Large Power Devices Research Articles

Bio-inspired pulsed power switch under shock wave

The spark gap switch is a crucial component in the primary energy drive system for large pulse power devices. The switch electrodes are composed of high-density artificial graphite, possessing excellent erosion resistance. However, insufficient mechanical strength in the graphite electrodes makes them especially susceptible to mechanical damage under the enormous impact force caused by the increasing arc current, which seriously affects the reliability and service life of the switch. The distribution of the shock wave overpressure on the graphite electrode surface is deduced and calculated, and the refraction and reflection process of the shock wave from the air to the graphite interface is analyzed based on the Huygens–Fresnel principle. Furthermore, the doubling of refracted shock wave intensity into the graphite electrode is a preliminary characterization. The propagation process of stress wave after the shock wave enters the electrode is investigated by establishing two conventional graphite electrode structure models, namely T-shape and reverse T-shape, which reveal that severe stress concentration occurs in both structures. Drawing inspiration from the physiological structure of the woodpecker’s head, renowned for its exceptional impact resistance, the macroscopic geometry of the graphite electrode and the assembly structure of the switch have been bionically designed. The simulation results demonstrate that, in comparison to the conventional electrode structure, the bionic electrode structure eliminates stress concentration at the bolt end and electrode corner, while significantly reducing maximum equivalent stress and the degree of the stress concentration on the bottom surface of the electrode. These features contribute to the enhancement of the current capacity and reliability of the spark gap switch.

Optimal Design of Large Signal Performance of AlN/GaN Hetero-Structural IMPATT and MITATT Diodes

Hetero-structure of AlxGa1-xN/GaN exhibits important applications in high frequency and large power devices. In this paper, AlN/GaN is adopted to optimal design the large power impact avalanche transit time (IMPATT) and mixed tunneling avalanche transit time (MITATT) diodes operating at the atmospheric low loss window frequency of 0.85 THz. The static state and large signal characteristics of the devices are numerically simulated. The values of peak electric field strength, break-down voltage, avalanche voltage, the maximum generation rates of avalanche and tunneling, admittance-frequency relation, output power, conversion efficiency, quality factor of the proposed hetero-structural IMPATT and MITATT diodes are calculated, respectively. Via comparing the obtained results of (n)AlN/(p)GaN and (n)GaN/(p)AlN IMPATT diodes to those of the MITATT counterparts, there exists little performance difference between IMPATT and MITATT devices while implies significant difference between the (n)AlN/(p)GaN and (n)GaN/(p)AlN diodes.

Prediction of Nonsinusoidal AC Loss of Superconducting Tapes Using Artificial Intelligence-Based Models

Current is no longer sinusoidal in modern electric networks because of widespread use of power electronic-based equipments and nonlinear loads. Usually AC loss is calculated for pure sinusoidal current, while it is no longer accurate when current is nonsinusoidal. On the other hand, efficiency of cooling system in large scale power devices is dependent on accurate estimation and prediction of the heat load caused by AC loss in design stage. Therefore, estimation of nonsinusoidal AC loss of high temperature superconducting (HTS) material would be of great interest for designers of large-scale superconducting devices. In this paper, at first nonsinusoidal AC loss of a typical HTS tape was calculated under distorted currents using H-formulation finite element method. Then, a range of artificial intelligence (AI) models were implemented to predict AC loss of a typical HTS tape. In order to find the best and more adaptive AI model for nonsinusoidal AC loss prediction, different regression models are evaluated using Support Vector Machine regression model, Generalized Linear regression model, Decision Tree regression model, Feed Forward Neural Network based model, Adaptive Neuro Fuzzy Inference System based model, and Radial Basis Function Neural Network (RBFNN) based model. In order to evaluate robustness of developed models cross-validation technique is implemented on experimental data. To compare the performance of different AI models, four prediction measures were used: Theil's U coefficients (U_Accuracy and U_Quality), Root Mean Square Error (RMSE) and Regression value (R-value). Obtained results show that best performance belongs to RBFNN based model and then ANFIS based model. U coefficients and RMSE values are obtained less than 0.005 and R-Value is become close to one by using RBFNN based model for testing data, which indicates high accuracy prediction performance.

