Analysis And Compensation On Power Harmonics Of Active Distribution Networks

In the face of the stress of resources environment carrying capacity and energy reduction,the power industry needs a low carbon transition urgently.Renewable energy sources such as solar,wind and biomass energy,combine to the grid on a large scale in the form of distributed generation(DG),bring a series of challenges to the traditional distribution network.However,due to the interaction between high permeability of DGs and nonlinear loads,the characteristics of harmonics distribution in active distribution networks(ADN)are different from those in traditional distribution network.Also,there is room for further development of compensation for harmonics.A compensation strategy is proposed based on an accurate analysis on mechanism of harmonics generation and regularities of harmonics distribution.As a result,the residual capacities of DGs are fully utilized and the power quality of the whole system reaches the highest level while controlling a few nodes.The main contributions of this thesis is as follows:?(1)The background and significance of the active distribution network is introduced.The research status of harmonics characteristic analysis and compensation strategy are also summarized.(2)The harmonics models of nonlinear load and DG are made.For the nonlinear load,a switching function model and a harmonic coupled admittance matrix model of threephase voltage source converter is made based on modulation theory.The coupled effects among all harmonics currents and voltages are taken into full consideration.For the DG,a Norton equivalent model of the gird-connected inverter is made.On these bases,the harmonics generation mechanism of nonlinear load and DG is analyzed in detail.(3)The harmonics characteristics of the active distribution network are analyzed based on harmonic power flow calculation.The calculation procedure and algorithm characteristics of alternating iterative method decoupling method of harmonic power flow calculation are given respectively.A calculating case is analyzed in order to get the influencing rules of the number and location of the DGs in parallel.It is instructive to the control strategy for the DG operation.(4)A compensation strategy on power harmonics for active distribution network is proposed.A composite control strategy which utilize the residual capacity of DGs is introduced aim to compensate harmonics actively.A coordination control strategy is used aim to distribute the harmonic power among multiple DGs legitimately.In order to make up with the shortfall of DGs compensation,a centralized control strategy using active power filter(APF)is adopted.Based on the concept of pinning control,this thesis presents a method to select the best installation locations of APF to make the power quality of the whole grid achieve the best level.It is of guiding significance to the selection of the installation locations of harmonic control equipment.