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Cascaded H-bridges (CHB) converter equipped with pulse width modulated (PWM) rectifiers has been widely adopted in medium-voltage motor drive applications for the ability of power regeneration. But capacitor in each submodule suffers severe issue of voltage fluctuation at twice the inverter frequency, which can be worse when motor works at low speed and heavy load. The causes of voltage fluctuation are studied in this paper, including low running speed and fluctuating instantaneous power of inductors in front-end rectifiers. The fluctuating power of inductors will cause large voltage fluctuation on capacitors, and this issue is ignored in previous studies. This paper also proposes an improved power feedforward method to tackle the issue of fluctuating power of inductors, in which the input power and output power of submodules are totally counteracted. By counteracting power of input and output totally, voltage fluctuation decreases dramatically and capacitance can be minimized. Therefore, electrolytic capacitors can be replaced by film capacitors with small size and long lifetime. Simulation results based on 6kV, 710kW motor verify the effectiveness and validity of the proposed method.

The self-healing performance of metalized film capacitors is studied by building a repeated charging and discharging setup and a self-healing signal testing setup. The charging and discharging setup imitates the working condition of the metalized film capacitor. The process is repeated until the lifetime of the capacitor came to an end. During the experiment, the self-healing signal was detected and counted at the same time, which was achieved by building a self-healing signal detection setup. The self-healing signal detection setup was used to achieve the acquisition of self-healing waveforms and amplitudes and the number of self-healing signals. In the research, it was found that only the capacitance changed monotonously. The waveform of self-healing discharge has a certain regularity. In the initial stage of the aging test, the waveform is relatively regular, but when the aging test continues to approach the end of the capacitor's lifetime, the waveform is distorted, and the cause of the distortion is analyzed. When the performance of the capacitor continues to deteriorate, the frequency of self-healing discharges also begins to become more frequent, and the amplitude increases. Besides, by dissecting the capacitor, it can be found that the self-healing discharge point is mainly located at the margin. That means the field strength distribution at this place needs to be optimized.

The novel types of electrodes segmentation patterns for metallized film capacitors were suggested. Electrodynamic destruction of segmented electrodes due to self-healing process was numerically calculated using COMSOL Multiphysics software. The dependence of electrodynamic destruction energy versus destruction time was used as a criterion of segmentation pattern efficiency. Advantages and disadvantages of novel electrodes segmentation types were determined. It was found that bridge-diamond segmentation is the most effective patterns configuration.

The DC-link may suffer from overvoltage during motor transient process due to the use of slim film capacitors in the diode rectifier front end.

High-brightness light-emitting diodes (HB-LEDs) is next generation of green lighting. However, the bulky electrolytic capacitor in converters is required to compensate the difference of pulsating power, thereby restricting the lifetime of the whole system. Meanwhile, the existence of full-bridge rectifier circuit and multi-stage transformation hinders the further improvement of power density. In this paper, a three-port network for single-stage bridgeless LED driver is proposed with the way of sharing so as to reduce the use of devices, thus higher power density is achieved; and additional port dedicated to power decoupling function so as to dramatically reduce the decoupling capacitance, thus allowing for film capacitors to be used. Operating principle, design considerations and performance comparisons are examined in detail. Finally, all the superior performances of proposed LED driver are verified by the PSIM platform.

With the increasing application of nonlinear electrical equipment in the industrial field, the harmonic content in the power grid is gradually increasing, which brings great harm to the foil-film capacitors used in the system. In order to study the breakdown characteristics of the dielectric in the foil-film capacitor under DC superimposed harmonic voltage at different temperatures, a breakdown test platform is established for the foil-film capacitor immersed in benzyl toluene and the foil-film capacitor elements are subjected to DC voltage, DC superimposed 3rd harmonic voltage, DC superimposed 5th harmonic voltage at 40°C, 55°C, 70°C and 85°C respectively. The results show that under the same type of voltage, the breakdown strength of the insulating medium in the foil-film capacitors decreases with the increasing temperature. Besides, in the temperature range of 40°C ~85°C, the breakdown strength of the insulating medium of the foil-film capacitors decreases with the increase of the harmonic order of the harmonic voltage at the same temperature.

In order to meet the challenges of the harsh working conditions for capacitors at high temperatures (>150°C), dielectric polymers with high glass transition temperature (Tg) have been considered as the candidate for the next generation of film capacitors. In addition to high operating temperature, many efforts have been made in developing high dielectric constant and low loss in high Tg polymers. Recently, we report the finding that the dielectric constant of high Tg dielectric polymers can be increased markedly by very small amount of nanofiller loadings (< 1 vol%) without increasing the loss. In nanocomposites, it is well known that the interface effects between the polymer matrix and nanoparticles play important role in determining the performance. In this work, chemically modified nanoparticles are employed to investigate the interface effects of nanofillers in the enhancement of dielectric responses of these nanocomposites.

