Abstract
Hybrid High Voltage Direct Current (HVDC) system, combining the advantages of line commutated converter (LCC) and modular multilevel converter (MMC), has become an important developing direction for power grids. Analysis of fault traveling wave characteristics is vital for protection design of hybrid HVDC grids. In this paper, a fault traveling-wave calculation method for hybrid HVDC grids is presented. Firstly, the equivalent models of LCC station and MMC station are analyzed and the bus impedance matrix of the entire HVDC grids is established. Then a fault calculation method is proposed, which calculates in the frequency domain. The numerical inversion of the Laplace transform is applied to obtain the voltages and currents in the time domain. Finally, to verify accuracy of the mentioned method, the simulation model of a three-terminal hybrid HVDC system is established in PSCAD/EMTDC, and the simulation results show that the proposed method is accurate within 3 ms after the DC fault occurs.
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