Advanced AC Power Flow-Based Cascading Outage Simulation Method to Address Voltage Issues

This paper addresses two key voltage issues in cascading outages simulation based on the widely used AC power flow model. First, the main unsolved flaw affecting the simulation continuation and accuracy of cascading outages is the divergence of conventional AC power flow, caused mainly by voltage instability. This divergence further prevents capturing the operation of undervoltage load shedding protection. Second, AC power flow cannot capture the stalling and disconnection at low voltages of induction motors, the main load in power systems. To overcome these issues, a new fast method for AC power flow-based cascading outages simulation is proposed. It enables computing some relevant points of the power system trajectory by combining: (i) the extension of the simulation model to short-term operation, based on load short-term characteristic, (ii) detailed model of induction motors, and (iii) the inclusion of the interplay of these two models with the specific operation of under-voltage load shedding. To enhance accuracy, the proposed simulator also models other typical features like islanding and frequency issues. Compared to existing methods, the numerical results show the importance and effectiveness of each new aspect of the method. Dynamic simulation validates the accuracy of the proposed simulator on the IEEE-39 bus system, widely used for both cascading outages and dynamic simulation. The method is scalable to large power systems, e.g. of 9,241 buses.