High Power Applications Research Articles

Flexible, symmetric supercapacitor using self-stabilized dispersion-polymerised polyaniline/V2O5 hybrid electrodes

Supercapacitors are attracting significant interest owing to their potential in high power applications. The lack of energy density is one of the main drawbacks observed in supercapacitors. A hybrid electrode made from polyaniline (PANi) synthesized by an organic mediated self-stabilized polymerisation method and V2O5 nanoparticles, is introduced in this work and the electrochemical performance is evaluated both in three- and two- electrode symmetric configurations. The incorporation of this high molecular weight PANi with nanostructured V2O5 effectively addresses the shortcomings of these individual materials and exhibits a synergistic effect as evident from the performance of the hybrid electrode. From the different compositions of PANi and V2O5 studied, the PV3 electrode (PANI: V2O5 = 3:1) exhibits the highest gravimetric capacitance of 498 F g−1 at a current density of 1 A g−1. This champion electrode retains 84% of its initial capacitance even at a high current density of 20 A g−1. The symmetric supercapacitor fabricated using this binder-free electrode exhibits a capacitance of 260 F g−1 at a current density of 1 A g−1 and displays a high energy density of 36 Wh kg−1 at a power density of 1 kW kg−1. The symmetric device is also found to be highly flexible and shows a cycling stability of 94.4% even after 10,000 continuous charge–discharge cycles at a current density of 10 A g−1. These results point towards the potential of this hybrid electrode for next generation wearable electronic applications.

Precipitate-domain wall topologies in hardened Li-doped NaNbO3

Ferroelectric hardening is an absolute requirement for potential applications of piezoceramics in high-power devices. A very recent work demonstrates that ferroelectric hardening by pinning domain walls with precipitates introduced during processing is feasible, akin to precipitation hardening in metals. With the precipitation of plate-like LiNbO3 in Li-doped NaNbO3 piezoceramics, ferroelectric hardening was achieved, exhibiting an enhanced mechanical quality factor (Qm). The specific morphology and corresponding orientation of the LiNbO3 platelets, exhibiting {110}PC habit planes, were characterized by transmission electron microscopy (TEM). The experimentally revealed crystallographic structures and strain incompatibility were found to correlate well with the thermodynamic simulation of the minimum-energy aspect ratio. In particular, the topology of the precipitate-domain wall assembly was clarified, revealing a full pinning on the domain walls by the incorporated plate-like precipitates. The revealed topology provides a fundamental basis for future optimization strategies for platelet hardening in new lead-free piezoceramics for high-power applications.

State of The Art In The Practical Implementation, Modeling Methods, and Control Approaches For Modular Multilevel Matrix Converters

The Modular Multilevel Matrix Converter (MMMC) is a novel power converter topology that is ideal for high-power AC applications. Studies have demonstrated that the converter offers various advantages, including modularity, power redundancy, and control flexibility. However, the topology and control system design can be challenging due to the large number of cells and floating capacitors. To maintain acceptable levels of capacitor voltage, multilayer nested control systems are required. There are no existing review papers that have discussed the MMMC's modelling, control systems, and applications. Thus, this paper seeks to provide a comprehensive review of the technology, focusing on the modelling and control strategies, to facilitate further research.

Aberration-induced vortex splitting in amplified orbital angular momentum beams.

Here we report the generation and power amplification of higher-order (l = 2) orbital angular momentum (OAM) beams using a compact end-pumped Nd:YAG Master-Oscillator-Power-Amplifier (MOPA) design. We analysed the thermally-induced wavefront aberrations of the Nd:YAG crystal using a Shack-Hartmann sensor as well as modal decomposition of the field and show that the natural astigmatism in such systems results in the splitting of vortex phase singularities. Finally, we show how this can be ameliorated in the far field through engineering of the Gouy phase, realising an amplified vortex purity of 94% while achieving an amplification enhancement of up to 1200%. Our comprehensive theoretical and experimental investigation will be of value to communities pursuing high-power applications of structured light, from communications to materials processing.

High comprehensive energy storage properties in (Sm, Ti) co-doped sodium niobate ceramics

Ceramic capacitors are ubiquitously used in high power and pulse power applications, but their low energy density, especially at high temperatures (>150 °C), limits their fields of application. One of the reasons is the low energy efficiency under high electric fields and/or at high temperatures. In this work, equimolar Sm3+ and Ti4+ cations were doped in NaNbO3 to increase relaxor characteristics and energy storage properties. The optimal recoverable energy density Wrec of 6.5 J/cm3 and energy efficiency η of 96% were attained in the ceramics with 10% (Sm, Ti) concentration (SmT10). Dense microstructure and low dielectric loss were attributed to the high energy storage performance. Impedance spectra analysis revealed that the grain boundary resistance dominates at low temperatures, while the grain resistance dominates at high temperatures. The ceramics show stable Wrec and η in a broad temperature range of −90 to 200 °C and repeated charge–discharge cycles up to 105. The comprehensive energy storage performance indicates SmT10 ceramics are among potential candidates for ceramic capacitors working at high temperatures.

