Improved RF power performance of InAlN/GaN HEMT by optimizing rapid thermal annealing process for high-performance low-voltage terminal applications

Improved radio-frequency(RF)power performance of InAlN/GaN high electron mobility transistor(HEMT)is achieved by optimizing the rapid thermal annealing(RTA)process for high-performance low-voltage terminal applications.By optimizing the RTA temperature and time,the optimal annealing condition is found to enable low parasitic resistance and thus a high-performance device.Besides,compared with the non-optimized RTA HEMT,the optimized one demonstrates smoother ohmic metal surface morphology and better heterojunction quality including the less degraded heterojunction sheet resistance and clearer heterojunction interfaces as well as negligible material out-diffusion from the barrier to the channel and buffer.Benefiting from the lowered parasitic resistance,improved maximum output current density of 2279 mA·mm^(-1)and higher peak extrinsic transconductance of 526 mS·mm^(-1)are obtained for the optimized RTA HEMT.In addition,due to the superior heterojunction quality,the optimized HEMT shows reduced off-state leakage current of 7×10^(-3)mA·mm^(-1)and suppressed current collapse of only 4%,compared with those of 1×10^(-1)mA·mm^(-1)and 15%for the non-optimized one.At 8 GHz and V_(DS)of 6 V,a significantly improved power-added efficiency of 62%and output power density of 0.71 W·mm^(-1)are achieved for the optimized HEMT,as the result of the improvement in output current,knee voltage,off-state leakage current,and current collapse,which reveals the tremendous advantage of the optimized RTA HEMT in high-performance low-voltage terminal applications.

Hydrodynamic Response and Power Performance of A Heave and Pitch Buoy Wave Energy Converter Under Bimodal Ochi-Hubble Wave Spectrum

In coastal sea areas with the bimodal Ochi-Hubble wave spectrum, such as parts of the China Sea and Indian Ocean,wave energy is the superposition of wind wave and swell. Traditional heaving buoy wave energy converters developed with narrowband wave spectrums suffer from big energy loss in these areas, leading to lower power absorption efficiency and higher generating costs. In contrast, multi-freedom buoy has different resonant frequencies and maximal power capture wave frequencies in different degrees of freedom(DOFs). Therefore, this study proposed using two DOFs to capture the energy of wind wave and swell correspondingly. A heave and pitch buoy model was established by potential flow theory and validated by experimental data. Coupling effect on the motion and power absorption, power capture frequency distribution and power absorption with different linear power takeoff system damping coefficients were analyzed to reveal the hydrodynamic response and the power performance of the two DOFs. The results indicate that by using heave and pitch DOFs, the wave energy components of wind wave and swell were captured in a targeted manner. It demonstrates that the 2-DOF buoy is an effective tool to avoid the energy loss and realize the efficient power absorption in coastal sea areas with bimodal Ochi-Hubble waves.

Probabilistic Load Flow Algorithm with the Power Performance of Double-Fed Induction Generators

Probabilistic load flow(PLF)algorithm has been regained attention,because the large-scale wind power integration into the grid has increased the uncertainty of the stable and safe operation of the power system.The PLF algorithm is improved with introducing the power performance of double-fed induction generators(DFIGs)for wind turbines(WTs)under the constant power factor control and the constant voltage control in this paper.Firstly,the conventional Jacobian matrix of the alternating current(AC)load flow model is modified,and the probability distributions of the active and reactive powers of the DFIGs are derived by combining the power performance of the DFIGs and the Weibull distribution of wind speed.Then,the cumulants of the state variables in power grid are obtained by improved PLF model and more accurate power probability distributions.In order to generate the probability density function(PDF)of the nodal voltage,Gram-Charlier,Edgeworth and Cornish-Fisher expansions based on the cumulants are applied.Finally,the effectiveness and accuracy of the improved PLF algorithm is demonstrated in the IEEE 14-RTS system with wind power integration,compared with the results of Monte Carlo(MC)simulation using deterministic load flow calculation.

