接地故障保护的设置和整定(三)

7 TT系统接地故障保护 TT系统的电源中性点直接接地,而电气设备的外露可导电部分则经各自的PE线接地。这样在大多数情况下,由于故障回路包括两个接地电阻,使接地故障电流太小,不足以使过电流保护动作切断接地故障电流。而且由于故障电流小,故障点未被熔焊,故障点阻抗是难以估计的接触电阻。因此,TT系统接地故障回路阻抗和故障电流难以估算。所以,必须设置漏电电流动作保护。     

一种低压高精度CMOS带隙基准

设计了一种改进的带隙基准电压源,通过采用分段电流补偿的方法,实现了低压高精度供电。研究基于TSMC 0.35μm CMOS 3V工艺基础,重点考虑主要工作温度区域输出电压随温度变化的精度问题。仿真结果表明,该电路可提供低至500mV的低压,实现了高阶电流补偿,在-40℃～+100℃温度范围内其温漂系数仅为3.7ppm/℃,在芯片主要工作温度范围内,输出基准电压最大偏差小于8μV,低频时电源抑制比为-70dB。     

浅谈低压断路器的现状及其主要技术性能

文章介绍了低压断路器的现状,阐述了智能型万能式断路器、智能型塑壳式断路器、剩余电流动作断路器、用于双电源自动切换的断路器等产品的主要特点及主要技术性能。     

低压电器的可靠性及其试验研究(四)

从可靠性的定义出发,阐述了低压电器可靠性的重要性。详细介绍了国外有关低压电器的可靠性标准,开展可靠性试验研究和现场调查的内容和结果,并列举IEC标准中有关低压电器可靠性的规定。文章着重介绍了我国开展低压电器产品可靠性试验研究和考核评定工作。涉及的产品包括:电磁式中间继电器、小容量交流接触器、切换电容接触器、有填料熔断器、剩余电流动作断路器、框架式断路器和塑壳式断路器等。详细介绍上述各类产品的可靠性试验内容、步骤、可靠性试验装置、可靠性指标和试验方法、可靠性考核评定及其结果以及可靠性增长试验研究等。最后对我国低压电器可靠性试验研究工作提出建议。     

一种新的低压大电流DC-DC变换器的研究

该文比较了低压大电流DC-DC变换器各种拓扑结构的优缺点，对称半桥一倍流整流对于48V的输入电压是一种合适的拓扑结构。它可以通过两个滤波电感纹波电流的叠加，极大地减小滤波电容上的纹波电流。从而可以减小滤波电感的值。而且在滤波电容旁串联一个电感，可以极大地发挥它的作用，将滤波电容上的纹波电流进一步减小。给出了电路的仿真模型，并使用PSpice对该模型进行仿真，最后得到的仿真结果同理论分析一致，取得满意效果。     

低压无功补偿装置不宜频繁投切

分析了以接触器为投切开关的低压电容无功补偿装置不宜频繁进行电容器投切的原因 ,阐明了投切时产生的过电压和冲击电流对自愈式电容器的各种危害 ,提出了合理的建议     

Nonlinear maximum power point tracking control and modal analysis of DFIG based wind turbine

The doubly fed induction generator based wind turbine (DFIG-WT) has strong nonlinearities originated from the aerodynamics of the wind turbine and the coupled dynamic of the DFIG, and can operate under a time-varying and wide operation region. This paper investigates a feedback linearisation controller based on the detailed model of the DFIG-WT, the control objective is to maximize energy conversion for this system. The original nonlinear system is partially linearized to a third-order linear system and a remained second-order internal nonlinear system. Fully decoupled control of the external dynamics is achieved, and the stability of the remained internal dynamics is analyzed via Lyapunov stability method. Moreover, modal analysis is applied for the nonlinear system controlled by the proposed nonlinear controller to verify its global optimal performance and low-voltage ride-through (LVRT) capability over various wind operation range. Simulation studies verify that more accurate tracking and better LVRT capability can be achieved in comparison with conventional vector control (VC).     

Solution-processed ytterbium oxide dielectrics for low-voltage thin-film transistors and inverters

High permittivity (high k) metal-oxide thin films fabricated via solution processes have recently received much attention for the construction of low-operating voltage and high-performance thin-film transistors (TFTs). In this report, amorphous ytterbium oxide (Yb₂O₃) thin films were fabricated by spin coating and their applications in TFTs were explored. The physical properties of the solution-processed Yb₂O₃ thin films processed at different annealing temperatures were systematically investigated using various characterization techniques. To explore the feasibility of the Yb₂O₃ thin films as gate dielectrics for oxide TFTs, In₂O₃ TFTs based on Yb₂O₃ dielectrics were integrated. All the devices could be operated at 3 V, which is critical for the applications in portable, battery-driven, and low-power electronic devices. The optimized In₂O₃/Yb₂O₃ TFT exhibits high electrical performances, including field-effect mobility of 4.98 cm²/V s, on/off current ratio of ~ 10⁶, turn-on voltage around 0 V, and subthreshold swing of 70 mV/decade, respectively. To demonstrate the potential of In₂O₃/Yb₂O₃ TFT toward more complex logic application, the unipolar inverter was further constructed.     

Low-voltage low-power FGMOS based VDIBA and its application as universal filter

This paper presents Floating gate MOS (FGMOS) based low-voltage low-power variant of recently proposed active element namely Voltage Differencing Inverting Buffered Amplifier (VDIBA). The proposed configuration operates at lower supply voltage ±0.75 V with the total quiescent power consumption of 1.5 mW at the biasing current of 100 µA. Further the operating frequency of the proposed VDIBA is improved by using the resistive compensation method of bandwidth extension in Operational Transconductance Amplifier (OTA) stage of the block. By using resistive compensation method of bandwidth extension, the bandwidth of OTA stage increases from 92.47 MHz to 220.67 MHz. As an application, proposed FGMOS based VDIBA has been used to realize a novel resistorless voltage mode (VM) universal filter. The proposed universal filter configuration is capable of realizing all the standard filter functions in both inverting and non-inverting forms simultaneously without any matching constraint. Other important features include independently tunable filter parameters, cascadibility and low sensitivity figure. The proposed filter is tunable over the frequency range of 4.1 MHz to 12.9 MHz and is capable of compensating for process, voltage and temperature (PVT) variation. The simulations are performed using SPICE and TSMC 0.18 µm CMOS technology parameters with±0.75 V supply voltage to validate the effectiveness of the proposed circuit.     

Y-△起动接线方式的改进

主要阐述传统Y-△起动接线的不足,通过改进接线方式,实现了Y接起动时降低流过KY接触器主触点的电流,并解决了因各种原因造成电动机Y接法所不能转换成△接,从而保证电动机安全、可靠的运行。