Research On The Detection And Analysis Algorithms Of Power Quality

In recent years, with the ever increasing non-linear load and wide-used sensitive electronic equipments in power networks, a variety of issues’have occured accordingly in power quality. The improvement of the power quality requires power companies to detect, identify and classify the static and transient power quality, especially the disturbances, and also needs to adopt proper, rapid and quick algorithms. Transient power quality disturbances cover voltage dips, voltage rise, voltage interruption, harmonics, transient pulse and oscillation. This paper mainly elaborates the following contents:1. It defines the power quality, then makes a simple classification, and introduces several power quality indexes mainly discussed in the paper, including the public harmonic wave of power network, voltage fluctuations and flicker, three-phase unbalance and temporary overvoltage as well as instantaneous overvoltage. The national standards or limiting values corresponded to the above indexes in actual detection are mainly introduced, which is convenient to the comparison between the results of it and the the results obtained in the paper.2. This paper detailedly introduces basic principles of several algorithms on power quality, with the most common and wide-adopted Fourier algorithm being first. The fast Fourier transformis is used in the paper to detect the harmonic waves, which lays foundation for the algorithm of the following voltage fluctuation. And voltage flicker is obtained through a discretization algorithm. The paper gives a brief introduction about the basic principles of these two algorithms, and futher draws an algorithm flow chart. Based upon the Fourier transformis, the paper also introduces basic principles of the three-phase unbalance algorithm, including the symmetrical component method and the phase-transformation method. Then, algorithms used in the transient power quality are elaborated:wavelet transform, S tranform, Energy of the Threshold as well as Dynamic Measurement, and the detailed calculation flow chart of the Dynamic Measurement is drawed.3. Analysing the static power quality index. Firstly, detection of the harmonic waves is got by the fast Fourier transformis and modulus reduction. Assumed signals and several real data are adopted to check reliability of the algorithm in harmonic wave detection; Secondly, the paper briefly introduces and checks the algorithmic steps of voltage fluctuation and voltage flicker; Finally, the symmetrical component method gets checked by using two sets of the assumed signals, then results are got and comparisons are made through the combination of the symmetrical component and the phase-transformation method, as well as the use of two real voltage data, and lastly test the reliability of the algorithm.4. The paper makes a simulated analysis towards the transient power quality with two parts. In the first part, detection of the three common voltage dips is made by means of the expanding S transformation, through which sag depth, phase jump and time of duration can be obtained, and problems caused by harmonic waves are analyzed in detail. In this way, detection of the characteristic of voltage dips can be achieved under various disturbance sources.In the second part, with the help of Dynamic Measurement, Energy of the Threshold, the wavelet transform method, the thesis makes an accurate detection and a time location towards disturbances cover voltage dips, voltage rise, voltage interruption, harmonics, transient pulse and oscillation of the power quality. Analyzing examples of the disturbing signals, Dynamic Measurement can well detect all the above disturbing signals and locate the time, also can estimate the disturbance amplitude; the wavelet transform method can make a rapid and accurate location for time, but can not fix the disturbance amplitude; Energy of the Threshold is the most intuitionistic and visual location method, however, it would cause errors on the innial location of the disturbance (these errors are within permission).