Experimental investigation of galinstan based minichannel cooling for high heat flux and large heat power thermal management

This paper is dedicated to experimentally investigate the liquid galinstan based minichannel cooling for high heat flux and large heat power thermal management. Firstly, a compact electromagnetic pump towards effectively driving liquid metals was developed, which can provide high pressure head up to 100 kPa. Then, the minichannel heat sink was designed and manufactured, with width of channel 1 mm, height of channel 5 mm. Furthermore, the galinstan based minichannel cooling system was established and experimentally tested under different heating loads and pumping powers. The results show that galinstan based minichannel cooling system can dissipate heat with heat flux 300 W/cm2 and heat power 1500 W. And the thermal performance and hydrodynamic characteristic of minichannel heat sink using galinstan as coolant were obtained. It indicates that compared to water based minichannel cooling, galinstan based minichannel cooling can obtain a rather larger heat transfer enhancement, and the pressure losses of galistan based minichannel heat sink is much lower than that of water based microchannel cooling. Moreover, it is also found that heat capacity thermal resistance becomes a rather important factor for the thermal performance of galinstan based minichannel, due to the high thermal conductivity and lower heat capacity of galinstan. Furthermore, the galinstan based minichannel cooling system can operate silently, steadily and smoothly by using electromagnetic pump, which has no moving parts. Overall, the galinstan based minichannel cooling is proven to be a powerful and practical way for the thermal management of high heat flux and large heat power devices.

An analysis of harmonic heating in smart buildings and distribution network implications with increasing non-linear (domestic) load and embedded generation

Harmonic distortion is generally not taken into account within domestic installations and the associated wiring systems, as its potential is considered sufficiently small to be neglected. Standards to limit harmonic manifestations in the low voltage (LV) network are available, but these can be breached as a consequence of advancements in power electronics in some modern household devices contributing higher levels of harmonic distortion than permitted. While these devices individually might not be considered serious in terms of system level harmonic distortion manifestations, electrical equipment failures and insulation failures - increasingly being derived from harmonic cable heating - suggest a different story. A 10% increase in THD in a circuit will result in an increase of 10% in cable heat. Recently, attempts have been made to offer harmonic derating factors for building electrical circuit design in BS7671, but this approach currently prioritizes large power devices. This article explores the need for harmonic considerations during the design stage of electrical services engineering projects. Best practice suggestions, in the context of the dissemination of heat caused by harmonics related to household load deployments/configurations, are also provided based on the analysis conducted with real household data. This is further extended to a practical distribution network where the effect of harmonic heating at the network level is explored. The results suggest that the harmonics in the distribution network can amass to cause a cumulative effect on the network. Furthermore, it can be observed from the results that in a distribution network containing (domestic) solar photo voltaic (PV) systems, the harmonic heating issue can be reduced. This benefit is not without consequence however, as increasing PV penetration does not reduce the harmonic content of the overall system and therefore presents a further concern that may need to be addressed in due time.

Design and Realization of the Explosion-Proof Three-Level Frequency Conversion Equipment for Coal Mine

The realization method of the explosion-proof three-level frequency conversion equipment for coal mine is introduced in this paper. The frequency conversion equipment uses diode clamped three-level inverter unit topology structure, it overcomes some disadvantages of two-level converter that harmonic content of voltage output is higher, electromagnetic interference is serious and on-off loss is higher. The frequency conversion equipment is suitable for coal mine high voltage and large power devices such as draught fan, pumps and belt conveyers.

Infrared Thermography application to functional and failure analysis of electron devices and circuits

In this paper the principal and more important application of Infrared Thermography are discussed. In particular the application of this experimental technique, both in its transient and steady-state mode of operation, are reported and illustrated through a broad set of experiments and examples. Functional application to the characterization of VLSI devices, application to the failure analysis of large area power devices, current monitoring in state-of-art heterojunction and organic devices prove the high potential of this technique.

A step forward in the characterization of the partial discharge phenomenon and the degradation of insulating materials through nonlinear analysis of time series

The partial discharge (PD) phenomenon is an electrical discharge that affects only part of a dielectric connecting two conductors [1]. This process may occur in the vacuoles of solid insulation, in gas bubbles in insulating liquids, or between dielectric layers. PDs can also occur on spikes or sharp edges of metal surfaces. Generally, the PDs affect the insulator integrity only if it persists for a long time. However, the continuous release of small amounts of energy may cause a slow and progressive deterioration of the dielectric that can lead to its final breakdown [2], [3]. The degradation rate depends more or less on the microscopic structure of the dielectric, the production process, the types of electrical stresses, and other operating conditions [4]. At the beginning of the 20th century, the problem was not even recognized. However, after the middle of the century, along with the introduction of new dielectrics, the development of more compact insulators, and a general increase in the operating voltages, diagnostics of PDs have become a primary issue in electrical engineering [5]. Today, measuring PDs is a common practice even in operational medium- and high-voltage devices. The data gathered are useful to determine the weak points of the components before irreversible damage occurs. Thus, PD detection and recognition have become important tools for the evaluation of insulating degradation in large power devices. The phase ϕ, the apparent charge q, and the occurrence n have generally been accepted as the basic parameters for the pattern recognition of PDs by means of the standardized algorithm termed phase-resolved PD analysis (PRPDA) [6].

