Capacitive Power Research Articles

Enhanced energy-storage properties in (Bi0.5Na0.5)TiO3 ceramics by doping linear perovskite materials Ca0.85Bi0.1(Sn0.5Ti0.5)O3

For energy storage applications in Bi0.5Na0.5TiO3 (BNT)-based materials, the key challenges are the premature polarization saturation and low breakdown electric field (Eb), which confine the energy storage capacity of BNT and significantly restrict progress in advancing pulsed power capacitors. Hence, the cooperative optimization strategy of band structure and defect engineering was proposed, which successfully obtained a high recoverable energy density of 3.83 J/cm3 and an energy efficiency of 77.9 % in the Bi0.5Na0.5TiO3-0.12Ca0.85Bi0.1(Sn0.5Ti0.5)O3 (BNT-0.12CBST) ceramics. Doping the BNT matrix with CBST has been shown to not only reduce grain size but also enhance relaxor behavior, which collectively improves breakdown strength and delays polarization saturation. Furthermore, the x = 0.12 ceramic also exhibits a commendable discharge power density of 91.9 MW/cm3 and a transient discharge time of 40 ns. The higher resistivity and lower oxygen vacancy concentration are conductive to acquire superior breakdown electric field and energy storage performance. We determine the crystal structure, dielectric and ferroelectric properties of the studied ceramics in a wide range of temperatures and concentrations, and a phase diagram is constructed, which illustrates the complex phases present and their transformation behavior. Our work provides an effective strategy to optimize the energy-storage of dielectric ceramics, and shows great potential for practical applications in pulse power systems.

Design, synthesis and Characterization of a novel antiferroelectric solid solution (1-x)PbHfO3-xBiAlO3

Antiferroelectric (AFE) materials are potentially useful for energy storage applications. Lead hafnate (PbHfO3) is one of the prototypical AFE materials. However, its critical field (Ecr) which is needed to induce the AFE to ferroelectric phase transition is close to the dielectric breakdown strength. To reduce Ecr, we prepare the solid solutions of (1-x)PbHfO3–xBiAlO3 (x = 0.00–0.04) via solid state synthesis. The crystal structures, dielectric behaviour, ferroelectric properties, and energy storage properties are investigated. A temperature-composition phase diagram is established. At room temperature, the crystal symmetry of all compositions is orthorhombic with the Pbam space group. Upon heating, the transition to the AFE orthorhombic Imma phase is observed at the temperature TC1, which slightly decreases with increasing x, followed by the transition to the cubic phase at the temperature TC2, which does not depend on x. Distinct dielectric anomalies are observed at TC1 and TC2. It is found that BiAlO3 substitution reduces Ecr and the polarization–electric field relations display characteristic double hysteresis loops. For x = 0.04, at a comparatively small applied field of 130 kV/cm, the values of recoverable energy density (Wrec) and efficiency of 0.24 J/cm3 and 84 %, respectively, are obtained. At 190 °C, a Wrec = 0.75 J/cm3 and a very high efficiency of 92 % are obtained at the field of 50 kV/cm. Thus, the prepared material can potentially be used in high-temperature pulsed power capacitors for energy storage applications within the temperature range from room temperature up to 190 °C.

Suitability of capacitor allocation methods in different kinds of distribution networks

In the context of power systems with “a high percentage of renewable energy” and “a high percentage of power electronic equipment”, reactive power capacitors are demanded to support the voltage and keep the economic operation of the distribution network. Reasonable configuration of reactive power compensation including capacitor location and compensation capacity can keep the system voltage at a reasonable level, improve the system voltage stability, and reduce the network loss. In this paper, a reactive power optimization model based on three capacitor allocation methods, namely the reactive power sensitivity method, the active power loss method, and the voltage stability method, was established. Considering the stability and economy of distribution network operation, the suitability of the different methods in different kinds of distribution networks was evaluated in terms of the indicators of minimizing the network loss, minimizing the voltage offset, and minimizing the system operation cost. The simulation results show that the active power loss method is the most suitable for reducing voltage fluctuations and network losses.

