Risk Assessment Of Cascading Outages In Power System With High Wind Power Penetration

In recent years,there have been many blackouts around the world.The frequency of large blackouts is very low,but each time it causes huge economic losses,which seriously affects people's daily lives and threatens national security.The cascading outage is the main cause of many blackouts,which has attracted the attention of many scholars.The cascading outage risk assessment can quantitatively analyze cascading outages and is a way to deeply understand the mechanism of cascading outages.With the development of energy transformation,the proportion of renewable energy continues to increase,and the high proportion of wind power integration will become an inevitable development trend and important feature of China's power system.Although Large-scale wind power integration eases energy shortage,it also brings some hidden dangers to the stability of the power system.For example,the fluctuation and randomness of wind power increases the uncertainty of the grid,and occasionally wind turbines trip-off faults occur.Therefore,in order to improve the ability to prevent and control large blackouts,it is necessary to consider the impact of large-scale wind power integration in the cascading outage risk assessment.The research object of this paper is the cascading outage risk assessment of power systems with high wind power penetration.The main contents include the modeling of wind power output scenarios considering the correlation of prediction errors and the cascading outage risk assessment methods considering the impact of wind power integration.Firstly,the theoretical basis of the cascading outage risk assessment of power system with high wind power penetration is introduced.The evolution mechanism of cascading outages of power system with wind power penetration and the theory of cascading failure risk assessment are described.Besides a wind power output model considering the correlation of prediction errors is introduced in detail.The model considers the correlation of prediction errors,models with Copula function,and uses the fuzzy C-means clustering method to reduce the scene.It can not only calculate the wind power output scene at a certain moment,but also generate a possible wind power output curve for a period of time.Taking the data of two wind farms with similar geographical locations in northern Hebei in 2013 as an example,the wind power output modeling method considering the correlation of prediction errors is illustrated,and the model effect is demonstrated.Then,the current research on cascading outage risk assessment is insufficient to consider the uncertainty of wind power output.To solve this problem,a fault chain model is proposed based on stochastic power flow calculation and Value at Risk(VaR)theory.In the process of generating the fault chain,the stochastic power flow calculation is introduced to replace the traditional power flow calculation,and the fault probability and fault consequences are combined to construct the subsequent fault search indicators,and the subsequent fault links are selected according to the VaR.The fault consequences are calculated based on the wind power scene.When calculating the probability,misoperations and refusals of the protections and circuit breakers are considered.The risk indicator is established from the perspective of loss of load.Comparing all the fault chain risks of the calculated operating points with the acceptable loss-of-load loss curves,it can be judged whether the current operating point is in a safe area or a high-risk area.The simulation results show that for a set operating point,with the increase of wind power permeability,the load loss risk and load loss increase.Compared with using the wind power forecast value as the actual wind power output,after considering the wind power forecast error distribution,the system cascading outage load loss risk assessment value is significantly improved.Finally,the existing cascading failure model pays insufficient attention to the interaction between wind farm and grid line faults.Aiming at this problem,considering the wind power trip-off,a multi-timescale cascading outage risk assessment model is proposed.This model is suitable for future power systems with high wind power penetration.The model divides multiple dynamic processes in the cascading outages such as wind power trip-off,emergency control,random failure,security correction,wind power and load fluctuations into three time scales according to the action occurrence time.Thus,the development process of such a cascading failure can be more rationally simulated.The wind power trip-off response model considers two cases.One case is when a fault occurs in the grid,the action of wind farm voltage protection causes the wind power trip-off.In another case,when the island balance is performed,the wind power frequency protection action is caused by the insufficient frequency modulation capability of the subsystem,thereby causing the wind power trip-off.The selection of random faults considers two types of faults:random short-circuit faults on heavy-haul lines and open-circuit faults caused by misoperations.Taking the improved IEEE39 node system with 7 wind farms as an example,the rationality of setting random short-circuit faults in the cascading outage model considering wind power trip-off is illustrated.The simulation results show that the load loss risk and load loss of the system increase after considering the wind power trip-off,which proves the necessity of considering the wind power trip-off response in the cascading outage risk assessment of power systems with high wind power penetration.