A comparison of two wave energy converters’power performance and mooring fatigue characteristics-One WEC vs many WECs in a wave park with interaction effects

The production of renewable energy is key to satisfying the increasing demand for energy without further increasing pollution.Harnessing ocean energy from waves has attracted attention due to its high energy density.This study compares two generations of floating heaving point absorber WEC,WaveEL 3.0 and WaveEL 4.0,regarding their power performance and mooring line fatigue characteristics,which are essen-tial in,e.g.,LCoE calculations.The main differences between the two WECs are the principal dimensions and minor differences in their geometries.The DNV software SESAM was used for simulations and anal-yses of these WECs in terms of buoy heave motion resonances for maximising energy harvesting,motion characteristics,mooring line forces,fatigue of mooring lines,and hydrodynamic power production.The first part of the study presents results from simulations of unit WEC in the frequency domain and in the time domain for regular wave and irregular sea state conditions.A verification of the two WECs’motion responses and axial mooring line forces is made against measurement data from a full-scale installation.In the second part of the study,the influence of interaction effects is investigated when the WECs are installed in wave parks.The wave park simulations used a fully-coupled non-linear method in SESAM that calculates the motions of the WECs and the mooring line forces simultaneously in the time domain.The amount of fatigue damage accumulated in the mooring lines was calculated using a relative tension-based fatigue analysis method and the rainflow counting method.Several factors that influence the power performance of the wave park and the accumulated fatigue damage of the mooring lines,for example,the WEC distance of the wave park,the sea state conditions,and the direction of incoming waves,are simulated and discussed.The study’s main conclusion is that WaveEL 4.0,which has a longer tube than WaveEL 3.0,absorbs more hydrodynamic energy due to larger heave motions and more efficient power production.At the same time,the accumulated fatigue damage in the moorings is lower compared to WaveEL 3.0 if the distance between the WECs in the wave park is not too short.Its motions in the hor-izontal plane are larger,which may require a larger distance between the WEC units in a wave park to avoid losing efficiency due to hydrodynamic interaction effects.

Ship speed power performance under relative wind profiles in relation to sensor fault detection

Statistical data analysis and visualization approaches to identify ship speed power performance under relative wind(i.e.apparent wind)profiles are considered in this study.Ship performance and navigation data of a selected vessel are analyzed,where various data anomalies,i.e.sensor related erroneous data conditions,are identified.Those erroneous data conditions are investigated and several approaches to isolate such situations are also presented by considering appropriate data visualization methods.Then,the cleaned data are used to derive various relationships among ship performance and navigation parameters that have been visualized in this study,appropriately.The results show that the wind profiles along ship routes can be used to evaluate vessel performance and navigation conditions by assuming the respective sea states relate to their wind conditions.Hence,the results are useful to derive appropriate mathematical models that represent ship performance and navigation conditions.Such mathematical models can be used for weather routing type applications(i.e.voyage planning),where the respective weather forecast can be used to derive optimal ship routes to improve vessel performance and reduce fuel consumption.This study presents not only an overview of statistical data analysis of ship performance and navigation data but also the respective challenges in data anomalies(i.e.erroneous data intervals and sensor faults)due to onboard sensors and data handling systems.Furthermore,the respective solutions to such challenges in data quality have also been presented by considering data visualization approaches.

Fuzzy Based Intelligent Monitoring of Critical Lines in the Restructured Power Market

Restructured electric market environment allows the power wheeling transactions between the power producers and customers to meet the growing load demand. This will lead to the possible of congestion in the transmission lines. The possible contingencies of power components further worsen the scenario. This paper describes the methodology for the identification of critical transmission line by computing the real power and reactive power performance indices. It also demonstrates the importance of fuzzy logic technique used to rank the transmission lines according to the severity and demonstrated on IEEE-30 bus system.

A Study on Relationship among Blade Camber Direction and Pitch Angle and Performance of a Small Straight-Blade Darrieus Wind Turbine by Using Scale Test Model and Gurney Flap