ENSURING THE THREAD CAPACITY OF ELECTRICAL TRANSMISSION LINES UNDER THE CONDITIONS OF THEIR RESERVATION

A method of increasing the power transmission capacity in the post-emergency mode is considered, when a redundant line is connected to one of the working power transmission lines (LEP) with a voltage of 10 kV using the point of automatic switching on of the reserve (AVR). The effectiveness of such redundancy in most cases turns out to be low due to the limited capacity of trunk sections of mutually reserved lines with smaller cross-sections of wires at the end sections of these lines, which were built as radial lines. This leads to increased losses of active power and voltage, and, as a result, unacceptable deviation of voltage in remote load nodes of the redundant power transmission line. In order to improve the parameters of the operation mode of power transmission, it is proposed to use devices of longitudinal capacitive compensation and reactive power compensation in the scheme of the AVR point. An assessment of the effectiveness of the proposed measure was made.

Enhanced energy storage performance of Na0.5Bi0.5TiO3-based relaxor ferroelectric ceramics by synergistic optimization strategies

Despite the fact that Na0.5Bi0.5TiO3 (NBT) based lead-free ceramics have attracted widespread interest due to their various advantages, their lower recoverable energy storage density (Wrec) and energy storage efficiency (η) limit their development in pulsed power capacitors. In this work, we propose a synergistic optimization strategy to enhance the energy storage performance of 0.65Na0.5Bi0.5TiO3-0.35SrTiO3(NBST) based lead-free ceramics by introducing Bi0.8La0.2(Ni0.5Zr0.5)O3 (BLNZ) and employing viscous polymer process (VPP). The former converts the macroscopic domains into microscopic domains, limiting the polarization response hysteresis to give a large Pm–Pr. The latter reduces the thickness and porosity of the samples, resulting in a substantial increase in breakdown strength. Ultimately, by stepwise optimization of this strategy, the x = 0.15 ceramic by VPP (0.15VPP) achieves excellent energy storage performance (Wrec = 7.6 J/cm3, η = 92%) under 620 kV/cm and reliable temperature stability from 20-140 °C. The combined excellent results of this study show that our synergistic optimization strategy can effectively enhance the energy storage performance of NBT-based dielectric ceramics and could be further extended to other ceramic materials for pulsed power capacitors.

Fault Ride-Through Method for Interline Power Flow Controller Based on DC Current Limiter

The interline power flow controller (IPFC) based on a modular multilevel converter with a half-bridge configuration can control the active and reactive power flows of multiple alternating current (AC) lines. However, it forms a multiterminal system on the direct current (DC) side, which leads to DC faults. To reduce the protection and clearance requirements on the DC side of IPFCs, this paper proposes a hybrid current limiter topology suitable for generating a DC-side fault ride-through scheme. The current limiter employs a low-loss branch in steady-state conditions; when the fault occurs, a commutation capacitor and controllable power electronic devices are used to transfer the fault current to the current-limiting branch. To clarify the operating principles of the current limiter, the working states of each stage and electrical stress of each device are analyzed. Different components with varying limiter parameters are also discussed, and optimal parameters to achieve the best limitation effect are discussed. PSCAD simulations show that the proposed limiter can limit the overcurrent effectively, and DC-side fault clearance can be achieved easily with this fault ride-through strategy.

A Critical Review of Compensation Converters for Capacitive Power Transfer in Wireless Electric Vehicle Charging Circuit Topologies

A Critical Review of Compensation Converters for Capacitive Power Transfer in Wireless Electric Vehicle Charging Circuit Topologies

A case study on transformer ferroresonance for subsea cable connected 230 kV substations using PSCAD

This research paper presents a comprehensive procedure on how to perform a ferroresonance study in a system dealing with the addition of subsea cable interconnector-2 between two 230 kV substations which is previously linked by subsea cable interconnector-1. Addition of a subsea cable interconnector-2 needs to be investigated for ferroresonance in planning and designing stages itself since the interaction between cable capacitive reactance and power transformers-magnetizing core which is a non-linear inductance may cause ferroresonance. The investigation is conducted in three stages namely energisation, de-energisation and stuck pole conditions of circuit breaker. Each stage concentrates on the overvoltage patterns as ferroresonance is characterized by overvoltage. The analysis is conducted in PSCAD/EMTDC software and the modelling of entire study network is done according to the CIGRE WG C4.307. The maximum overvoltage for each stage is found by performing 200 cases of statistical simulation and it is compared with the rated withstand voltage of the equipment. Through a rigorous analysis of overvoltage characteristics under different scenarios, suggestion has been given whether the subsea cable interconnector-2 can be safely operated during the studied cases without the risk of ferroresonance.