Dielectric polymer film capacitor with high energy density and efficiency is one of the enabling technologies for the development of flexible electronics and power systems. Herein, we introduce wide-bandgap inorganic fillers into the polymer matrices to yield polymer nanocomposites. It is found that the leakage current is largely decreased, and the charge-discharge efficiency is significantly improved of the nanocomposites, especially at high fields and elevated temperatures, compared to polymer matrices. The increase in activation energy indicates that the presence of wide-bandgap nanofillers in the polymer matrix gives rise to a higher barrier to be overcome for occurring conduction processes. In addition, a strong dependence of high-field conduction behavior on the filler morphology is revealed. Compared to zero- and one-dimensional fillers, two-dimensional nanoplate enables the shortest hopping distance, and is the most efficient in inhibiting conduction loss of the polymer composites.

As the applied voltage increases, partial discharge has become one of the most important factors affecting the service life of metallized film capacitors. Therefore, the insulating structure of the capacitor needs to be optimized to increase the insulating strength. In this paper, a metallized film capacitor is studied by simulation. Its simulation results show that the maximum electric field strength occur at the edges (inside) of the metallization, the thickness of the metallization and the smoothness of the metallization edges also have a great influence on the maximum electric field strength, and the calculation results of the model established after reducing film number and film width in the correct way are valid. Therefore, a targeted increase in the thickness of the dielectric at the metallization edges is an effective way to reduce the occurrence of partial discharge as well as enhance the reliability of capacitors. In addition, proper metallization thickness and metallization edge treatment can also improve the dielectric strength of the capacitor to some extent.

In this paper, a Four-Switch quasi-Switched Boost Inverter (FS-qSBI) is derived from the embedded type-2 qSBI topology. It has all the advantages of qSBIs such as continuous input current, higher ac output voltage, simultaneous operation with both ac and dc loads, and shoot-through immunity. Additionally, it has one less switch and one more capacitor compared to the qSBIs. In order to address the inherent dc-side low-frequency ripple issue of FS-qSBI, this paper also proposes a low-frequency ripple damping scheme so that size of the capacitor can be significantly reduced without using any additional hardware component. Thus, highly reliable film capacitors can be used instead of conventional electrolytic capacitors, which results in improved power density, system lifetime and reliability. A stability analysis of the system, exploring the impact of capacitor reduction, is also presented. The FS-qSBI is implemented in hardware to verify the theoretical analysis and the proposed low-frequency ripple damping scheme.

This paper proposes control techniques for a three-phase diode rectifier with an instantaneous reactive power compensator (IRPC) whose the dc-link voltage is connected to a buck converter to control power of a dc load. At the dc-link voltage, a small film capacitor is inserted in the system causing a square waveform for the ac currents of the rectifier. Moreover, the three small ac inductors are used to reduce the current ripple from the switching frequency of the buck converter. These ac inductors cause the commutation overlap in the diode rectifier, and the control system would be unstable because of the resonant frequency between the ac inductors and the dc-link capacitor. Hence, this paper presents the analysis and the control technique performance of the system based on estimated power of the rectifier without detecting ac current of the rectifier. A 4.5-kW experimental setup was used to verify the control methods. As a result, the proposed techniques can control the grid current as a sinusoidal waveform with a THD i and an efficiency of 4.68% and 97.8%, respectively.

Nowadays, the three-level T-type inverters are extensively applied for photovoltaic (PV) generation systems. The neutral-point voltage of the T-type inverter may is subjected to low-frequency oscillation which causes output current distortion and disrupts the maximum power point tracking (MPPT) process of PV panels. In this paper, a new hybrid modulation is proposed to suppress the neutral-point voltage oscillation and control the average neutral-point voltage simultaneously. Consequently, the dc-side capacitors of the inverter are selected smaller and film capacitors can be replaced with electrolytic capacitors to increase the lifetime of the inverter. Moreover, the average neutral-point voltage is controlled to interact with the MPPT process. The experimental tests have been accomplished to prove the effectiveness of proposed modulation.

To meet the stringent requirements of next-generation film capacitors for power electronics, multilayer films (MLFs) are fabricated with the advantage of achieving high temperature rating, high energy density, and reasonably low loss simultaneously. In this study, a high permittivity polar polymer, poly(vinylidene fluoride) (PVDF), is multilayered with a linear, low loss dielectric polymer such as high-temperature polycarbonate (HTPC). However, the dielectric loss of these MLFs was still high as compared with current state-of-the-art biaxially oriented polypropylene (BOPP) films. The goal of this work is to decrease the dielectric loss and enhance dielectric insulation by achieving flat-on primary PVDF crystals in MLFs via nanoconfined melt-recrystallization. Based on simultaneous small- and wide-angle X-ray scattering experiments, edge-on lamellar crystals were observed for all as-extruded MLFs, regardless of different PVDF layer thicknesses. However, after melting at 180 °C followed by recrystallization, flat-on primary crystals were successfully achieved when the PVDF layer thickness was below 39 nm. Above 78 nm for the PVDF layer, major edge-on primary crystals with minor flat-on secondary crystals were observed. From leakage current, breakdown, lifetime, and electric displacement-electric field loop studies, MLFs with the flat-on primary crystals exhibited reduced loss and enhanced dielectric insulation as compared to as-extruded MLFs and those with edge-on primary/flat-on secondary crystals. This was attributed to the effective blockage of charge carriers by the flat-on PVDF primary crystals and their reduced ferroelectric switching.