Analysis of Trapping Effect on Large-Signal Characteristics of GaN HEMTs Using X-Parameters and UV Illumination.

GaN high-electron-mobility transistors (HEMTs) have attracted widespread attention for high-power microwave applications, owing to their superior properties. However, the charge trapping effect has limitations to its performance. To study the trapping effect on the device large-signal behavior, AlGaN/GaN HEMTs and metal-insulator-semiconductor HEMTs (MIS-HEMTs) were characterized through X-parameter measurements under ultraviolet (UV) illumination. For HEMTs without passivation, the magnitude of the large-signal output wave (X21FB) and small-signal forward gain (X2111S) at fundamental frequency increased, whereas the large-signal second harmonic output wave (X22FB) decreased when the device was exposed to UV light, resulting from the photoconductive effect and suppression of buffer-related trapping. For MIS-HEMTs with SiN passivation, much higher X21FB and X2111S have been obtained compared with HEMTs. It suggests that better RF power performance can be achieved by removing the surface state. Moreover, the X-parameters of the MIS-HEMT are less dependent on UV light, since the light-induced performance enhancement is offset by excess traps in the SiN layer excited by UV light. The radio frequency (RF) power parameters and signal waveforms were further obtained based on the X-parameter model. The variation of RF current gain and distortion with light was consistent with the measurement results of X-parameters. Therefore, the trap number in the AlGaN surface, GaN buffer, and SiN layer must be minimized for a good large-signal performance of AlGaN/GaN transistors.

Advanced Rapid Predictive and Modulation Model for PV System

In the real-time case of the power management system, renewable energy improves power generation to reduce demand. Since this type of renewable energy system is not sufficient to generate power to the load with controlled energy in grid systems and other related high-power applications. The existing models refer to the static parameters to control the regulation factor of the DC converter. This leads to a delay in step response and the other related features which will affect the output power with noise and surge peaks. In this work, a novel model of the optimal controlling model was proposed to improve the switching activities of the converter circuit. In this, the DC–DC converter design needs to enhance for reducing the noise at converted DC output. The controller tunes gain the parameters according to the feedback signal dynamically to reduce the step response time. For this process, a rapid model predictive and modulation-based controller with maximum power point tracking analyzer are used to estimate operating point of the PV system and control the switching devices accordingly. This improves the high-frequency switching activities to reduce the noise level in DC output. This can also reduce the noise at DC output. The inverter was connected at the output terminal of DC–DC converter for the AC load components. The space vector pulse width modulation technique was used for driving the inverter switches to reduce the total harmonic distortion from the output waveform to the load terminal. The simulation result and the experimental result show the performance of the proposed controller comparing with traditional controlling models.

A Comprehensive Overview of Power Converter Applied in High-Power Wind Turbine: Key Challenges and Potential Solutions

The increasing penetration of offshore wind power generation promotes the revolution of wind turbine toward high power application. The development of high-power wind turbine undoubtedly poses new technical challenges. This paper presents a comprehensive overview for high-power wind energy conversion system (WECS) from key technique aspects including topologies, stability, reliability, and ancillary service capability, and further investigates the key challenges and potential solutions. The various topologies of power converter applied in high-power wind turbine are first reviewed and discussed. The different semiconductor technology, including recent wide bandgap (WBG) devices, and their potential contributions for offshore high-power converters are discussed. Furthermore, the potential stability issues of high-power WECS are investigated and reviewed. Also, the stabilization control strategies are discussed. Further, the reliability issue and enhancement strategies of high-power WECS are discussed, including condition monitoring, active thermal control strategy and fault-tolerant operation method. In addition, the ancillary service capability of high-power WECS including frequency-active power control capability and voltage-reactive power control capability is reviewed. Finally, the future trends and potential solutions are discussed in this paper.

