Small Changes,Big Impact: Tungsten Bronzes with Extremely Large Second Harmonic Generation Achieved by the Transition Metal Doping on the B-Site

Two novel transition metal-doped tungsten bronze oxides, Pb_2.15Li_0.85Nb_4.85Ti_0.15O₁₅ (PLNT) and Pb_2.15Li_0.55Nb_4.85W_0.15O₁₅ (PLNW), are synthesized by high-temperature solid-state reactions. The Rietveld method using the high-resolution synchrotron radiation indicates that PLNT and PLNW crystallize in the orthorhombic polar noncentrosymmetric space group, Pmn2₁ (no. 31). As a class of tungsten bronze oxide, PLNT and PLNW retain a unique rigid framework composed of d⁰ transition metal cation (Ti⁴⁺ or W⁶⁺)-doped highly distorted NbO₆ octahedra along with the subsequently generated Pb/LiO₁₂ and PbO₁₅ polyhedra. Interestingly, the d⁰ transition metal-doped tungsten bronzes, PLNT and PLNW, exhibit extremely large second-harmonic generation (SHG) responses of 56 and 67 × KH₂PO₄, respectively. The observed immeasurably strong SHG is mainly attributed to a net polarization originating from the alignment of highly distorted NbO₆ octahedra with doped transition metals in the frameworks. It is believed that doping transition metal cations at the B-site of the tungsten bronze structures should be an innovative strategy to develop novel high-performance nonlinear optical materials.     

Deterministic Polymorphic Engineering of MoTe2 for Photonic and Optoelectronic Applications

Developing selective and coherent polymorphic crystals at the nanoscale offers a novel strategy for designing integrated architectures for photonic and optoelectronic applications such as metasurfaces, optical gratings, photodetectors, and image sensors. Here, a direct optical writing approach is demonstrated to deterministically create polymorphic 2D materials by locally inducing metallic 1T′-MoTe₂ on the semiconducting 2H-MoTe₂ host layer. In the polymorphic-engineered MoTe₂, 2H- and 1T′- crystalline phases exhibit strong optical contrast from near-infrared to telecom-band ranges (1–1.5 µm), due to the change in the band structure and increase in surface roughness. Sevenfold enhancement of third harmonic generation intensity is realized with conversion efficiency (susceptibility) of ≈1.7 × 10⁻⁷ (1.1 × 10⁻¹⁹ m² V⁻²) and ≈1.7 × 10⁻⁸ (0.3 × 10⁻¹⁹ m² V⁻²) for 1T′ and 2H-MoTe₂, respectively at telecom-band ultrafast pump laser. Lastly, based on polymorphic engineering on MoTe₂, a Schottky photodiode with a high photoresponsivity of 90 AW⁻¹ is demonstrated. This study proposes facile polymorphic engineered structures that will greatly benefit realizing integrated photonics and optoelectronic circuits.     

吊车钢丝绳非线性谐振建模及消谐控制

对于欠驱动吊车而言, 已有的方法都只考虑如何消除摆角. 然而当钢丝绳的摆角很小时, 钢丝绳上可能仍 然会存在严重的谐振. 针对吊车的消谐问题, 本文率先提出了一种基于钢丝绳–电机轴的非线性谐振力矩模型. 具体而言, 先利用振动力学的方法, 建立了非线性谐振力矩模型, 该模型可以将钢丝绳上的非线性谐振力矩归算到电机轴上, 然后通过电机控制器调节电机的输出力矩, 使得电机输出的基波主力矩上叠加一个大小相等方向相反的非线 性谐振力矩, 以达到消除钢丝绳上的谐振力矩的目的. 最后通过Simulink仿真和实验证明该方法具有良好的控制性 能, 不仅可以有效消除钢丝绳上的谐振, 并且能进一步减小摆角.     

基于ETAP的海上风电场接入对电能质量的评估分析

由于海上风资源的多变性,以及风力发电机中存在较多的电力电子元器件,海上风电场并网后会产生电能质量问题。本文选取某海上风电场作为研究对象,基于风电场实际运行数据,参考国标规定,对该风电场的电能质量（电压偏差、电压闪变、电压波动、谐波）进行求解。基于风机的无功特性,本文对某海上风电场接入电网公用变电站的无功补偿容量进行研究。在电能质量计算与分析方面,参考相关规程规定,完成电压偏差、电压闪变、电压波动部分指标的限值与实际值计算,并进行对比;通过ETAP软件中的谐波分析模块,进行谐波模拟仿真,得到谐波指标的实际值,并与理论计算的限值对比。当谐波电流超出国家标准的时候,通过在母线接入单调谐滤波器的方法,进行谐波治理,达到电能质量相关要求。     

