Study On The Power Quality Analysis And Evaluation Method Based On Time Domain Characteristic Analysis

With the development of the science and technology, more and more nonlinear and impactive load are used in the power system. And it makes the power quality problems more and more serious. The power quality disturbances like voltage sag, swell, fluctuation and flicker, and oscillatory transients appear in the power system more frequently. So the traditional evaluation method like the index power supply reliability is not enough for the demand of the power quality evaluation nowadays. It is a desiderating problem to be solved that how to classify the power quality disturbances correctly and evaluate the disturbance parameters. It is also the basis of the control and improvement of the power quality problems.In detail, the major contributions of the thesis are as following:A novel classification method of power quality disturbances is proposed in the paper on the basis of the analysis of present power quality disturbance classification methods in and abroad. Four characteristic parameters F1~F4 are proposed based on analyzing the power quality disturbances signals time domain characteristics. And the parameters can be used to classify power quality disturbances well. F1 reflects the variation of the fundamental wave amplitude. It can be used to judge whether the voltage amplitude disturbances exist (like voltage sag, swell, interruption and fluctuation). F2~F4 can be used to judge whether additive disturbances exist (like harmonics, interharmonics, oscillatory transients). F2 equates the THD (Total Harmonic Distortion). F3 indicates the average variation of F1. And F4 indicates the mutation of F1. The features extracted by this method have advantages as follows: (1) The features have clear physical meanings. So it profits to evaluate the disturbance parameters. (2) Some feature or some features can determine one disturbance only. Then the disturbance classification will not be probability. (3) The features of some disturbance will not change because of other disturbances existence. So it can classify mixed disturbances. Matlab simulation and analysis show that this proposed method can classify more single or complex disturbances signals effectively and loses less computation time of detecting and classifying electrical disturbances. So it is proper to be used in online analysis.The evaluation of the common power quality disturbances are made based on the classification method proposed. It is easy to evaluate because the four characteristic parameters all have clear physical meanings. F1 can be used to evaluate the starting time, the end time and the amplitude of the voltage sag and swell. It can also be used to evaluate the fluctuation and flicker's modulation frequency and amplitude. Otherwise, the curve of F1 can be used to fit the oscillatory transients attenuation constant and the oscillatory frequency. F2 can be used to evaluate frequently used power quality index—the voltage harmonics content.The author develops a power quality analyzer based on TMS320F2812 DSP to prove the theory. The software of the analyzer is the algorithm mentioned above. TMS320F2812 of TI Company is used as the CPU to assure the real-time calculation. And the peripheral hardware includes 16 bit A/D converter microchip AD7656 which can assure the accuracy of the A/D. The experiment tests the classification effect of the analyzer using dSPACE DS1104 A/D D/A converter board of dSPACE Company as the disturbance signals generator. The results shows that the power quality analyzer developed can classify the power quality disturbances correctly and evaluate the disturbance index accurately.