An Activity Smoothen Circuit with bidirectional Buck-Boost Converter (AS-BBC) was approached to smoothen the output power of a power factor correction (PFC) converter, which is an AC/DC converter, without using any electrolytic capacitors in this paper. In order to smoothen the output pulsation current of the PFC converter, electrolytic capacitors have been used generally, since electrolytic capacitors have a large magnitude capacity. However, there is a lifespan to electrolytic capacitors. On the other hand, film capacitors have a semi-permanent lifespan with so much less magnitude capacity than electrolytic capacitors. A way of using the AS-BBC to make a small capacitor work like a large capacitor as a smoothing capacitor to handle the output power is presented in this paper. Approximately 47% of the pulsation output is suppressed with a $4.4\mu \mathrm{F}$ film capacitor with the AS-BBC. Since there is no electrolytic capacitor adapted, a semi-permanent lifespan PFC converter is achieved successfully.

EMI (electromagnetic interference) filters are widely used in electronic devices and systems. They have considerable effects on the Electromagnetic Compatibility (EMC) performance of circuits. However, after long-term operation, the filters can exhibit severe degradation due to the intrinsic ageing mechanism and external thermal and electrical stresses. To be specific, the performance of the internal capacitors, typically represented by their capacitance value and equivalent series resistance, will largely deviate. These issues weaken the filters’ functionality, the service life as well as their EMC compliance. However, other parasitic parameters, like parasitic inductance, dielectrics insulation which are necessary for evaluating the performance, are usually neglected. In this study, the deviations of the EMI filters cause by the ageing of the capacitors are analyzed based on complex impedance analysis. The ageing characteristics of the filters with respect to the capacitor’s deviations, where nearly all parasitic parameters were taken into account, are identified by conducting an electrical overstress accelerated ageing test.

In this work, an easy, low-cost, and widely applicable method was developed to improve the compatibility between the ceramic fillers and the polymer matrix by adding 3-aminopropyltriethoxysilane (KH550) as a coupling agent during the fabrication process of BaTiO3-P(VDF-CTFE) nanocomposites through solution casting. Results show that the use of KH550 can modify the surface of ceramic nanofillers; therefore, good wettability on the ceramic-polymer interface was achieved, and the enhanced energy storage performances were obtained by a suitable amount of the coupling agent. This method can be used to prepare flexible composites, which is highly desirable for the production of high-performance film capacitors. If an excessive amount of coupling agent is used in the process, the non-attached coupling agent can participate in complex reactions, which leads to a decrease in dielectric constant and an increase in dielectric loss.

Driven by an urgent need for the development of high-power energy storage devices, both scientists and engineers pay increasing attention to the electrostatic capacitor, which possesses the highest power density among various types of energy storage technologies [1-5]. As the passive electronic component, electrostatic capacitor stores and releases electrical energy through rapid electric field induced polarization and depolarization. In its simplest form, electrostatic capacitor consists of two electrically conductive plates and a dielectric layer. Among various types of electrostatic capacitors, the film capacitor using an insulating polymeric film as the dielectric layer is highly desirable in the electric power systems due to the high electrical breakdown strength (Eb) of the polymeric film. However, the miniaturization of the power system and the realization of compact energy storage technologies are severely hindered by the low volumetric energy density and operating temperature of the polymeric film. For example, the energy density of biaxially oriented polypropylenes (BOPP), the best commercially available film with a market share of 50%, is merely 1-2 J/cm 3 , which is at least one order of magnitude lower than those of electrochemical supercapacitors and batteries. Additionally, the highest operating temperature for BOPP film is limited to 105 °C due to the low melting temperature of PP resin. As a result, an extra cooling system is required to decrease the environmental temperature so that the BOPP film capacitor can be operated at a safe temperature, accordingly leading to the dramatic increases in the weight, volume and cost of the power system. Therefore, improvements in the energy density and operating temperature of the polymeric film have become essential for the development of advanced film capacitors.

Dielectric materials are the core elements of dielectric capacitors that are one of the most important passive components in advanced electrical and electronic systems. dielectric performance deteriorates significantly under elevated temperature and the maximum operating temperature of BOPP is only 105 °C which cannot meet the urgent demands for film capacitors operating under harsh environment. For example, the ambient temperature of power inverters near the engines in hybrid electric vehicles (HEVs) exceeds 140 °C. To maintain the regular work of DC/AC inverters, a secondary cooling system is introduced into present HEVs, bringing extra volume and weight. The development of wide-bandgap semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN), is expected to bring about the revolution of electronic devices, enabling higher operating temperature of over 150 °C. The dielectric performance of these polymers can be further improved by modifying the molecular structures. In addition, combination of polymer and inorganic nanomaterials to form the nanocomposites may overcome some common limitations of polymer dielectrics and obtain favorable features for high-temperature applications. The fundamental theories on the relationship between the chemical structures and thermal stability or dielectric performance of polymers, which are essential to the rational design of high-T g polymer dielectrics, are largely unexplored

Metallized film capacitors are the core equipment of converter stations and the polypropylene (PP) films act as the main insulation. The microstructure of polypropylene films will be damaged in the long-term operation under DC voltage and eventually leads to insulation failures. In this paper, the PP films were prepared with different contents of nucleating agent. The micromorphology was observed and the crystallization properties were investigated. The breakdown experiments were conducted and the average DC breakdown strength of the PP film with 0.01 wt.% nucleating agent is increased by approximately 25.7% compared with that of the original sample. The conclusion can be drawn that the improvement of the insulation performance through crystallization control is feasible and shows a great potential in practical applications.