Dielectric properties and excellent energy storage density under low electric fields for high entropy relaxor ferroelectric (Li0.2Ca0.2Sr0.2Ba0.2La0.2)TiO3 ceramic

High entropy relaxor ferroelectrics, are a representative type of dielectric with exceptional properties and play an indispensable role in the next-generation pulsed power capacitor market. In this paper, a high-entropy relaxor ferroelectric ceramic (Li0.2Ca0.2Sr0.2Ba0.2La0.2)TiO3 successfully designed and synthesized using the traditional solid-state reaction method. The microstructure, dielectric properties, and energy storage characteristics of the ceramics were systematically investigated. The ceramic exhibited a dense microstructure with a single-phase perovskite structure and small grain size. The unique microstructure and high insulation not only wides the band gap, but also minimizes residual polarization and resulting in higher energy density (Eb) 1.51 J/cm3 and efficiency (η) of 89.6% at a low field strength of 260 kV/cm. Furthermore, the observed anomalous behavior in dielectric relaxation was explained within the context of high entropy ceramics. The material also exhibited excellent temperature/frequency stability and fast charging-discharging speed (∼35 ns). These results demonstrate the effectiveness of high entropy strategy to develop high-performance energy storage capacitors.

Optimal voltage set-point of automatic tap changer transformers and generators and reactive power compensation to increase power system predictability

In recent years, renewable energy sources (RESs) such as wind turbines (WTs) have received much attention in both the operating and planning of power systems. These sources have caused many uncertainties in the operation of power systems due to their unpredictable nature. Mentioned uncertainties besides load demands uncertainty, and possible failures in power system components, make the system state unpredictable. The operational decisions are completely challenging in these situations. Any efforts to increase the network operator awareness from the system state will be completely valuable for making accurate decisions.This paper tries to increase the predictability of the power system state through optimal regulating of the voltage setpoint of automatic tap changer transformers and generators besides the reactive power of shunt capacitors. However, conventional objectives such as decreasing losses are considered, simultaneously. This paper uses the K-medoids data clustering method to evaluate the effect of uncertainties. Also, the correlation between input uncertain variables is considered and handled by the Cholesky decomposition technique combined with the Nataf transformation technique. The multi-objective optimization problem is tackled using an improved version of the non-dominated sorting genetic algorithm (NSGA-II). To ensure for validity of the results, studies are repeated using the multi-objective particle swarm optimization (MOPSO) algorithm as another evolutionary-based method.The proposed approach is applied to the IEEE 14 and 30 bus standard system. The results showed that the predictability of the power system can be considerably increased while keeping the losses approximately at its minimum amount.

Capacitive Wireless Power Transfer System with Misalignment Tolerance in Flowing Freshwater Environments

Capacitive Wireless Power Transfer System with Misalignment Tolerance in Flowing Freshwater Environments

Nonisolation Model and Load Virtual-Grounding Design Method for Capacitive Power Transfer System With Asymmetric Four-Plate Coupling Interface

Nonisolation Model and Load Virtual-Grounding Design Method for Capacitive Power Transfer System With Asymmetric Four-Plate Coupling Interface

Modeling, simulation and experimental validation of solid media in capacitive wireless power transfer

Capacitive wireless power transfer (CPT) employs an electric field to transmit energy through a medium. Air is the most often used and a well-understood medium. However, CPT can also bridge other solid media and even benefit from them as the dielectric properties of the medium govern the strength of the capacitive coupling. The parasitic elements of the coupling are influenced by the medium, in particular the leakage resistance. In this work, an analytical model is proposed that quantifies the leakage resistance losses in CPT systems for media. The model is validated by both finite element simulations and experiments on three different media: air, plexiglass and polytetrafluorideethylene (PTFE). As a result, at 1 MHz, the leakage resistance of plexiglass is 6 times higher than that of air while that of PTFE is 1.7 times smaller. This proves that a material with a large dipole moment generates larger losses in the medium which negatively affect system efficiency.

