Non-uniform Power Research Articles

A 4–20 GHz, multi‐watt level, fully integrated push–pull distributed power amplifier with wideband even‐order harmonic suppression

This study presents the first fully integrated, push–pull, high power distributed amplifier (DA) for wideband applications in 0.25 µm Gallium arsenide (GaAs) pseudomorphic high electron mobility transistor process. A triple-stacked field-effect transistor cell is employed for each stage of the DA along with the non-uniform distributed power amplifier topology to maximise the output power. The experimental results show that the amplifier exhibits from 7 to 10 dB gain with vi30–32 dBm output power at 1 dB compression (P1 dB) and 32–35.4 dBm saturated output power (Psat) covering a frequency bandwidth from 4 to 20 GHz. The measured second harmonic suppression is >33 dBc from 8 to 40 GHz at the P1 dB operating condition.

Generalized Self-Interference Model for Full-Duplex Multicarrier Transceivers

In the modeling of full duplex (FD) transceivers using multicarrier modulations, it is usually assumed that the intercarrier interference of the coupling path is negligible. Therefore, the system can be analyzed on a subcarrier basis, because the model reduces to a set of orthogonal flat channels. However, for more general FD transceivers, or when hardware components introduce nonlinear distortion, the orthogonality is lost and a more rigorous model is needed. In this paper, we introduce a model for the coupling interference of FD systems, which allows the uplink and the downlink to have different time and frequency offsets, and different parameters such as the number of subcarriers and symbol length. In addition, we present a linear approximation for the nonlinear coupling based on a generalization of the Bussgang's theorem, for the case of transmitters with nonuniform power allocation. We validate the proposed model with measurements and show numerically that it improves the accuracy of the signal to interference plus noise ratio expression, and the formulation of optimization problems. Therefore, the proposed model paves the way for a more realistic performance analysis and the derivation of more accurate power allocation strategies than is possible with the classic model.

A New Definition of Fairness for Non-Orthogonal Multiple Access

Fairness in non-orthogonal multiple access (NOMA) may be defined in different ways, taking into account the physical layer alone or also including the process of radio resource management. The latter has been frequently used in the recent literature, implying a significant advantage of this technique compared with conventional orthogonal multiple access (OMA). In this letter, we look at the fairness issue from another angle and introduce a fundamental definition of fairness, which measures the difference between the rates that can be achieved by the users and the fair rates suggested by the power distribution among them. With this definition, the fairness issue is inexistent in OMA and it appears as a NOMA-specific problem due to interference between users and the detection process. The new fairness index we advocate incorporates the power distribution of different users. Thus, in a cell with a non-uniform power distribution, fairness implies that a user with a higher power should get a higher rate, and hence, the index should measure the rate of each user by accounting for the fraction of total power allocated to it. Our index achieves its maximum value of 1 only when all users get their fair rates, and it goes to zero when one user gets all resources in the case of uniform power distribution. We provide an asymptotic analysis of fairness at high and low signal-to-noise ratio (SNR) values and give a comprehensive illustration in the two-user case.

DNB type critical heat flux prediction in rod bundles with simplified grid spacer based on Liquid Sublayer Dryout model

Five published Liquid Sublayer Dryout (LSD) models are assessed using the Groeneveld Look-up table 2006 (LUT-2006) and critical heat flux (CHF) experimental data in circular tube under both subcooled boiling conditions and saturated boiling conditions. The flow regime transition from inverted annular flow to dispersed flow at post-CHF is postulated as the upper limit of the LSD model application range in saturated boiling region. Lee and Mudawar’s LSD model modified by W.X. Liu shows good agreement when void fractions is lower than 0.7. The modified L&M’s LSD model is coupled into subchannel code, COBRA-TF, to predict DNB type CHF in rod bundles. In present study, the gap clearance or thermal equivalent diameter of rod bundles is adopted as characteristic length in the modified L&M’s LSD model. For rod bundles with simplified grid spacers, Karman velocity distribution equation is utilized to calculate the velocity distribution normal to pin wall. The rod bundle CHF predictions by COBRA-TF coupled with LUT-2006, Bowring’s CHF correlation and the modified L&M’s LSD model, are compared with the CHF experimental data in 2 × 2 rod bundles with non-uniform power profile. Based on reasonable predictability on both the input power and axial position at CHF, the deviations of CHF predictions by the modified L&M’s LSD model, which adopts gap clearance instead of thermal equivalent diameter as characteristic length, and Bowring’s CHF correlation are within ±20% as void fraction approaching to 0.7.