The performances of dielectric film capacitors depend directly on the dielectric materials. High-performance capacitors must be supported by dielectric materials with high dielectric properties and high energy storage density. The dielectric constant of conventional dielectric materials has inherent contradiction with its dielectric strength, therefore, the development of a new film dielectric material with excellent dielectric performance and suitable for efficient energy storage density is conducive to greatly increasing the capacity of capacitors and miniaturization of applications. This paper introduces the research progress of high-performance with nanofiller modified film materials, discusses the modification technology on improving the electrical properties, and discusses the feasible blending, grafting and nano modification technologies of polypropylene. The analysis shows that the modification of nano - blend polypropylene can improve the dielectric constant and dielectric strength of materials.

For the applications where a single capacitor is incapable to meet the needs, multiple capacitors are connected in series or in parallel as a bank to fulfill the capacitance and voltage rating requirements. Even though some commercial products have already existed in the market, most of the designs use the same capacitors or combine different types of capacitors by experience, so that the volume, cost, reliability, and power loss are not optimized. To the best knowledge, no quantitative design considering all these design aspects is available for capacitor banks. This article proposes a model-based optimal design method for hybrid capacitor banks consisting of both electrolytic capacitors and film capacitors. Performance factors, such as impedance characteristics, lifetime, power loss, cost, and volume, are modeled and considered in the optimization process. The selection of the capacitance ratio between the two types of capacitors and the number of capacitors connected in parallel are analyzed based on specific design constraints. A case study of the dc-link capacitor bank design for a 5.5-kW inverter is presented to demonstrate the modeling and optimal design process.

This paper presents a design and control approach of a virtual DC-Link for a full GaN-based single phase converter with high power density. Low frequency power ripple on the DC bus is an inherent problem for single phase PWM converter. The topology consists of a totem pole PFC with an added virtual DC-Link, which forces this low frequency power ripple on the DC output side to divert to an auxiliary capacitor. It results in significantly reduced required capacitance and e.g. enables the use of film capacitors instead of electrolytic capacitors. The proposed control for the topology is reduced to a minimum amount of sensor requirements while still maintaining the full functionality without bulky DC-link capacitors. Simulation and and experimental results up to 3 kW are provided to validate the performance of the proposed method.

A typical approach to minimizing the early failures (“infant mortality”) of the modern metallized film capacitors (MFCs) is to conduct a burn-in test at applied voltage slightly more (at 30 – 50%) than nominal value. During the test, an external capacitor bank is used as a capacitive storage device with an energy significantly exceeding the energy level of the capacitor under the test. Thus, the amount of energy in the self-healing (SH) process is practically unlimited, which may lead to catastrophic failure of the capacitor. Recently, the soft training test for application of such capacitors in overload modes has been proposed. This can significantly improve the MFCs technical characteristics. We present the results of experimental and theoretical study on SH processes of MFCs in soft training test, allowing the capacitors to operate at voltages 3 – 5 times higher than nominal value. The MFC’s degradation is associated with the equivalent parallel resistance (EPR) decreasing due to numerous SH events. On the base of the developed physical model, the relationship between critical value of testing voltage and EPR as a diagnostic parameter is offered.

Energy storage devices are one of the hot spots in recent years due to the environmental problems caused by the large consumption of unsustainable energy such as petroleum or coal. Capacitors are a common device for energy storage, especially electrical energy. A variety of types including electrolytic capacitors, mica capacitors, paper capacitors, ceramic capacitors, film capacitors, and non-polarized capacitors have been proposed. Their specific applications depend on their intrinsic properties. Dielectric capacitors have reasonable energy storage density, with current research focusing on the enhancement of energy density and making the materials more flexible as well as lightweight. Improvement strategies are based on the premise that use of two or more different materials (e.g. polymers and ceramics/metals) at an optimal formulation can result in properties that combine the advantages of the precursor materials. Different polymers especially fluoropolymers (e.g. PVDF and PVDF based co-polymer) are the main components in dielectric nanocomposites for capacitors with high energy storage performance. In this article, we have briefly summarized the recent advances in functional polymers nanocomposites for energy storage applications with a primary focus on polymers, surface engineering, functional groups and novel synthesis/manufacturing concepts applied to new materials. The article presents a unique integrated structure and approaches providing key knowledge for the design and development of novel, low-cost, multifunctional next-generation energy storage materials with improved efficiency.

