Stochastic unit commitment to determine frequency response ramp rate including wind turbines with synthetic inertia and virtual synchronous generator

Abstract

In this paper, the dynamic frequency constraints are derived for power systems incorporating full-converter wind turbines. These wind turbines could be equipped with a virtual inertia by either synthetic inertia control or virtual synchronous generator concept. In the former scheme, deviations in the wind turbines rotor speed remain in synchronism with the system frequency. However, the wind turbines start to restore their rotor speed before the system frequency recovery initiation, in virtual synchronous generator scheme. The restriction on the virtual inertia are determined considering a limit variable on wind turbines rotor speed drop. The frequency response requirements are derived in terms of governor’s base power, ramp rate and reserve power. A linear frequency nadir constraint is also proposed for the synthetic inertia strategy. Then, the constraints are integrated into the stochastic unit commitment to be consistently and economically met over 24-hour period. As such, the contingency size management are coordinated with the virtual inertia provision. The unit commitment results of IEEE 118-bus system including multiple wind farms reveal that the virtual synchronous generator concept can be an optimal solution for future low-inertia grid’s challenges. Finally, accuracy of the unit commitment results is validated through time-domain simulations of the detailed system model.