一种变频器和工频电网之间同步切换的方法

工频旁路运行是变频器的一种重要运行方式,变频器与工频电网间切换若不当,则会引起很大的电流冲击和严重的电磁干扰.文章提出了一种软件估算工频电源频率的方法,介绍了一种使用三相锁相环使变频器的输出频率和相位与工频电源的相同的方法,以改善工频切换性能.     

大功率交流异步电动机变频转工频切换存在的问题及解决思路

分析异步电动机变频转工频的切换过程,针对限制切换冲击电流提出解决思路。     

高层住宅变频调速恒压供水系统设计

结合一工程实例,介绍了PLC控制的变频调速恒压供水系统的工作原理及其特点;探讨了主副泵切换的阀值流量、阀值频率;并时住宅建筑变频调速恒压供水系统存在主泵不能自动切换为副泵工作的问题,提出了引入流量控制元的改进方法。实际运行表明:该变频调速恒压供水系统可进行主副泵切换,运行可靠且节能。     

凝结水泵变频改造及节能分析

针对火力发电机组凝结水泵能耗高、效率低等问题,提出采取“一拖二”自动变频/工频切换控制的方案进行变频改造,取得了良好的节能效益.     

变频与工频的切换问题

分析了低压变频调速系统中变频与工频切换过程中的暂态过程,根据不同负载暂态过程的特点,提出了不同的切换要领,并介绍了以风机和供水水泵为代表的具体切换方法。     

基于PLC的PID控制算法在恒压供水系统中的应用

介绍一种基于PLC的PID控制算法的恒压供水控制系统。阐述了变频输出与工频市电之间的切换方法,使每台泵的电机均可通过同一变频器实现软起动,避免了电机受冲击、水锤作用、临界点电机频繁起动。使用增量式PID控制,提高了系统的自适应能力,稳定性好。     

工作面泵站变频恒压控制系统

<正>由天地(常州)自动化股份有限公司研制推出的工作面泵站变频恒压控制系统主要针对工作面的乳化液泵、喷雾泵进行控制,实现乳化液泵的变频软启动、按需恒压供液、智能轮换调度、自动配比乳化液、自动补水补液,并控制喷雾泵与采煤机进行联动,实现整个工作面泵站控制系统的远程监控。该系统功能特点:1根据支架用液量,自动调节乳化液泵转速;2除可人工就地启停单台泵外,还可根据工作面是否用液自动启停     

连铸液压传动系统的变频控制方案

本提出了一种连铸液压传动系统变频控制方案，可以采用一台变频器通过PLC实现3台油泵的软启、软停及自动变频工频切换，从而实现了系统油压的稳定控制，而且在提高设备寿命及节约电能方面也具有显效果。     

一种以AT89C2051单片机为核心的复合开关

在工业电器设备电源切换控制中,通常采用机械触点开关或无触点的电子开关。机械开关(含继电器)在正常工作时接触点电阻极小,几乎无功率消耗。但是,机械触点切换时会产生冲击电流,由冲击电流产生的电弧不但会烧蚀开关触点,还会使负载和电网特性变坏。以可控硅为核心的无触点电子开关具有过零切换特性,几乎不产生冲击电流。但是可控硅导通时有管压降,造成可控硅电子开关有功率损耗、散热等问题。冲击电流和功率损耗,是大功率负载开关电路中不容忽视的问题。     

恒压供水模糊控制应用

针对传统PID控制变频恒压供水系统稳定性差、参数调解困难的情况,利用DB-2000控制器的模糊控制功能,改进变频恒压供水系统。运行结果表明,改进的控制系统响应快、泵切换时管网冲击小,水压稳定,且系统可靠,节能效果显著。     

一种可测量简谐振荡频率的振动频率传感器

以压电式加速度传感器和信号处理电路为核心,研究了一种可以测量简谐振荡频率的振动频率传感器,给出了该频率传感器核心控制电路的设计方法。仿真和实验表明该频率传感器能实时、准确地测量出以简谐规律振荡的振动频率,测量误差小于±2.3%。     

Cognitive frequency diverse array radar with symmetric non-uniform frequency offset

Frequency diverse array (FDA) radar with uniform inter-element frequency offset generates a beam pattern with maxima at multiple range and angle values. Multiple maxima property allows interferers located at any of the maxima to affect the target-returns. As a result the signal to interference noise ratio (SINR) and probability of detection decreases. In this paper, we propose a cognitive uniformly-spaced FDA with non-uniform but symmetric frequency offsets to achieve a single maximum beam pattern at the target position. Moreover, these non-uniform frequency offsets are calculated using well known mu-law formulae. The design sharpens or broadens the transmitted beam pattern based on the receiver feedback to achieve a better detection probability and an improved SINR as compared to the previous designs. The performance is also analyzed by considering the Cramer-Rao lower bound (CRLB) on target angle and range estimation.     