With the rise of temperature and humidity, the electrode corrosion of metallized film capacitors under AC voltage becomes more significant. And the corresponding capacitance loss makes capacitors behave abnormally. This paper concentrates on the capacitance loss analysis of metallized film capacitors. Firstly, this paper establishes an experimental platform with a voltage of 305Vrms. The ambient temperature is 85°C, 60°C and 35°C, respectively. And the ambient humidity is 35%, 60%, and 85%, respectively. Secondly, the mechanism of capacitance loss is studied based on experiment results and the anatomical analysis of the capacitors. Finally, the capacitance loss of the metallized film capacitor with the effects of temperature and humidity is studied. The results indicate that: (1) The process of capacitance loss can be basically divided into 4 stages. Each stage corresponds to different mechanisms;(2) The duration of the moisture ingress process decreases as humidity rises or temperature decreases, while the capacitance loss is accelerated with the rise of temperature and humidity.

The working section of metal film capacitors is made of two pieces of polymer films covered with directly metallized electrodes. In some applications, the current densities in electrodes can reach values leading to its degradation. Thereby, the destruction of nanoscale thickness Al and Zn films by high current densities was studied at atmospheric air conditions. The current density $\sim 10^{12}\mathrm{A}/\mathrm{m}^{2}$ was found to be a threshold value leading to strata origin. This process was accompanied by propagating demetallized areas, called strata, forming across the applied electric field. Additionally, the surface flashover was shown to allow strata growth even when the sample divides into two parts as stratum reaches its edge. As a result, the current and voltage waveforms were obtained for both stages. Additionally, the breakdown channel dynamic resistances corresponding to surface flashover phase were calculated.

electrodynamic destruction due to electrothermal evaporation of segmented zinc electrodes used in metallized film capacitors was experimentally studied. Numerical model of segmented electrodes electrothermal evaporation was developed using COMSOL Multiphysics software. This model takes into account all necessary electrical and thermal material’s parameters. The results of simulation are in good agreement with experimental data. Numerical model can be used for optimization of segmented electrodes parameters and checking its efficiency.

Charge-discharge efficiency of more than 90% is a necessary condition for electrostatic capacitors with polymer dielectrics as storage media of electrical charges considering their practical application, how to achieve high energy storage density and high charge-discharge efficiency at the same time is now a research hotspot. Film capacitors generally work under electric field strength below 200 MV/m, at which the charge-discharge efficiency of less than 80% of polyvinylidene fluoride (PVDF) films limit their application in many cases. Herein, Epoxy/PVDF/Epoxy composite films in sandwich structure with different volume ratios of epoxy resin are prepared, cross section of which is characterized by SEM and EDS, expected energy storage properties would be both high energy storage density and high charge-discharge efficiency of 95% under electric field strength below 200 MV/m. Dielectric spectrum and energy storage properties have been tested. The trilayered composite films with varied volume ratios of epoxy resin are capable of operating with equivalent level of charge-discharge efficiency (up to 96%) as biaxially oriented polypropylene (BOPP) films and concurrently delivering energy storage density (1.6 J • cm−3) which indicates an 300% enhancement over the commercial used BOPP films under electric field strength of 200 MV/m, this work provides preliminary proof of a means of using crosslinked epoxy resin to improve charge-discharge efficiency of PVDF.

It has been found that the long-term thermal aging at the temperature of 100 °C and relative humidity 54 %, causes a low change of the capacitance and a high change of the loss factor of polypropylene (PP) film capacitors. The goal of the work has been to find main reasons of these changes. Dismounting of aged capacitors has shown that the metal layers on the PP film, which form the capacitor electrodes, near the metal contacts on the ends of the body of the capacitor are strongly corroded and sometimes even totally absent. On the other hand, the change of the total electrodes area is not significant, because the capacitance decreases only slightly during the thermal aging. Because the PP film as well as the sprayed contacts are resistant to heat aging, the main reason of a significant increase in the loss factor must be the increase the resistance of the metal layers that form the capacitor electrodes.

This paper mainly studies the high power factor control strategy of single-phase electroless capacitor variable frequency speed control system. The power factor of 0.977 can be obtained through matlab/simulink simulation. The single-phase non-electrolytic capacitor frequency conversion speed regulation system uses small-capacity film capacitors instead of traditional large-capacity electrolytic capacitors. It has the advantages of high power density and high input power factor on the grid side.

A two-stage power decoupling for a single-phase photovoltaic (PV) inverter is proposed in this paper. By controlling the DC link voltage ripple, the amount of decoupling power can be controlled on both DC and AC sides. The inverter is first modelled with differential and common signals in the dq frame. Then conventional PI controllers are designed to control the grid current, DC link voltage, and its voltage ripple, respectively. The experimental results show that the amount of decoupling power on the DC sides is controllable by regulating its voltage ripple. The power decoupling on the AC side drastically reduces the DC-link capacitance, i.e., from 900 uF to 68 uF, which makes it possible to replace the electrolytic capacitor by the film capacitor with high reliability.