Arrangement for reliable power supply to emergency commercial customers with techno-economic performance improvement of PV enhanced distribution systems

Accelerating engagement of distributed energy resources unleashed the dependency on traditional electric power generation. To reduce the craving for traditional power dependency and unplanned outages the power distribution sectors are gradually adopting cleaner and reliable electrification. However, the unscheduled and unorganized engagement of stochastic generation from renewable energy sources (RES) makes the distribution system operation more vulnerable. For reliable and continuous power supply with RES, scheduled operation of BSSs and power capacitor (CAP) units can be integrated to provide emergency power supply support to consumers. In this paper, the supply of continuous and reliable power to commercial and emergency customers has been investigated subject to complete reliability (CR). The benefit-to-cost ratio (BCR) has been maximized to give reliable power to consumers by the minimum investment cost by utility, which can benefit both electric customers and power distribution operators in a single platform. The maximization of BCR has been evaluated by optimal S-CDS of the BSSs and S-S of CAP units’ operation through the PSO technique in the considered 28-bus active distribution network in different seasons. The techno-economic benefit of integrating only BSSs and BSSs with CAP units in the prospective locations has been analyzed. The improvement in battery life and decrease in SAENS, SADPL, and SADD have been obtained, which shows the efficacy of the proposed work.

Compact inductive and capacitive combined wireless power transfer system for unmanned aerial vehicle applications

Compact inductive and capacitive combined wireless power transfer system for unmanned aerial vehicle applications

Incorporating Gadolinium Oxide (Gd2O3) as a Rare Earth Metal Oxide in Carbon Nanofiber Skeleton for Supercapacitor Application

AbstractIn this study, we synthesized gadolinium oxide nanoparticles (Gd2O3 NPs) incorporated heteroatom‐doped microporous carbon nanofibers (CNF) to serve as electrode materials for enhancing supercapacitive energy storage. Our primary focus is on elucidating the impact of these hybrid electrode materials on key supercapacitor performance properties such as specific capacitance, specific energy, and specific power. To comprehensively assess the structural and chemical attributes of Gd2O3 NPs‐incorporated heteroatom‐doped microporous CNFs (CNF/Gd2O3) we employed an array of advanced characterization techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy (RAMAN), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS). Our research has yielded impressive results, demonstrating a significant increase in supercapacitive performance. Specifically, the CNF/Gd2O3‐1 symmetric supercapacitor cell (SSC) has demonstrated a good specific capacitance of 162.3 F/g and a high specific energy of 8.12 Wh/kg at a specific power of 300 W/kg. These findings could be a new pathway to prepare composite electrodes for use in energy storage applications and promote further development for other rare‐earth nanostructures.

Enhanced energy storage properties in BNST-based lead-free relaxor ferroelectric ceramics achieved via a high-entropy strategy

The 0.65(Bi0.5Na0.5)TiO3–0.35SrTiO3-based materials are essential for the development of pulse power capacitors. However, their low recoverable energy storage density and breakdown field strength have hindered further improvement. To address this, a high-entropy strategy based on multiscale regulation is proposed, which involves synergistically manipulating the activation energy and microstructure evolution in BNST-based ceramics through the introduction of Ba(Zr0.2Ti0.2Sn0.2Hf0.2Ta0.2)O3. The inclusion of high-insulating oxides can significantly raise the activation energy of the entire system. Furthermore, the high-entropy material can significantly increase the atomic disorder and lattice distortion, resulting in strong local polar fluctuations on several nanoscales and excellent energy storage characteristics. As a result, this approach yields an impressive Wrec of ∼ 4.89 J/cm3 and a high efficiency of ∼92.1 % at 351 kV/cm, and the outstanding thermal endurance (20∼150 °C), frequency stability (5∼1000 Hz) and fatigue (100∼105 cycles). This study provides an effective strategy for achieving excellent comprehensive performances in high-entropy ceramics.

Breaking the Mutual Constraint between Polarization and Voltage Resistance with Nanograined High-Entropy Ceramic.

