Capacitive Power Research Articles

Improvement of high-power thyristor trigger circuit with switching-mode power supply for differential-mode noise reduction

This paper focuses on the differential-mode (DM) noise of high-power thyristor (HPT) trigger circuit with switching-mode power supply (SMPS) in capacitive pulsed power supply (CPPS). Parasitic parameter models of components are discussed and analyzed. Based on the parasitic parameter models of components, a DM noise prediction model of HPT trigger circuit with SMPS is developed. The generation mechanism and propagation paths of the DM noise in HPT trigger circuit with SMPS are investigated. To reduce the DM noise, a capacitive SMPS technique is adopted in the HPT trigger circuit with SMPS. Simulation results validate the theoretical analysis.

Stabilizing polar P21ma phase in Bi0.5Na0.5TiO3-Na0.91Bi0.09Nb0.94Mg0.06O3 relaxors by CaTiO3 additive to promote energy storage density, efficiency and discharge rate

Eco-friendly Bi0.5Na0.5TiO3 relaxor ferroelectric has attracted considerable attention for pulsed power capacitor applications due to its large saturation polarization. However, high remnant polarization and low breakdown strength (Eb) restrict its application. Herein, linear dielectric CaTiO3 (CT) is introduced into Bi0.5Na0.5TiO3-Na0.91Bi0.09Nb0.94Mg0.06O3 (BNT-NBNM) ceramic to enhance its Eb. Interestingly, CT additive can stabilize polar orthorhombic P21ma phase. As a result, a high recoverable energy density of 6.4 J/cm3 and a high efficiency of 92% at 400 kV/cm as well as an ultrafast discharge rate of 57 ns are obtained in 0.63BNT-0.27NBNM-0.1CT ceramic. Furthermore, temperature dependent Raman spectra reveal that the superior temperature stability of energy storage properties over the temperature span of 30–150 °C is due to insensitive B-O vibration to temperature. The results demonstrate an effective strategy to construct superior and stable BNT-based energy storage materials for pulsed power capacitor applications.

Improved energy storage performance of Bi(Mg0.5Ti0.5)O3 modified Ba0.55Sr0.45TiO3 lead-free ceramics for pulsed power capacitors

(1–x)Ba0.55Sr0.45TiO3–xBi(Mg0.5Ti0.5)O3 (x = 0, 0.08, 0.1, 0.12, 0.15, 0.2) ceramics were fabricated via a solid-state reaction route. The ultrahigh recoverable energy density (Wrec = 4.05 J cm−3), efficiency (η = 78%), maximum polarization (Pmax = 51.40 μC cm−2), and high dielectric breakdown strength (BDS = 230 kV cm−1) were achieved for the 0.9BST−0.1BMT ceramic. The fast discharge rate (t0.9∼0.14 μs), current density (CD∼637.02 A cm−2), high power density (PD∼38.70 MW cm−3), good temperature stability (20−180 °C), frequency stability (10−500 Hz), and fatigue endurance for cycling (105) of 0.9BST−0.1BMT ceramic make it suitable for the development of energy-storage devices. The relaxor behavior with a high Wrec (3.06 J cm−3) and η (93%) at BDS (220 kV cm−1) was also achieved for the 0.8BST−0.2BMT ceramic. This study systematically investigates the correlation among the structural, dielectric, impedance, and energy storage properties of BMT-doped BST ceramics.

High energy storage performance in BaTiO3-based lead-free relaxors via multi-dimensional collaborative design

The application of advanced pulse power capacitors strongly depends on the fabrication of high-performance energy storage ceramics. However, the low recoverable energy storage density (Wrec) and energy efficiency (η) become the key links limiting the development of energy storage capacitors. In this work, a high Wrec of ∼5.57 J cm−3 and a large η of ∼85.6% are simultaneously realized in BaTiO3-based relaxor ceramics via multi-dimensional collaborative design, which are mainly attributed to the ferroelectric-relaxor transition, enhanced polarization, improved breakdown electric field, and delayed polarization saturation. Furthermore, the excellent temperature stability (ΔWrec < ± 5%, 25–140 °C), frequency stability (ΔWrec < ± 5%, 1–200 Hz), and outstanding charge/discharge performance (current density ∼1583.3 A cm−2, power density ∼190.0 MW cm−3) with good thermal stability are also achieved. It is encouraging that this work demonstrates that multi-dimensional collaborative design is a good strategy to develop new high-performance lead-free materials used in advanced dielectric capacitors.

