| In recent years, along with the rapid economic development, about 100 valve casting enterprises have been established in Qingtian, which mainly located in central and western part. They are high energy-consumption factories and pollution sources to power grid. While bringing economic benefits, they cause negative effects on the local power grid, such as harmonic pollution. Therefore, it is necessary to study the related technical problems of harmonic treatment. The problems such as harmonic detection algorithm and application, harmonic source orientation and harmonic control measures are mainly studied in this paper, and obtain some interesting results.As an important means to find harmonic problem, harmonic detection is powerful foundation to take harmonic treatment measures. Fourier transform is the elementary method for the analysis of harmonics, which mainly disadvantage is that it exists the spectral leakage and fence effect, its frequency resolution is inversely proportional to the sample data length in asynchronous sampling. The windowed interpolating Fourier transform is the effective method to restrain spectral leakage and eliminate fence effect. On the basis of analyzing the Hanning window and Blackman window interpolation FFT algorithm, the three Nuttall window interpolation FFT algorithm is derived in this paper. Simulation results show that the three Nuttall window interpolation FFT algorithm has better performance. Adaline neural network is one of the effective approaches to the harmonic measurement which is suitable for short data condition. Adaline neural network measures harmonics, without prior sample training of the neural network weights. But Adaline requests the signal frequency known in advance, otherwise small frequency deviation may generate large analytical error. The enhanced Adaline neural network model treated the fundamental frequency as the weight to be determined, so as to estimate the frequency, amplititudes and phases at the same time. recursive least square algorithm was used to enhanced Adaline neural network, that could improve the convergence speed. The actual sampling harmonics current signals of an office and a hospital in Hangzhou are analyzed to applying Nuttall window interpolation FFT algorithm and enhanced Adaline, that verified the validity and practicability of the proposed methods.Harmonic source orientation is a very important peoblem in power harmonics, which has guiding significance for harmonic treatment location choice. This paper introduced several methods of harmonic source orientation, and compared the advantages and disadvantages of these methods. The method based on load impedance characteristics for identifying harmonic sources is more suitable for engineering application.Finally, several methods of harmonic suppression in power system are introduced. The harmonic suppression principles of using active filters and passive filter and their respective advantages and disadvantages are mainly discussed in this paper. Through the data analysis before and after throwing in filter of a steel factory in Qingtian, that validated better suppression effect of filter to harmonics. |
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