电力系统密集型频率信号的测量与分析

针对非同步采样条件下密集频率信号无法准确测量的问题,提出一种密集型频率信号检测方法。基于离散傅里叶变换建立密集型频率信号模型,然后对单通道观测信号做周期延拓,形成多路信号。使用可变主成分分析法进行去相关性处理。再基于极大似然盲源分离法求解密集型频率信号模型。最后根据比例系数校正各频率成分参数。仿真和实验结果表明,所提方法具有较高的精度和一定的抗噪声能力。     

基于改进生成对抗网络的谐波状态估计方法

传统的基于最小二乘法的谐波状态估计受到量测装置少、精确的谐波阻抗获取难、网络拓扑结构复杂以及电网运行方式变化等因素的限制,造成量测方程欠定、系统非全局可观以及节点间耦合关系难以准确提取等问题。文中提出了一种基于改进生成对抗网络的谐波状态估计方法。该方法基于pix2pix谐波状态估计网络拟合监测节点与目标节点间的耦合关系,利用采集的历史谐波数据,对模型进行批量训练,通过训练之后的生成网络估算目标节点谐波电流、谐波电压幅值,实现基于数据驱动的谐波状态估计。在加噪环境下对模型进行测试,仿真结果验证了所提方法的有效性。     

Harmonic control of a dual-valve hydraulic servo system with dynamically allocated flows

Modern industries face increasing demands to improve the precision and workability of equipment, leading to stringent requirements for hydraulic servo systems in terms of flow, accuracy, and output power. High-flow servo valves and multi-valve synchronous control methods have seen more applications in the industry to meet these demands. However, high-flow servo valves are expensive and have unsatisfactory performance, and synchronous control methods require servo valves to have the same hydraulic characteristics, resulting in higher cost and lower accuracy of high-flow hydraulic servo systems. Also, very little has been conducted on controlling single actuators using multiple valves. In this study, we design a novel dual-valve hydraulic servo system structure with a high-flow proportional directional valve that is connected in parallel with a low-flow servo valve and further develop the mathematical model of this dual-valve system. Next, a harmonic control scheme was proposed, which included a flow allocation layer and trajectory tracking layer. Thereby, we achieved optimal control of two valves, and robust performance was guaranteed. Finally, we investigate the relationships between the flows of two valves, the deadband of the proportional directional valve, and trajectory tracking errors. Experimental results show that the proposed control scheme can effectively adjust the output flow of each valve dynamically according to the tracking trajectory and the hydraulic characteristics of the two valves, and the tracking performance of the servo system is significantly improved. This method is promised to enable the realization of an economical, high-flow, high-precision hydraulic servo system that can be generally used in various fields, such as marine engineering and construction.     

基于汉宁窗的配电网同步相量测量装置算法及应用

配电网量测环境复杂、恶劣,输电网的传统同步相量算法难以满足要求。分析了常用窗函数下傅立叶算法的谐波抑制能力,利用3个等间隔的加汉宁窗离散傅立叶变换（FFT）推导出定间隔采样下同步相量测量算法,在理论上消除了非额定频率下的频率泄露影响,能满足高精度的相位测量要求,具有很好的谐波/间谐波抑制能力。针对多个信号同时存在时频谱泄露影响计算精度问题,分析比较了加汉宁窗FFT插值算法相对其他窗函数的优势。理论分析和实际测试表明,采用上述方案后,提升了相量、谐波/间谐波等量值的测量精度。     

基于EL模型的TNPC型APF自抗扰无源控制策略

提出一种基于三电平T型中性点箝位(TNPC)型有源电力滤波器(APF)自抗扰无源控制策略,有效解决了传统TNPC型APF控制策略存在控制性能不佳的问题。建立了TNPC型APF的欧拉-拉格朗日(EL)模型,基于系统的无源性,采用注入阻尼的方法,设计了电流内环的无源控制器,从理论上保证了系统的稳定性。在电压外环使用了自抗扰控制(ADRC)技术,有效提高直流侧电压控制能力,缓解了超调的问题,使系统具有良好的动静态性能,并维持了直流侧电压的稳定。仿真和试验结果验证了所提控制策略的可行性和优越性。     

基于双谐波绕组的混合励磁发电机励磁控制系统

为了解决不同运行工况下混合励磁同步发电机端电压恒定的问题,设计了一种基于全桥变换器拓扑的励磁控制系统。励磁系统采用以电枢绕组电压为外环、定子谐波励磁绕组电流为内环的双闭环控制策略,以谐波无刷混合励磁同步发电机端电压为反馈信号,通过调节定子谐波励磁绕组电流,以维持发电机端电压恒定。阐述了双谐波绕组的混合励磁发电机的基本结构和工作原理,设计了励磁控制系统的软硬件,并测试了励磁控制系统的性能。实验结果表明：调节定子谐波励磁绕组电流,可以很好的调节发电机的端电压;通过励磁控制系统的自动调节功能,实现了发电机在不同负载情况下的输出电压恒定。