A More Realistic AC-QSS Cascading Failure Model with Decentralized UVLS and Centralized RAS

Currently, the divergence problem of AC-Quasi-Steady-State (QSS) cascading failure models is addressed by uniform load shedding (ULS) that trips load in same fraction at all buses till convergence is achieved. However, in reality there exist pre-designed undervoltage load shedding (UVLS) relays that shed load in the subset of buses where voltage descends bellow a threshold, thereby preventing voltage collapse. This might not be captured by ULS, which in turn leads the cascade propagation to a different path. We attack the problem by proposing a new AC-QSS model, which combines voltage magnitude and Q-V sensitivity to predict buses that have undergone UVLS tripping in reality. Moreover, we introduce a centralized AC optimal preventive control approach to alleviate cascade propagation. We use a simple AC-QSS model with ULS as benchmark to contrast results of UVLS model and further demonstrate the effectiveness of preventive control on IEEE 118-bus system and a 2383-bus Polish network.