Impact Of Parallel FACTS Element With Energy Storage On The Development Of Cascading Failures

Flexible AC transmission system is studied more in recent years, because it can replace the traditional electromagnetic machinery and other means of control, it can effectively improve the power controllability of AC system, significantly reduce network loss and the cost of power generation, it can improve the stability and reliability of the system. It is widely used in the study of network system.Usually, one or several components failure may be the cause of the cascading failure, during running state transfer process after protection action, the trend of redistribution caused by a new round of protection or automatic device action causes a series of interrelated events, the rapid spread of the fault, voltage oscillation, frequency oscillation, power angle oscillation and disorderly large power grid splitting, and ultimately the formation of a series of uncontrollable accidents chain, resulting in collapse of the system, it is the blackout. The FACTS element with energy storage can absorb or release the active power and reactive power quickly, adjust the system power flow, improve the voltage especially under transient conditions, enable the system to avoid the occurrence of cascading accidents in certain circumstances. This paper focuses on the effect of parallel FACTS element with energy storage on cascading failures of power system.The model of parallel FACTS element with energy storage is built up based on PSASP user defined module, and used to analyze its influence to power system under the light load, normal load and heavy load. The IEEE39 system simulation results show that parallel FACTS element with energy storage can reduce the use of generation shedding and load shedding or other control measures in a certain extent, it can inhibit the continuation of cascading failure. Optimal location of parallel FACTS element with energy storage is studied from both steady state and transient state aspect:line overload index can evaluate line vulnerability from steady-state aspect, line transient potential energy impact index can evaluate its ability to withstand attack from transient aspect, voltage beyond limits index can be important indicator to study bus importance from both steady and transient state aspects, so a comprehensive evaluation index method is presented to select optimal location by integrating these three indices, which can improve steady-state and transient-state performance of electric power system at the same time, the WEPRI-11 system and IEEE39 system are taken as sample cases to verify the proposed method. Finally, impact of parallel FACTS element with energy storage to system vulnerability is analyzed by IEEE39 node system, it shows installation of parallel FACTS element with energy storage can decrease the vulnerability of the whole system and the possibility of cascading failure occurrence, the effect is better than that of HVDC.