Research On Harmonic Responsibility Determination Under Conditions Of Time-varying Parameters In The Distribution Network

As the development of power electronics technology,a large number of non-linear loads acess to the distribution network,which result in the harmonics injecting into the grid and depravation of the power quality.To instruct the power quality management,it is necessary to quantitatively determine the harmonic responsibilities of the harmonic sources properly in the distribution network.In the actual power grid,time-varying operation conditions such as system harmonic fluctuation,system harmonic impedance change,customer harmonic impedance change still exist,resulting in the unaccuracy of traditional harmonic responsibility calculation.Research on precise harmonic responsibility calculation is needed under conditons of time-varying parameters.In this paper,methods to quantitative harmonic responsibility determination under the above three conditions are studied.A method combining both the dominant fluctuation filtering method and the quantile regression is proposed to study the determination of harmonic responsibilities in the condition of the system harmonic fluctuation.Firstly,the dominant fluctuation filtering method is introduced to estimate the system harmonic impedance,which uses the filtering principle in statistics to determine the customer dominant harmonic current fluctuation,and it can also eliminate the effects of system harmonic fluctuation.Then,the determination of harmonic responsibility problem is described into the estimation of the intercept of the regression equation.On the basis of estimating system harmonic impedance accurately,quantile regression method is applied to assessing the harmonic responsibilities,as the method has the advantages of better robustness and enough utilization for the fluctuation of system harmonic currents.The tests were implemented on the IEEE 13-bus system which verify that the proposed method can provide more precise and reasonable results for the determination of customer harmonic responsibilities in conditions of the system harmonic fluctuation.A method employing both the wavelet transform modulus maximum method and the robust total least squares regression is proposed to determine harmonic responsibilities in the condition of the system harmonic impedance change.Firstly,the windows are added on the harmonic voltage and current measurement data to get the rough estimation of system harmonic impedance.Then,wavelet transform modulus maximum is employed to detect the change time of system harmonic impedance,based on which the measurement data can be segmented into several sections.On the basis of the segmentation,robust total least squares regression is applied to every section to accurately estimate the system harmonic impedance.Hence the harmonic responsibility of every section can be calculated.Besides,indicator of total harmonic responsibility is defined to quantitatively assess the impact of harmonic source.Simulations are carried out in three-feeder system and IEEE 13-bus system,which verify the validity and accuracy of the proposed method when the system harmonic impedance changes.A variable coefficient regression method is proposed to calculate the harmonic responsibilities in the condition of customer harmonic impedance change.Firstly,the time-dependent relationship model of harmonic voltage and harmonic current is established.Then the regression coefficients of the model are calculated by variable coefficient regression method,according to which the system harmonic impedance vector is obtained.And the harmonic responsibility of each harmonic source can be calculated.Simulations are carried in the IEEE 13-bus system,which indicate that the variable coefficient regression method is valid in estimating the system harmonic impedance and harmonic responsibility,as well as effectively tracking the variation law of the harmonic impedance.The theoretical analysis and simulation results show that,the three methods proposed in this paper are applicable to the harmonic responsibility calculation on the condition of system harmonic fluctuation,system harmonic impedance change,and customer harmonic impedance change.The calculation results are closer to the theoretical value,and the methods can provide an important theoretical basis for future harmonic monitoring and harmonic management.