VOLUMETRIC MASS TRANSFER COEFFICIENT BETWEEN SLAG AND METAL IN COMBINED BLOWING CONVERTER

The effects of operation parameters of combined blowing converter on the volumetric mass transfer coefficient between slag and steel are studied with a cold model with water simulating steel, oil simulating slag and benzoic acid as the transferred substance between water and oil. The results show that, with lance level of 2.1m and the top blowing rate of 25000Nm3/h, the volumetric mass transfer coefficient changes most significantly when the bottom blowing rate ranges from 384 to 540Nm3/h. The volumetric mass transfer coefficient reaches its maximum when the lance level is 2.1m, the top blowing rates is 30000Nm3/h, and the bottom blowing rate is 384Nm3/h with tuyeres located symmetrically at 0.66D of the converter bottom.

Study on the optimization of the combined blown converter process in Chongqing Iron and Steel Company

The effects of lance height and bottom blown flowrate on the mixed time, the splashing amount, the penetrating depth, and the level fluctuation of an 85 t combined blown converter have been studied using a water model. The results show that the maximal stirring energy is provided to the bath at the top lance height of about 50-100 mm. When the top lance height is in the range ofg0- 110 mm, the splashing amount caused by the top jet can reach the maximal value. The appropriate operational parameters of Chongqing Iron and Steel Company （CISC） converter have been established that the top lance height is 1600-1760 mm and the bottom blowing flowrate is 240-480 Nm^3/h in the primary phase of a heat, 1100-1300 mm and 160-200 Nm^3/h in the second phase, and 1040-1120 mm and 200-350 Nm^3/h in the end phase. Also, the trial shows that the metallurgical result of the studied blow pattern is better than that of the former pattern. At the starting 3-4 min of a heat, the strong splashing is eliminated. 2008 University of Science and Technology Beijing. All rights reserved.

Extreme Responses of An Integrated System with A Semi-Submersible Wind Turbine and Four Torus-Shaped Wave Energy Converters in Different Survival Modes

Offshore wind power is a kind of important clean renewable energy and has attracted increasing attention due to the rapid consumption of non-renewable energy.To reduce the high cost of energy,a possible try is to utilize the combination of wind and wave energy considering their natural correlation.A combined concept consisting of a semi-submersible wind turbine and four torus-shaped wave energy converters was proposed and numerically studied under normal operating conditions.However,the dynamic behavior of the integrated system under extreme sea conditions has not been studied yet.In the present work,extreme responses of the integrated system under two different survival modes are evaluated.Fully coupled time-domain simulations with consideration of interactions between the semi-submersible wind turbine and the torus-shaped wave energy converters are performed to investigate dynamic responses of the integrated system,including mooring tensions,tower bending moments,end stop forces,and contact forces at the Column-Torus interface.It is found that the addition of four tori will reduce the mean motions of the yaw,pitch and surge.When the tori are locked at the still water line,the whole integrated system is more suitable for the survival modes.

Model predictive control of three-level active front-end converter with low switching frequency

In medium voltage-high power(MV-HP)applications,the high switching frequency of power converter will result in unnecessary energy losses,which directly affect efficiency.To resolve this issue,a novel finite control set-model predictive control(FCS-MPC)with low switching frequency for three-level neutral point clamped-active front-end converters(NPC-AFEs)is proposed.With this approach,the prediction model of three-level NPC-AFEs is established inα-βreference frame,and the control objective of low average switching frequency is introduced into a cost function.The proposed method not only achieves the desired control performance under low switching frequency,but also performs the efficient operation for the three-level NPC-AFEs.The simulation results are provided to verify the effectiveness of proposed control scheme.

Comprehensive predictive control of neutral-point voltage balancing for back-to-back three-level NPC converters

A comprehensive predictive strategy was proposed for the neutral-point balancing control of back-to-back three-level converters. The phase currents at both sides and the DC-link capacitor voltages were measured for the prediction of the neutral-point current. A quality function was found to balance the neutral-point, and a metabolic on-times distribution factor was used as a predicator to minimize the quality function at each switching state. Simulation results show that the proposed method produces smaller ripples in tested signals compared with the established one, namely, 9.15% less in a total harmonic distortion(THD) of line-to-line voltage, 1.08% less in the THD of phase current, and 0.9 V less in the ripple of the neutral-point voltage. The obtained experimental results show that the main harmonics of the line-to-line voltage and the phase current in the proposed method are improved by 10 d B and 6 d B, respectively, and the ripple of neutral-point voltage is halved compared to the established one.