Thermal-hydraulics analysis of flow blockage events for fuel assembly in a sodium-cooled fast reactor

The subchannel code ATHAS-LMR has been improved for analyzing thermal-hydraulics characteristics of flow blockage events in the fuel assembly of a sodium-cooled fast reactor (SFR). Based on the in-depth study of the phenomenon of flow blockage and combined with the characteristics of fast reactor assembly, enhanced models for the wire-wrap spacer and convective heat transfer have been added to account for changes in transverse flow in the presence of blockages. And appropriate transverse mixing and local resistance model are also implemented in ATHAS-LMR-FB. The improved code has been assessed against experimental data obtained at adiabatic and diabatic conditions in SFR assemblies with simulated flow blockages. Good agreement between predictions and experimental data on velocity and temperature distributions downstream of the blockage has been observed. Comparison of predictions of various analytical tools have also been performed. Predictions of the improved ATHAS-LMR code are shown to be compatible with those of other analytical tools. An in-depth analysis of effects of location and size of blockage has been carried out for the fuel assembly of the China Experimental Fast Reactor. Boiling has been predicted to occur for blockage ratios greater than 55.61% at the central location of the fuel assembly. Peak cladding and coolant temperatures are predicted at the axial location 70% of the rod length (just downstream of the maximum local power position of the non-uniform axial power profile).

Numerical modeling and experimental validation of two-phase microfluidic cooling in silicon devices for vertical integration of microelectronics

The vertical integration of microelectronics is an appealing approach that offers significant performance advantages over conventional planar devices. However, one of the main challenges for implementing such technology is the limited volume for heat dissipation. Microfluidic interlayer cooling is a feasible solution for the thermal management of such devices, but several challenges remain to achieve a comprehensive solution that is compatible with electrical and structural parameters. In the present study, a Thermal Demonstration Vehicle (TDV) is numerically and experimentally investigated in an effort to provide a practical cooling solution for vertically integrated devices with heterogeneous heating. The flow boiling of the dielectric refrigerant HFE-7200 is investigated to provide insights regarding the two-phase flow regimes, heat transfer, and pressure drop characteristics in this type of microgaps. The physics of the flow boiling mechanisms are also explored through a mechanistic phase change model, which can be used with commercial computational fluid dynamics and heat transfer (CFD-HT) codes. The numerical modeling approach is validated with experimental results in representative layouts with variable density of pin fins and non-uniform power inputs, making this technique an attractive alternative for the design of practical two-phase micro-cooling layers operating in realistic conditions with hotspots.

Optimal Transmission Using a Self-Sustained Relay in a Full-Duplex MIMO System

This paper investigates wireless information and power transfer in a full-duplex MIMO relay channel where the self-sustained relay harvests energy from both source transmit signal and self-interference signal to decode and forward source information to a destination. We formulate a new problem to jointly optimize power splitting at the relay and precoding design for both the source and relay transmissions. Using duality theory, we establish closed-form optimal primal solutions in terms of the dual variables, based on which we then design a customized and efficient primal-dual algorithm to maximize the achievable throughput. Numerical results demonstrate the rate gains from using multiple transmit and receive antennas in both information decoding and energy harvesting, and the significant benefit of harvesting energy from self-interference signals. We also extend our analysis to the case when channel state information is only available at receiving nodes and show how our algorithm can optimize the power splitting at the relay for it to remain self-sustained. Through analysis and simulation, we demonstrate that an optimal combination of non-uniform power splitting, variable power allocation, and self-interference power harvesting can effectively exploit a full-duplex MIMO system to achieve significant performance gains over existing uniform power splitting and half-duplex transmissions.

Optimizing Throughput in a MIMO System With a Self-Sustained Relay and Non-Uniform Power Splitting

We present a novel approach to maximizing the transmission rate in a MIMO relay system, where all nodes are equipped with multiple antennas and the relay is self-sustained by harvesting energy. We formulate an optimization problem and use dual-characterization to derive a closed-form solution for the optimal power splitting ratio and precoding design. We propose an efficient primal-dual algorithm to jointly optimize the power allocation at source and relay for transmission and the power splitting at relay for energy harvesting, and show that using non-uniform power splitting is optimal. Numerical results demonstrate the significant rate gain of non-uniform power splitting over traditional uniform splitting especially at low source transmit power. We also analyze our algorithm numerically and demonstrate its efficiency at reducing the run-time by several orders of magnitudes compared to a standard solver, \textcolor{blue}{and existing algorithms in literature

