Fault Location Method Of DC Distribution Network With Power Electronic Transformers

The DC distribution network with power electronic transformers is the current research hotspot.The fault location technology of DC distribution lines is an important technical support for quickly locating fault points and restoring power supply as soon as possible.Two kinds of fault location methods for DC distribution networks with power electronic transformers are proposed: ranging methods based on high-frequency components of current and ranging methods based on DC components.By performing differential filtering and full-cycle Fourier decomposition on the measured fault transient current waveform,the elimination of the attenuated DC component and the extraction of the fault high-frequency component are realized;the ratio of the fault transient current and voltage waveform obtained by the measurement is compared.Schiff low-pass filtering realizes the extraction of low-frequency components,and further calculates the DC component by solving the integral mean value.Then,using the characteristics of the same voltage from the converter outlet to the transition point of the fault point,the ranging function of the two methods is derived.To achieve fault location.Firstly,on the basis of summarizing the research results of the predecessors and combining the requirements of the relevant indicators of the demonstration project,the structure of the power electronic transformer used in the AC/DC hybrid distribution networkis described in detail and the model is constructed.The fault mechanism of the medium voltage DC port of the power electronic transformer in the event of unipolar ground fault and interpole short circuit fault is analyzed,and the two stages of the fault process are divided.At the same time,combined with the circuit analysis theory,the discharge mathematical expression and the inductor current expression of the DAB module's outlet capacitance after fault are given.Secondly,on the basis of summarizing VSC-based flexible DC distribution network and traditional AC distribution network ranging method,this paper proposes two fault location methods for DC distribution line: DC-distribution method based on current harmonics for DC distribution lines and DC-base method.Component DC distribution line double-ended fault location method.Based on the analysis of fault characteristics of DC distribution network,the single-pole ground fault and the inter-pole short-circuit fault are set in different combinations of fault distance and transition resistance respectively,and the proposed ranging algorithm is verified for diversification.In addition,in order to better meet the actual operation of the power grid,three common scenarios with different system parameters on both sides are set in the simulation verification,and the engineering application value of the proposed ranging scheme is examined in multiple dimensions.The PSCAD simulation verifies that the proposed method can accurately achieve fault location in a variety of fault situations.It still has high ranging accuracy when the system parameters are asymmetrical on both sides,and has good engineering practice value.Finally,the topology of the “T” type DC distribution network with power electronic transformers is established,the method and process of determining the fault section are analyzed and described.At the same time,based on the fault location,combined with the three-terminal DC distribution network fault equivalent circuit,the fault location function of the two ranging methods is deduced in detail.The PSCAD simulation results verify the effectiveness of the ranging method.This paper completed the fault location method of DC distribution network with power electronic transformers,including fault location of two-terminal DC distribution network composed of two power electronic transformers and multi-terminal DC distribution composed of three power electronic transformers.Research on fault location method of power grid has innovative and good engineering application value.