On contingency assessment in power networks with grid-forming VSC-based distributed energy resources performing power sharing

Decision-making in energy control centers is heavily reliant on contingency assessments. This involves efficient and accurate post-contingency power flow calculations to promptly detect potential system overloading. This study presents an improved contingency assessment method to address power networks with distributed energy resources (DERs) performing power sharing. The classical method using shift factors is extended to incorporate renewable DERs coupled with voltage-sourced converters (VSC). Building on incremental modeling, VSC-based DERs respond to contingencies according to their droop controls, respecting the physical power constraints of the VSC-based generators. The present method also improves the transmission loss calculation through an incremental power loss model that is a function of shift factors for seamless integration in the overall formulation. Accordingly, the calculated post-contingency power flows accurately reflect the system’s dynamic behavior. The extended approach provides accurate assessments of critical risks and a reliable contingency ranking for real-time system operation. Its effectiveness was evaluated on the IEEE 9-bus and 24-bus test systems including several renewable DERs against full dynamic simulations carried out with PSS®E package using WECC dynamic models. Results demonstrated that the present method accurately calculates post-contingency power flows and ranks contingencies adequately for power networks with high capacity of grid-forming VSC-based DERs.