Study On Simulation Of AC/DC Power System And Commutation Failure

The advantages of HVDC mainly include high transmission capacity, low power loss, flexible and fast power control, as well as the ability of asynchronous networking, which make DC power transmission more and more important in long-distance power transmission and grid connection. Besides, the fast developing HVDC Light has its unique advantages in wind power transmission and island power supply, thus HVDC transmission is world widely used and rapid developing.By 2020, 27 HVDC transmission projects will be established in China, six of which are UHVDC projects, forming multi-infeed AC-DC grids in East China and South China.HVDC transmission technology optimizes energy configuration and brings enormous benefits to society and economy. But the interaction between AC and DC may cause a series of problems, which becomes more complex when there are several HVDC links in one AC grid. In order to study this complicate problem, the thesis conducts a deep analysis on East China multi-infeed grid:(1) Compare two different definitions of Multi-infeed Short Circuit Ratio(MSCR) and deduce their relationship, furthermore, Multi-infeed Interaction Factor(MIIF) as a function of the system impedance is also deduced. Then calculate these parameter values of East China grid and get some meaningful conclusions.(2) Analyze the mechanism & influence factors of commutation failure, and point out that commutating bus voltage drop is the main cause of commutation failure, EMTDC/PSCAD is also used to calculate the threshold voltage value that can be used for commutation failure research in electromechanical transient program.(3) Transient stability research is also applied to study the AC and DC system stability through N-1, N-2 AC faults and DC block with transient stability program BPA.