Evaluation and Modeling of SiC Based Power Converter for Low Temperature Operation

Cryogenic power electronics is regarded as the next step to improve the power converter efficiency and power density. Thus, investigations on component and converter performances under low temperature operations are of great importance. Silicon carbide (SiC) devices have gradually replaced traditional Silicon (Si) devices in high voltage and high power applications. This is due to their fast switching speed and low switching loss. In this article, the performance of SiC device based power converters are investigated under low temperature operation. Firstly, the individual component performances are evaluated under low temperatures. Then, a 600 W resonant converter based DC transformer was built and tested under low temperatures. The efficiency for the tested converter with ferrite cores drops from 97.86% at room temperature (298 K) to 93.44% at 143 K. The converter power loss model under low temperature operation was developed to facilitate the understanding of converter performance at various operating temperatures.

Active Gate Driver for Dynamic Current Balancing of Parallel-Connected SiC MOSFETs

In high-power applications, parallel connection of discrete silicon carbide (SiC) MOSFETs is necessary to increase the current rating. However, the unbalanced dynamic current during switching transient may cause unequal power loss and thermal distribution, which is a great challenge in parallel applications. In this paper, a dynamic current balancing method based on a new active gate driver (AGD) is proposed to improve the current sharing. The principle of the AGD is based on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</i> feedback control and voltage controlled current source to adjust gate drive current of SiC MOSFETs. Therefore, the switching trajectory of the paralleled devices can be changed to achieve current balance. In addition, by using master-slave control strategy, the proposed AGD can be easily used for multiple paralleled devices. The double pulse tests are conducted to verify the effectiveness of the proposed AGD. For two paralleled devices, the turn-on and turn-off switching energy imbalances are reduced from 13.4% and 56.0% (12.1% and 52.9%) to 8.8% and 15.3% (8.0% and 8.8%) by the current source (current sink) circuit. For six paralleled devices, the degrees of turn-on and turn-off switching energy imbalances can be reduced from 21.8% and 16.1% to 11.8% and 7.8% by the proposed AGD. <fn fn-type="other" id="fn3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This work was supported by Key-Area Research and Development Program of Guangdong Province under Grant 2021B0101310004, and the research program sponsored by Eaton. (<i>Corresponding author</i>: <i>Junming Zhang</i>) Y. He, X. Wang, S. Shao, and J. Zhang are with the College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China (e-mail: ; ; ; ). </fn>

PO-01-094 LESION SIZE INDEX-GUIDED HIGH POWER ABLATION FOR PULMONARY VEIN ISOLATION IN PATIENTS WITH PAROXYSMAL ATRIAL FIBRILLATION: PROCEDURAL DATA AND LONG TERM OUTCOME

Lesion size index (LSI) is useful to complete pulmonary vein isolation (PVI) for atrial fibrillation (AF). High-power application with LSI guided ablation strategy (HP-LSI) may shorten the time to complete PVI. However, the long-term outcome for HP-LSI was limited. To assess the rhythm outcome between HPSD and HP-LSI ablation strategies. 147 paroxysmal AF patients who underwent PVI by TactiCath ablation catheter were enrolled retrospectively. The first 80 patients were assigned to high power short duration ablation strategy (HPSD, anterior wall 50W, posterior wall 40 W, 10 seconds for each lesion), and the subsequent 67 patients were applied with HP-LSI strategy (anterior wall 50W/LSI at least 5.0, posterior wall 40W/LSI 4.0 to 4.5, with 20 seconds limited for each lesion). The primary outcome was AF recurrence between groups. PVI time and first-pass isolation rate were considered as the secondary outcome. Over 12 months of follow-up, there was a significantly lower rate of AF recurrence in the HP-LSI group compared to the HPSD group (14.9% vs. 32.5%, p = 0.020). The PVI time was shorter (63.7 minutes vs. 87.7 minutes, p < 0.001), and the first pass isolation rate were higher for both PVs (RPV: 42.2% vs. 13.7%, p = 0.003; LPV: 66.7% vs. 31.4%, p = 0.001) in HP-LSI group than HPSD group. Besides, there were fewer gaps found in several PV segments in the HP-LSI group after the first pass PV circumferential ablation. HP-LSI can shorten PVI time with a higher first-pass isolation rate in both PVs compared to HPSD. HP-LSI guided strategy decreases gap rates both in RPV and LPV. Compared to HPSD, the HP-LSI ablation strategy can result in a durable PVI outcome.

Improved Marx Pulse Generator With Auxiliary Trigger Topology (2022)

Marx multi-stage circuits based on avalanche transistors are widely used in high-power nanosecond pulse applications. In response to the low reliability of the conventional Marx circuit, this paper analyzed the corresponding failure mechanism and discovered that the conduction modes were the main cause of failure. Based on this, a new topology is designed, by changing the conduction mode from "overvoltage switching-on" to "triggering switching-on". The simulation and measurement results show that the new structure has the advantages of high efficiency, stable operation, low output delay and short output pulse front. Meanwhile, to further improve the output efficiency,= a multiplexed stacking solution is designed based on the new structure, and the simulation results show that the output efficiency is up to 95%. The research in this paper can provide solutions for accurate and reliable synchronous triggering of key units such as gas switches in pulsed power systems, and also provide references for the design of high-efficiency nanosecond pulse generators.

