High Current Load Research Articles

Zero-Sequence Current Control of Modular Active Power Filter for High Power Three-Phase Three-Wire Electrical Networks

Since the development of the first control strategy for the active power filters (APF) introduced by H. Akagi [H. Akagi, Y. Kanazawa,A. Nabae, Generalized theory of the instantaneous reactive power in three-phase circuits, in: Proceedings of International Power Electronics Conference, Tokyo, Japan (1983) 1375–1386.], many efforts have been concentrated to improve their performances. However, when electrical networks supplies high current non-linear loads, a single inverter-based APF has limited power capability. In this paper, we studied parallel operation achieving high power level. More particularly, we examined a modular APF based on two three-phase inverters. This structure allows zero-sequence current circulating through the inverters, as demonstrated by using averaged modelling of the APF. To solve this problem and based on previous averaged model, we proposed a new optimal control strategy, suppressing the zero-sequence circulating current. Simulation results validate the proposed control.

Analysis of the oxygen reduction process on SOFC composite electrodes

The electrochemical characteristics of composite cathodes consisting of Lanthanum Strontium Manganite (LSM) and Yttria Stabilised Zirconia (YSZ) have been analysed in order to emphasise the opportunity offered by these electrodes in the attempt to reduce the temperature of solid oxide fuel cells. Impedance analysis and potentiodynamic polarisation have been used as tools to evaluate the main electrochemical parameters and the results show that a volume ratio between LSM and YSZ close to 1 gives the best electrochemical activity because of the extension of the three phase boundary (TPB) in the electrode. Electrodes of this composition were subjected to high current load to verify the stability of the electrochemical performance and the results confirmed good cathode reliability.

Electrical Current Phase Transformation of Sn–9Zn–1Ag Alloy

The current load not only easily induces the electromigration effect and thermal strain, but also destroys the effectiveness of solders. As of now, temperature and phase transformation problems caused by the high current load have still not been discussed. This study investigates the structural characteristics of the Sn–9Zn–1Ag alloy under an electrical current test and heat-treatment. The results indicate that the Ag existed mostly in Ag–Zn compounds, and the Zn concentration in the Ag–Zn compounds was higher than in the needle-like Zn-rich phase and Sn–Zn eutectic phase. The Sn–9Zn–1Ag alloy had no transformation during oil heat-treatment, while the structure underwent phase transformation under electrical current testing. After current testing, the needle-like Zn-rich phases had decomposed into finer particle-like features, the Ag–Zn compounds had grown and the Sn–Zn eutectic phases had increased, and the content of Sn-rich phase had decreased. Meanwhile, the current effect also caused the content of Sn to increase but Zn and O both decreased for the Zn-rich (SZO) phases in the relative composition.

Degradation of SOFC Single Cells Under Severe Current Cycles

In this contribution, the degradation of solid oxide fuel cells (SOFC) is accelerated by means of high current load cycles. The ageing phenomena are studied and characterised by material analyses. The results show that degradation of cell performance is mainly caused by the delamination of the cathode layer. The accumulated delamination is ascribed to a loss in mechanical stability at the cathode-electrolyte interface. We find that the interface adhesion is degraded due to the formation of lanthanum zirconate between the cathode and electrolyte. This process is intensified by current density. Therefore, our contribution is of particular interest for the stability of the (La,Sr)MnO 3 -zirconia system. Furthermore, the results are an important preparatory step for applying Accelerated Life Testing (ALT) to SOFCs. In reliability engineering, ALT is a well known method that allows rapid lifetime evaluation.

Templated mesoporous carbons for supercapacitor application

Mesoporous carbons prepared by an inverse replica technique have been used as electrodes for electrochemical capacitors. Such well-sized carbons were prepared from mesostructured SBA-16 silica materials that served as templates whereas polyfurfuryl alcohol was the carbon precursor. Two highly mesoporous carbons characterized by 3 and 8 nm average pore diameter were tested in various electrolytic solutions (acidic, alkaline and aprotic). It can be concluded that templated mesoporous carbons with tailored pore size distribution are very promising materials to be used as electrodes in supercapacitors. The design of their pore size allows suiting the dimensions of electrolyte ions and efficient charging of the electrical double layer is achieved especially at high current load. Definitively better capacitance performance has been found for carbon with 3 nm pores range, however, cycling performance depends not only on the pore size.