Straight-blade Darrieus vertical axis wind turbines are used as medium and small size wind turbine because of higher power output in vertical axis wind turbine (VAWT). In our previous study, the relationship between the performance and Reynolds number based on airfoil chord length had been investigated by using small-scale test models of lift-type VAWT, and the results showed that the performance of tested wind turbine models with small diameter was clearly lower than that of the large-scale field test machine, and its performance also varies significantly with the blade pitch angle. In this study, we focused on the performance of a small-scale straight-blade Darrieus VAWT, the relationship among the blade airfoil camber direction and the pitch angle, and the performance of the small-scale VAWT was examined experimentally by using a small-scale VAWT test model with Gurney flap which was a small flat plate. Gurney flaps with its height h, as a ratio to the blade chord length c, h/c = 0.036 to 0.055, were attached to the blades of the VAWT test model, in addition, the attaching direction of the Gurney flap on the blade was examined for both inward and outward of the rotor, and the pitch angle was also examined for a range of −5 to 10 degrees. These results are discussed comparing with the result of the VAWT without Gurney flap and considering the numerical results for the single blade with/without the Gurney flap. The results showed that the performance of the tested VAWT was reversed between the inward and outward Gurney flaps around a pitch angle of 10 degrees. That is, the inward Gurney flap was superior at a pitch angle of less than 10 degrees, while the outward Gurney flap was effective at a pitch angle of more than 10 degrees. Furthermore, for the tested small-scale VAWT model, the optimum pitch angle was about 5 degrees, and the inward and shorter Gurney flap showed higher power performance of the VAWT under this pitch angle condition.

汽油机动力性能多目标优化及试验研究

针对某发动机高速动力性较同排量发动机偏低的问题,采用多目标优化与试验相结合的方法对发动机动力性能进行优化。建立并标定了发动机一维模型,采用DOE(试验设计)方法分析了进气延迟角、进气凸轮最大升程、压缩比等多因素对发动机外特性的影响,分析结果响应拟合度较高;采用遗传算法对发动机高速大负荷工况下的工作性能进行了多目标优化;对进气道流动特性进行了CFD(计算流体动力学)分析,通过改进进气道结构以提高其流量系数。最后搭建了进气道稳流试验台和发动机试验台,试验结果表明:改进后的进气道流量系数最大提高了6.51%,发动机功率提高了15.59%,扭矩提高了11.92%,燃油消耗率降低了3.33%。

Hybrid Loader Automatic Shift Strategy Based on Neural Network

Hybrid loader 's comprehensive performance mainly depends on the performance of hydraulic torque converter during its driving and working. Hybrid loader and hydraulic torque converter are taken for the research objects. The primary characteristic curve of hydraulic torque converter and the traction curve of hybrid loader are acquired by analyzing the characteristic parameters of hydraulic torque converter, the characteristic parameters of engine, the characteristic parameters of battery pack and geometric parameters of hybrid loader. The gear shift curves based on the best energy saving performance and the best power performance are acquired respectively with the opening of throttle,the speed of pump wheel and the speed of turbine as parameters. Then the two curves are combined to get the comprehensive gear shift curve. Radical basis function( RBF) neural network is applied to building the gear shift strategy to keep hybrid loader with the best power performance and energy saving performance. The experimental bench is set up for experimental verification. It proves that both of the power performance and energy saving performance of hybrid loader are improved effectively by using the automatic shift strategy.

Power Extraction Performance of a Semi-activated Flapping Foil in Gusty Flow

A numerical investigation on the power extraction performance of a semi-activated flapping foil in gusty flow is conducted by using the commercial software FLUENT. The foil is forced to pitch around the axis at one-third chord and heave in the vertical direction due to the period lift force. Different from previous work with uniform flow, an unsteady flow with cosinusoidal velocity profile is considered in this work. At a Reynolds number of 1100, the influences of the mechanical parameters （spring constant and damping coefficient）, the amplitude and frequency of the pitching motion, the amplitude of the gust fluctuation and the phase difference between the pitching motion and the gusty flow on the power extraction performance are systematically investigated. Compared with the case of uniform flow, the capability energy harvesting of the system is enhanced by the introduction of the gusty flow. For a given pitching amplitude and frequency, the power extraction efficiency increases with the gust fluctuation amplitude. Moreover, with an optimal phase difference between pitch and gust （φ = 180°）, the efficiency can be further enhanced due to the generation of high lift force.

终压变动对变转速汽轮机功率的影响

本文讨论变转速汽轮机终压变动时其功率变化的规律.通过在汽轮机机组上的试验,验证了导出的公式,这些公式具有推广意义.结论指出:变转速汽轮机功率的变化只受终压的影响.