To manage the instantaneous input and output power mismatch, existing Photovoltaic (PV) inverters usually utilize large electrolytic capacitors or an extra ripple port, leading to short lifespan, low power density or high cost of the system. To address this issue, recently the swinging bus (SB) technique was proposed which only requires thin film capacitors to handle power mismatch. However, existing SB controllers have not yet experimentally demonstrated reactive power capability, which is a requirement in newly released grid codes. In addition, SB controllers are normally unique to specific inverter topologies. To address these challenges, this paper proposes a Four-Mode Three- State (FMTS) swinging bus controller that is applicable to many types of single-phase PV inverter topologies. The approach manages power mismatch using only a small film capacitor, even while achieving reactive power compensation. Simulation and experimental results, based on a series-capacitive-link PV inverter topology, have verified the effectiveness of FMTS SB controller.

Polyvinylidene fluoride (PVDF), as an electroactive polymer, has been attracting increasingly attention for its broad potential applications ranging from film capacitors, actuators, to energy harvesters. The capability of a PVDF film to sustain a high working voltage is highly demanded to achieve these applications. Herein, we find that blending two PVDF polymers with low and high molecular weights can achieve higher dielectric strength (Eb = 479 MV/m) than either of the two original ones (PVDF-1 with Mw of ~180,000, Eb = 412 MV/m and PVDF-2 with Mw of ~441,000, Eb = 391 MV/m). The underlying synergetic effect is deduced from the analysis of the crystallization of PVDF by wide-angle X-ray diffraction and small-angle X-ray scattering from a synchrotron source. It involves crystallite polymorphism, the transition of crystalline phases, the variation of crystalline lattice spacing at different strain spaces, and the long periods and the distribution of crystallite sizes. Understanding these underlying influences is beneficial to process PVDF films with desirable and reliable dielectric properties.

Due to the use of electrolytic capacitor, the life span and operating temperature range of traditional light emitting diode (LED) drivers are limited. In order to solve these problems, many researchers focus on electrolytic capacitor-less design. In this paper, a new electrolytic capacitor-less LED driver with power factor correction (PFC) function is proposed. By using a coupled inductor, a single-stage topology with optimized energy-flow-path and higher efficiency is proposed. With this new topology, electrolytic capacitor can be replaced by film capacitor with lower capacitance value and longer lifetime so that the life span of the LED driver can be prolonged. Simulation results are presented to verify the proposed design.

In this paper, two soft-switching single-stage converters are proposed: A Zeta-based inverter and a SEPIC-based rectifier. These two converters are capable of both stepping up and stepping down the voltage in a wide range. Moreover, these converters use a very small film capacitor at the link, instead of electrolytic capacitors that are used in most of the conventional two-stage inverters and rectifiers. Electrolytic capacitors have a shorter lifetime compared to other components of a power electronic converter and their elimination significantly improves the reliability of a converter. This feature is feasible due to having an ac link voltage instead of a dc link. All the semiconductor switches in the proposed converters benefit from zero-current-switching with the help of a very small inductor placed in series with the link capacitor with no auxiliary/additional active switch/diode. Due to the small size of the link capacitor, which is the main energy transferring component of the converters, the dynamic response of both converters is very fast, making these converters suitable for very fast response (VFR) applications. Furthermore, a high-frequency transformer can be employed at the link in case galvanic isolation is needed, thanks to the high-frequency ac voltage of the link. In this paper the principles of the operation of these converters are explained, and their performance is evaluated through simulation and experiments.

Active power decoupling methods in single-phase systems aim to reduce the required capacitance for twice-line frequency power ripple buffering, with added power conversion (i.e., active techniques) to improve the energy utilization ratio of the capacitors. While many active buffer solutions can improve the energy utilization ratio of the capacitor to a certain extent and reduce the required capacitance, they require the use of high energy density ceramic capacitors to achieve comparable power density to the passive electrolytic capacitor bank solution. The ceramic capacitors have to be carefully assembled and packaged, and they are also costly and heavy in weight. In this work, a bipolar ripple port converter, which allows the use of the minimum buffering capacitance in single-phase conversion with 100% energy utilization ratio, is implemented with metal film capacitors, and two flying capacitor multilevel (FCML) legs operated as a full-bridge to shrink the filter inductor size and improve efficiency. A compact hardware prototype with a new digital control scheme is implemented. Experimental results demonstrating the active power ripple decoupling at 2 kW, 400 V dc bus are provided and discussed.

Among different micro inverter topologies, single stage micro inverters duo to their lower component, low cost and simple control structure are paid more attentions. One of the biggest problem in single phase micro inverter is power ripple in twice frequency of line. This phenomena causes voltage and current ripple in the side of PV so that designing MPPT controller becomes very hard. To eliminate power ripple (power decoupling) in conventional micro inverters, large electrolytic capacitors are used in parallel of PVs. Drawbacks of electrolytic capacitors are large ESR and lower life cycle in comparison of other type of capacitors. In this paper, a power decoupling method for Single stage flyback based current fed micro inverter is presented. By this method, the required capacitance for power decoupling and current stress of semiconductors are decreased which film capacitors can be used instead of electrolytic. The effectiveness of this method is confirmed for 100w micro inverter by PSIM simulation.

