Robust, coordinated control of SSO in wind-integrated power system

This study presents a robust, coordinated control methodology for damping sub-synchronous oscillations (SSOs) while considering power output variations from multiple wind farms. The proposed damping control strategy utilises the mixed H-2/H-infinity control with regional pole placement to suppress the oscillations. For ensuring applicability over a wider operating range, the convex polytopic theory is utilised by using different operating points as the vertices of a convex polytope. The centralised, coordinated controller for damping SSOs is designed using linear matrix inequalities. Furthermore, unmeasurable state variables, if present, are represented by corresponding output variables. The damping signal is implemented as active power and reactive power modulation of the rotor-side converter of the doubly fed induction generators. A 4-machine, 2-area system and a 39-machine New England system are used to demonstrate the performance of the proposed control. The simulation results show that the polytopic controller can not only provide requisite damping to the SSO modes of interest, but also has good control performance when the wind power outputs change over a wide range.