Research On Fault Location For Transmission Lines In A Flexible AC/DC Hybrid System

Modular multilevel converter-based flexible direct current transmission technology which leds to the development of the flexible AC/DC hybrid system,plays an increasingly important role in the field of renewable energy integration and long-distance transmission in the western region,due to its outstanding advantages in flexible control,powerquality and tansmission losses.Limited by the frequent fault problem of the overhead line,accurate and reliable fault location technology is of great significance to improve the economy and reliability of the system operation.At present,the existing traditional fault location methods is not suitable for,so a fault location method with high ranging accuracy is necessary.First of all,this paper introduces a model of the flexible AC/DC hybrid system topology and the working principle of the modular multilevel converter,the analysis of the existing various control strategies of the converter and a fault ride through control strategy is put forward.Then,the differences between the transmission line model with distributed parameter characteristics are compared,in order to lay the foundation for the proposed fault location method.Secondly,this paper takes the AC export transmission line with a single-phase-to-ground fault as the research object,and proposed a novel single-terminal fault location method.The influence of the control strategies to the fault compound sequence network is analyzed and the least squares method is combined.Through a large number of simulations,the validity of the proposed fault location method and the superior range performance are verified.In addition,the applicability of the proposed fault location method for the phase-to-phase fault is analyzed,combining its compound sequence network.Finally,this paper takes the DC transmission line with a pole to ground fault as the research object,and proposed a single-terminal fault location method with higher ranging precision.The rich harmonic characteristics of the three-phase half-wave uncontrolled rectifier operation mode are derived,and the frequency variable characteristics of the transmission line are considered.Compared with existing methods,its advantage on the ranging precision is verified.