Power Density Optimization Based Parameter Design Method for the Capacitive Power Transfer System With Magnetic-Core Inductors

Power Density Optimization Based Parameter Design Method for the Capacitive Power Transfer System With Magnetic-Core Inductors

The design of inductive power transfer system for fish aquarium using class-E inverter and LCCL impedance matching

&lt;p&gt;Nowadays, the accessories in fish aquarium systems such as water pump, internal filter, and LED light are powered using cables. This will cause to safety issue such as tangled wire, and risk of electric shock. Therefore, this work aims to design a wireless power transfer system to power up the fish aquarium’ accessories wirelessly without require any physical connection between source and loads. To be more specific, inductive power transfer (IPT) is used instead of capacitive power transfer (CPT) due to high efficiency ability owned by IPT. Class-E inverter circuit is proposed in this paper to convert DC to AC at nearly 100% efficiency. The inverter provides a low switching loss which is important as the circuit operates at high frequency, 1 MHz operating frequency. Furthemore, LCCL impedance matching circuit is added into receiver part of the system to enhance the efficiency of overall circuit. The analyses were done based on the distance between the coils and the misalignment of the coils against the output power and efficiency. The developed prototype is supplied by 24 V DC and capable to deliver 5 W power. The overall efficiency of the prototype is 87.81%.&lt;/p&gt;

Remaining Opportunities in Capacitive Power Transfer Based on Duality With Inductive Power Transfer

Wireless power transfer (WPT) has proven to be an effective solution for electric vehicle charging. As two mainstream near-field WPT technologies, inductive and capacitive power transfer (IPT and CPT) have many similarities. This paper aims to explore the remaining opportunities in CPT systems, not yet reported in existing literature, based on duality with the mature IPT technology. First, a generic modeling method based on two-port network theory is proposed, which contributes to unified modeling and analysis for both inductive and capacitive couplings. Then, power transfer mechanism of IPT and CPT couplers is compared, and unified transfer efficiency is derived, promoting CPT theory developments. Last, the duality between existing IPT and CPT circuits is demonstrated in two aspects: compensation circuit configuration and resonant relationship. 14 CPT topologies are derived based on duality with the existing 7 mainstream IPT circuits, of which 11 circuits do not exist in literature, offering future opportunities in CPT. Detailed comparison and evaluation of the derived 14 CPT circuits are conducted, and high-performance circuits are recommended. As a demonstration, a case study of a 2.1kW 3MHz CPT system is implemented in hardware based on the newly proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SS</i> topology. This example system achieves a peak efficiency of 93.19% with the predicted circuit properties of load-independent constant-voltage (CV) output and zero-phase-angle (ZPA) property.

Production enhancement of long string photovoltaic plants during partial shading through switching capacitor power optimizer circuit

Long series connections are widely preferred by photovoltaic (PV) power plants because they offer advantages such as higher voltage, independent operation of modules at optimal voltage, ease of installation, and lower losses. However, PV power plants are highly susceptible to partial shading and suffer high power losses, resulting in large financial losses. The existing solutions have numerous weaknesses, such as multiple peaks in the characteristic’s curves, erroneous tracking losses, lower power generation and extraction, and limited applications. To overcome the above limitations, a power optimizer based on a switching capacitor circuit has been proposed in this paper to improve the reliability of long strings in power plants under partial shading scenarios. The power optimizer provides higher power output and a single peak in the characteristics curves by minimizing the voltage differences between modules in the string to enable smoother operation of PV systems under partial shading. To evaluate the application and performance of the proposed power optimizer, two PV system sizes are considered and compared with the conventional techniques under static, moving, and progressive partial shading scenarios. From the in-depth analysis, it is found that the power optimizer minimizes the mismatch between modules by reducing the power losses from 70.83 % in the conventional system to 35.13 %. By implementing the power optimizer in the string, a power extraction of up to 68.68 %, generation efficiency of more than 99 %, and power improvement of 54.21 % are achieved along with single-peak characteristics curves.

Excellent Energy Storage Performance in Epoxy Resin Dielectric Polymer Films by a Facile Hot-Pressing Method.

