Risk Assessment of Cascading Failure in Urban Power Grid Based on Probabilistic Power Flow

Abstract

With the development of distributed power generation, the fluctuation of its power output may bring a higher risk of serious cascading failure in an urban power grid with the change of natural conditions. The existing risk assessment methods fail to consider the fluctuation of distributed power generation. Therefore, this paper proposes a risk assessment method for cascading failures in urban power grids including distributed power generation and electric vehicles. Firstly, based on the probabilistic models of wind power, photovoltaic, and electric vehicles, the random power flow algorithm based on semi-invariants is applied to solve the power flow. And then, a fault chains model which can characterize cascading failures of urban power grids is established. According to the fault chains model, the probability of fault chains is determined by obtaining the probability density of line power flow, and the sum of load shedding control loss and island balance loss is taken as load loss capacity. The risk index is the product of occurrence probability and load loss capacity. Finally, take the IEEE39-bus system as an example, it is verified that the proposed method can consider the impact of distributed power output fluctuations on cascading failures, and realize rapid risk assessment, which has a positive contribution to prevent cascading failures of the urban power grid.