Improved Multi-infeed Effective Short Circuit Ratio And Its Application

The uneven distribution of China's energy resources center and the load center, is bound to bring a wide range of energy, large-scale transfer. HVDC transmission has benefited from its advantages in long-distance, large capacity transmission and developed rapidly. According to the safety evaluation of AC/DC system, the system is of great significance to the safe and stable operation of the system. In the planning and operation of AC/DC systems, the short circuit ratio index method is an effective method for voltage stability analysis, which has been widely applied to the academic and engineering. As the number of DC lines connected to one AC system increases, the complexity of system structure and the interaction between the subsystems reveal the shortcoming of short-circuit ratio. In this paper, we have explored and researched the voltage stability evaluation of AC/DC system based on short-circuit ratio. The main work of this paper includes the following parts:(1) We theoretically analyzed the impact of the electrical distance between DC terminal location, the equivalent impedance of receiving-end AC system and shunt capacitor to MIIF, and also verified the theoretical analysis results by the simulation of test system and actual power system.(2) The deficiency of the existing multi-infeed effective short circuit ratio(MESCR) evaluating the adverse effects of the shunt capacitor on the power system was pointed out. To solve this problem, we have proposed a improved multi-infeed effective short-circuit ratio(IMESCR) which can take the impact of the shunt capacitors into account by converting the capacity of shunt capacitors to inverter station of HVDC. The feasibility and accuracy of the proposed IMESCR are validated through simulation study of Zhejiang power grid.(3) The installation of STATCOM can enhance voltage stability of the AC/DC system. However, the existing multi infeed short-circuit ratio is hard to reflect the beneficial effect of STATCOM on the stability of system. Therefore, we have proposed multi infeed short-circuit ratio considering the impact of the STATCOM, the index can accurately describe the voltage stability status of a HVDC system with STATCOM. Based on the multi infeed short-circuit ratio considering the impact of the STATCOM, we have proposed allocation method of STATCOM in a multi-infeed DC system, which can take both integrity and balance of the strength of DC systems into account. Finally, the proposed method was applied to the test system, working out a STATCOM scheme which improve the voltage stability of the system, which can prove correctness and applicability of the proposed method.