双层复合衬砌隧洞运行安全预警监控指标研究

双层复合衬砌结构是一种新型隧洞衬砌结构型式,其外衬承受外部水土压力,内衬承受内水压力,体现了"结构联合、功能独立"的新型输水隧洞设计理念,目前该衬砌型式已成功应用到我国北方某输水工程中,如何确定双层复合衬砌隧洞安全预警监控指标是工程运行管理的重点和难点。本文基于以往研究成果,提出了工程结构监控指标及监控阈值确定的统一技术路径;根据双层复合衬砌结构受力特点,开展可能破坏模式分析;基于破坏模式与监测量的敏感性分析,提出层间渗压作为双层复合衬砌隧洞结构核心监控指标,内衬处的钢筋计测值以及外衬处的测缝计测值作为辅助监控指标,为双层复合衬砌隧洞安全运行提供借鉴和参考。     

Performance Comparison of Circuits for Pole‐Mounted STATCOM Using SiC Devices

The recent years have seen an increasing trend in the cumulative installed capacity of distributed generators. As a result, voltage management may become difficult in existing power distribution systems in the future. A STATCOM (STAtic synchronous COMpensator) is a promising option for solving this problem because it can control reactive power rapidly and continuously. For a distribution system, STATCOM needs to be pole‐mounted to realize its low cost. However, a transformer for a STATCOM is large and heavy, and hence it is difficult to install a STATCOM on a distribution pole. We adopt a transformerless STATCOM to reduce STATCOM size and use SiC devices with low‐loss performance to obtain a more compact and efficient STATCOM. There are a large number of circuits available for a STATCOM, and there has been considerable research on performance comparisons among these circuits. However, these comparisons were drawn under different conditions, including switching frequency and level number for the circuits. In addition, these comparisons do not include the use of SiC devices. We made an equitable comparison for a 100 kVa pole‐mounted STATCOM using SiC devices. We discuss the performance and characteristics of each circuit in terms of efficiency and volume.     

A high efficiency input/output magnetically coupled interleaved buck–boost converter with low internal oscillation for fuel-cell applications: Small signal modeling and dynamic analysis

Dynamic behavior of DC–DC converters plays a crucial role in stability of renewable energy exploitation systems. This paper presents small signal modeling of an input/output magnetically coupled interleaved buck–boost converter for fuel-cell applications to help the designers with the better understanding of converter dynamics. Aiming to have a continuous converter transfer function for a smooth transition between the operation modes and an improved inner dynamics, a damping network and an input/output coupling have been added to the interleaved structure of well-known cascaded buck–boost converter. Having the same step-up/step-down voltage transfer ratio, smooth transition and improved inner dynamics make this converter quite suitable for renewable energy applications. The paper presents a small signal ac equivalent circuit model of the proposed converter based on state space averaging (SSA) method. Simulation results show remarkable improvements in converter dynamic behavior in both time and frequency domains. Prototype setup of 360 W and 36 V output voltage for a fuel cell with a brand of “FCgen 1020ACS” Ballard Power Systems, Inc. was implemented. Experimental results are presented to verify the theoretical model and its expected merits.     

中高压变频器冷却方案比较和选型分析

随着电力电子器件的发展,性能优异的中高压变频器在各行各业中得到越来越广泛的应用,能否处理好变频器的散热问题是其长期稳定运行的关键。分析了中高压变频器热量产生来源,并从技术可行性、可靠性、经济性等角度对不同冷却方案的特点进行比较,并结合实际的工程案例,给出合理的变频器冷却方案选型建议,可作为工程电气设计时中高压变频器冷却方案选型参考。     

硬煤工作面煤壁破坏与防治机理

高强度、大采高开采条件下,硬煤煤壁破坏的频率及程度逐渐严重,为提高该类工作面煤壁稳定性,实现安全、高效开采,采用室内试验、理论分析及现场实测综合手段对硬煤煤壁破坏形式、发生机理及影响因素进行分析。软煤、硬煤在单轴压缩条件下分别表现为静态、动力破坏,泊松比不同是煤体出现不同破坏形态的内在原因,三轴抗压试验表明围压可有效改变硬煤破坏的静-动转化;将煤壁、顶板及支架组成的平衡系统抽象出2种边界条件,根据煤体弹模、泊松比及边界条件的不同提出压剪、拉剪及拉裂3种煤壁破坏形式,硬煤多发生后2种破坏形式;推导出拉剪、拉裂型破坏的发生判据,得到拉剪型破坏起裂角、拉裂型破坏深度的确定方法及影响因素;拉剪型破坏对各影响因素的敏感度依次为黏聚力、顶板压力、支架阻力、抗拉强度,采高、护帮板压力及护帮高度对煤壁稳定性的影响不明显,拉裂型破坏对各影响因素的敏感度依次为抗拉强度、采高、顶板压力、支架阻力和控顶距等。     

Deterministic and probabilistic ship pitch prediction using a multi-predictor integration model based on hybrid data preprocessing,reinforcement learning and improved QRNN

