The Research On Impact Of Inductive Filtering Method To The Operation Charactristics Of Multi-infeed HVDC Transmission System

In recent years, in south China and east China, it has already appeared multiple dctransmission lines connected to the same ac busbar or the ac bus electrical distance isvery close, which formed the structure of multi-infeed dc transmission systems structrue.The new structure brings new challenges for the operation of HVDC transmission systemoperation.Inductive filtering technology combines the transformer design with harmonicsuppression, and gives full exploration of the electromagnetic potential of transformer.It can suppress harmonic and compensate reactive power nearby nonlinear loads, andhas the characteristics of green, energy saving. Inductive filtering method can improvecommutation characteristics of dc transmission system as well as the system stability.The introducation of inductive filtering technology into the mutil-infeed dctransmission system will be expected to solve the typical problems such as harmonicinteractions, commutation failures and interaction issues of multi-infeed HVDCsystem.The CIGRE HVDC standard model and parameter is used to establish an inductivefiltering based dc transmission model, and to set up a new-type converter transformer dccircuits and CIGRE dc circuits of two feed-in HVDC simulation test model, in-depthdevelopment of inductive filtering technology on both ends of feed in dc transmissionsystem and the application of the HVDC system may provide the basis.The mathematical model of the new converter transformer under the fundamentaland the harmonic frequency is established, and its harmonic model and decouplingcircuit is analyzed. On this basis, the equivalent circuit and harmonic transfer functionof the new mutil-infeed dc transmission system are deduced to reveal the harmonicdistribution characteristics of the new mutil-infeed dc transmission system. Harmonictest experiments and simulation experiment validates the theoretical analysis.The mechanism and influence factors of commutation failure in HVDC systemare clarified, and the influence of inductive filtering to the commutation parameters ofthe new mutil-infeed dc transmission system is discussed. Based on this, the local andconcurrent commutation failures in new mutil-infeed dc transmission system arestudied in-depth. The results show that the inductive filtering technology caneffectively reduce the commutation reactance and improve commutation margin, improve the resist ability of the new mutil-infeed dc transmission system to the localand concurrent commutation failure, as well as improve system stability.The performance of the new mutil-infeed dc transmission system is studied inthe environment of PSCAD/EMTDC, by using the established system model. Theinfluence of inductive filtering to the dc transmission power and the converter’sreactive power is analyzed, and the steady-state volt-ampere characteristic of thesystem from the rectifier and inverter side are studied. Finally, the fault recoverycharacteristics of the new system are analyzed. The research results show that theinductive filtering technology can improve the transmission capacity, and reducesystem losses and prevent the occurrence of transient overvoltage as well as reduce theimpact of one dc circuit to other dc circuit and fault recovery characteristics. Theinductive filtering technology can improve the whole stability and anti-interferenceability of the multi-infeed dc transmission system structure.