Epoxy resin (EP), as a kind of dielectric polymer, exhibits the advantages of low-curing shrinkage, high-insulating properties, and good thermal/chemical stability, which is widely used in electronic and electrical industry. However, the complicated preparation process of EP has limited their practical applications for energy storage. In this manuscript, bisphenol F epoxy resin (EPF) was successfully fabricated into polymer films with a thickness of 10~15 μm by a facile hot-pressing method. It was found that the curing degree of EPF was significantly affected by changing the ratio of EP monomer/curing agent, which led to the improvement in breakdown strength and energy storage performance. In particular, a high discharged energy density (Ud) of 6.5 J·cm-3 and efficiency (η) of 86% under an electric field of 600 MV·m-1 were obtained for the EPF film with an EP monomer/curing agent ratio of 1:1.5 by hot pressing at 130 °C, which indicates that the hot-pressing method could be facilely employed to produce high-quality EP films with excellent energy storage performance for pulse power capacitors.

Enhanced electrochemical performance of oxygen, nitrogen, and sulfur trial-doped Nypa fruticans-based carbon nanofiber for high performance supercapacitors

The utilization of biomass-derived carbon materials, which exhibit nanofiber structures and possess advantageous properties such as porosity, abundant availability, heteroatom content, and high specific surface area, is important in the development of green energy technologies and sustainability. Therefore, this research focuses on the synthesis of Nypa Fruticans Fiber (NFF)-derived carbon nanofiber materials through activation and carbonization processes as well as doping of oxygen (O), nitrogen (N), and sulfur (S) heteroatoms. O doping was carried out internally (activation process) while N-S doping was carried out externally using thiourea (0.1, 0.3 and 0.5 g) which aims to produce high physical properties of carbon electrodes (crystallinity structure, surface morphology, surface area specific) related to the performance improvement of supercapacitor cells. Furthermore, the NFF electrode with O-N-S doping has the physical properties of a low crystallinity structure, a high specific surface area of 1230.05 m2g−1 and the formation of a large number of nanofiber structures. The electrochemical properties of the NFF-03 supercapacitor cell electrode had the highest specific capacitance, specific energy, and specific power values of 430 Fg−1, 248 Wkg−1, 64 Whkg−1, respectively, at a current density of 1 Ag−1 in 1 M H2SO4 electrolyte solution, at a voltage of 1 V with doped 0.3 g of thiourea. The results of this research provide a clear reference that the trial heteroatom (O-N-S) doping process can produce high physical properties of carbon electrodes leading to increased performance of biomass-derived supercapacitor cells with a simple, relevant and low-cost synthesis strategy.

Comparison of Temperature Rise Test Methods for Series Reactors Connected with High Voltage Power Capacitors

In substation, phase advance capacitors are used to improve the power factor. Series reactors are generally connected with the capacitors to reduce the waveform distortion and suppress the inrush current. The fifth harmonic current usually flows into the series reactors for a high voltage power capacitor. Japanese Industrial Standards provide three types of temperature rise test methods, and manufacturer chooses one of them. However, which test method should be selected has not been examined. In this paper, compare the advantages and disadvantages of the test methods using a prototype reactor.

A Proposal of a New Temperature Rise Test Method for Series Reactors Connected with High Voltage Power Capacitors

In substation, phase advance capacitors are used to improve the power factor. Series reactors are generally connected with the capacitors to reduce the waveform distortion and suppress the inrush current. The fifth harmonic current usually flows into the series reactors for a high voltage power capacitor. Japanese Industrial Standards provide three types of temperature rise test methods. Each test method has its own problems. To alleviate them, we have devised a new test method called “Middle Frequency Test” which uses a meddle frequency between the fundamental and fifth harmonics for excitation. This paper presents an implementation method and demonstrates the usefulness of the proposed test method.

A Simplified Three-Order Small-Signal Model for Capacitive Power Transfer System Using Series Compensation

Capacitive power transfer is promising for highefficiency wireless charging. A small-signal model is required to evaluate the system stability under different control approaches. This paper focuses on the modeling and simplification of the highorder system using series compensation. Based on the extended describing function method, this paper proposes a series of model transformation and approximation to effectively reduce the circuit order of the resonant tank. The number of resonant components is reduced from ten to two. Combining with the inverter and rectifier model, a third-order equivalent circuit model is firstly derived for the whole system with clear physical meaning and explicit transfer function. The experiment results show the model is accurate up to 1/5 of the switching frequency.