Experimental tests and post-test analysis of non-uniformly heated 19-pins fuel bundle cooled by Heavy Liquid Metal

An experimental campaign was performed on a non-uniformly heated 19-pins wire-spaced fuel pin bundle simulator, cooled by Heavy Liquid Metal and installed in the NACIE-UP (NAtural CIrculation Experiment-UPgrade) facility located at the ENEA Brasimone Research Center (Italy). The experimental tests concerned mass flow rate transition of the primary coolant from forced to natural circulation, with fuel pin bundle simulator characterized by non-uniform power distribution. The main objective of the experimental campaign was to perform integral system and local thermal-hydraulic analysis, investigate different flow regimes and the transition from forced to natural circulation flow and, more specifically, analyze the behavior of the 19-pins wire-spaced Fuel Pin Simulator (FPS) during such transient. Indeed, the performed test were characterized by non-uniform heating of the bundle (i.e. just some pins switched on), so the effects of this non-uniformity on the local temperatures and on the overall system behavior was evaluated. A deep investigation on the local temperature distribution was performed thanks to the accurate instrumentation provided in the bundle (67 thermocouples). The obtained experimental data provided useful information for the characterization of the bundle and the computation of the heat transfer coefficient.A post-test validation is made by a detailed CFD model of the test section. Three monitored section at different levels are compared both for wall and bulk temperatures. This post-test comparison with this experimental configuration is unique and represents a further step towards the validation of the CFD models and methods in fuel bundle geometries cooled by HLM.

Кинематический накопитель энергии для децентрализованной энергетики

In mastering the use of decentralized renewable energy sources, problems of connecting them to the common grid are encountered, including those stemming from the nonuniform power output produced by them. The use of a kinematic energy storage (KES) as an additional source of power for a wind farm is considered. In addition, a high-speed three-phase permanent-magnet synchronous machine equipped with an output electronic module, with which the energy storage can operate with a variable rotation frequency, is proposed to be used as the KES motor—generator unit. The parameters of a KES with the inertia moment equal to 100 kgm[1] made using different materials (steel, aluminum, titanium, and high-strength composite material) have been calculated for different flywheel diameter-to-height ratios. It is shown that the energy storage equipped with a 624-kg flywheel made of composite material can produce the power output equal to 5 kW for 8 h in the rotation frequency range 18000—6000 min-1. A three-phase permanent-magnet motor-generator is proposed for such KES.

14th International Scientific and Technical Conference “Problems of energy systems and thermal power complexes”

14th International Scientific and Technical Conference “Problems of energy systems and thermal power complexes” (PESPC)30 October – 1 November 2018, Saratov, Russian FederationThe international scientific and technical conference “Problems of energy systems and thermal power complexes” has a long history. It is conducted based on Yuri Gagarin State Technical University of Saratov and the Saratov Scientific Center of the Russian Academy of Sciences once every two years, and from October 30 to November 1 2018, the 14th conference will be held.The conference focuses on the study of the physical and technical problems of the power industry with the aim of improving and developing new energy equipment, including cogeneration plants, increasing the efficiency of renewable energy sources, improving the safety, reliability and cost-effectiveness of power generating units, including nuclear power plants. Discussed problems: non-uniform power consumption schedules, the creation of energy storage devices, including hydrogen technologies, the scientific basis for improving energy complexes.

Minimize fission power peaking factor in radial direction of water-cooled and water-moderated thermionic conversion reactor core

The paper investigates the possibility for reducing the radial power peaking factor kr inside the core of a water-cooled water-moderated thermionic converter reactor (TCR). Due to a highly nonuniform power density, the TCR generates less electric power and the temperature increases in components of the thermionic fuel elements, leading so to a shorter reactor life. A TCR with an intermediate neutron spectrum has its thermionic fuel elements (TFE) arranged inside the core in concentric circles, this providing for a nonuniform TFE spacing and reduces kr. The water-cooled water-moderated TCR under consideration has a much larger number of TFEs arranged in a hexagonal lattice with a uniform pitch. Power density flattening in a core with a uniform-pitch lattice can be achieved, e.g., through using different fuel enrichment in core or using additional in-core structures. The former requires different TFE types to be taken into account and developed while the latter may cause degradation of the reactor neutronic parameters; all this will affect the design’s economic efficiency. It is proposed that the core should be split into sections with each section having its own uniform lattice pitch which increases in the direction from the center to the periphery leading so to the radial power density factor decreasing to 1.06. The number of the sections the core is split into depends on the lattice pitch, the TFE type and size, the reflector thickness, and the reactor design constraints. The best lattice spacing options for each section can be selected using the procedure based on a genetic algorithm technology which allows finding solutions that satisfy to a number of conditions. This approach does not require the reactor dimensions to be increased, different TFE types to be taken into account and developed, or extra structures to be installed at the core center.

