Study On Control Strategies To Suppress Commutation Failure Based On DC Control System

Owing to the reverse distribution of energy and economy in China,HVDC has developed rapidly in recent years.At present,there are more than 30 HVDC lines in operation in China.No matter the number of lines or the transmission capacity,they all rank first in the world.China's power grid has gradually formed a large AC-DC hybrid power grid with close AC-DC coupling.In this new form of power grid,the commutation failure of DC converters has gradually become another common fault of power grid.According to statistics,54 commutation failures occurred in multi-infeed HVDC transmission system in East China Power Grid in 2012.On average,commutation failure occurs once a week.The frequent occurrence of commutation failures is threatening the safe and stable operation of AC/DC hybrid power grid.It is urgent to take effective measures to suppress commutation failures with good performance.Therefore,in-depth study of the suppression measures of commutation failure is of great significance.In the suppression measures of commutation failure,the effect of suppressing the commutation failure by adjusting the DC control method is obvious,but there are still some shortcomings in the prediction and control strategy of the commutation failure.In order to make up for these shortcomings,based on the deep excavation of the essence of commutation failure,this paper introduces it into the prediction and control strategies of commutation failure,and carries out a series of in-depth research.Firstly,on the basis of fully analyzing the commutation failure mechanism and excavating the essence of commutation failure,a commutation failure prediction method based on commutation area is proposed.The PSCAD/EMTDC simulation results show that the prediction method has good performance for commutation failure prediction.Secondly,based on detailed introduction of DC control system and detailed analysis of fault response of control system after AC fault,this paper points out the shortcomings of DC control system in suppressing commutation failure,and proposes an improved control strategy based on voltage unilateral fault detection.The PSCAD/EMTDC simulation results show that the control strategy has good performance in suppressing commutation failure caused by single-phase faults in AC system.Finally,the essence of commutation failure is introduced into the control of firing angle of the inverter,and a control strategy based on commutation area quantization firing angle is proposed,which innovatively quantifies the firing angle of the inverter side after the fault,instead of relying on the empirical value setting.So that the firing angle control after fault is more accurate and the standard is more unified.The PSCAD/EMTDC simulation results show that the control strategy has excellent performance in restraining commutation failures caused by different types of faults in AC system under various fault conditions,and comprehensively improves the ability of HVDC system to resist commutation failures.