Dynamic FFR from wind power - from simulation to reality

Abstract

Abstract As future forecasts of less inertia in the power system require new types of reserves, dynamic Fast Frequency Reserve (FFR) is a new suggested ancillary service that is investigated in this project to be provided by wind power. Two different prototypes were developed to test dynamic FFR from wind power, through simulations and practical tests with Chalmers wind turbine at Björkö. Both prototypes work by adding an additional torque contribution from a dynamic FFR controller, which follows a frequency input signal dynamically, to the electrical reference torque estimated by the National Renewable Energy Laboratory (NREL) controller. To mitigate that the NREL controller counteracts dynamic FFR, the prototypes offer different solutions in adjusting the rotational speed entering the NREL controller. Prototype A works by slowing down the effects of the NREL controller, while prototype B tries to estimate an unaffected rotational speed as input to the NREL controller. The overall results indicate that dynamic FFR from wind power looks promising, as the dynamic response allows for intended energy recovery. Step tests with both prototypes show clearly that the power increases or decreases as intended, and that the rotational speed consequently decreases or increases, but also that the endurance could be a potential problem. Furthermore, simulations show that efficiency decrease due to dynamic FFR could be an issue. Different wind conditions are also a potential challenge, but dynamic FFR could still be enabled during low wind velocity conditions by adjusting the torque-rotational speed curve. Closed loop simulations with the power system show that both prototypes improves the frequency minimum, nadir, and following maximum, zenith, during a large disturbance. Bode plots show that prototype A, given the settings that were used for the prototype, almost fulfils requirements set for Power Oscillation Damping - active power (POD-P), and that the frequency stability of the power system can be improved by dynamic FFR provided by prototype A in situations with inertia down to 100 GWs. Specifics on design and technical requirements must be further investigated, and practical tests must be carried out on conventional wind turbines, since they might not face the same issues with endurance due to greater moment of inertia.