Investigation of cross flow mixing on rod bundle safety margins using sub-channel analysis framework

An investigation on effect of cross flow mixing on rod bundle thermal hydraulic safety margins is carried out using a sub-channel analysis framework. In the present study, general purpose automated sub-channel analysis framework is developed to carry out the thermal hydraulic analysis of nuclear reactor core. The framework involves the preprocessor to generate the sub-channel layout of the fuel assemblies of different sizes and shapes such as square and triangular pitched pin bundle. The analyses are carried out for different simulated rod bundles of square pitched array of typical nuclear fuel assembly. The parameters considered in this study are the size of the bundle, p/d ratio, intensity of turbulent mixing, mass flux, uniform and non-uniform axial power distribution. The coolant local conditions are significantly affected due to the inter channel mixing between sub-channels. The sub-channel layouts for fuel bundles of different sizes varying from 2 × 2 to 10 × 10 and 17 × 17 for same p/d and w/d ratios of 1.05 to 1.3 are generated. The analyses are carried out by varying the intensity of turbulent mixing parameter (c) from 0 (no mixing) to 0.1 (high mixing) using the developed framework. It is found that hot channel temperature decreased by 26% in smaller bundle due to strong interaction between wall and corner channel. In case of large sized assembly above 5 × 5, hot channel temperature is less affected. The estimation of coolant temperature, fuel pin surface temperature and local quality are also carried out without considering the inter-channel mixing. The results are compared with a change in the local conditions for different degree of mixing among the fuel bundle sub-channels. The developed Framework is used for performing the sensitivity-studies during the design and analysis phase of nuclear reactor core for estimation of thermal hydraulic safety margins in an efficient way with minimum human intervention.

Least-Square-Based Nonuniform Borehole SAR Imaging for Subsurface Sensing

This paper presents the least-square-based nonuniform borehole synthetic aperture radar (SAR) imaging method with cosine accuracy factor for subsurface sensing. Based on the Stolt migration, the frequency-wavenumber spectrum of nonuniform data is efficiently approximated in the least-square-sense for the target space generation. The nonuniform power exponent basis is interpolated into several uniform power exponent bases with cosine accuracy factors, and then a virtual uniform sample set with a larger scale is generated for frequency-wavenumber spectrum approximation and imaging process. The proposed method can give accurate subsurface image result with nonuniform data at a greatly reduced computational cost. The approximation error and computational cost of the proposed method are analyzed and compared with those of Gaussian nonuniform imaging method. The imaging capabilities of the proposed method are theoretically simulated and experimentally demonstrated for distributed targets. The results show that the normalized mean square error and normalized maximum error of the proposed method are at least 8.07 dB and 4.29 dB, respectively, lower than those of conventional Stolt migration method. The imaging properties of this proposed method are shown to be superior to the conventional Stolt migration method, Gaussian nonuniform imaging method and Kirchhoff migration method, which is suitable for large nonuniform SAR imaging applications.

A review on the methods to mitigate the challenges in photovoltaic system

The quantity of electricity produced from the photovoltaic (PV) system is depends on the PV panel’s performance itself. Recently, the challenges in the PV system have been greatly discussed by researchers and environmentalists. The non-uniform PV output power, partial shading conditions and high operating temperature of PV cells are the challenges that always known to reduce the PV system’s performance. This paper provides a literature review on the challenges and methods to mitigate the challenges. The future works involving of modelling and computational techniques also has been proposed to overcome the problems, hence, enhancing the PV system’s performance.