Exciton–dopant and exciton–charge interactions in electronically doped OLEDs

The electronic dopants, like tetrafluorocyanoquinodimethane (F 4–TCNQ) molecules, used for p-doping of hole transport layers in organic light-emitting diodes (OLEDs) are found to quench the electroluminescence (EL) if they diffuse into the emissive layer. We observed EL quenching in OLED with F 4-TCNQ doped N,N′-diphenyl-N′N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine hole transport layer at large dopant concentrations, >5%. To separate the effects of exciton–dopant quenching, from exciton–polaron quenching we have intentionally doped the emissive layer of (8-tris-hydroxyquinoline) with three acceptors (A) of different electron affinities: F 4-TCNQ, TCNQ, and C 60, and found that C 60 is the strongest EL-quencher, while F 4-TCNQ is the weakest, contrary to intuitive expectations. The new effects of charge transfer and usually considered energy transfer from exciton to neutral (A) and charged acceptors (A −) are compared as channels for non-radiative Ex–A decay. At high current loads the EL quenching is observed, which is due to decay of Ex on free charge carriers, hole polarons P +. We consider contributions to Ex–P + interaction by short-range charge transfer and describe the structure of microscopic charge transfer (CT)-processes responsible for it. The formation of metastable states of ‘charged excitons’ (predicted and studied by Agranovich et al. Chem. Phys. 272 (2001) 159) by electron transfer from a P to an Ex is pointed out, and ways to suppress non-radiative Ex–P decay are suggested.

Surface catalysis based on ruthenium dioxide for effective activation of aluminium sacrificial anodes

Several studies have been focusing on alloying and structural modification of aluminium alloy sacrificial anodes using different activators including intermetallic compounds. With a novel approach, the present work explore and evaluate the feasibility of effective aluminium activation by RuO 2 in 95 + 5 Al–Zn alloy substrates. The electrodes prepared in the present work, by making RuO 2 film on the substrate, were found to possess good surface interaction, low surface resistivity and facilitate interlayer diffusion of aluminium ions. The electrodes showed excellent galvanic performance under different experimental conditions in 3% NaCl electrolyte. The RuO 2 layer was found to persist on the electrode surface even after the electrode size was reduced to one-third of its original size due to long period of galvanic exposure, evidencing its mobile character. The electrodes are economically efficient, convenient to prepare as other conventional hanging electrodes, tolerable to very aggressive media and highly efficient even under high current load.

Ruthenium oxide for effective activation of aluminium sacrificial anodes: a new approach

Ruthenium oxide, one of the excellent electrocatalysts having high conductivity and high chemical and thermodynamic stability, has been coated onto the surface of an electrode made from a Al–5 wt-%Zn alloy. The activated aluminium ion was able to diffuse through the porous catalytic hydrophilic layer. Ruthenium oxide coated Al–Zn alloy anodes displayed high open circuit potential and high closed circuit potential during galvanic exposure with mild steel cathodes. A galvanic efficiency as high as 86% with an actual current capacity of 2573 A h kg-1 was achieved. The RuO2 film underwent very little deterioration and a considerable mass of the ruthenium oxide film persisted on the anode surface, even after the electrode size had been reduced to one third of its original size owing to galvanic dissolution. These electrodes are economically efficient, as convenient to prepare, install and use as other conventional electrodes, are tolerable of very aggressive media and highly efficient, even under high galvanic current loads.

Condensed metal vapor on alumina ceramic in vacuum interrupters

Investigations have been carried out on the dielectric performance of the ceramic (high-purity alumina, Al/sub 2/O/sub 3/) surface in vacuum interrupters after switching. In order to examine the influence of the shielding on the protection of the ceramic surface against metal vapor condensation different types of vacuum interrupters (VIs) have been tested: VIs with and without shielding. Additionally, two contact materials CuCr: 75:25 wt% and WCAg: 56:4:40 wt% have been investigated to compare the adhesion of different metal vapors to alumina ceramic surfaces. After having performed a HV conditioning of the VIs, dc arcs with arbitrary arcing times were triggered between the contacts simulating the generation of metal vapor during high current interruption and load break switching. Between the arcing tests the insulation levels of all VIs have been tested by means of HV ac source. Afterwards the VIs were opened and the microstructure of the metallic condensate on the inner ceramic surface was analyzed by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The integral chemical composition of the metallic film was investigated by inductive coupled plasma (ICP).

