考虑变幂数的畸变动力学相似试验模型设计方法及试验研究

动力学相似理论广泛应用于大型结构的振动试验，其中畸变相似用于解决结构的设计参数不满足等比例缩放时的相似问题，针对畸变相似关系中幂数为定值导致预测精度低的问题，提出考虑变幂数的畸变动力学相似试验模型设计方法。首先，在敏感性分析与中心差分理论推导的幂数表达式的基础上，将中心差分的范围不断扩大得到一组随相似比变化的幂数。采用最小二乘法将这组幂数拟合为关于相似比的函数并建立相似关系。然后，在多盘转子系统的数值算例中将变幂数法与文献中的两种方法进行对比，结果表明，变幂数法的预测精度较文献中的方法有很大提高。最后，通过试验研究验证了数值算例中动力学模型及临界转速求解的正确有效性。相似关系的建立是以模型的临界转速为基础，因此也验证了数值算例中的相似预测结果。     

Effect of carriers on deposition morphologies and catalytic performances of NiCo2O4

In this study, NiCo₂O₄ with different morphologies were fabricated using carriers by homogeneous coprecipitation combined with a sintering method. The phase and microstructure were characterized by XRD, SEM, EDS, TEM and BET, and the catalytic performances were investigated by NaBH₄ hydrolysis experiments. These studies revealed that the deposition morphology of NiCo₂O₄ can be adjusted by using different kinds of carrier templates, and the supported NiCo₂O₄ samples presented the pine-needle-like, network-like, ball-cactus-like and dandelion-like morphologies respectively. The optimal catalytic activity, durability and stability make the network-like NiCo₂O₄ an appropriate catalyst for hydrogen generation of NaBH₄ hydrolysis. It was found that the network-like NiCo₂O₄ is the most reusable and durable catalyst for ten consecutive cycles and 100% hydrogen generation conversion rate without obvious decrease among these morphologies.     

Process-induced variability modeling of subthreshold leakage power considering device stacking

The dominance of leakage currents in circuit design has been impelled by steady downscaling of MOSFET into nanometer regime, and has become a significant component of total IC power dissipation. The issue is further aggravated with the inability to gauge the tolerance of process parameters around their nominal value. Consequently, the drive to improve the static power prediction has enticed accurate and reliable modeling of leakage current, specifically for ultralow power applications. In contrast to gate- and band-to-band-tunneling leakages, subthreshold leakage exhibits high susceptibility to process variations and hence has been considered for variability modeling. Fluctuations in the device electrical and geometry parameters result in a wider distribution of subthreshold leakage current. Hence, taking into account stacking effect, an analytical variability model to estimate subthreshold leakage power in subthreshold circuits, in the presence of threshold voltage variations is proposed. Further, the impact of threshold voltage variability on subthreshold leakage power is modeled in conjunction with simultaneous variations in gate length and width. The leakage power variability is characterized by model-generated distributions obtained using Monte Carlo analysis and validated against SPICE simulations. The proposed model is about 700 computationally faster than SPICE simulations with mean error being less than 0.19%.     

Reducing cycling costs in coal fired power plants through power to hydrogen

The increase of renewable share in the energy generation mix makes necessary to increase the flexibility of the electricity market. Thus, fossil fuel thermal power plants have to adapt their electricity production to compensate these fluctuations. Operation at partial load means a significant loss of efficiency and important reduction of incomes from electricity sales in the fossil power plant. Among the energy storage technologies proposed to overcome these problems, Power to Gas (PtG) allows for the massive storage of surplus electricity in form of hydrogen or synthetic natural gas. In this work, the integration of a Power to Gas system (50 MWe) with fossil fuel thermal power plants (500 MWe) is proposed to reduce the minimum complaint load and avoid shutdowns. This concept allows a continuous operation of power plants during periods with low demand, avoiding the penalty cost of shutdown. The operation of the hybrid system has been modelled to calculate efficiencies, hydrogen and electricity production as a function of the load of the fossil fuel power plant. Results show that the utilisation of PtG diminishes the specific cost of producing electricity between a 20% and 50%, depending on the framework considered (hot, warm and cold start-up). The main contribution is the reduction of the shutdown penalties rather than the incomes from the sale of the hydrogen. At the light of the obtained results, the hybrid system may be implemented to increase the cost-effectiveness of existing fossil fuel power plants while adapting the energy mix to high shares of variable renewable electricity sources.     

