Power Devices Research Articles

A single-chip PFM-controlled LED driver with 0.5% illuminance variation

A high-efficiency LED driver with the pulse frequency modulation (PFM) control method to generate nearly consistent illuminance is demonstrated in this investigation. The illuminance consistency is achieved by sensing the feedback voltage and the temperature to modulate the on time of power devices such that automatic illuminance regulation is carried out. The recommended LED driver using the PFM control method is featured with an up-and-coming illuminance equalizer. Thus, it does not need any compensation circuit. Utilizing a 0.5-μm High Voltage CMOS process, the prototype has successfully fabricated, occupying 3.2 mm2 of chip area. The measurement outcomes of the chip demonstrate that the current error remains within 1% when the LED output current set at 20 mA. Moreover, the variation in illuminance is exceptionally low, measuring a mere 0.5%. Furthermore, the efficiency reaches 91% verified by the measurement results.

Torque and flux control of induction motors fed by synchronized and symmetrical voltage pulses

SummaryThe low switching frequency in high‐power motor drives is mandatory for reducing thermal stress on power devices but often results in significant current harmonics. Synchronized space vector modulation (SynSVM), a widely used low‐carrier‐ratio PWM strategy, offers a simple implementation and reduced harmonics. However, implementing SynSVM in traditional AC motor current regulation poses challenges due to fixed voltage samples. To address this, a high‐performance control scheme based on SynSVM is proposed in this manuscript. It ensures the stator flux vector follows a predefined trajectory by integrating voltage pulses from the original SynSVM. The basic voltage vector switching is facilitated through high‐frequency monitoring and compensation of torque and flux errors, resulting in a fast torque response. Furthermore, synchronized and symmetrical voltage pulses, inherent in the original SynSVM, are equivalently generated, to effectively mitigate current harmonics. This proposed method liberates designers from the complexities of current regulation based on SynSVM. Both simulations and experiments validate the efficacy of the proposed method.

Rapid detection of capture and emission processes in surface and buffer traps: Understanding dynamic degradation in GaN power devices

This study utilized a rapid detection technique, Isothermal Capture Transient Spectroscopy (ICTS), to identify and evaluate defects related to GaN device surface and buffer traps, and investigated the mechanisms by which they affect the dynamic performance of GaN based devices. Interface states and dielectric bulk traps were analyzed, unveiling distinctive device behavior under positive gate pulse-biased ICTS. The observed S-shaped threshold voltage (VTH) instability and dynamic gate-drain capacitance (CGD) issues were directly associated with these interface states and bulk traps. Negative gate pulse-biased ICTS revealed the presence of logarithmic electron trapping originating from extended electron traps, and spatial wide distributed hole traps within the GaN buffer layer, significantly impacting the dynamic on-resistance (RON) during off-state stress of the devices. The rapid assessment capabilities of this method provide a valuable tool for optimizing GaN epitaxy and manufacturing processes.

Greatly improved energy storage density of SrO2–BaO2–Nb2O5–SiO2–Al2O3–B2O3 glass ceramics by various amount CeO2 doping

Glass ceramic dielectric materials with high power density and high energy density have important application value in the miniaturization and integration of lightweight pulse power devices. In this work, SrO2–BaO2–Nb2O5–SiO2–Al2O3–B2O3 glass ceramics doped with various contents of CeO2 were prepared via high-temperature melting combined with temperature-controlled crystallization process. Results showed that CeO2 doping increased the content of Ba0.27Sr0.75Nb2O5.78 tungsten bronze phase precipitate from the glass matrix in glass ceramics (from 55.7% to 82.2%), thereby increasing dielectric constant of SrO2–BaO2–Nb2O5–SiO2–Al2O3–B2O3 glass ceramics (from 66.5 to 101.9). Besides that, CeO2-doped ceramics exhibited excellent temperature stability and low loss (below 0.015). The highest breakdown strength (1590 kV/cm) and energy density (12.88 J/cm3) were achieved in the ceramic with a CeO2 doping concentration of 3.0 mol.%, being 3.03 times higher than those in undoped glass ceramic. The increase in energy density of the ceramics was attributed to moderate CeO2 doping concentration that improved the crystallinity (from 83.8% to 89.8%) and reduced the interfacial activation energy of the glass ceramics.

