Research On Diagnosis Fof Short-circuit Fault And IGBT Open-circuit Fault In VSC-HVDC Rectifier

After the protection operation caused by the short-circuit fault occurs in the voltage source converter based high voltage direct current transmission(VSC-HVDC)system converter,it is necessary to deal with the fault quickly so that the VSC-HVDC system can be restarted to ensure the power transmission and the stability of the system.However,the short-circuit protection of the VSC-HVDC converter can act on all short-circuit faults in various converter areas,so it is impossible to determine the specific type and location of the fault based on the protection action.In addition,the IGBT open-circuit is also a kind of fault concerned in the research field of the VSC-HVDC converter.Although the IGBT open circuit fault of the converter will not cause the protection to act immediately,it will result in distortion of the voltage or current of the system.In severe cases,it may even cause normal IGBTs or other equipment in the converter station to be overloaded and the VSC-HVDC system to shut down.Therefore,short-circuit and open-circuit fault diagnosis methods of VSC-HVDC converter need to be studied to improve the operation and maintenance efficiency of the VSC-HVDC system,so as to ensure the safety of the equipment and the reliable and stable operation of the system.Therefore,this paper takes the diagnosis of rectifier short-circuit fault and IGBT open-circuit fault as the target,and carries out the following research work:(1)The VSC-HVDC system model with two terminals and two levels is built.Based on the RT-LAB semi-physical experiment platform and the VSC-HVDC test system standard of conference international des grands reseaux electriques(CIGRE),a VSC-HVDC system model with two terminals and two levels is built.By setting the mutation of the active power target quantity,reactive power target value and the DC voltage target quantity of the VSC-HVDC system on the model,the static characteristics of the system model is analyzed.This part provides a verification platform for the research on short-circuit fault and IGBT open-circuit fault diagnosis of the VSC-HVDC system rectifier.(2)The diagnosis method of the short-circuit fault in the VSC-HVDC rectifier with short-circuit protection is studied.Based on the influence of the short-circuit protection in the rectifier on the faults electrical characteristics,the electrical characteristics of three types of grounding faults and three types of non-grounding faults in the VSC-HVDC rectifier after short-circuit protection starting IGBT blocking operation caused by the faultare analysed.Based on it,and by using three-phase currents on the AC side of the rectifier,the DC support capacitors current,and the high-side and low-side currents on the DC side within the period of 5ms to 25 ms after blocking the IGBTs,the classification criteria of short-circuit faults in different positions are designed.Furthermore,a diagnosis scheme for short-circuit faults in the VSC-HVDC rectifier is proposed,and the method is tested based on the VSC-HVDC system model.The experimental results illustrate that the proposed diagnosis scheme can identify six types of short-circuit faults,and the phase in which the phase to phase short-circuit fault occurs as well as the arm in which the arm short-circuit fault occurs accurately.(3)The IGBT open-circuit fault diagnosis method for VSC-HVDC rectifier based on voltage residual is studied.The switching function model of the VSC-HVDC rectifier based on its topology is obtained,and the definition of three-phase voltage residual based on the switching function is given.The three-phase voltage residual calculation formulas of two types of single arm IGBT open circuit and four types of double arm IGBT open-circuit faults are derived,and the voltage residual characteristics of IGBT open-circuit faults are analyzed.Based on this,by setting the voltage residual threshold and the IGBT fault flag,a method for IGBT open-circuit fault diagnosis based on voltage residual is proposed.The experimental results of the proposed method based on the VSC-HVDC system model show that the method is able to diagnose single arm and double arm IGBT open-circuit faults accurately,which is promising in engineering application.