Study On Coordinated Parameter Design For Power System Stabilizers To Enhance Overall Rotor Angle Stability

The fundamental framework of Chinese national power grid has now been settled as"power transfer from West to East, between North and South, with countrywide interconnection". The electrical link and power interchange between regional power systems have thus been greatly improved, but still low-frequency oscillations happen from time to time, especially in certain areas. Quite a few of the low-frequency oscillations reported at home and abroad are due to large disturbances. Power system stabilizers (PSS) could be detrimental to the transient stability while boosting the small-signal stability, with the whole rotor angle stability spoiled. This dissertation tries to solve the above issue by coordinated design of PSS parameters in the multi-machine power system. There are possible balancing solutions where the overall angle stability is enhanced. The contents of this dissertation are as follows.Using several classical analysis approaches, it is confirmed in this dissertation that the excessive damping torque component offered by PSS is accompanied by its negative synchronizing torque component, which is the cause for the boosted small-signal stability and the impaired transient stability.The current simulated annealing method used for coordinated PSS parameter design is improved on the treatment of the bound constraints of arguments. A new objective function is proposed to ensure the damping ratio and oscillation frequency within a specified range. The merit is that it is easy to specify reasonable gate values for different power systems. Pattern search, another simple and practical method, is also adopted to solve the proposed optimization problem. The effectiveness and efficiency of these methods are proved on the 10-generator New England test power system.The trajectory sensitivity (TS) method used for coordinated PSS parameter design is further developed by this dissertation. The TS method is utilized to compute the gradient vector of the dynamic performance index of the power system with respect to PSS parameters to be tuned. Moreover, the search direction for updating the PSS parameters is given, and new PSS parameter configuration could be found for better overall angle stability. Compared to the original implementation, the dissertation modifies the selection of intermediate variables, formula derivation, the pick up of initial values, the sifting of searching interval, the arrangement of gradient information etc.A technique called"backward integration along trajectory"(BIAT) based on the calculus of variation in optimal control is proposed to solve the aforementioned problem of coordinated PSS parameter design. The features of both the TS and BIAT methods are compared in details. Promising effect is suggested by the case studies on the 4-machine 2-area test power system and the 10-machine New England test power system.An additional logic controller with simple structure is proposed to remove the possible unfavorable effect offered by PSS on the synchronizing torque component for the generator. The results are tested on the aforementioned test power systems.