Characteristics of 4-inch (100) oriented Mg-doped β-Ga2O3 bulk single crystals grown by a casting method

In this Letter, 4-inch diameter (100) magnesium-doped monoclinic gallium oxide (Mg:β-Ga2O3) bulk single crystals were grown by a casting method. The crystallographic structure, electrical, optical properties, and defects of Mg-doped β-Ga2O3 was thoroughly investigated by XRD rocking curves, AFM, non-contact resistivity measurements, XPS, optical transmission spectra, Raman spectroscopy, and defect-selective chemical etching processes. Comparing to the UID samples, the larger bandgap of 4.75 eV and high resistivity of 3.50×1012 Ω∙cm indicated Mg a proper dopant for fabricating semi-insulating β-Ga2O3 substrates which could be preferred for power devices. XPS spectra exhibited the ability of Mg2+ to inhibit the formation of oxygen vacancy defects in the crystals. Meanwhile, the high crystalline quality and low density of defects demonstrated the advantages of casting method in achieving large-size and high-quality β-Ga2O3 bulk single crystals with changeable resistivity. This result indicates a high potential to achieve high-quality and low-cost substrates which satisfy the requirement of high-performance power electronic devices.

Condition Assessment of Electrical Power Devices using Infrared Thermography: A Review

Departures from the stable operation of electrical equipment usually appear as changes in parameters such as vibrations, pressure, temperature, power, and flow. Excessive changes in these parameters will indicate significant damage, leading to total or partial breakdown of equipment. This paper reviews the use of infrared thermography (IRT) for the operating condition temperature monitoring of electrical equipment. Infrared thermography is a contactless method that is based on thermal radiation principles and used for determining the temperature distribution on the surface of objects by measuring the intensity of radiation emitted by the object. The basic principles underlying IRT are presented in this review, showing its pros and cons, the various IRT methods, processes involved in IRT image acquisition, intelligent techniques for IR image analysis, and factors that affect the accuracy of results, including technical, environmental, and procedural factors. Also presented is an overview of common applications of IRT condition monitoring to solar energy, medicine, civil infrastructure, and aerospace equipment. Common faults in electrical equipment, including those in transformers, circuit breakers, feeder pillars and arrestors, are discussed with illustrations from recent research studies. These studies have demonstrated the effectiveness of IRT in the predictive maintenance of electrical installations. Hence, the replication of the techniques reviewed in this work is recommended so as to reduce current costs incurred in maintaining and replacing damaged equipment, and the associated time losses.

Control and Analysis of a Hybrid-Rotor Bearingless Switched Reluctance Motor with One-Phase Full-Period Suspension

In the traditional control scheme of a 12/8-pole bearingless switched reluctance motor (BSRM), radial force and torque are usually controlled as a compromise due to the conflict between their effective output areas. Additionally, each phase requires individual power circuits and is excited in turn to produce a continuous levitation force, resulting in high power device requirements and high controller costs. This paper discusses a 12/8-pole single-winding hybrid-rotor bearingless switched reluctance motor (HBSRM) with a hybrid rotor consisting of cylindrical and salient-pole lamination segments. The asymmetric rotor of the HBSRM slightly increases the complexity of its structure and magnetic circuit, but makes it possible to generate the desired radial force at any rotor angular position. A control scheme for the HBSRM is developed to utilize the independent excitation of the four windings in one phase to generate the desired levitation force at any rotor angular position, and it requires only half the number of power circuits used in the conventional control scheme of a 12/8-pole single-winding BSRM. Different from the average torque chosen to be controlled in traditional methods, this scheme directly regulates the instantaneous total torque produced by all excited phases together and presents a current algorithm to optimize the torque contribution of each phase so as to reduce torque pulsation, and the improved performance of this bearingless motor is finally validated by simulation analysis.

Application of UV/O3 treatment enhancing the performance of Sb2Se3 thin-film solar cells

Because of its exceptional photoelectric qualities, exceptional stability, and plentiful element resources, the antimony selenide (Sb2Se3) can be used as an absorber layer. The performance of solar cells needs to be further improved. Comprehending the various surface treatment conditions is instrumental in optimizing device performance. In this research, we pre-treated the fluorine-doped tin oxide (FTO) surface with ultraviolet ozone (UV/O3) and investigated how the device (FTO/CdS (53 nm)/Sb2Se3(203 nm)/Spiro(120 nm)/Au(80 nm)) performance was affected by temperature of the substrate during the UV/O3 treatment. It's interesting to note that the solar cells made with FTO after exposure to UV/O3 have better interface quality and lower recombination losses, which significantly improves the Open circuit voltage (VOC) and Fill factor (FF). The result is an improvement in the device's Power Conversion Efficiency (PCE) from 7.13% to 8.14%. The work is aimed at developing an efficient strategy to improve the performance of Sb2Se3 solar cells.