High luminous efficiency of a phosphor-in-glass plate by optimization of the glass and phosphor content for high-power LED applications

Generally, white light-emitting diodes (LEDs) are fabricated by combining blue LED chips with yellow phosphors. When fabricating white LEDs, the phosphor is typically mixed with an organic resin and applied to the LED chips as a paste. A phosphor-in-glass (PiG) plate can alternatively be used to address the poor high-temperature reliability of the paste method. However, because pores form in the PiG plate during the sintering process, this method results in a loss of optical efficiency. Accordingly, we aimed to improve the fluidity of glass and light efficiency by optimizing the sintering temperature of the glass powder and the phosphor content respectively for reducing internal porosity in the PiG. In this study, glass powder was sintered at different temperatures to produce glass plates, while also varying the phosphor content to fabricate PiG plates. The optimal light characteristics were realized with a glass sintering temperature of 640 °C and a phosphor content of 20 wt%.

Performance Evaluation and Comparison of Three-Phase and Six-Phase Winding in Ultrahigh-Speed Machine for High-Power Application

This article investigates the influence of multiphase winding topologies in high-power ultra-high-speed machines (HP-UHSM) of 500 kr&#x002F;min. At this speed level, increasing the rotor&#x0027;s magnetic loading excites its critical bending resonances and leads to structural breakdown. On the other hand, increasing the stator&#x0027;s electric loading using the three-phase winding increases unwanted vibrations in a slotted stator and reduces the electromagnetic inter-action of the stator and rotor in a slotless stator. Consequently, the maximum output power level of UHSM (500 kr&#x002F;min or more) is limited to a few hundred watts only in the state-of-the-art. To over-come such a critical limitation, this article proposes a new design methodology for HP-UHSM, where the rotor&#x0027;s bending resonances and centrifugal stresses are restricted by limiting the maximum aspect ratio (<i>L&#x002F;D</i>), and an optimal multiphase winding is adopted in the slotless stator to increase the power level by effective electric loading. Also, a Multiphysics optimization is utilized to obtain the optimum magnetic loading and electric loading, where the bending resonance and other system limits are defined using multi-disciplinary design constraints. It is observed that the multiphase winding provides an added degree of freedom to increase the power level of UHSM without exciting the rotor&#x0027;s bending resonances and structural breakdown. Using the proposed method, a multiphase 2 kW 500 kr&#x002F;min HP-UHSM has been designed for the safety-critical AMEBA system and compared its Multiphysics performance with the three-phase machine having the same volume. Finally, exten-sive experiments are performed on both prototypes to validate the effectiveness of the proposed method. It is shown that the multi-phase HP-UHSM has no critical bending resonance below the 500 kr&#x002F;min, and it has 16.3&#x0025; higher output power with 1.18&#x0025; higher efficiency and 28.6&#x0025; lower back-EMF than the three-phase design.

Designing hybrid-guidance large mode area fiber for high-power lasers

All-solid large-mode-area antiresonant fibers possess unique characteristics of broadband, low-loss transmission of fundamental mode with effective single mode operation. Hinging on the principle, we propose a unique hybrid guidance mechanism, combining antiresonant guidance with total internal reflection-based guidance to design bend-tolerant, ultra large mode field area (>3000 µm2) fibers for high-power laser applications. Low-index rods are strategically interspersed into the antiresonant cladding to enhance the modal confinement in the fiber, resulting in lower confinement loss of the fundamental mode and its increased tolerance to bending and to the refractive index dip caused by non-uniform doping of active ions in the fiber core. We show that total internal reflection guidance greatly helps confine the fundamental mode without masking the characteristic features of antiresonant guidance, like effective single mode operation over broad spectral bandwidth. We present a detailed theoretical analysis to design a bendable, effectively single-moded passive and active hybrid-guidance antiresonant fibers, optimized to work in the 1 µm wavelength band. The design principles are universal and can be extended to shift the operating wavelength to the 2 µm range as well.