Statistical demodulators for frequency shift keying with fast frequency hopping

This work is devoted to the problems of information transmission with frequency shift keying and fast frequency hopping in special channels where the signal/noise ratio is low, and a high energy interfering signal is present. We propose a demodulation algorithm that is significantly more stable to the influence of a powerful interfering signal as compared to other known algorithms. Under these conditions, we show a statistical criterion that lets one significantly reduce error probability on the demodulator’s output. For the chosen criterion we prove several lemmas that let us speed up the demodulation algorithm. Computer modeling results show that the proposed demodulation algorithm has better correcting ability under a powerful interfering signal than previously known ones.     

Parallel frequency filtering

The frequency filtering method is a robust and efficient ILU-like solver for large sparse systems (cf. [9,10]). Combining this method with the so-called Schur-complement DD method, we obtain a fast parallel solver. In this context, frequency filtering can be applied as solver inside the subdomains as well as for the treatment of the arising Schur complements. Especially for those, the method is well suited since it is highly parallelizable by recursively applying the same decomposition as to the original system. In this paper, an implementation of the frequency filtering domain decomposition (FFDD) method on a multiprocessor system will be presented and the numerical results of some variants thereof be discussed. The scaling behaviour of the algorithm for an increasing number of processors is almost optimal.     

一种高频低相噪频率合成器的设计

在无人机着陆系统中需要一种高频稳度的频率合成器,本文基于集成锁相环PE3240芯片设计了一种具有高频低相位噪声性能的频率合成器,并对影响相位噪声的因素进行了分析,电路测试结果表明设计达到了预期要求.     

基于隐马尔可夫模型的短波认知频率选择方法

针对短波频谱利用率低下及频率选择不够智能的局限性,提出一种基于隐马尔可夫模型(HMM)的短波认知频率选择方法。应用认知无线电原理,将短波传统用户作为主用户,将采用认知无线电技术的短波电台作为认知用户。首先,建立隐马尔可夫模型,结合频谱感知历史数据预测主用户信道状态;其次,在预测空闲的基础上估计信道参数;最后,根据估计的信道参数选择最优频率。仿真结果表明,所提方法能够准确预测传统短波用户信道状态,快速估计信道参数。在设定的仿真条件下,所提方法的成功传输率分别较HMM预测和能量感知随机信道选择方法有5.54%和10.56%的提升,能够选择最优信道。     

Scaling laws of spatial visitation frequency: Applications for trip frequency prediction

The relationship of the built environment to human travel is one of the mainstream themes in urban studies. It provides a foundation for transport prediction. The existing literature is limited in accuracy when predicting spatial temporal travels from built environment. Understanding the scaling laws of spatial visitation frequency sheds new light on the issue. The scaling laws connect travel and the built environment by ordered-rankings, which make it possible to predict the number of arrivals from environmental variables. This research analyses the scaling laws of dynamic spatial visitation frequency using taxis' global positioning system (GPS) records, and proposes a model to predict spatial temporal arrivals from points of interest (POIs). The results show that: (i) the scaling law of spatial visitation frequency is exponential; (ii) the exponential scaling law is explained by the linear preferential attachment effect and a logarithmic travel growth process; (iii) the exponential scaling law is not sensitive to time; (iv) the proposed model predicts spatial temporal arrivals with high accuracy (R² > 0.6).     

一种用于OFDM时域频偏估计的频偏取值判决机制

提出了一种可适用于OFDM时域频偏估计的频偏取值判决机制,根据两个自相关峰值估算出大范围频偏粗值和小范围频偏粗值,由频偏取值控制状态器根据大范围频偏粗值和小范围频偏粗值的数值逻辑关系,确定频偏取值状态,由频偏取值执行器根据频偏取值状态计算准确的最终频偏数值。经802.11n接收机系统的频偏仿真测试表明,在IEEE TGN多径信道A~信道F条件下,其频偏估计均方误差<10-2误差(SNR>5),估算范围达正负2.5倍子载波频率间隔。     

广义频分复用与正交频分复用的比较

广义频分复用是德国5GNOW项目组提出的一种5G物理层解决方案,采用的是非矩形脉冲成型。首先对GFDM基本模型进行研究,指出其本质是DFT滤波器组,然后分别用DFT滤波器组实现OFDM和GFDM多载波调制系统,分析三者间的联系与区别,突出循环卷积降低GFDM计算复杂度的特点。从CP加入方式和原型滤波器两个方面对GFDM和OFDM进行比较,指出GFDM使用更少的CP,提高了频谱效率。最后通过实验仿真,对二者的原型滤波器频域响应性能和SER性能进行比较,强调非矩形滤波器有更好的频域响应性能,GFDM的SER性能较差是因为放弃了子载波的严格正交条件,导致子载波间干扰增大。