An aqueous rechargeable lithium battery of excellent rate capability based on a nanocomposite of MoO3 coated with PPy and LiMn2O4

A nanocomposite of MoO3 coated with polypyrrole (PPy) was prepared as an anode material for ARLBs. When nanochain LiMn2O4 is used as the cathode, the ARLB can deliver an energy density of 45 Wh kg−1 at 350 W kg−1 and even maintain 38 Wh kg−1 at 6 kW kg−1 in 0.5 M Li2SO4 aqueous electrolyte, corresponding to an good rate capability. In addition, its cycling behavior is greatly improved compared with the virginal MoO3. Our findings provide valuable clues to improve the comprehensive performance of ARLBs for practical application. This unique performance demonstrates that this battery will be of great promise as a power source for large power devices such as power loading and the storage of solar and wind energies.

Fluxless bonding of silicon wafers to molybdenum substrates using electroplated tin-rich solder

A novel fluxless bonding process of silicon wafer on molybdenum substrate is successfully developed. Si-to-Mo bonding can be used for packaging power devices, especially when a device consists of an entire wafer. 300 A Cr layer and 1,000 A Au layer are first deposited on Si wafers and Mo substrates. The Cr/Au dual layer is used as underbump metallurgy and seed layer of electroplating. To reduce plastic shear strain on the solder in a bonded pair, thick Sn layer (70 μm) is electroplated over Mo substrates having Cr/Au structure, followed immediately by thin (0.1 μm) Ag layer. This Ag layer acts as the capping layer to prevent inner Sn from oxidation. The bonding process is performed in 50 millitorrs vacuum to inhibit oxidation. The bonding condition is 290 °C for 15 min without the use of any flux. The bonding layer thickness is controlled at 50 μm by small spacers placed between Si wafer and Mo substrate. Microstructure and composition of the joints are studied under scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Scanning acoustic microscopy (SAM) is also used to verify the quality of joints over the entire sample. Without using any flux, high quality and uniform bonding layer is achieved. The composition of the joint is more than 97 at.% Sn. No intermetallic compound layers exist in the joint. This novel fluxless bonding process should be valuable in packaging large high power devices.

Research on effects of current spreading and optimized contact scheme for high-power GaN-based light-emitting diodes

GaN-based light-emitting diodes (LEDs) grown on sapphire substrate have current transport along the lateral direction due to the insulating nature of the substrate, and the anode and cathode contacts are in a side-by-side configuration. The resistance of the n-type material of the GaN and the lower confinement layer is not negligible, which causes the current to crowd near the edge of the n-contact pad. The current crowding problems will become more severe for large area and high power devices. In this paper, the current spreading effect is qualitatively analyzed. The applied current density and the effective length of the lateral current transport are found to have a considerable effect on the uniform current spreading. Based on these findings, an optimized contact scheme of high-power GaN-based LEDs is proposed to alleviate current crowding effect and reduce the series resistance of the devices. It is clearly shown that the high-power GaN-based flip-chip LEDs with optimized ring-shape interdigitated contact scheme have a relatively uniform temperature distribution by measuring the surface temperature distribution of the device with infrared thermal imaging system. It is confirmed that the current distributes more uniformly over the contact, and current densities in a localized region of the device are reduced, which can decrease the joule heat generated and improve the reliability of the GaN-based LED.

Reverse Biased Electrochemical Etching of SiC-SBD

With development of very-low-micropipe-density substrate, reduction of other device killer defects becomes important for large size power devices. We employed reverse biased electrochemical etching (RECE) method in order to elucidate where the current leaks out in Schottky barrier diode. Low concentration 4H-SiC epi-layer with Al implanted guard rings was electrochemically etched under reverse bias voltage up to 400V in HF-based electrolyte. The surface of the substrate was observed with Nomarski microscopy before and after RECE. In guard ring area, holes appeared which are aligned toward off-direction of the substrate. The length of the aligned holes is about 25μm. The guard ring surrounding the holes were etched uniformly but limited as though there exists a boundary parallel to the steps. In Schottky contact area, not all but some of carrot defects showed an etched feature after RECE. Such etching features are also observed at different position without carrot. We consider that threading screw dislocation is one cause of leakage current in SBD. An etching feature like tangled strings also appeared. Its outer dimension is more than 1mm with thickness of about 50μm. The origin of tangled-string-like feature is not clear yet.

