Analysis Of Effect Of Fault On The AC Side On AC/DC Interconnected Network Systems And Its Countermeasures

Owing to the unbalanced economic development and supply-demand of primary energy,the gap between the power demand and the electricity supply in the developed areas is getting bigger and bigger.In this context,DC transmission came into being.With the rapid development of DC transmission technology,the problems caused by the increasing number of DC lines on the sending end and the receiving end of AC network have also increased year by year.Due to the close relationship between AC system and DC system,AC system fault can have a serious impact on the DC system,and the chain reaction on the DC side can also interfere with the electrical quantity measurement of the AC side,which can easily lead to a series of accidents,so it is very necessary to deeply study the influence of the AC side fault on the AC/DC interconnected system.The paper mainly did the following work:First of all,the interaction between AC and DC power grids is analyzed when there is a fault,and the way of fault transmission is analyzed.And the failure modes such as commutation failure are analyzed.The PSCAD/EMTDC simulation model of Multi-feed DC transmission system is established.Further,decouple AC and DC power and describe DC transmission power with AC bus voltage,Considering the characteristics of DC current,a method of judging commutation failure under multi-infeed system is proposed from the perspective of AC/DC system,so that the calculated value close to the actual value.Through the simulation,the correctness and rationality of the criterion are verified,and the influencing factors that may lead to commutation failure are comprehensively analyzed.Finally,the nonlinear parameters intrusion into the DC system when the AC side fault will have impact on the DC protection that the 100HZ protection is analyzed.The commutation failure caused by the AC side fault causes the DC side current feed into the AC grid and the AC side fault current together,so that there will be some risk of misconduct on the AC grid protection such as distance protection and direction comparison protection system.In the end,some countermeasures and suggestions are given.In summary,this paper analyzes the characteristics of AC/DC interconnection system,focuses on the research of multi-infeed HVDC transmission system,and gives a judgment method for the occurrence of simultaneous commutation failure.Finally,it also gives some reasonable suggestions on the impact of protection,through the simulation to verify its effectiveness.It provides some reference and reference for the fault prediction of large AC/DC hybrid power system.