Dielectric ceramics with a high energy storage capacity are key to advanced pulsed power capacitors. However, conventional materials face a mutual constraint between polarization strength and the breakdown strength bottleneck. To address this limitation, the concept of nanograined high-entropy ceramics is introduced in this work. By introducing a large number of constituent elements into the A-site of perovskite material lattice, high-entropy (Bi0.2K0.2Ba0.2Sr0.2Ca0.2)TiO3-0.2 'CuO relaxor ceramic with nanoscale grains have been successfully prepared, which breaks the mutual constraint between polarization strength and breakdown strength bottleneck and results a recoverable energy density (Wrec ∼ 6.86 J/cm3) and an efficiency (η ∼ 87.7%) at 670 kV/cm. Moreover, its excellent stability makes it potentially useful under a variety of extreme conditions, including at high temperatures and high/low frequencies. These obtained results demonstrate that this nanograined high-entropy lead-free perovskite ceramic has great potential for energy storage applications.

A-site disorder induced ferroelectric to relaxor phase transition of Na(Nb0.75Ti0.25)O3 ceramics by Bi3+ for ultra-high energy storage properties

The present work introduces a new insight into effect of A-site disorder to develop the energy storage properties of Na(Nb0.75Ti0.25)O3 ceramic. Lead-free (Na1-xBix)(Nb0.75Ti0.25)O3 (x = 0.0, 0.05 and 0.1) (abbreviated as NNTBx) ceramics were synthesized using solid-state reaction technique. The introduction of Bi3+ shown a significant effect into the crystal structure, dielectric, ferroelectric and energy storage properties of NNT ceramics. The addition of Bi2O3 induced ferroelectric to relaxor phase transition with psedu-cubic crystal structure at 0.1. Significant inhibits of grain size to sub-micrometer has been achieved at 0.1 sample due to lower ionic radius of Bi+3 (1.34 Å, CN=12) to the ionic radius of Na1+ (1.39 Å, CN=12). Meanwhile, the dielectric constant increased from 300 to 1500 when the Bi3+-content increased from 0.0 to 0.1. Effectively increasing in maximum polarization (Pmax) and significant reducing in remnant polarization (Pr) resulting in increasing ΔP (Pmax – Pr) has been obtained at 0.1 content of Bi2O3. This enhancement is attributed to hybridization between Bi3+ 6Pand O2− 2P instead of Na1+ 2S and O2− 3S orbitals. On the other hand, the substitution of monovalent (Na1+) by trivalent (Bi3+) lead to create sodium vacancies into the A-sites of NNT lattice subsequently reducing the Pr value. The tolerance factor (τ) decreased from 0.955 to 0.953 when Bi2O3 increases from 0.0 to 0.1 indicate increasing the cations disorder, charge misfit and relaxor degree of NNT ceramics. The sample with 0.1 of Bi2O3 demonstrate remarkably high energy storage density (Wrec = 17.5 J/cm3), and high relatively energy storage efficiency (n = 80 %) at ultra-high dielectric breakdown strength (Eb = 700 kV/cm). Partially, (NNTB0.1) exhibit an outstanding stability of energy storage properties in terms of temperature (25 to 150 °C) and frequency (2–50 Hz). The variation of Wrec and n were observed about 1 % within the whole range of applied temperature and frequency. These results imply the high potential of (Na0.9Bi0.1)(Nb0.75Ti0.25)O3 ceramic in temperature-stable advanced pulsed power capacitor applications.

Temperature stability lock of high-performance lead-free relaxor ferroelectric ceramics

Lead-free dielectric ceramics are considered a highly promising material for pulse power capacitors due to their excellent energy storage performance. However, it is challenging to achieve high-temperature energy storage performance of dielectric ceramics to meet the needs of practical applications. Here, an effective strategy for constructing temperature stability lock is designed to regulate the phase composition and temperature stability based on the polymorphic polarization structure. By realizing the ergodic-state-dominated metastable relaxation structure, high energy storage performance and temperature-insensitive structure can be achieved in relaxor ferroelectric ceramics. Taking the Bi0.5Na0.5TiO3-based solid solution as an example, we demonstrate the metastable relaxation structure induced by the proportion of phase composition. This leads to a large recoverable energy density (Wrec) of 10.7 J cm−3 and a high efficiency (η) of 91 %. Together with the good thermal stability of Wrec (7.1 ± 0.1 J cm−3) and η (86 ± 5 %) values at 500 kV cm−1 in the temperature range from 20 °C to 200 °C, outperforming all reported Bi0.5Na0.5TiO3-based energy storage ceramics. Our work provides a method for obtaining lead-free dielectric ceramics with high-temperature energy storage performance through temperature stability lock.