Research On Harmonic Emission Level In Power Distribution Network

In modern society, people’s living standards are improving day by day. Power quality also affects the production of requirements. With the rapid economic development, power quality problems have attracted the attention of customers, and it has become an important research topic in the power system. Due to a variety of impact and the proportion of non-linear loads in the grid continuing to increase, and the increasing of the non-symmetric load, resulting in a power grid harmonic components and increasing the proportion of such a serious deterioration in power quality.To ensure the quality of power supply and enable electricity networks safe operation, while enabling users to get a better power quality, we need to take effective measures to improve the power grid environment. Thus, the electricity network can complete the buy and sell electricity between good and users. We can effectively deal with interference which is generated by user in the system, that reflects the common goal between the power network and users. Therefore, we should draw a clear distinction between system and user, which is the most important research questions.At present, the basic method of harmonic division of responsibilities is the harmonic impedance detection, and estimating voltage drop both system and user generated at the common connection point of harmonic currents. Therefore, the more accurately and effectively on the harmonic emission level assessment is the basis for controlling power quality and harmonic.Many methods about the localization of harmonic source and the estimation of the harmonic emission level are described in detail, the advantages and disadvantages of each method are systematic analysis and summary from qualitative and quantitative aspects. Then, on the basis of existing methods, the methods based on bias compensation recursive least squares identification and generalized least squares are proposed to assessing harmonic impedance and the harmonic emission level. The first method is that utilizing the signals of harmonic voltage and harmonic current measured at PCC. Regression coefficients are worked out through bias compensation recursive least squares identification. The comprehensive variables which can explain dependent variables most effectively are distilled, and then the useful information and noise are identified. Therefore, the disadvantage of variable dependence in establishing of the system model is overcome. After that, the supply harmonic impedance is got,consequently the harmonic emission level of customer is calculated. The second method is that converting the colored noise to the white noise through whitening filter,then on the basis of the first filter disposal of the observational data, the least square method can be used to identify the disposed data, which overcomes the effects of variable and the correlation between variables. Based on these two methods, MATLAB as a platform to build the corresponding simulation model, the validity of the method is verified by the simulation analysis of the experimental circuit.