Iterative Search Algorithm to Maximize System Capacity in Time-Varying MIMO DAS

In this paper, an iterative search algorithm to maximize system capacity in a time-varying MIMO distributed antenna system (DAS) is proposed. A common DAS model is employed, in which the transmit antennas are distributively located and the receiver can move arbitrarily in the region. Due to the small-scale fading effect and the receiver movement, the transmitters and receiver cannot obtain accurate channel state information (CSI) or optimize the system capacity. Therefore, we present a time-varying MIMO DAS model and corresponding channel evolution model to predict the time-varying channel. With the channel evolution model, the proposed iterative search algorithm can calculate the precoding matrix, and an iterative search process is employed to determine the optimal precoding matrix from a precoding matrix set. Meanwhile, error analysis show the error on the instantaneous mutual information with the proposed algorithm has a close relationship with the element number of the precoding matrix set and small-scale fading evolution coefficient. We also propose a non-uniform power allocation strategy which can improve the system capacity. Simulation results are presented to verity the analysis above and demonstrate the performance of system capacity with the proposed iterative search algorithm.

Spectral Efficiency Enhancement With Power Allocation for Massive SC-SM MIMO Uplink

The combination of massive multiple-input multiple-output (MIMO) and single-carrier (SC) aided spatial modulation (SM), is recently proposed for uplink multi-user transmission over dispersive channels, which has also attracted plenty of research interest. In this letter, first the spectral efficiency (SE) lower bound with non-uniform power allocation for uplink single-cell massive SC-SM MIMO systems is proposed, in which, the base station (BS) applies maximum ratio combining and many non-ideal factors of the wireless channels are all considered. Then, a barrier function-based gradient projection method is proposed to allocate power of each transmit antenna (TA) in terms of SE maximization. The SE lower bound is shown to be tight via simulation results, and simulation results also show that the SE gain introduced by our proposed PA algorithm is mainly dependent on the TA correlation and number of TAs.

Method for Quantitative Estimation of the Risk Propagation Threshold in Electric Power CPS Based on Seepage Probability

Because of the non-uniformity of the electric power CPS network and the dynamic nature of the risk propagation process, it is difficult to quantify the critical point of a cyber risk explosion. From the perspective of the dependency network, this paper proposes a method for quantitative evaluation of the risk propagation threshold of power CPS networks based on the percolation theory. First, the power CPS network is abstracted as a dual-layered network-directed unweighted graph according to topology correlation and coupling logic, and the asymmetrical balls-into-bins allocation method is used to establish a "one-to-many" and "partially coupled" non-uniform power CPS characterization model. Then, considering the directionality between the cyber layer and the physical layer link, the probability of percolation flow is introduced to establish the propagation dynamic equations for the internal coupling relationship of each layer. Finally, the risk propagation threshold is numerically quantified by defining the survival function of power CPS network nodes, and the validity of the proposed method is verified by the IEEE 30-bus system and 150-node Barabsi-Albert model.

All-Normal Dispersion Chalcogenide PCF for Ultraflat Mid-Infrared Supercontinuum Generation

We numerically study the dispersion-engineered chalcogenide photonic crystal fiber (PCF), which allows us to generate ultraflat broadband supercontinuum (SC) spectra in all-normal dispersion regime. A 1-cm-long chalcogenide hexagonal PCF made using Ge11.5As24Se64.5 glass pumped at $1.55~\mu \text{m}$ produced an SC bandwidth 700 nm at a peak power of 1 kW. By shifting pump at $2~\mu \text{m}$ , SC spectra can be extended with a bandwidth of 1900 nm at the same peak power level. In both cases, nonuniform spectral power distribution observes over the entire output bandwidth owing to the lower dispersion slop on the long wavelength side of the dispersion curve. To spanning SC further in the mid-infrared as well as to reduce the spectral asymmetry, we optimize another design for pumping at 3.1 $\mu \text{m}$ in such a way that the pump source can be employed vicinity to the peak of the dispersion curve. Employing the largest pump peak power up to 5 kW, SC can be extended up to 6 $\mu \text{m}$ (1.5 octaves), and the power distribution among the spectral components over the entire SC bandwidth can be improved significantly by this design. To enhance the spectral flatness, we optimize a second PCF geometry by reducing its pitch length, and it is possible to obtain ultraflat coherent SC spanning from 2 to 5.5 $\mu \text{m}$ (>1 octave) by this structure maintaining nearly symmetric power distribution between both side of its spectral components.

Symmetry of Arc Furnace Operation

The electrical asymmetry in the operation of arc furnace with an asymmetric triangular configuration of the electrodes is noted. Experimental data from the DSP-100 furnace permit analysis of how the electrical parameters affect the arc characteristics. Nonuniform power distribution over the phases of the electrofurnace decreases the component of the useful power consumed in heating the metal and slag. The power consumption by the furnace may potentially be reduced by 7.4% and the electrode consumption by 9%. The results confirm the need for research on phase-by-phase regulation of the power of ac arc furnaces.