大规模新能源基地柔性直流送出系统强度评估方法

System strength is generally used to describe the system performance under a disturbance and quantify stability margin. The system strength assessment based on short-circuit ratio has provided a simple and intuitive reference for the grid operation and stability analysis. However, the existing methods rely on the assumption that synchronous generators in the grid provide short-circuit capacity and voltage support, so that they may be unsuitable for renewables sending systems with voltage source converter-based high voltage direct current (VSC-HVDC), where all apparatuses are power-electronic interface. In this paper, we discuss its system strength evaluation problem in terms of small-disturbance stability. The generalized short-circuit ratio theory is expanded into this all inverter-based system based on the voltage-source equivalent analysis of VSC-HVDC. Then, a source-grid coordination method is presented to evaluate the system strength by combing the renewables apparatus critical short-circuit ratio. Results show that with consideration of the voltage support characteristics of VSC-HVDC, the generalized short-circuit ratio can be calculated without the short-circuit analysis, instead analyzing the multi-port current-voltage sensitivity matrix; the system strength can be evaluated by comparing generalized short-circuit ratio and its critical value and the assessment of small-disturbance stability margin and static voltage stability margin is realized rapidly. Finally, the validity of the proposed method is verified by a typical example of multi-wind farms sending system with VSC-HVDC.