The Study On Detection Method For Commutation Failure In HVDC Transmission System Based On Current Characteristics

Commutation failure is one of the most common faults in HVDC transmission systems.Commutation failure will cause the DC voltage to drop and the DC current to rise.And continuous commutation failure may even affect the normal operation of the converter equipment and cause the interruption of the transmission power,posing a threat to the safe and stable operation of the system.Based on the theory of circuit and power electronics theory,this paper deduces the commutation failure process and the characteristics of valve current and valve-side current.Commutation failure detection methods based on the characteristics of valve current and valve-side current is proposed.The main work of the thesis is as follows:(1)Considering the influence of the specific system conditions,12-pulse converters and he control system,the general process of once commutation failure,twice continuous commutation failures and twice discontinuous commutation failures and related electrical quantity characteristics are analyzed.Focusing on the differences from the traditional research,the specific valve action process and valve current characteristics of once commutation failure,twice continuous commutation failures and twice discontinuous commutation failures are deduce and analyzed.The waveforms characteristics of valve-side current during once commutation failure,twice continuous commutation failures and twice discontinuous commutation failures are calculated and verified with the simulation waveform.(2)The characteristics of valve current in the case of commutation failure are analyzed,and the commutation failure criterion based on the characteristic of valve current was proposed,and a detection method of commutation failure based on characteristic of valve current was designed,which mainly includes three parts: detection of valve current extreme point and the rate of valve current change before or after the extreme point,detection of maximum valve current and detection of the time that valve current lasts for non-zero after the extreme point.Taking CIGRE BENCHMARCK HVDC model as an example,detection module of commutation failure based on characteristic of valve current was established in PSCAD / EMTDC electromagnetic transient simulation software.The simulation results verify the correctness of the theoretical analysis and the validity and accuracy of the proposed method.(3)Taking the valve-side current of the converter transformer with more engineering practicality as the research object,a commutation failure criterion based on the characteristics of the valve-side current is proposed.And a detection method of commutation failure based on characteristics of valve-side current was designed.Taking CIGRE BENCHMARCK HVDC model as an example,detection module of commutation failure based on characteristic of valve-side current was established in PSCAD / EMTDC electromagnetic transient simulation software.The simulation results showed the correctness of the analysis of the characteristics of valve-side current during commutation failure occurs,and the proposed method can correctly and quickly detect whether commutation failure occurs.