| Summary: | This study first introduces the structure and principle of the control system of ultra-high-voltage direct current (UHVDC) transmission system with hierarchical connection mode, mainly including the whole control logic, the voltage balance control module of high-end and low-end converter stations and the commutation failure prediction function. On this basis, this study sets up an electromagnetic transient equivalent model of UHV AC/DC interconnected system with hierarchical connection mode by simulation software electromagnetic transient design and control/power systems computer-aided design (EMTDC/PSCAD) based on Zhundong–Huadong ± 1100 kV UHVDC transmission project. The simulation analysis was first carried out in steady-state operation. Comparing the electrical parameters of the model under the condition of bipolar total voltage with the actual project, the model is consistent with actual engineering parameters. Next, the simulation was undertaken when single-phase grounding fault occurs on AC bus of rectifier side and inverter side. Finally, simulation waveforms and corresponding conclusion are summarised in this study. The results indicate that the DC control system established with hierarchical connection mode under the PSCAD/EMTDC environment has good adjustment effect and can provide a good reference for practise.
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