计及损耗的双馈感应风力发电机高电压穿越控制策略

利用换向原理分析其电磁暂态特性，在此基础上，对DFIG输出无功功率与其铜损耗的解析关系进行了理论分析，推导出了使铜损耗最低的DFIG输出无功功率最优参考值。同时，转子的瞬时功率补偿分量减小了DC总线电压的波动，从而减少了转换器的功率损耗。由此，提出了考虑DFIG铜损和转换器损耗的DFIG高电压穿越控制策略。仿真结果表明，该控制策略可以在保证DFIG高电压穿越能力的同时降低DFIG铜损耗与换流器损耗，并具有较好的暂态特性。     

单相并联型有源电力滤波器主电路参数耦合关系研究

单相并联型有源电力滤波器(SAPF)主电路参数之间存在一定的耦合关系,这对各参数值的合理选择有较大的影响。通过分析现有单/三相SAPF主电路交流侧电感以及直流侧电压、电容值等参数的计算方法,得到了具体的单相SAPF电路参数解析表达式。针对所得表达式各变量之间的耦合关系,在MATLAB中进行建模优化分析,得出一套完整的参数设计方案。保证在特定负载下补偿后谐波含量低于2%的综合优化目标。仿真和实验过程验证了所选参数的正确性。     

采用绝热式自燃测试方法分析煤的自燃倾向

对煤的自燃倾向进行快速有效鉴别,有助于对煤的自燃倾向采取分级分类管理从而有效防治煤矿火灾,因而采用绝热式自燃测试方法对煤的自燃倾向进行准确分析很有必要。简要介绍绝热式自燃测试方法的测试原理及其仪器结构,模拟煤炭自燃的物理过程,通过采用包括反应器、气体预热铜管和跟踪温度控制方式等综合绝热措施以实现300 g煤样的自然发火实验,记录煤样从40℃上升到70℃的升温速率(或前30 h的升温速率),测试煤样的自燃特性曲线并分析曲线特征。即建立煤绝热氧化产热速率计算模型,结合实验数据计算所得的煤在绝热氧化条件下的升温速率和产热速率可鉴定煤自燃倾向性的强弱。采用绝热式自燃测试方法对不同煤的自燃倾向分析后表明,无烟煤和部分烟煤的自燃倾向较低,褐煤的自燃倾向较高,故而在煤矿开采时需特别注意褐煤的自燃倾向。     

Enabling supercapacitors to compete for ancillary services: An important step towards 100 % renewable energy

While wind and solar generation has increased dramatically over the past decade, there has been a much larger increase in gas generation (eia, 2019). This is driven in part by low gas prices but also in part by how electricity markets are organized. The intermittent nature of wind and solar generation increases the need for more flexible and reliable generation; a role gas plants fill well. However, current market structures and rules unfairly tip the balance in their favor compared to energy storage systems. They have created market barriers restrictive enough to prevent market participation of a technology key to a 100 % renewable grid: supercapacitors. Adjusting markets to remove the market barriers to supercapacitor and other energy storage systems will allow for increased renewable penetration while simultaneously improving grid performance and reducing costs.     

CNG-电混动公交车道路行驶工况与排放特性研究

CNG-电公交车以天然气作为发动机燃料,辅以电机共同驱动的混合动力车辆,车辆行驶速度低、启动频繁等特性,发动机实际运行工况与型式检验工况具有较大差异。为研究其实际行驶工况与排放特性,选取4辆国V排放标准的CNG-电混合动力公交车,往返于市区与城郊,使用PEMS(portable emission measurement system)实时收集车辆行驶及NO_X排放数据。结果表明,发动机运行工况集中于中低功率段,与型式检验工况差异较大,污染物排放集中于发动机切入车辆传动系统的临界车速附近。     

电厂管理按要素划分区域精准成本控制

为了降低发电企业运行成本,本文提出按生产要素划分为水、煤、电三个区域,精准分析造成煤耗、电耗、水耗高的原因,对可控成本的关键指标采取针对性措施,实现了电厂降低生产成本、节能降耗的目标。