APPLICATION OF STATIC SYNCHRONOUS COMPENSATOR (STATCOM) AS REACTIVE POWER CONTROL IN DFIG WIND FARM AND GRID INTERCONNECTION SYSTEMS

The most difficult aspect of optimizing a wind farm is creating an accurate wind farm model, especially if the farm is connected to the grid. The inconsistency and unpredictability of wind speeds exacerbates this issue. When dealing with wind farms, it is possible that the reactive power addition capabilities of individual wind turbines are insufficient to meet network requirements. This is due to cable losses and line losses between the wind farm and PCC. This study employs a doubly fed induction generator (DFIG) and a Static Synchronous Compensator (STATCOM) compensator to keep the output voltage amplitude more constant. Using two PI controller loops, the STATCOM will generate reactive (capacitive) power if the DFIG voltage is lower. The STATCOM will then absorb reactive (inductive) electricity if the DFIG system voltage is greater. STATCOM's ability to regulate the flow of reactive power can increase the network's stability. By optimizing the network's reactive power, the power factor is increased and stabilized up to 0.99. In addition, the system's harmonics never exceed the 5% limit specified by the IEEE 519-1992 standard.

Boron-based composites anode leads to ultrahigh power and energy density of lithium-ion capacitor

There is an urgent need to find a way to increase the energy density of supercapacitors while preserving their high power. Building lithium-ion hybrid capacitors (LICs) is recognized as a powerful strategy. However, until now, at relatively high power density (around 40 kW kg−1), the energy density of LIC only reaches 15–25 Wh kg−1, which is far from reaching the range of energy density of lithium-ion batteries(50–150 Wh kg−1). Here, a new type of LIC device with amorphous Co-B nanoparticles/graphene composites as anode and nitrogen-doped porous carbon as cathode has been fabricated. Coupling the amorphous Co-B nanoparticles/graphene composites (ACB-G) and nitrogen-doped porous carbon (NPC), the lithium ion capacitors device delivers a high energy density of 139 Wh kg−1 at 200 W kg−1, and an excellent 83% capacity retention after 10,000 cycles. Even at 40 kW kg−1, the energy density can reach 61 Wh kg−1. Such as-prepared LICs mainly benefit from the amorphous boron-based material's ability to embed lithium quickly and in large quantities. The study of amorphous anode material in LICs may reveal a new perspective towards application of high-performance storage devices.

Excellent energy storage properties, domain mechanism, and temperature stability of lead-free BaTiO3-Bi(Mg1/2Sn1/2)O3 bulk ferroelectrics

Pulsed power systems require high-performance capacitors with high energy storage density. In this work, (1 − x)BaTiO3-xBi(Mg1/2Sn1/2)O3 ferroelectric ceramics were synthesized in a solid-state solution. The sample of x = 0.12 (0.88BT-0.12BMS) has excellent energy storage density, wide temperature, and wide frequency stability. The excellent energy density of 4.87 J/cm3 at 315 kV/cm and the energy efficiency of 72% at room temperature for 0.88BT-0.12BMS ceramics were achieved. Furthermore, the 0.88BT-0.12BMS ceramics demonstrated well temperature stabilities in the range of 20–100 °C and very good frequency stability in the range of 1–100 Hz. Through pulsed charging–discharging testing, the current density is calculated as 314.01 A/cm2, and the power density is 21.98 MW/cm3. Moreover, the oxygen vacancies' defects and ferroelectric domain mechanism for enhanced breakdown strength as well as high energy density were discussed. These findings broaden the horizon for lead-free dielectrics and show promising applications for pulse power capacitors.

Reactive power optimization in distribution systems considering load levels for economic benefit maximization

Introduction. The need for electrical energy has been increased sharply due to hasty growth in industrials, social and economic improvements. From the previous studies, it has been agreed that almost 13 % of the total power generated is wasted as heat loss at distribution level. It has been extensively recognized that the node voltage profile along the distribution system can be enhanced under steady state power transfer controlled by proper reactive power compensation. Capacitors have been acknowledged as reactive power compensating device in distribution systems to achieve technical and economical benefits. Novelty of this work is the application of Archimedes optimization algorithm for reactive power optimization in distribution systems so as to obtain an improved solution and also a real 94-bus Portuguese network and modified 12-bus network has been taken and validated for three different load levels which are totally new. Purpose of the proposed work is to maximize the economic benefit by reducing the power loss and capacitor purchase cost at three different load conditions subject to satisfaction of equality and inequality constraints. Methods. The economic benefit has been validated using Archimedes optimization algorithm for three load levels considering three distribution systems. Results. The computational outcomes indicated the competence of the proposed methodology in comparison with the previously published works in power loss minimization, bus voltage enhancement and more economical benefit and proved that the proposed methodology performs well compared to other methods in the literature.

