Study Of Power Quality Comprehensive Management For Three-phase Four-wire Distribution System

With the development of modern society, as well as a wide variety of loads are constantly appearing in the grid, the power quality problems of distribution network are more serious. Three-phase four-wire structure is the main structure of the distribution network in our country, and compared to the three-phase three-wire structure, it has a more line-neutral line. And with the emergence of a variety of single-phase and nonlinear loads and power electronic devices, it is very easy to cause the three-phase unbalanced, and make the reactive power demand increase, and it will produce a large number of harmonics, which leads to a zero-sequence current superimposed in the neutral line, so that the neutral line overload. The series of power quality problems continue to emerge in our daily lives, lower the quality of our lives. Therefore, improving the power quality has a very important significance.In this paper, for the common power quality problems in three-phase four-wire distribution system, several methods is introduced for traditional power quality governance, and through analysis and comparison, a distribution static compensator(DSTATCOM) based on transformer is presented for power quality comprehensive compensation. In this scheme, first several transformers with different ways of connecting are introduced, and a new T-connected transformer is proposed, and their respective advantages and disadvantages are analyzed in the neutral current suppression. Then the DSTATCOM compensation current detection algorithm is analyzed, the p-q theory, i_p-i_q theory based on instantaneous reactive power theory and the dqO theory are introduced, and determining to use a non-phase-locked-loop of improved dqO synchronous coordinate transformation method to detect the harmonic current, reactive current and other compensation current. Finally, using the MATLAB/Simulink to build a 10/0.4kV distribution power system, and the scheme is simulated, the results show that the scheme is viable for harmonic suppression, reactive power compensation, voltage regulation, improving the unbalanced three-phase and other common power quality problems governance.