An engineering applicable dynamic equivalent method for large-scale AC system connected to VSC-HVDC
To test the software and hardware functions of VSC-HVDC control and protection device, an efficient way is to carry out the hardware-in-loop (HIL) tests and setup a detailed AC/DC transient model in real-time digital simulator. However, taking into account capability of the simulator and details of the simulation, the large scale AC network outside the converters should be simplified and equivalent. In this paper, based on a principle that the short circuit levels should be consistent before and after equivalent, a new equivalent method to calculate the equivalent generator parameters for large scale AC power system is proposed. Firstly, rated capacity and access reactance of equivalent generators are calculated according to equivalent bus's short-current. Secondly, a new criterion is provided based on short-current contribution ratio, according to short-current and short-reactance of the equivalent bus. Finally, this criterion is used to choose dominate controller of the equivalent generators, and calculate controller parameters. At the same time, the Ward method is improved. The negative line resistance and generator active output are corrected. Finally, the proposed method is used for Xiamen equivalent grid which derived from a large scale of “Sanhua” China power grids and validated by comparison of the bus voltages, power flows, short-circuit levels and the dynamic response characteristics of the equivalent network, the validity of the proposed method is proved.