Impact of urban shielding on radiological risk after a hypothetical nuclear event

Nuclear events have always represented a threat to societies, and nowadays, the concept of tactical nuclear weapons occupies a prominent place in the field of concern. The actual use of such a weapon has not yet been recorded. However, studies involving computationally simulated hypothetical scenarios are periodically published. This study considers a hypothetical event involving the activation of a tactical nuclear device in an urban area. The central objective was to evaluate the protective capacity of urban structures (buildings) for reducing the radiation dose to which the population may be subjected. Analytical computational simulation was applied to create the event. The threshold dose for deterministic effects is the interest isodose for the scenario that considers a 10 kT power device. The concept of Margin of Safety (MoS) was applied to the results in order to turn them into useful information for decision-makers. Applying MoS allowed to organize the urban structures according to their dose reduction capacity (reduction factors). It can be foreseen that in the case of a real application, the proposed methodology will facilitate the classification of structures distributed throughout the urban area, supporting the decision, especially regarding the prioritization of urban zones, and the type of structure. The results showed that it is useful to discriminate urban structures according to criteria conditioned on radiation doses related to deterministic effects. The discrimination introduces scientific basis to advice and support for decision-making, which may increase confidence levels for decision-makers. Therefore a possible positive impact on the optimization of resources and improved conditions for crisis management can be expected.

Mixtures of regressions using matrix-variate heavy-tailed distributions

AbstractFinite mixtures of regressions (FMRs) are powerful clustering devices used in many regression-type analyses. Unfortunately, real data often present atypical observations that make the commonly adopted normality assumption of the mixture components inadequate. Thus, to robustify the FMR approach in a matrix-variate framework, we introduce ten FMRs based on the matrix-variate t and contaminated normal distributions. Furthermore, once one of our models is estimated and the observations are assigned to the groups, different procedures can be used for the detection of the atypical points in the data. An ECM algorithm is outlined for maximum likelihood parameter estimation. By using simulated data, we show the negative consequences (in terms of parameter estimates and inferred classification) of the wrong normality assumption in the presence of heavy-tailed clusters or noisy matrices. Such issues are properly addressed by our models instead. Additionally, over the same data, the atypical points detection procedures are also investigated. A real-data analysis concerning the relationship between greenhouse gas emissions and their determinants is conducted, and the behavior of our models in the presence of heterogeneity and atypical observations is discussed.

Robust residual convolutional neural network based pupil tracking for low-computational power applications

Existing Deep Fully Convolutional Network (DFCN) based pupil segmentation models have been shown to perform robust and accurate pupil detection. However, they lack high computational resources when real-time predictions for low computational wearable devices such as Raspberry Pi are of interest. Simple FCN (Fully Convolutional Network) models, on the other hand, can provide real-time yet not as accurate predictions with low computational power devices. In this study, we address this dilemma by proposing a CNN (Convolutional Neural Network)-based model, Residual CNN, with several advanced operations such as residual connections, Squeeze and Excitation (SE) attention, and Atrous Spatial Pyramid Pooling (ASPP) to improve the prediction performance without complicating the model. Moreover, we leverage transfer learning by training synthetic images, then fine-tuning them with authentic eye images. We also fully quantize our model parameters to speed up the predictions and apply the Quantization Aware Training (QAT) strategy to obtain accurate predictions. Our experiments show that our quantized Res-CNN model trained by QAT strategy with 40x30 resolution images provides robust yet real-time predictions with an average of 1.351 Root Mean Square Error (RMSE) for the pupil center predictions and 8.317 ms response time per image on Raspberry Pi.

A multi‐objective optimization approach for modeling and analyzing the impact of drive parameters in SiC power converters

SummaryThis paper introduces an equivalent model including the parasitic parameters analysis of silicon carbide (SiC) MOSFETs in order to enhance their performance for high‐power density applications. The model is used to establish a mechanism that evaluates the effect of drive parameters on switching losses and electrical stress of power devices, providing a theoretical basis for optimizing the design of drive parameters. The paper finds the Pareto solution of the multi‐objective optimization model through iterative calculation of design variables, using this mechanism. The methodology is validated through experimental results from an SiC power prototype, showing an efficiency of 98.9% and safe electrical stress levels under 1500 V/100 kW operating conditions.

