Harmonic Contribution Assessment Of Active Distribution Network Based On Micro-PMU

In recent years,with the advancement and deepening of the national strategy "energy structure transformation" and "supply-side reform",large-scale access of new variety of power supplies and loads such as distributed power and electric vehicles and other to the distribution network have led to the penetration rate of power electronic devices in today's power distribution network has risen remarkably.As a typical harmonic source,the inherent waveform distortion characteristics of power electronics have exacerbated harmonic pollution in today's distribution networks.As a new type of harmonic source,power electronic equipment has small monomer capacity,strong randomness of harmonic emission and significant uncertainty of space-time distribution.Therefore,the applicability of traditional harmonic contributon determination model has declined.In addition,the application and promotion of micro-synchronous phasor measurement units(micro-PMU)and distribution automation systems have changed the measurement and control methods of distribution networks today.Traditional harmonic contribution determination methods based on traditional data formats and application forms of algorithm are no longer fully applicable in the background of the nowadays power grid.This paper focuses on the harmonic contribution determination of the distribution networks with large-scale new variety of power supplies and loads,and studies the data processing,harmonic contribution determination model and intelligent application of methods.The main contents of this thesis and outstanding achievements are as follows:(1)The identification and removal method of data interferenced by short-circuit fault in distribution network is proposed.The characteristics of four short-circuit faults(single-phase ground fault,two-phase short-circuit fault,two-phase ground short-circuit fault and three-phase short-circuit fault)are analyzed.The identification of non-single-phase ground fault is simplified by considering the action of relay protection device.For the single-phase ground fault,considering the influence of the neutral grounding method on the single-phase ground fault characteristics,phasor relationship in single-phase ground fault of three typical configurations of distribution network as the neutral point ungrounded,the neutral point through the resistance grounding and the neutral point through the arc-extinguishing coil are analyzed.Wavelet transform is used to detect the start and end moments of data mutation,based on which the identification and removal process of data interferenced by short-circuit fault are proposed.(2)A background harmonic decoupling method based on harmonic coupling matrix model is proposed.The harmonic coupling matrix model of the harmonic source is established,and the coupling relationship between the harmonic voltages and the harmonic currents of the harmonic source is linearly analyzed.In order to improve the computational efficiency of the model and enhance the adaptability of the method to the data,M-CPLS is derived based on PLS.A background harmonic decoupling method is proposed based on the harmonic coupled matrix model of harmonic source.(3)The harmonic contribution determination method based on the micro-PMU is studied.The data characteristics and layout characteristics of the micro-PMU are analyzed.For the data characteristics of micro-PMU such as data is phasor and the data record frequency is high,M-CPLS is used for linear regression.Compared with the traditional PLS,the M-CPLS can simplify the linear regression model of complex data and improve computational efficiency.Considering the data characteristics and layout characteristics of the micro-PMU,the hierarchical harmonic contribution determination method is proposed based on the traditional harmonic contribution determination principle.The harmonic contribution determination accuracy will be maximized according to the layout of micro-PMU.Considering the difference of harmonic characteristics of the new variety of power supplies and loads,a multi-scale harmonic contribution comprehensive evaluation index is proposed to improve the rationality and comprehensiveness of harmonic contribution determination.(4)The online harmonic contribution evaluation mechanism and the topology and measurement adaptive harmonic contribution determination algorithm are studied.The startup and data exchange mechanism of online harmonic contribution evaluation are designed,considering the data scenario of the distribution automation main station,to realize the reasonable startup and data summoning of the online hannonic contribution evaluation.The topology and measurement adaptive harmonic contribution determination algorithm is developed to automatically identify and adjust the algorithm model for the changes of network topology and micro-PMU measurement layout that may occur in actual operation,and effectively deal with any possible harmonic-exceeding scenarios in the power grid to determine harmonic contribution accuratly and rationally.The overall process of online harmonic contribution evaluation for the main station of distribution automation is proposed.