基于Logic Converter的组合逻辑电路设计

介绍了虚拟仪器Logic Converter的主要特点和使用方法 ,并以典型组合逻辑电路进行分析。实例表明,基于Logic Converter的组合逻辑电路设计不仅方便、简洁,而且大大提高了学生的学习兴趣,巩固了课程教学效果。

Effect of Surface Charge on Flashover for Oil-Pressboard Insulation under AC-DC Combined Electric Field

For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electric field distortion, trend to trigger surface discharge of barriers. This paper studied the influence of surface charge on flashover voltage of oil-impregnated pressboard under AC-DC combined electric field. The study finds that the flashover voltage of oil-pressboard interface under negative polarity DC superimposed AC electric field is higher than that.of positive DC superimposed AC voltage to form composite electric field. It was found that homopolar surface charge has been accumulated on the interface of oil-pressboard with positive or negative DC voltage through measuring surface potential by the electrostatic capacitive probe. The surface charge produced electric field in the opposite direction, which weakening the synthetic electric field strength. What＇s more, under the same conditions, the negative surface charge density oil-pressboard is much larger than the positive.

An Improved Modulation Strategy for Single-phase Three-level Neutral-point-clamped Converter in Critical Conduction Mode

Two-level totem-pole power factor correction(PFC)converters in critical conduction mode(CRM)suffer from the wide regulation range of switching frequency.Besides,in highfrequency applications,the number of switching times increases,resulting in significant switching losses.To solve these issues,this paper proposes an improved modulation strategy for the single-phase three-level neutral-point-clamped(NPC)converter in CRM with PFC.By optimizing the discharging strategy and switching state sequence,the switching frequency and its variation range have been efficiently reduced.The detailed performance analysis is also presented regarding the switching frequency,the average switching times,and the effect of voltage gain.A 2 k W prototype is built to verify the effectiveness of the proposed modulation strategy and analysis results.Compared with the totem-pole PFC converter,the switching frequency regulation range of the three-level PFC converter is reduced by 36.48%and the average switching times is reduced by 45.10%.The experimental result also shows a 1.2%higher efficiency for the three-level PFC converter in the full load range.

High Power Density Three-Level Three-Phase AC-DC 48 V Power Supply

International standards impose several constraints concerning the electric power quality and require that the harmonic content of the line current of grid connected equipment is below assigned limits; for this reason, operating of AC-DC converters with high power factor and low line current distortion has become essential. In this paper, the prototypal realization of a three-phase AC-DC 48 V power electronic converter for telecom system supplying is described and experimental testing results are discussed. The main constraints in the power supply design are the required power density of about 900 W per dm3 as well as the absence of the neutral wire in the supply grid. The carried out investigation is focused on three-level power converter configurations which are considered in order to reduce voltage rating of power switches. As a result of the reduced voltage, low on-resistance metal-oxide-semiconductor field effect transistors can be used in the power stage, solution which allows to achieve improved efficiency as well as increased switching frequency with respect to the insulated gate bipolar transistors based two-level topologies.

光储联合发电系统不对称故障穿越控制策略

针对电网不对称故障下光伏发电系统输出功率与直流侧电压二倍频波动问题,提出了一种光储联合发电系统低电压穿越控制策略。在低电压穿越期间,充分利用光伏并网逆变器和储能变流器容量向电网输送有功和无功功率;在此基础上令储能变流器采取基于负序虚拟电导的负序电压补偿控制策略;同时,分析了单台以及多台储能变流器参与负序电压补偿的原理,并对负序虚拟电导进行了自适应优化设计。仿真结果表明,所提控制策略能够有效削弱光伏发电系统输出功率与直流侧电压的二倍频波动。

基于微阵列波能装置的半潜式风浪联合系统运动与获能研究

为实现海上风浪资源的高效利用,以Windfloat型风力机平台为基础,结合摇臂式波能装置,建立联合获能系统数值模型,并分析了波周期、PTO(powertake-off)阻尼、浮子直径及摇臂长度等关键参数对联合系统运动与获能的影响。研究发现,随波周期的增大,平台运动幅度整体呈增大趋势,装置获能先增大后减小;随PTO阻尼的增大,平台纵荡、纵摇运动幅度逐渐减小,垂荡运动幅度及装置获能先增大后减小;随浮子直径、摇臂长度的增大,平台纵荡运动幅度逐渐减小、垂荡、纵摇运动幅度逐渐增大,装置获能随浮子直径的增大而增大,随摇臂长度的增大先增大后减小。

一种组合式宽输入高效率DC-DC变换器

针对车载DC-DC变换器输入电压变化范围大的问题,提出一种组合式宽输入高效率DC-DC变换器。该变换器包括飞跨电容(FC)型三电平Buck电路和LLC谐振电路两部分,FC三电平Buck电路输出端口与LLC谐振电路输入端口串联,通过控制FC三电平Buck电路占空比实现输出电压调节以适应宽输入电压范围,同时三电平结构降低了开关管电压应力、减小了损耗;LLC谐振电路传输负载所需全部功率,采用定频开环控制以获得高效率和稳定增益,同时实现了电气隔离。详细分析了组合式变换器的拓扑结构、直流增益以及工作效率,并与相同电路构成的级联式变换器进行了效率特性对比,根据组合式变换器的拓扑结构和工作特性,提出一种解耦控制策略,实现输出电压稳定和飞跨电容电压平衡,最后搭建了一个200~400 V输入、12 V/20 A输出的实验电路进行验证,实验结果表明所提组合式变换器的正确性和可行性。

