Steady-State Simulation of Cascading Outages Considering Frequency

Frequency is a pivotal indicator of the balance between power generation and load. Frequency variations and frequency-related system behaviors and characteristics are crucial during cascading outages, but they have not been considered by many steady-state power-flow-based models used for simulating cascading outages. This chapter introduces a steady-state approach for simulating cascading outages (Ju et al., IEEE Access 6(1), 37784–37795 (2018)), named as Steady-State Simulation of Cascading Outages Considering Frequency (SSCOF). This SSCOF approach includes a power-flow-based model that comprehensively incorporates the static power-frequency characteristics of generators and loads. It enables the frequency deviation to be calculated resulting from active power imbalances during cascading outages. Additionally, the SSCOF approach considers an ac optimal power flow model that integrates the frequency deviation. This model facilitates the simulation of remedial control actions in response to a highly system condition against system collapse, signaled by power flow divergence. The SSCOF approach also enables an under-frequency load shedding and generator frequency protections to be modeled and simulated, enhancing the accuracy in steady-state simulation of cascading outages. Some case studies are presented to demonstrate the effectiveness of the SSCOF approach. First, the frequency calculated from the power-flow-based model is compared and benchmarked with the steady-state frequency obtained from the time-domain simulation on a two-area power system. Then, the SSCOF approach is demonstrated for cascading outage simulation on the IEEE 39-bus system and the Northeast Power Coordinating Council (NPCC) 48-machine, 140-bus power system. The simulated scenarios of cascading outages are compared with those generated from a conventional approach that uses the power flow and ac optimal power flow models without taking frequency into consideration. The results verify the superiority of the SSCOF approach. By accurately capturing frequency variations and considering frequency-related system behaviors during cascading outages, the SSCOF approach more precisely captures the mechanism of outage propagation and enhances the steady-state simulation of cascading outages. The conventional approaches that do not consider frequency might underestimate the risks and consequences of cascading outages.