Strontium Titanate (BST) capacitor intended for radio-frequency applications are reported. With a bias voltage from 0 V to 20 V, the Ba 0.7 Sr 0.3 TiO 3 capacitor fabricated demonstrates 49% of tunability. The quality factor and the microwave (MW) loss tangent are calculated from 500 MHz to 5 GHz. Using an one-tone measurement setup, the small signal S-parameters measurements for the BST thick film capacitor are also presented by applying input signals from -20 dBm to 4 dBm. The linearity and loss tangent are analyzed considering a comparison of two different bias voltages, 0 V and 10 V. For the first time, the BST thick films fabricated with EPD are implemented and measured in the MW regime.

Single-phase inverters and rectifiers require the use of an energy buffer to absorb twice-line-frequency power ripple. Historically, this challenge has been addressed by the use of large electrolytic capacitors. Lifetime constraints and the need for improved system performance have motivated designers to seek other capacitor technologies, such as ceramic and film, which are frequently used in conjunction with active filtering converters to reduce the capacitance required. Active filtering converters cycle the capacitor voltage over a wide voltage range while maintaining a constant dc bus voltage. This large-swing operation demands different capacitor qualities than most other filtering applications, and the data sheet parameters available for commercial capacitors may be ineffective or require special care for calculating characteristics, such as efficiency and energy storage capability. This work presents an experimental setup for evaluating capacitor performance under a large voltage swing along with detailed experimental results. Energy storage data for a number of capacitors in the 50–630 V range from several manufacturers are included. The approach and findings of this paper can serve as an aid to power electronics designers for the selection and evaluation of capacitors in energy buffering applications.

In this paper, a new class of bidirectional partial-resonance power converters is presented. The proposed family can be configured to interface single- or multi-port dc, single- or multi-phase ac systems at input-side and/or output-side. The proposed family offers a very modular structure, which can lead to cost reduction from a common designed module. In this converter, which accomplishes power conversion in a single stage, a small inductor placed in series with the input and output switch-bridges forms the link. This small link inductor is responsible for transferring power between different ports of the system. The proposed topologies can operate in buck, boost, and buck–boost modes of operation to step up and/or step down the voltage. In buck–boost mode of operation, the converter is controlled such that the power is entirely transferred through the link inductor; whereas, in buck or boost modes of operation only a fraction of the power is transferred through the link inductor, and the remaining power is directly transferred from input phases to the output phases. Galvanic isolation, which is typically a prominent factor contributing to power density of a converter, can be provided by means of a compact and lightweight single-phase high-frequency transformer added to the link. In comparison with earlier generations of partial-resonance inductive-link power converters, in the proposed converter, the level of link peak current and consequently power-loss, as well as voltage and current stress of switches are dramatically decreased. A very small film capacitor can be placed in parallel with the link inductor to facilitate zero-voltage-switching (ZVS) operation for all the switches/diodes. Apart from increasing the overall efficiency, minimized dv/dt stress and improvement in power density are achieved by adding the link capacitor. The proposed converter employs four-quadrant switches, i.e., bidirectional-conducting bidirectional-blocking switches, and charges the link inductor in both positive and negative directions in each cycle. In view of this, better utilization of the link inductor and lower total harmonic distortion (THD) are offered. Furthermore, two distinct switching algorithms are developed for the proposed family of converters. In this paper, the detailed behavior of the proposed family is investigated analytically, and simulation and experimental results are presented to evaluate the performance and effectiveness of the proposed converter. A low-power proof-of-concept prototype with input voltage of 59 V/161 V, load voltage of 178 V/73.5 V, maximum switching frequency of 4.9 kHz/3.65 kHz at 215 W/450 W in a step-up/step-down operation is considered for the experimental verification.

High-temperature-resistant dielectric films, the heart of energy storage components in film capacitors, are key elements to ensure that the capacitors operate properly in harsh environments. Herein...

AC-connected light emitting diode (LED) drivers experience imbalanced energy between input and output in a half-line cycle. To achieve the flicker-free operation, the imbalanced energy needs to be buffered, often by energy-dense electrolytic capacitors. However, electrolytic capacitors are also well-known for their short lifespan. These capacitors are the limiting factor of an LED drivers’ lifespan. High voltage film capacitors and a buck converter have been used in the proposed LED driver to buffer the imbalanced energy. When P in > P LED, the extra energy is transferred from the ac input directly to the high voltage film capacitors. When P in P LED, the energy is transferred from the high voltage film capacitors to the output by the buck converter. The imbalanced energy goes through two power conversion steps in the proposed LED driver, which is one time less than other comparable electrolytic capacitor-less designs, enabling a higher efficiency to be achieved. A 28 W flyback topology based experimental prototype had been built and tested to verify the proposed design.