多机系统锁相环振荡模式的数值域稳定判据

针对锁相环变流器多机系统的振荡问题,提出了面向多机系统锁相环振荡模式的数值域稳定判据,完善了广义Nyquist判据的可解释性。根据实际工程运行方式,通过保留变流器导纳矩阵中主导振荡的关键元素完成模型简化,进而利用矩阵数值域代替广义Nyquist判据,将多机系统的频域导纳矩阵等效为单机系统传递函数,以其Nyquist曲线不包围点(-1,0)作为多机系统稳定的充分条件。分析结果揭示了多机系统小干扰稳定性具有不同单机外特性相互折中的现象,为实用化的电网强度分析奠定了理论基础。通过特征值分析和时域仿真说明了所提方法的有效性。

国内120t转炉高效冶炼工艺研究进展

对比研究了国内钢厂120 t转炉供氧制度和底吹工艺的优化实践以及智能冶炼和冶炼新工艺的应用实践。结果表明:适用于120 t转炉的氧枪喷头孔数为5个;120 t转炉底吹系统通常配置4~8支底吹管路,通过提高转炉底吹强度,可降低炉渣Fe_(t)O含量和钢水终点磷含量;副枪和投弹仪均可应用于120 t转炉,但副枪与转炉炉口的有效距离需大于400 mm。

Vector Control Strategy of a T-type Three-level Converter Driving a Switched Reluctance Motor

A novel 12 voltage vector control strategy for switched reluctance motors(SRM)with a T-type three-level converter is proposed in this study.Based on a causal analysis of torque ripple under the control of conventional six voltage vectors,six new voltage vectors are added for further reduction of torque ripple.An optimized control rule is adopted based on the division method of the 12 new voltage vectors.A zero-voltage vector is used to adjust the duration of the 12 voltage vectors,the time of which is varied at different parts of the vector sectors according to the torque error.In addition,the windings are connected in a delta configuration,therefore,the number of connections between the converter and SRM is reduced.Finally,the results of MATLAB/Simulink and RT-LAB are presented to verify the validity of the proposed scheme.

顶底复吹转炉冶炼双相不锈钢的试验研究

通过500 kg多功能顶底复吹转炉吹炼铁水,进行双相不锈钢冶炼试验。采取钢水脱磷、降碳保铬、钢水深脱硫以及钢水增氮的方法,得到在碳质量分数降到2.0%时,钢水温度控制在1360~1440℃,炉渣的碱度控制在1.4~1.8,炉渣中FeO质量分数控制在15%~20%,钢水中的磷质量分数可以脱除75%以上;在钢水降碳保铬过程中,钢水温度始终控制在1660℃以上,同时随着碳含量降低,逐渐降低氧气比例,增加氩气比例,减少铬元素的氧化;合金化后继续对炉渣进行还原,碱度控制在2.0左右,钢水温度控制在1550~1600℃,渣中的FeO和MnO质量分数之和控制在1%以下,钢水中的硫质量分数可以由0.0040%降低到0.0010%;顶底复吹转炉冶炼双相不锈钢奥氏体和铁素体的占比在49%~51%,钢板的冲击性能远高于标准值180 J,性能满足用户的要求。

交直流电力系统与供热系统联合经济调度

随着热电联产等技术的广泛应用,电力系统和供热系统耦合日益紧密,电热联合调度得到了广泛的关注,但现有电热联合调度忽略了热网供电来源的多样性,由此提出了交直流电力系统与供热系统联合经济调度方法。首先,建立交直流电力系统模型,并提出一种线性近似方法对电压源变换器模型所带来的强非线性进行处理;然后,以运行成本最低为目标,建立考虑热网热惯性的交直流电力系统与供热系统联合调度模型,该模型中供热系统通过热电联产机组和交流电锅炉与交流电网耦合,通过直流电锅炉与直流电网耦合;最后,通过算例仿真验证了所提方法的有效性并说明了在电热联合调度中考虑交直流电源的必要性。

基于晶闸管的模块化组合式直流泄能装置及其协调控制策略

针对模块化多电平换流器(modular multilevel converter,MMC)高压直流输电技术(high voltage direct current,HVDC)受端交流系统故障引起的直流过电压问题,文中提出一种基于晶闸管的模块化组合式直流泄能装置拓扑及协调控制方法。该直流泄能拓扑包括模块化分布式泄能部分、限流电抗器和集中式泄能电阻3部分,对子模块工作模式进行设计,提出可避免直流泄能装置反复投切的弹性调节泄能的协调控制策略,推导直流泄能装置功率控制及其内部电气耦合关系,给出泄能装置元件参数的设计方法。最后,基于PSCAD/EMTDC搭建MMC-HVDC及所提出的直流泄能装置模型,研究单相和三相接地故障下直流泄能装置的特性及直流过电压抑制效果。结果表明,所提直流泄能装置在协调控制策略下能够分阶段弹性调节泄能功率,有效抑制直流过电压,并有利于故障后的快速恢复。