Abstract
Lu-Gao-Zhao three-terminal DC project is the first ±500kV multi-terminal line-commutated converter-based high voltage direct current (LCC-HVDC) transmission project in China. Different with the two-terminal LCC-HVDC situation that only the rectifier can operate in power control mode, Gaopo converter station of the Lu-Gao-Zhao three-terminal DC project can operate in power/dc-current control mode for both the rectified and inverter-fed conditions. Sub-synchronous torsional interactions between thermal power plants and the rectified power control converter have been well researched, but the effects of the inverter-fed power control converter on sub-synchronous torsional stability have seldom been analyzed. Based on the concepts of damping and synchronizing coefficients, this paper presents a small-signal model of the SG connected to HVDC converter system to compare the effects of rectified and inverter-fed power control converters on sub-synchronous torsional stability, and reveals the mechanism of the effect differences. The results have been adopted to the practical Lu-Gao-Zhao three-terminal DC project, and verified by the DPT test and actual operation.
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