Study On The Impact Of Operating Conditions Of The Sending-end AC System On The Failure Of DC Commutation

The mutual influence and interaction of the AC and DC hybrid system make it show different dynamic characteristics from the traditional AC system.When the AC system is disturbed,the voltage fluctuation will affect the cut-off angle of the DC system,which can easily cause the commutation failure of the DC inverter.Continuous commutation failure will cause continuous power changes.Insufficient will cause serious harm to the stability of the system.DC blocking due to continuous commutation failures,reducing power transmission,will also adversely affect the safe operation of the sending and receiving system.At present,the research on the failure of DC commutation mainly focuses on two aspects:the criterion of the failure of the DC commutation caused by the AC fault and the influence of the failure of the DC commutation on the receiving system.There are few studies on the state of the sending end system,the failure of DC commutation and the duration of commutation failure.This paper has carried out research work in the following aspects:Starting from the analysis of the mechanism of DC system commutation failure,on this basis,the reason for commutation failure is introduced;in order to study the relationship between DC line transmission power and commutation failure,the proportion of DC line transmission power is increased in two ways,A method to change the output of the synchronous machine to adjust the transmission ratio of the DC line based on the fixed DC transmission power,another method to adjust the transmission power of the DC line to adjust the proportion of the DC transmission power based on the output of the fixed synchronous machine,To verify the relationship between DC transmission power and commutation failure;in order to analyze the system of the inertial time constant of the sending end synchronous machine to the DC commutation failure,the concept of transient energy is introduced,and the system is changed by adjusting the rotational inertia of the synchronous machine The transient energy of the inertia,and then analyze the influence of the inertial time constant on the commutation failure,on this basis,the general law of the influence of the inertial time constant on the commutation failure is summarized;it provides more efficient and accurate modeling for the AC and DC hybrid system The method provides a reference for the research on the mechanism of instability after a weak synchronous power grid fault.