Autonomic Performance and Power Control on Virtualized Servers:Survey, Practices, and Trends

Modern datacenter servers hosting popular Internet services face significant and multi-facet challenges in performance and power control. The user-perceived performance is the result of a complex interaction of complex workloads in a very complex underlying system. Highly dynamic and bursty workloads of Internet services fluctuate over multiple time scales, which has a significant impact on processing and power demands of datacenter servers. High-density servers apply virtualization technology for capacity planning and system manageability. Such virtuMized computer systems are increasingly large and complex. This paper surveys representative approaches to autonomic performance and power control on virtualized servers, which control the quality of service provided by virtualized resources, improve the energy efficiency of the underlying system, and reduce the burden of complex system management from human operators. It then presents three designed self-adaptive resource management techniques based on machine learning and control for percentile-based response time assurance, non-intrusive energy-efficient performance isolation, and joint performance and power guarantee on virtualized servers. The techniques were implemented and evaluated in a testbed of virtualized servers hosting benchmark applications. Finally, two research trends are identified and discussed for sustainable cloud computing in green datacenters.

Performance comparison of power fading mitigation techniques in multiband OFDM-UWB signals transmission along LR-PONs

The single sideband （SSB） modulation is assessed as a means to mitigate the dispersion-induced power fading on the distribution of ortogonal frequency division multiplexing （OFDM） ultra wideband （UWB） radio signals along long-reach passive optical networks （LR-PONs）. Particularly, two different SSB ar- chitectures, namely, Sieben＇s architecture and four phase modulator （FPM） architecture are optimized to provide maximum sideband suppression. The minimum optical signal-to-noise ratio （OSNR） required to simultaneously distribute all the 14 OFDM-UWB sub-bands along the LR-PON distances ranging between 80 and 100 km is also evaluated through numerical simulation. FPM architecture is preferable over Sieben＇s architecture because the latter SSB architecture generates carriers-carriers beat term at the photodetector output with high power, thereby causing significant degradation in the OFDM-UWB sub-bands with lower central frequencies. The simultaneous distribution of the 14 SSB OFDM-UWB sub-bands in the LR-PON using the FPM architecture shows a minimum OSNR penalty of 3 dB compared with the centralized dis- persion compensation technique.

Increasing power plant efficiency with clustering methods and Variable Importance Index assessment

Power plant performance can decrease along with its life span,and move away from the design and commissioning targets.Maintenance issues,operational practices,market restrictions,and financial objectives may lead to that behavior,and the knowledge of appropriate actions could support the system to retake its original operational performance.This paper applies unsupervised machine learning techniques to identify operating patterns based on the power plant’s historical data which leads to the identification of appropriate steam generator efficiency conditions.The selected operational variables are evaluated in respect to their impact on the system performance,quantified by the Variable Importance Index.That metric is proposed to identify the variables among a much wide set of monitored data whose variation impacts the overall power plant operation,and should be controlled with more attention.Principal Component Analysis(PCA)and k-means++clustering techniques are used to identify suitable operational conditions from a one-year-long data set with 27 recorded variables from a steam generator of a 360MW thermal power plant.The adequate number of clusters is identified by the average Silhouette coefficient and the Variable Importance Index sorts nine variables as the most relevant ones,to finally group recommended settings to achieve the target conditions.Results show performance gains in respect to the average historical values of 73.5%and the lowest efficiency condition records of 68%,to the target steam generator efficiency of 76%.

DSOI—a novel structure enabling adjust circuit dynamically

A double silicon on insulator（DSOI） structure was introduced based on fully depleted SOI（FDSOI）technology.The circuit performance could be adjusted dynamically through the separate back gate electrodes applied to N-channel and P-channel devices.Based on DSOI ring oscillator（OSC）,this paper focused on the theoretical analysis and electrical test of how the OSC＇s frequency being influenced by the back gate electrodes（soi2n,soi2p）.The testing results showed that the frequency and power consumption of OSC could change nearly linearly along with the back gate bias.According to the different requirements of the circuit designers,the circuit performance could be improved by positive soi2 n and negative soi2 p,and the power consumption could be reduced by negative soi2n and positive soi2p.The best compromise between performance and power consumption of the circuit could be achieved by appropriate back gate biasing.