Study On The Influencing Factors Of Yunguang UHV DC Commutation Failure And Its Suppression Method

With the operation of a large number of DC transmission projects,China's power grid has gradually become a large AC-DC hybrid system,with the characteristics of large scale,cross-regional,large capacity and so on.The interaction between AC and DC systems is increasing,the electrical coupling degree is becoming more and more complex,the AC side system failure causes the AC voltage amplitude to decrease and the phase offset,then causes the HVDC system to have the continuous commutation failure,when serious will cause the DC transmission system bipolar locking,causes the huge impact to both sides AC system,seriously affects the AC and DC interconnection system safe and stable operation.Therefore,it is very important to study the effective methods to suppress the continuous commutation failure of HVDC transmission system.At present,the research results of control methods have been mainly focused on the improvement of a certain method to the voltage dependent current order limiter.However,the improvement of one method has obvious advantages and disadvantages,and the in-depth study of joint operation with other methods is lacking to realize the complementary advantages and achieve the purpose of suppressing commutation failure.This paper focuses on the measures to suppress DC system commutation failure.Through the analysis of AC system inverter side converter normal commutation and commutation failure process,as well as DC system after the failure of the operation logic.It is pointed out that the inverter side of HVDC system enters the low voltage current limiting link too early,which is the important reason for the failure of continuous commutation.In this paper,a control method based on virtual resistance is proposed,which can change the conventional voltage dependent current order limiter to obtain the compensation voltage,and make the low-voltage current limiter put into use at a more suitable time.Because the conventional VDCOL control method can not limit the current growth reasonably at low voltage,it has the characteristic of reflecting the dynamic characteristics of fault system.At the same time,the simulation model of cloud-wide direct current transmission is built in the PSCAD/EMTDC,which embodies the composition,working principle and related control methods of the DC system.Finally,the control method proposed in this paper is verified and analyzed more accurately on the RTDS platform,which makes the control method proposed in this paper more suitable for application in Yun-Guang UHVDC,it obviously improves the ability of Yun-Guang DC to resist the failure risk of commutation,and has important reference significance for maintaining the safe and stable operation of AC-DC interconnection system.