Probing the temperature during switching of YBCO films

The switching of YBCO thin films under high current load is fundamental for fault current limiters and active power switches. Its mechanism is still under debate, however, with thermal and nonthermal models being discussed. To clarify the situation, we have placed an array of thermometers directly on top of a YBCO strip and have measured the quench propagation with high spacio-temporal resolution. We compare the results with a numerical model of heat diffusion in 3D with temperature dependent material parameters and find nearly quantitative agreement. This confirms thermal runaway as the mechanism of switching.

低温動作カソードにおける寿命特性および電子放射層の変化

An electron emitter pellet for low temperature operating cathode has been developed by integrating a mixture of (Ba, Sr, Ca)CO3 powder, Ni powder and Sc2O3 powder using hot isostatic pressing (HIP). During the exhaustion process of cathode ray tube (CRT), an emitting layer composed of oxide emitter is formed on the pellet surface. During emission, this emitting layer plays an important role. In this study, we performed life tests of the pellet at high current density. Emission properties were evaluated by measuring maximum cathode currents and observing cathode images. In addition, time course changes of the emitting layer were examined. Superior life characteristics of less than 3% and 20% reduction in the maximum cathode current 1.5×104h and 3.5×104h, respectively, after the start of the high current application life test with an average current density of 3A/cm2, ten times as large as practical current density of CRTs, were obtained. These conditions reveal that the pellet exhibits superior life properties against high current loads. The emitting layer on the pellet surface develops irregularities 1.5×104h after the start of the life test, with a part of Ni exposed. The emission properties of the pellet do not deteriorate regardless of such irregularities in the emitting layer; this is considered to be because Ba is supplied from the inside of the pellet, and BaO covers the entire pellet surface.

Aerosol processing of functionally engineered cermet emitters

Aerosol processing techniques have been used to produce a new type of high conductivity cermet emitter for thermionic cathode application. The versatility afforded by the process has been exploited to engineer a range of variously oriented, interconnected and graded structures within the composite with a view to maximising conductivity whilst minimising the volume fraction of non-emitting metallic phase. Improvements in reliability under high current loading conditions have been obtained without adversely affecting the other emission characteristics of the material.

Flip chip die attach development for multichip mechatronics power packages

New package innovations are needed to address the next generation system requirements of the automotive market. Enhanced system functionality from semiconductor components and overall cost reduction demands drive multichip package solutions. The use of semiconductor devices to switch, control and monitor high current loads will integrate logic and power devices on a common substrate with requirements for effective power dissipation, current carrying capability and fine width conductor features for the control device and interconnections. To achieve these goals Motorola's Advanced Interconnection Systems Laboratory, Munich, has developed a new package concept, a multichip mechatronics power package, utilizing flip chip die attach technology and electroplated eutectic SnPb solder bumps. With the goal to deliver an advanced package platform to cover different power levels in the system architecture,the several substrate technologies were evaluated.

Developing Principles for an Electrochemical Low-Waste Production of Chloramines T, B, and KhB

Two approaches to organizing a low-waste production of chloramines T, B, and KhB are suggested and experimentally substantiated. One is based on the electrolysis of proper arylsulfamides in a saturated aqueous NaCl solution, involves a multiple recycling of spent solutions, and may be realized in a diaphragmless electrolyzing cell at high current loads (6 kA m-2). The yield of the target products is no less than 90% at a purity of 98%. The other technique leans upon the traditional technology commonly adopted in an industrial production of the above chloramines and includes, in addition to the earlier existing steps, a step we proposed for purifying waste water. The proposed step involves an additional chlorination of residual chloramine and arylsulfamide present in the waste water to dichloramide insoluble in aqueous media. The dichloramide is then quantitatively converted into the target chloramine. The aqueous NaCl solution thus purified is subsequently used for an electrochemical production of chlorine and alkali. This approach makes it possible to recycle spent solutions and increase the yield of target products by 20–30% as compared with the existing technology.