In this paper, an improved sensorless vector control method for an interior permanent magnet synchronous motor (IPMSM) drive with small DC-link capacitors is proposed. First, a fast sliding-mode observer was applied, to enlarge the observer bandwidth. Then, an improved estimator based on a proportional integral resonant controller was designed for the estimate speed shaping, which means the actual speed can be tracked. This not only reduces the position estimate error, but also enhances the grid power factor and suppresses the input current harmonics. Simulation and experiments were conducted on a sensorless IPMSM drive system with a small film capacitor. The effectiveness of the proposed estimation method was verified by the simulation and experimental results. The estimated error was reduced and the grid current harmonics satisfy the requirements of EN61000-3-2.

На 43 страницы, 26 рисунков, 5 таблиц, 22 источника. Тема выпускной квалификационной работы: «Исследование влияния конфигурации сегментированных электродов на электрическую прочность металлопленочных конденсаторов». В данной работе было исследовано методом численного моделирования в COMSOL электрическое поле на краю электрода металлопленочного конденсатора, полученного напылением толщиной от 10 нм до 50 нм. Материал диэлектрика - полипропилен толщиной 6 мкр. Среда моделирования - Comsol Multiphysics 5.5. Цели работы: 1. Построить упрощенную модель пленки с сегментной металлизацией в среде мультифизического моделирования COMSOL Multiphysics 5.5. 2. Произвести моделирование электрического поля для металлизации разной толщиныи проанализировать распределение электрического поля. 3. Сделать выводы о возможном влиянии толщины электрода на электрическую прочность. По итогам работ получены результаты: 1. Выведено распространение поля при разных толщинах электрода. 2. Показана аппроксимация графиков зависимости напряженности поля в характерных точках от толщины напыления. 3. Произведен литературный обзор работ в области электрического разрушения электрода и диэлектрика, а также по теме существования объемного заряда в диэлектрике и его влияния на систему. 4. Произведен сравнительный анализконденсаторов отечественного и зарубежного производства. Выводы по итогам исследования: 1. Напряженность поля на краю электрода Emax пропорциональна толщине электрода в степени -0,5. 2. Размер области с напряженностью более пробивной не меняется при изменении толщины электрода, а зависит только от средней напряженности электрического поля. Исследование проведено применительно к металлопленочным конденсаторам (МПК)., 43 pages, 26 figures, 5 tables, 22 sources. The theme of graduate qualification work: "Research of influence of configuration of segmented electrodes on electric strength of metal-film capacitors". In this work was investigated by the method of numerical simulation in COMSOL electric field at the edge of the electrode of metal-film capacitor, obtained by sputtering with thickness from 10 nm to 50 nm. The dielectric material is polypropylene with thickness of 6 microns. The modeling medium is Comsol Multiphysics 5.5. Aims of work: 1. To build a simplified model of the film with segmental metallization in a multiphysical simulation environment - COMSOL Multiphysics 5.5. 2. To model an electric field for metallization of different thicknesses and analyze the electric field distribution. 3. To draw conclusions about possible influence of electrode thickness on electric strength. The results of the work are obtained: 1. The field distribution at different electrode thicknesses is derived. 2. Approximation of graphs of field strength dependence at characteristic points on spraying thickness is shown. 3. Literary review of works in the field of electric destruction of the electrode and the dielectric, and also on a theme of existence of volume charge in the dielectric and its influence on system is made. 4. The comparative analysis of capacitors of domestic and foreign manufacture is made. Conclusions on results of research: 1. The field strength at the edge of Emax electrode is proportional to the electrode thickness in degree -0,5. 2.The size of the area with the intensity more punchy does not change when the electrode thickness changes, but depends only on the average intensity of the electric field. The study was carried out with respect to metal-film capacitors (MFCs).

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. The flexoelectric effect also contributes to the regulation on energy storage performances by bending the flexible films. This work provides an candidate for the flexible film capacitors with giant application potentials in wearable energy storage devices.

The capacitor is a passive electrical device, used to collect electrical energy by generating a potential difference. It is generally consisting of combination of two conductors placed next to each other separated by dielectric medium. The performance of a capacitor expressed in terms of the capacitance (C) depends on the dimension/geometry of the plate/electrode and the dielectric constant of the material, where the dielectric can be defined by insulating medium having permittivity, with no AC power losses or DC leakage. The capacitor shows different response to AC and DC sources. These are mainly used to supply power in several electronic and electrical systems. Therefore, this chapter provides the fundamental aspects of the capacitors and their basic properties. It emphasizes on the parallel plate model, the basic terminologies associated with the capacitors along with the equivalent circuits of the capacitor and its response to the externally applied AC and DC sources. It also describes about different types of capacitors that are being fabricated using different materials and different construction techniques. These different types of capacitors provide some unique properties.

Increasing the dielectric strength of polymer films has been a key theme as it is directly responsible for increasing energy density of relevant components such as film capacitors and insulation tapes. Dielectric films with higher roughness and surface defects are subject to the formation of an air gap at the interface between dielectric film and metallised polymer electrodes, which results in inaccurate dielectric strength. The air gap due to roughness was found to result in dielectric strength of 25% higher than that using depositing metal on dielectric films (integral electrode). The integral electrode method is proven to be a better way to test the genuine dielectric strength of thin and rough dielectric films. Surface defects, on the other hand, were revealed to cause lowering of dielectric strength because of their contribution to the localised electric field and charge injection. The detrimental effect of surface defects can be suppressed by submerging the film in oil or coating the film with an oxide layer.