The deterministic and probabilistic prediction of ship motion is important for safe navigation and stable real-time operational control of ships at sea. However, the volatility and randomness of ship motion, the non-adaptive nature of single predictors and the poor coverage of quantile regression pose serious challenges to uncertainty prediction, making research in this field limited. In this paper, a multi-predictor integration model based on hybrid data preprocessing, reinforcement learning and improved quantile regression neural network (QRNN) is proposed to explore the deterministic and probabilistic prediction of ship pitch motion. To validate the performance of the proposed multi-predictor integrated prediction model, an experimental study is conducted with three sets of actual ship longitudinal motions during sea trials in the South China Sea. The experimental results indicate that the root mean square errors (RMSEs) of the proposed model of deterministic prediction are 0.0254°, 0.0359°, and 0.0188°, respectively. Taking series #2 as an example, the prediction interval coverage probabilities (PICPs) of the proposed model of probability predictions at 90%, 95%, and 99% confidence levels (CLs) are 0.9400, 0.9800, and 1.0000, respectively. This study signifies that the proposed model can provide trusted deterministic predictions and can effectively quantify the uncertainty of ship pitch motion, which has the potential to provide practical support for ship early warning systems.     

Effect of utilization of hydrogen-rich reformed biogas on the performance and emission characteristics of common rail diesel engine

The utilization of renewable gaseous fuels in the diesel engine has gained significant interest in recent years due to its clean-burning nature and higher availability. In this study, hydrogen-rich reformed biogas was used as a gaseous fuel in a common rail diesel engine with diesel as pilot fuel. The hydrogen-rich reformed gas was synthesized through dry-oxidative reforming. The experimentations were performed in the load range from 6 to 24 N m with two different flow rates of gaseous fuel (0.5 and 1.5 kg/h) at a constant speed of 1800 RPM. The effects on engine performance parameters (brake thermal efficiency, brake specific energy consumption, and brake specific diesel consumption), combustion parameters (rate of pressure rise and maximum heat release rate) and emission parameters (Unburnt hydrocarbons, nitrogen oxides, carbon monoxide, and carbon dioxide) were assessed. The induction of gaseous fuel led to an increase in brake thermal efficiency by 10.5%, reduction in brake specific energy consumption by 13.6%, and a reduction of 26.4% in brake specific diesel consumption with a flow rate of 0.5 kg/h when compared to diesel-only mode at 24 N m load. The HC, NO_X and CO₂ emissions were reduced by 18.2%, 7.4% and 1.4% with a flow rate of 0.5 kg/h when compared to diesel-only mode at 24 N m load due to lower availability of carbon content in the combustible mixture. The utilization of renewable fuel like hydrogen-rich reformed biogas has great potential for overcoming the issue related to both biogas and hydrogen in diesel engines. Moreover, the higher diesel substitution also demonstrates the potential for cost-saving and fossil fuel conservation.     

An adaptive sliding mode observer based near-optimal OER tracking control approach for PEMFC under dynamic operation condition

Tracking control of oxygen excess ratio (OER) is crucial for dynamic performance and operating efficiency of the proton exchange membrane fuel cell (PEMFC). OER tracking errors and overshoots under dynamic load limit the PEMFC output power performance, and also could lead oxygen starvation which seriously affect the life of PEMFC. To solve this problem, an adaptive sliding mode observer based near-optimal OER tracking control approach is proposed in this paper. According to real time load demand, a dynamic OER optimization strategy is designed to obtain an optimal OER. A nonlinear system model based near-optimal controller is designed to minimize the OER tracking error under variable operation condition of PEMFC. An adaptive sliding mode observer is utilized to estimate the uncertain parameters of the PEMFC air supply system and update parameters in near-optimal controller. The proposed control approach is implemented in OER tracking experiments based on air supply system of a 5 kW PEMFC test platform. The experiment results are analyzed and demonstrate the efficacy of the proposed control approach under load changes, external disturbances and parameter uncertainties of PEFMC system.     

Microwave dielectric ceramics in (Mg1/3Sb2/3)O2-ZrO2-TiO2 system with near zero τf and low loss in a very wide range

A series of (ZrTi)_1-x(Mg_1/3Sb_2/3)_2xO₄ (0.04?≤?x?≤?0.36) ceramics were successfully synthesized through the conventional solid-state processing. Appropriate content of CuO was added as sintering aids to promote the density of ceramics. The XRD analysis revealed that the main crystalline phase of ceramics sintered at optimal temperature belonged to α-PbO₂-type structure. Raman spectroscopy and far infrared reflectivity (FIR) spectra were employed to study the phonon modes of ceramics, which explained the relationship between microwave dielectric properties and structure. It is interesting that the τ_f are near-zero (+6.6 ~ ?4.6?ppm/°C) and meanwhile the Q×f are relatively high (29,000–41,800?GHz) for samples with x in a very wide range of 0.10–0.36. In this range, their dielectric constants (ε_r) can be adjustable from 35.4 to 24.4. The results demonstrated this ceramic system is a potential candidate for microwave dielectric applications requiring an adjustable dielectric constants and near zero τ_f.