Key technologies for medium and low voltage DC distribution system

Development of the medium and low voltage DC distribution system is of great significance to a regional transmission of electric energy,increasing a penetration rate of new energy,and enhancing a safety of the operation of the AC/DC interconnected grid.This paper first summarizes the medium and low voltage DC distribution system schemes and plans put forward by many countries,and then elaborate status of under-construction medium and low voltage DC distribution system project cases in China.Based on these project cases,this paper analyzes key issues involved in the medium and low voltage DC distribution system topologies,equipment,operation control technologies and DC fault protections,in order to provide theoretical and technical reference for future medium and low voltage DC distribution system-related projects.Finally,this paper combines a current China research status to summarize and give a prediction about the future research direction of medium and low voltage DC distribution system,which can provide reference for the research of medium and low voltage DC distribution system.

Unified Hydrodynamics and Pseudorapidity Distributions of Charged Particles Produced in Heavy Ion Collisions at Low Energies at RHIC

In the context of unified hydrodynamics, we discuss the pseudorapidity distributions of the charged particles produced in Au-Au and Cu-Cu collisions at the low RHIC energies of √SNN = 19.6 and 22.4 GeV, respectively. It is found that the unified hydrodynamics alone can give a good description to the experimental measurements. This is different from the collisions at the maximum RHIC energy of √SNN = 200 GeV or at LHC energy of √SNN= 2.76 TeV, in which the leading particles must be taken into account so that we can properly explain the experimental observations.

Research on Low Voltage Series Arc Fault Prediction Method Based on Multidimensional Time-Frequency Domain Characteristics

The load types in low-voltage distribution systems are diverse.Some loads have current signals that are similar to series fault arcs,making it difficult to effectively detect fault arcs during their occurrence and sustained combustion,which can easily lead to serious electrical fire accidents.To address this issue,this paper establishes a fault arc prototype experimental platform,selects multiple commonly used loads for fault arc experiments,and collects data in both normal and fault states.By analyzing waveform characteristics and selecting fault discrimination feature indicators,corresponding feature values are extracted for qualitative analysis to explore changes in timefrequency characteristics of current before and after faults.Multiple features are then selected to form a multidimensional feature vector space to effectively reduce arc misjudgments and construct a fault discrimination feature database.Based on this,a fault arc hazard prediction model is built using random forests.The model’s multiple hyperparameters are simultaneously optimized through grid search,aiming tominimize node information entropy and complete model training,thereby enhancing model robustness and generalization ability.Through experimental verification,the proposed method accurately predicts and classifies fault arcs of different load types,with an average accuracy at least 1%higher than that of the commonly used fault predictionmethods compared in the paper.

Development of Surface Grating Distributed Feedback Quantum Cascade Laser for High Output Power and Low Threshold Current Density

We report on the room-temperature cascade laser （QCL） at λ -4.7μm. cw operation of a surface grating Both grating design and material distributed feedback （DFB） quantum optimization are used to decrease the threshold current density and to increase the output power. For a high-reflectivity-coated 13-μm-wide and 4- mm-long laser, high wall-plug efficiency of 6% is obtained at 20℃ from a single facet producing over I W of ew output power. The threshold current density of DFB QCL is as low as 1.13kA/cm^2 at 10℃ and 1.34kA/cm2 at 30℃ in cw mode. Stable single-mode emission with a side-mode suppression ratio of about 30 dB is observed in tile working temperature range of 20-50℃.

考虑新能源不确定性的电气热耦合系统分布鲁棒优化调度

在高比例新能源渗透的背景下,电气热耦合系统能提升能源利用效率,降低碳排放,是助力“双碳”目标的有效途径之一。因此针对考虑新能源不确定性的电气热耦合系统分布鲁棒优化调度开展研究。首先,结合Wasserstein度量与矩信息构建复合模糊集,以剔除分布鲁棒模糊集中极端分布信息,提升调度的经济性与可靠性;其次,结合复合模糊集与联合机会约束,建立考虑碳排放约束的电气热耦合系统分布鲁棒调度模型,以充分考虑新能源不确定性的同时限制系统碳排放;然后,提出一种基于对偶定理与McCormick包络的联合机会约束与目标函数转化方法,将分布鲁棒模型转为确定性线性调度模型;最后,通过算例仿真表明,提出的分布鲁棒联合机会约束模型,能够将成本降低10.04%,并且将总碳排放量降低27.9%。

Consumer-branch Connectivity Identification of Low Voltage Distribution Networks Based on Data-driven Approach

Accurate topological information is crucial in supporting the coordinated operational requirements of source-load-storage in low-voltage distribution networks.Comprehensive coverage of smart meters provides a database for low-voltage topology identification(LVTI).However,because of electricity theft,power line commu-nication crosstalk,and interruption of communication,the measurement data may be distorted.This can seriously affect the performance of LVTI methods.Thus,this paper defines hidden errors and proposes an LVTI method based on layer-by-layer stepwise regression.In the first step,a multi-linear regression model is developed for consumer-branch connectivity identification based on the energy conservation principle.In the second step,a significance factor based on the t-test is proposed to modify the identification results by considering the hidden errors.In the third step,the regression model and significance threshold parameters are iteratively updated layer by layer to improve the recall rate of the final identification results.Finally,simulations of a test system with 63 users are carried out,and the practical application results show that the proposed method can guarantee over 90%precision under the influence of hidden errors.

An ultra-broadband distributed passive gate-pumped mixer in 0.18μm CMOS

A broadband distributed passive gate-pumped mixer（DPGM） using standard 0.18μm CMOS technology is presented.By employing distributed topology,the mixer can operate at a wide frequency range.In addition,a fourth-order low pass filter is applied to improve the port-to-port isolation.This paper also analyzes the impedance match and conversion loss of the mixer,which consumes zero dc power and exhibits a measured conversion loss of 9.4—17 dB from 3 to 40 GHz with a compact size of 0.78 mm^2.The input referred 1 dB compression point is higher than 4 dBm at a fixed IF frequency of 500 MHz and RF frequency of 23 GHz,and the measured RF-to-LO, RF-to-IF and LO-to-IF isolations are better than 21,38 and 45 dB,respectively.The mixer is suitable for WLAN, UWB,Wi-Max,automotive radar systems and other millimeter-wave radio applications.