Gallium nitride powerbar transistors with via holes fabricated by laser ablation

Low ohmic through-hole vias are fabricated for AlGaN/GaN HEMT powerbar devices on SiC substrates using laser ablation technique. A complete processing technique has been developed. Through-wafer micro holes with an aspect ratio of 4 were drilled using pulsed UV laser machining. A plating technique on steep side wall could be established. Feasibility and performance of laser drilled via holes were tested with large power devices and proved successful up to the packaging level. The device demonstrated 14 dB of linear gain and a saturated output power of 40 W. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Applications of amorphous magnetic alloys in electronic devices

Some of the features of amorphous magnetic alloys that differentiate them from other soft magnetic materials include: low magnetic loss, fast flux reversal, high electrical resistivity and low acoustic loss. Furthermore, a wide range of B– H characteristics can be obtained through alloy design and heat-treatment of the alloys under different conditions. The versatile properties thus obtained can then be utilized in a number of magnetic applications ranging from large electrical power devices such as transformers and motors to recording heads and to anti-pilferage markers. This paper reviews the applications of various amorphous magnetic alloys in electronic devices including magnetic components in power electronics, telecommunication equipment, automotive parts and sensing devices. Relationships between property requirements and material capabilities are also discussed.

Driving and Protecting Large Die IGBT and MOS Power Devices

SummaryToday’s smart IC gate drivers from various manufacturers simplify the design tasks facing the power system engineers. The increased performance with greater reliability possible with the smart IC gate drivers cannot be ignored. For example, the almost instantaneous (within 200 ns) local shutdown available from a smart IC gate driver can easily protect high gain IGBT devices which can self destruct within 2 μs [1]. Output feedback current sensors or fuses just aren’t fast enough to protect these high gain IGBTs. The importance of proper drive and protection of large die size, high power discrete MOSFETs and IGBTs cannot be overemphasized. Modern single die discrete IGBTs can block up to 1400 V and conduct over 1800 A during a short circuit condition — over 2.5 MW of power dissipation in a little less than 6.5cm2!

Experimental study of AlGaAs/GaAs HBT device design for power applications

An experimental study of AlGaAs/GaAs heterojunction bipolar transistor (HBT) device design for optimizing key DC and RF performance parameters relevant to power device applications is reported. The design of the collector, base, and base-emitter junction is investigated for improved power device performance, and novel device structures are presented. Device scaling effects and the extent to which air-bridged interconnect can reduce parasitics in large power devices are also explored. Power HBTs employing some of the optimized design features have achieved a power output of 1.2 W (4 W/mm) with 43% power-added efficiency at 10 GHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low torque ripple drive of induction motor by multi-step PWN inverter.

In this paper, we propose a novel multi-step PWM inverter useful for the torque ripple reduction of an induction motor. The PWM waveform can be easily obtained by exchanging alternately neighbour two voltage vectors among six output voltage vectors together with a zero voltage vector every 60 degree interval.The basic principle and characteristics of the PWM inverter are shown at first. It is introduced that the harmonics Cn of the PWM voltage waveform approximately has the enough relation of _??_C6m-1/(6m-1)=C6m-1/(6m+1)_??_ to reduce the torque ripple of an induction motor by the cancellation of the 6m order power ripple components arising from the product of a fundamental component and 6m±1 harmonic components of the PWM waveform.And then, the driving characteristics of an induction motor by the proposed PWM inverter are investigated from some simulation and experimental results comparing with the conventional PAM, rectangular PWM and sinusoidal PWM inverter.The features of the PWM technique are high efficiency and low acoustic noise operations for the low torque ripple drive of an induction motor.The PWM technique may be suitable for the induction motor drive using relatively slow and large switching power devices such as GTOs.

Mobility profiling of GaAs power FET's by magnetotransconductance measurements

Mobility profiles of GaAs power MESFET's have been measured using the magnetotransconductance technique. Unlike devices with small gate widths, large periphery power devices exhibit significant parasitic resistance effects, and corrections have to be made. To obtain a realistic mobility profile of the channel, precise measurement of the magnetic field dependence of the transconductance and parasitic resistance is necessary. The technique for obtaining these accurate measurements is detailed. The FET's studied are standard microwave power devices for amplifier circuit applications. Devices having gate peripheries of up to 3.5 mm have been studied, and corrected mobility in the range of 3500-6000 cm2/V . s has been obtained.