【作者】 刘翠艳；

【导师】 张艳霞；

【作者基本信息】 天津大学 ， 电力系统及其自动化， 2005， 硕士

【摘要】 频率是电力系统运行的一个重要质量指标。它反映了电力系统中有功功率供需平衡的基本状态。本文在对技巧离散傅立叶算法(SDFT)[18]进行了理论分析的基础上,对算法进行了改进:修正计算公式、对数据进行平滑和加门槛值处理,使算法的精度增强,计算曲线更加平滑、更接近于真实值。仿真计算结果表明该算法能在电力系统正常工况运行时精确测量系统频率,在频率偏离额定值的情况下,能自动跟踪频率变化测得其精确值。电力系统发生故障后,向量的测量精度决定着继电保护装置的动作性能。现有的微机保护装置大都采用傅立叶算法。但是,在系统发生故障频率偏离50HZ时,傅氏算法并不能准确的计算出向量的幅值和相位。随着DSP(数字信号处理设备)的发展,为微机保护精确计算电流/电压的向量提供了条件。本文在对SDFT算法存在的问题进行分析的基础上,提出了改进的技巧离散傅立叶算法,并用ATP对改进的技巧离散傅立叶算法在各种短路情况下,以及振荡、振荡加故障情况下的测量电流/电压进行了仿真的分析。仿真结果表明,改进的技巧离散傅立叶算法能够滤除电流/电压中的非周期分量和高次谐波,精确测量电压/电流向量的幅值和相角。计算结果比传统的全波傅氏算法更接近于真实值、更精确。本文中采用的测量频率算法和测量向量算法计算量小,实现方便,能够满足实时测量的要求,因此有着很好的工程应用前景。更多还原

【Abstract】 Frequency is a very important quality in power system. It can show the dynamicenergy balance. The Smart Disctete Fourier Transforms (SDFT) has been improved inthis paper after analyzing it in rigorous mathematical deducing. The improvementsinclude three aspects: amending formula, smoothing datas, and adding threshold value.The improved SDFT can calculate more accurately and the data curve becomessmoother. Simulations prove that the improved SDFT can calculate accurate powerfrequency when the system is in normal condition and can track system frequencywhen power frequency deviates from 50HZ.In protection relay, vector’s measuring accuracy decides the protection relayequipment’action. Nowadays, Disctete Fourier Transforms (DFT) is widely adoptedto calculate vector’s amplitude and phasor in computer protection installation. ButDFT can’t get accurate vector’s amplitude and phasor when faults happening andfrequency deviating in power system. With the development of Digital SignalProcessing (DSP), it becomes possible for computer protection to calculate accuratefrequency. Some possible problems of SDFT have been analyzed, and SDFT has beenpromoted again. We call the improved SDFT as Improved SDFT (ISDFT). Wesimulate various current faults, oscillations, oscillation and faults by ATP to checkISDFT’s accuracy. The simulation results prove that ISDFT can remove DC offset andharmonics’ influence, and calculate power current/voltage’s amplitude and phasor.And what is more important is that the calculation results are more accurate and closerto real value than DFT.Moreover, the ISDFT is easy to realize. It will very suitable for use in real time.We can get a conclusion that it has a good applicable future in engineering.更多还原