An optrode array for spatiotemporally-precise large-scale optogenetic stimulation of deep cortical layers in non-human primates

Optogenetics has transformed studies of neural circuit function, but remains challenging to apply to non-human primates (NHPs). A major challenge is delivering intense, spatiotemporally-precise, patterned photostimulation across large volumes in deep tissue. Such stimulation is critical, for example, to modulate selectively deep-layer corticocortical feedback circuits. To address this need, we have developed the Utah Optrode Array (UOA), a 10×10 glass needle waveguide array fabricated atop a novel opaque optical interposer, and bonded to an electrically addressable µLED array. In vivo experiments with the UOA demonstrated large-scale, spatiotemporally precise, activation of deep circuits in NHP cortex. Specifically, the UOA permitted both focal (confined to single layers/columns), and widespread (multiple layers/columns) optogenetic activation of deep layer neurons, as assessed with multi-channel laminar electrode arrays, simply by varying the number of activated µLEDs and/or the irradiance. Thus, the UOA represents a powerful optoelectronic device for targeted manipulation of deep-layer circuits in NHP models.

Local outlier factor based condition monitoring for sub-module capacitors in modular multilevel converters

Modular multilevel converters (MMC) as a key technology for future power grids is rapidly developing. The failure rate of sub-module (SM) capacitors is only lower than that of power devices in MMC, so accurate evaluation of the reliability of capacitors is crucial for the safe operation of MMC. Both the increase of equivalent series resistance (ESR) and decrease of equivalent series capacitance (ESC) are features for capacitor deteriorating. ESC or ESR of the capacitor reaching to limited values indicates that the end of its lifespan and it must be replaced. Most of contemporary researches only focus on ESC or ESR. This article considering the characteristics of both ESC and ESR, proposes a method for monitoring the status of SM capacitors based on machine learning algorithm: local outlier factor (LOF). By utilizing the existing SM switching function and capacitor voltage signals within a fundamental frequency cycle in the control system of MMC, the proposed strategy can not only monitor the faulty capacitors, but also can sort the degrees of abnormal states of capacitors, and the strategy is applicable to MMC with single and multiple types of SM topologies. The proposed method is verified by the hybrid MMC model on Matlab/Simulink.

Strategy to solve the thermal issue of ultra-wide bandgap semiconductor gallium oxide field effect transistor

Gallium Oxide (Ga2O3) holds significant potential for the next generation of electronic devices following SiC and GaN due to its ultra-wide bandgap of approximately 4.5 eV - 4.9 eV and high theoretical critical breakdown field strength of 8 MV/cm. Nonetheless, Ga2O3 has a naturally low thermal conductivity, resulting in limited device output performance and hindering Ga2O3 devices from reaching their full theoretical potential. In this study, we demonstrate that the appropriate thermal management strategy can solve the above challenges. By comparing the thermal control schemes including the Ga2O3 FET devices on the original substrate, the thinned Ga2O3 substrate, the high thermal conductivity substrate, the heat sink packaging, and the flip-chip packaging, it is demonstrated that the flip-chip model is the most effective strategy to improve the heat dissipation performance of the Ga2O3 device. By utilizing the appropriate carrier in flip-chip packaging, the temperature elevation of the device at 2 W/mm power density will be diminished by around 91% in contrast to the initial basic device. Furthermore, the output performance of the device demonstrates significant enhancement. This thermal management technique successfully resolves the severe heat dissipation issue prevalent in Ga2O3 devices and eliminates primary obstacles concerning the industrialization of Ga2O3 RF and power devices.

Spatter reduction in deep penetration welding of pure copper using blue-IR hybrid laser

Bead-on-plate welding of pure copper with a blue-IR hybrid laser was conducted to achieve a spatter suppression in deep penetration welding of pure copper for the performance improvement of battery and power device of e-mobility. This hybrid laser combines an infrared (IR) laser and a blue diode laser as the welding source and preheating source, respectively. Preheating increases the light absorptivity of pure copper in the IR region. A 1.5-kW blue diode laser was employed to increase the light absorptivity by changing the phase of the preheated area from solid phase to liquid and gas phase. By experimentally investigating the influence of the blue diode laser intensity, the phase effects of the preheated area on pure copper welding with a blue-IR hybrid laser are elucidated. As a result, it was found that a liquid preheated area minimizes spatter during deep penetration welding.

Impact of carbon injection in 4H-SiC on defect formation and minority carrier lifetime

