Abstract：With the voltage source converter (VSC) technology continues improving, the development orientations of high-voltage direct current based voltage source converter (VSC-HVDC) system are high-voltage, large capacity and multi-terminal. For the technical difficulties of strong nonlinearity and multi-terminal coordination in VSC-HVDC system, an improved droop control method is proposed based on the first multi-terminal VSC-HVDC project of the world. In this method, multiple constant voltage control stations are in operation at the same time, thus during transient process, the system can continue to run when the voltage control stations exit. This can maintain the DC network power balance. Conversion between constant voltage control stations and power control stations can be realized by measuring DC voltage and changing controller output value dynamically. Namely, the switching controller selects power controller output or DC voltage controller output, without inter-station communication. Compared with the traditional single-point voltage-controlled multi- terminal VSC-HVDC system, it has better flexibility. In addition, the back stepping controller of DC voltage is designed for extreme conditions that voltage control stations fail completely. It can reduce transient overvoltage level effectively. Combined with droop control strategy, its multi-terminal coordinated control function is manifested and the immunity performance is improved. The simulations have verified the proposed methods.
吴杰, 王志新. 多端柔性直流输电系统的改进下垂控制策略[J]. 电工技术学报, 2017, 32(20): 241-250.
Wu Jie, Wang Zhixin. Improved Droop Control Strategy for Multi-Terminal Voltage Source Converter-HVDC. Transactions of China Electrotechnical Society, 2017, 32(20): 241-250.
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2017, Vol. 32 