Composition-Driven Polarization Distribution in Poly(vinylidene fluoride)-Based Copolymer Blends for High Power Density Capacitors

High power density capacitors have been highly demanded in modern electronics and pulsed power systems. Yet the long-standing challenge that restricts achieving high power in capacitors lies in the inverse relationship between the breakdown strength and permittivity of dielectric materials. Here, we introduce poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) into the host poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to produce PVDF-based copolymer blends, resulting in composition-driven 0-3 type microstructures, featuring nanospheres of P(VDF-TrFE) lamellar crystals dispersed homogeneously in a P(VDF-HFP) matrix together with crystalline phase evolution from the γ-phase to the α-phase. At the critical composition, the TrFE/HFP mole ratio is equal to 1, and the blend film achieves maximum energy storage performance with discharged energy density (Udis) ∼ 24.3 J/cm3 at 607 MV/m. Finite element analyses reveal the relationship between microstructures, compositions, and the distribution of local electric field and polarization, which provide an in-depth understanding of the microscopic mechanism of the enhancement in energy storage capability of the blend films. More importantly, in a practical charge/discharge circuit, the blend film could deliver an ultrahigh energy density of 20.4 J/cm3, i.e., 88.3% of the total stored energy to 20 kΩ load in 2.8 μs (τ0.9), resulting a high power density of 7.29 MW/cm3, outperforming the reported dielectric polymer-based composites and copolymer films in both energy and power densities. The study thus demonstrates a promising strategy to develop high-performance dielectrics for high power capacitors.

Fault detection and localization method for modular multilevel converters in offshore DC wind turbines

The offshore DC wind turbine, consisting of direct-drive permanent magnet synchronous generator (PMSG) and modular multilevel converter (MMC), has become a promising candidate for the large-capacity wind energy conversion system. Submodule (SM) failure detection and localization are crucial for reliable operation of the MMC. However, existing techniques mainly focus on the rated operation condition, which may not be suitable for the MMC in wind turbine due to varying wind speed. Moreover, proper injection of second-order harmonic circulating current (SHCC) is desirable to reduce capacitor voltage ripple and power loss, which may also affect the accuracy of fault detection. This paper proposes a fault-tolerant strategy immune to variable operation conditions, as well as SHCC injection, for the MMC with phase-shifted carrier modulation. Firstly, the inherent switching harmonics of circulating current with SM failure are analyzed, based on which the fault detection method is developed. Then, the localization approach is presented by measuring the difference of SM capacitor voltages. Compared with existing techniques, the proposed strategy requires neither estimator nor additional sensor, which is robust, simple, and economical. Finally, both simulation and experimental results demonstrate the effectiveness of the proposed method, which is not influenced by SHCC and varying wind speed.

Research on integrated micro-energy storage technology based on multi-type electrochemistry

Electrochemical energy storage is a process that utilizes chemical reactions to store and release electrical energy in the form of chemical energy. These include lead-acid, lithium-ion, flow, sodium-sulfur batteries, etc., while electrochemical energy storage materials and technologies are the keys to solving the utilization, conversion, and storage of clean energy. In order to solve the problem that the current energy storage technology has an extensive range of energy storage frequency fluctuations in the application process, this paper conducts research on a comprehensive micro-energy storage technology based on multi-type electrochemistry, which improves the stability of energy storage. Based on the introduction of multi-type electrochemical technology, MXene (Ti3C2) was selected as the dispersion liquid, and PVA was used as the gel electrolyte to complete both preparations. The device’s fabrication and assembly are completed based on calculating the rated power, rated capacity, and other parameters of the micro energy storage capacitor. Aiming at the ultra-low frequency oscillation problem that may exist in the energy storage process, this paper develops a micro energy storage control method that participates in primary frequency modulation. The comparison experiment proves that the frequency fluctuation of the new energy storage technology is within the controllable range in practical application, which can effectively improve the stability of energy storage.