Point defects in silicon carbide (SiC) can act as charge carrier traps and have a pronounced impact on material properties such as the mobility and carrier lifetime. Prominent among these traps is the carbon vacancy (VC) with a demonstrated detrimental effect on the minority carrier lifetime in 4H-SiC epitaxial layers. Hence, a variety of methods for VC removal have been proposed. Common to all is that they involve some sort of C-injection into the epi-layer that leads to annihilation of VC with C interstitials (Ci) via the reaction Ci＋ VC→0̸. However, many studies on injection of Ci for removal of VC do not take into account the potential effect of any additional defects that are formed as a result of excess C in the material, including electrically active defects that introduce energy levels in the SiC band gap. Herein, we study the formation and impact of carbon related defects that are introduced in 4H-SiC epi-layers by injection of excess carbon. C-injection is achieved by annealing 4H-SiC epi-layers covered by a graphitized photoresist known as a C-cap at 1250°C for different durations. The resulting appearance of defects in the samples is monitored using deep level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS) measurements, which reveal the formation of both minority and majority carrier traps as a result of the C-injection. Intriguingly, the injected carbon is also found to interact with a perennially present impurity in 4H-SiC epi-layers and a potentially lifetime limiting defect, namely boron. Furthermore, we monitor the minority carrier lifetime as a function of C-injection time and depth from the surface using cross-sectional time-resolved photoluminescence (TRPL) measurements. Both the defect distributions and the minority carrier lifetime are found to depend strongly on the duration of the C-cap anneal, with a marked depth dependence being present for all samples studied. The moderate temperature C-cap annealing treatment is proposed as a method for enhancing the carrier lifetime in n-type 4H-SiC epi-layers for power device applications.

Realization of High‐Resistive Ni‐Doped GaN Crystal by Hydride Vapor‐Phase Epitaxy

Herein, high‐resistivity GaN is studied for use as an epitaxial substrate in lateral power devices. Fe‐, C‐, Mn‐, and Zn‐doped GaN monocrystals have high resistivity at a doping concentration of ≈1 × 1018 cm−3. However, a low doping concentration is preferred for growing GaN monocrystals; therefore, other dopants for GaN that yield high resistivity at a doping concentration less than 1 × 1018 cm−3 must be identified. Herein, NiCl2 is used as a precursor to grow Ni‐doped GaN monocrystals on GaN substrates via hydride vapor‐phase epitaxy. Two Ni‐doped GaN substrates with Ni concentrations corresponding to 2.7 × 1017 and 2.9 × 1018 cm−3 are obtained by varying the partial pressure of NiCl2. The resistivity of Ni‐doped GaN monocrystals is measured as a function of temperature using Hall effect measurements. The GaN monocrystals doped with 2.7 × 1017 cm−3 of Ni have a higher resistivity than those doped with 2.9 × 1018 cm−3 of Ni at 600–900 K. Charge‐neutrality calculations have shown that the depth of the Ni acceptor level in GaN is 1.4–1.5 eV, indicating that Ni‐doped GaN monocrystals have high resistivity owing to the deep acceptor level of Ni.

GaN Drift Layers on Sapphire and GaN Substrates for 1.2 kV Class Vertical Power Devices

The development of processes for epitaxial growth of vertical gallium nitride (GaN) drift layers enabling 1.2 kV breakdown voltage on low‐cost sapphire substrates is presented in comparison to GaN bulk substrates. The targeted blocking capability demands drift layers with a thickness of 10 μm and low but controllable n‐type doping. Using a growth rate of 2.5 μm h−1 the concentration of unintentionally incorporated carbon is sufficiently low to adjust the n‐type carrier concentration to ≈1 × 1016 cm−3 for all types of substrates. To assess GaN drift region properties in terms of forward bias conductivity and reverse bias blocking strength, a quasi‐vertical p‐n‐diode structure is utilized. Bow reduction of GaN‐on‐sapphire structures is achieved using a stealth laser scribing process. Breakdown voltages higher than 1600 V and a specific on‐state resistance as low as 0.7 mΩ cm2 are obtained with diodes fabricated on GaN substrates. Similar structures grown on sapphire show breakdown voltages of about 1300 V due to higher levels of current leakage. Comparing different types of substrates, a direct correlation between dislocation density in the drift layer with the leakage current in p‐n diodes is deduced.

Gallium Ion Pre‐Insertion Protocol to (NH4)2V10O25·8H2O Cathode Materials for Reversible Aqueous Zn Battery

AbstractVanadate is one of the promising cathode materials for aqueous zinc ion batteries (AZIBs) due to its abundant resources and various valence states. However, the further development is restricted by their sluggish reaction kinetics between zinc ions and the host materials. In this work, several kinds of gallium ions pre‐intercalated vanadate electrode materials through a simple hydrothermal strategy are designed. Ga‐NHVO‐0.5 sample achieves a specific capacity of 438.23 mAh g−1 at current density of 0.2 A g−1. At the same time, it delivers an energy density of 250.34 Wh kg−1 at a power density of 55 W kg−1. The assembled button cells retain 83.84% of its initial capacity after 4000 times cycling, revealing their promising applications in portable power devices. Moreover, the devices still possess a favorable stability under different bending conditions.