Degradation of ZnSe/ZnTe multiquantum well contacts to p-ZnSe

The work presented in this paper studied the degradation of ZnTe/ZnSe multiquantum well contacts to p-ZnSe under high current loading (1000 to 1500 A/cm2). During degradation, localized heating (up to 200°C > the bulk substrate and heat sink) was observed to occur at the point were electrical power was supplied. Auger data from degraded samples indicated that due to the localized heating, Zn and Te from the ZnTe layers and Zn from the ZnSe layer diffused through the Au metallization to the samples surface. In addition, thermal stress from the localized heating generated micro-cracks in the ZnSe which acted as high diffusivity paths for impurities. Rectangular defects were also found to form in the degraded region. These defects were oriented to the micro-cracks and had similar geometries as dislocation patches (dark line defects) which have been reported to form in the quantum well region of degraded ZnSe based laser devices. The similarities between the rectangular defects and dark line defects suggest the formation of similar dislocation patches in the quantum well region of the multiquantum well contacts.

Power losses in PWM-VSI inverter using NPT or PT IGBT devices

This paper investigates the power losses for two different IGBT technologies (nonpunch through and punch through) for use in PWM-VSI inverters in order to choose the right device technology for a given application. A loss model of the inverter is developed based on experimental determination of the power losses. The loss model is used on two different modulation strategies which are a sine wave with a third harmonic added and a 60/spl deg/-PWM modulation where only two inverter legs are active at the same time. The two IGBT technologies are characterized on an advanced measurement system which is described. The total power losses in the inverter are estimated by simulation at different conditions and it is concluded that the nonpunch through (NPT) technology is most useful for higher switching frequencies, while the punch through (PT) technology is especially useful at lower switching frequencies and high load currents. It is also concluded that the 60/spl deg/-PWM modulation has the lowest power losses and the power losses are almost independent of phase angle cos(/spl phi/) for normal motor operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electrode phenomena in high-current, high-pressure arc heaters

The behavior of an arc in the cathode region of a high-pressure, high-current arc heater is investigated numerically. The study is conducted to determine the design features required for high-performance arc heaters needed for future aerospace research facilities. Computations are performed for operating pressures in the range 50-200 atm and load currents in the range 6000-18,000 amp. At high pressures, due to the high-current carrying capability of the dense gas, spot size remains reasonably small, even for high-load currents. Its value is 1.1 mm for a 50-atm arc with a load current of 18,000 amp. By increasing pressure, it can be reduced further. Smaller spot size may allow us to design thinner electrode rings. Spot temperatures are high enough to cause ablation of the electrode material. In order to reduce material ablation at very high currents and prolong electrode life, the operating pressure must be high and the arc should be rotated. Experimental studies to compare with these results would be desirable.

Discharge Behavior of Tubular PbO2 Electrodes: I . Experimental Investigations

The discharge behavior of tubular lead dioxide electrodes has been experimentally studied by means of electrochemical measurements, scanning electron microscopy, and electron probe microanalysis in order to investigate how the utilization of these electrodes is affected by the geometry, current load, and the tube envelope. Structural and kinetic parameters have been evaluated from polarization measurements at different concentrations. The one‐dimensional initial current density distribution could be satisfactorily described by a macrohomogeneous model with a cathodic transfer coefficient equal to two and an initial volumetric exchange current density, , that varied with the concentration according to the equation for . It was found that the cell geometry only has a minor effect on electrode performance at high and medium current loads in comparison to the effects of the tube envelope. Current constriction in the pores of the fabric causes three‐dimensional growth of dendritic lead sulfate crystals and severe hindrance to both migration and diffusion. The initial local current density as well as the utilization of the lead dioxide were found to be higher in the exterior parts of the electrode in the same way as that for flat, pasted electrodes.

Rechargeable iron/air cells employing bifunctional oxygen electrodes of oxide pyrochlores

Prototype secondary iron/air cells comprising pressed-type iron electrodes and oxygen electrodes of some oxide pyrochlores have been assembled and subjected to electrochemical charge/discharge tests for over 150 cycles at various load currents. The cells are found to exhibit little deterioration in performance. Oxygen electrodes using PbBiRu 2O 7− y oxide pyrochlores are superior to those with Pb 2Ir 2O 7− y , except under high-load currents.

ChemInform Abstract: Kinetics of a Manganese Dioxide Electrode in Aqueous and Non‐Aqueous Electrolytes.

AbstractThe mechanisms which are decisive for the discharge ability of MnO2 electrodes in both alkaline and organic electrolytes at higher current loads are examined with the help of probe experiments and model calculations.