Conventionally, dc-dc converters need a large input/output side electrolytic capacitor to suppress the voltage ripple which is caused by the PWM switching and achieve the desired voltage stable performance for the dc microgrid application. However, the large capacitor will increase the dc-bus short-circuit current dramatically when the short-circuit occurs. In this paper, a coupled-inductor-based filter, which ensures the lower voltage ripple and lower short-circuit current of the dc microgrid, is proposed to realize the electrolytic capacitor. Moreover, the long lifetime film capacitor can be used to replace the electrolytic capacitor by reducing the required capacitance. The computer simulations and hardware experimental results are shown to verify the performance of the proposed coupled-inductor filter and short-circuit current reduction technique.

Numerical simulation of metal-film capacitors segmented electrodes was conducted. Conventional segmentation with intersegment bridges and novel hybrid segmentation were simulated and compared with all-over metallized electrodes. The calculated characteristics are: surface resistance of the electrodes active area of the electrodes resulting in overall capacitance, current density distribution. It was established that surface resistance of hybrid-segmented metallization is much lower than one of bridge-patterned, and close enough for all-over metallization. The hybrid-segmented electrodes were found to be less overloaded by current.

The film-impregnated dielectric under operating conditions is subject to prolonged exposure to electric and thermal fields, as well as mechanical loading. In addition to critical partial discharges, the most serious drawback that impairs the film and condenser reliability in general is the deterioration of the electro-physical characteristics of the polypropylene film and liquid dielectric due to the gradual dissolution of the polymer in the liquid dielectric, which is determined by their chemical composition. This interaction of components, which was investigated in detail, has a thermo activation nature, which relates to the processes of rearrangement of atoms or molecules with the overcoming of potential barriers, and is manifested in the swelling of the polypropylene film with subsequent dissolution of the amorphous component in the polymeric component. As a consequence, irreversible structural changes of the film occur, which lead to a decrease in its electrical and mechanical strength, as well as to an increase in the dielectric loss of the liquid dielectric. Capacitor (Fig. 1 (a)) is designed to provide high-frequency communication at frequencies from 24 to 1500 kHz in power lines with a nominal voltage of 35, 110, 150, 220, 330, 500 kV AC 50 and 60 Hz. Coupling capacitor impregnated with environmentally friendly liquid - condenser oil. The short-circuits consist of capacitor sections (Fig. 1 (b)): a thin layer of dielectric is laid between two thin wide metal strips, and the dielectric film is placed on top and below the metal strips - capacitor covers. This paper gives the detail analysis of dielectric properties of capacitor paper.

The evolution of HEV/EV technology has completely changed the scenario of automotive industry with a set of new challenges and benchmarks in power electronics arena. These requirements brings new challenges to designers in terms of achieving high power density (compact) and highly immune to electromagnetic radiations (EMI/EMC). Automotive market is moving towards digitalisation and autonomous cars. IOT, AI and digital electronics plays a vital role in making autonomous car real. In near future the automotive industry completely ruled by autonomous vehicles. As technology grows the requirements of power electronic circuits are also in proposition. Each component in the power electronic circuits has its own importance. Such one of the component in these circuit boards is capacitor. At present most of the automotive suppliers are using the Multi-layer ceramic capacitor as one of the prominent and most depend components in the schematics. Currently electric & electronic industry suffering with shortage in these capacitors. These requirements made the authors to look for an alternative approach(s) in the design. To look into these issues the author(s) of the manuscript suggests two alternative approaches along with a technical assessment in purview of automotive industry. Recommended approaches could be a potential solution for designer(s) and not to compromise with design requirements. Such one of the capacitor, which could be an alternative to MLCC is Polyethylene Naphthalate (PEN) Film Capacitor. In the present manuscript, characteristics of MLCC are compared with Polyethylene Naphthalate (PEN) Film Capacitor with an automotive grade.

Micro-inverters have been known as promising structures for small-scale PV systems. However, these structures need energy storage elements to balance the instantaneous output and input power. Demanding a large size capacitor forces using an electrolytic type at the dc-link that affects the micro-inverter lifetime. This paper presents a new Active Power Decoupling (APD) circuit for the micro-inverters to reduce the capacitor size at the dc-link and utilize film capacitors instead of electrolytic types. The proposed APD circuit is based on a single-phase flyback converter. This structure is controlled based on the PQ theory and a Proportional Resonant (PR) controller for delivering the PV panel energy to the grid and eliminating the pulsation power through the switching pattern control. Simulations and experimental results of a 180 W single-phase micro-inverter prototype were performed to evaluate the performance of the proposed structure and the control scheme. It was found that this controller can accurately regulate the switching pattern to remove the ripples of input current and voltage. Furthermore, the robustness and fast dynamic performance of the proposed configuration have been confirmed during input power variation. In conclusion, this single-phase micro-inverter structure has an efficiency of ∼ 91%, THDi of 3.6%, and a long lifetime.