Research For Multi-channel Non-gapped Sampling And Analyzing Technique On-Line

In recent years, power quality has gradually become an important concern. The extensive applications for power electronic apparatus and nonlinear equipment distort the waveforms of voltages and currents. As a result, power quality is going much worse. In addition, due to the improvement of industrial automatization, such parts of an apparatus as MPU and PLC are applied to industrial process controls, which are disturbed easily by stirs from power system. Therefore modern industry needs higher power quality than old one does. At the same time, with the rapid development of electric power industry, stabile power quality issues, such as voltage fluctuation and flicker, frequency fluctuation, harmonics, have increasingly captured considerable attention from utility companies and their customers. Transient power quality issues have been becoming extrusive, such as voltage well, voltage sag and voltage interruption, and bring customers amount of loss. Because the length of sampling window is very long, traditional monitoring technique based on the theory of virtual value can not describe factual power quality issues. So it is very necessary to research for new monitoring technique.In practice, the disturbance of power quality (e.g. harmonic, instantaneous voltage fluctuation and so on) takes place at the same time. Power quality monitors in being adopt the series-processing technique based on 'sampling-analyzing-sampling', which skips over a lot of information on account of the data-analyzing intervals between two-samplings. Hence it doesn't do good todynamic monitoring. Aiming at the issues, the paper presents two methods, the multi-channel non-gapped sampling technique on-line and recursive FFT algorithm. The former is to separate and synchronize the clock of sampling control and the clock of data processing control, so it implements synchronously multi-channel data sampling and processing, and no data are lost at intervals when sampling and analyzing go by turns. The later changes concentrated operation into unequally operation among gaps of sampling points, so it can implement continuous sampling of measured signal and continuous FFT analysis. After analyzing the two methods, this paper adopts the former. In addition, after analyzing need and design of monitoring unit, such as sampling channels, synchronized sampling, the length of sampling window and so on, it uses FPGA (Field Programmable Gate Array) and DSP (Digital Signal Processor) to implement the technique. So the on-line multi-channel consecutive monitoring of power quality has been achieved.Aiming at power quality analysis, this paper advances analysis method based on period field, it can process and analyze not only a majority of parameters of our country power quality standard, but also short-time and long-time power quality issues, so it can realize real-time monitoring and quantificational analysis. Because time ruler mark of digital testing system is very limited, sampling is not really synchronized. But there is a kind of relation between non-synchronized sampling data and synchronized sampling data. This paper tries to use synchronized sampling serial and error item to express non-synchronized sampling serial, then advances a iterative formula. Non-synchronized data is close to synchronized data by iterative operation. From the point of view of spectrum of period signal, the method decreases and disappears even spectrum leaking. In addition, the method need not increase the amount of sampling points in one period, and sampling data of several sampling interval.