Thin Film Thermoelectric Generators for Powerful Applications

The power output of thin film thermoelectric generators (TEG) is not sufficient for large scale applications and is mainly used for low power applications. A thin-film TEG for high-power applications based on a new structure is proposed. The proposed new structure of the TEG ensures the mutual arrangement of flat thermocouples on a thin-film substrate of each layer with the formation of areas of hot and cold junctions, to which heat is efficiently supplied and removed, respectively. Layers are superimposed on each other and stacked in a package. TEGs generate electricity both from the heat of the sun and external heat sources. TEG, due to the high density of thermocouples that generate electricity on the substrates of many layers, generates sufficient power for their use in high-power applications and can be used in various fields as an autonomous source of electricity. Substrates and thermocouples are made of thin films. It is possible to manufacture them in nanoscale.

Numerical study of feature-distribution effects foranti-reflection structured surfaces on binary gratings.

Suppressing Fresnel reflections from dielectric boundaries using periodic and random antireflection structured surfaces (ARSSs) has been vigorously studied as an alternative to thin film coatings for high-power laser applications. A starting point in the design of ARSS profiles is effective medium theory (EMT), approximating the ARSS layer with a thin film of a specific effective permittivity, which has features with subwavelength transverse-scale dimensions, independent of their relative mutual positions or distributions. Using rigorous coupled-wave analysis, we studied the effects of various pseudo-random deterministic transverse feature distributions of ARSS on diffractive surfaces, analyzing the combined performance of the quarter-wave height nanoscale features, superimposed on a binary 50% duty cycle grating. Various distribution designs were investigated at 633nm wavelength for TE and TM polarization states at normal incidence, comparable to EMT fill fractions for a fused silica substrate in air. The results show differences in performance between ARSS transverse feature distributions, exhibiting better overall performance for subwavelength and near-wavelength scaled unit cell periodicities with short auto-correlation lengths, in comparison to equivalent effective permittivity designs that have less complicated profiles. We conclude that structured layers of quarter-wavelength depth and specific feature distributions can outperform conventional periodic subwavelength gratings as antireflection treatments on diffractive optical components.

Effect of TeO2 on optical and 1.06 µm emission in Nd3+-doped phosphate glass for high-power lasers

In this work, we deal with glass composition, 29P2O5+(60−x)ZnO+10Na2O+xTeO2 (x=5−40mol.%) doped with 1 mol.% of Nd2O3. The samples are characterized by x ray diffraction, micro-Raman, optical absorption, and photoluminescence techniques. Refractive index (n) linearly increased with TeO2 content, as well as the optical basicity (Λ) due to the strengthening of the covalent bond between cation and oxide ions. Such information was corroborated by Raman spectra via an increase of non-bridging oxygens. The maximum phonon energy is approximately 1010cm−1, which is lower than reported for P2O5−ZnO−Na2O phosphate glass (1164cm−1). Detailed spectroscopic and luminescent properties based on TeO2 content are discussed. From luminescence spectra, laser parameters were estimated, viz., radiative transition probabilities, radiative lifetimes, branching ratios, and emission cross sections. The results show that the optimal laser emission parameters are obtained for TeO2 content equal to 20 mol.%, which evinces this glass composition as a promising host material for 1.06 µm high-power laser applications.

Development of Integrated Thermoelectric Sensors for Power Components

Power components such as High Electron Mobility Transistors (HEMTs) are used for high power and high frequency applications. These tend to overheat and destroy their packaging and connections to the wire bondings. This paper presents planar micro-thermoelectric sensors (μTESs) developed to measure partial heat flow dissipated by the HEMTs to avoid the HEMTs from reaching critical temperatures. These sensors use the same active materials as well as the same fabrication process as the HEMTs, enabling them to be fabricated simultaneously for a simple integration. The HEMTs’ active layers consist in AlGaN/GaN heterostructures resulting in the formation of a 2D Electron Gas (2DEG) at the interface. Tension factors of 47 mV/(K.mm2) were obtained with these sensors and heat flows of 0.2 W to 7 W were measured.

Impact of the central refractive index dip of fibers on high-power applications

Central refractive index dip is a common phenomenon in the fibers fabricated by the modified chemical vapor deposition (MCVD) technology, which is the main fabrication technique for high-power laser fibers. In this paper, we present a numerical analysis of the dip effect on high-power-related parameters for the first time, to the best of our knowledge. Three aspects including mode field parameter, beam quality, and bending performance are studied under different dip parameters and bending radii. It is found that the dip is possible to increase the effective mode area and the bending loss, which offers a flexible way to suppress the non-linear effects and filter the higher-order modes by optimizing the dip parameters. Besides, different from the mode area and bending loss, beam quality exhibits an interesting trend when the dip radius increases. The results could facilitate a comprehensive understanding of the dip fiber properties, which also offer guidance to evaluate and design the fiber with central refractive index dip for high-power applications.