Integrated Inertial and Droop Frequency Controller for Variable Speed Wind Generators

One of the major and more challenging problem that is going to affect the future electricity system is the one relate to the frequency stability and support from generating units. In traditional power networks frequency support were transiently provided by the rotating mass of the generator (directly connected to the grid) while the steady state contribution to frequency is provided by a droop control primary regulation. With the massive diffusion of under-converter generation the system is facing and increasing of the overall installed capacity, and a reduction of the percentage of ”inertial responding” generators and of generator actively participating in frequency regulation. This situation negatively affects the system frequency response and may increase the risk of generation outages and blackouts. The aim of the present paper is that of analysing the possible contribution of variable speed wind generating units in frequency support, by means of the definition of dedicated control strategies to be implemented at power electronic level. Then, the paper also proposes the integration of inertial and droop frequency controller in order to define a control strategy capable of emulating the frequency response behaviour of a traditional generating unit. The performances and limits of the proposed controller is evaluated by means of dedicated simulations. Key-Words: Frequency controller, frequency stability, power system, protection scheme, wind turbine generator