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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 H2/H8 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. [ABSTRACT FROM AUTHOR]

The transient stability margin is affected by different fault locations, fault clearing time and fault types that could be provided by protection information. This study presents an analytical on-line method of determining transient stability margin quantitatively using protection information for multi-generator system. First, the multi-machine system is equivalent to a one-machine infinity-bus system with the help of complementary cluster centre of inertia-relative motion. Second, the asymmetric fault models are built using positive rule, and the transient stability margin is then deduced by modelling the piecewise models of generator angles. Third, the practical transient stability margin assessment algorithm is then obtained. The sensitivity and affection mechanism of stability margin affected by fault factors are further derived, and the analytical stability margin is put forward to online access the transient stability margin after fault with the acquisition of the protection information. Finally, four- generator system, New England system and a real large power grid are used as test systems to verify the effectiveness and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]