Structurally constrained WAC design to mitigate low frequency oscillations induced by load disturbances

Srujana, Yenigalla and Sarkar, Vaskar (2019) Structurally constrained WAC design to mitigate low frequency oscillations induced by load disturbances. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

This thesis introdues a strategy to design of wide area controller for damping the low frequency oscillations. The wide area controller is a state feedback or the output feedback controller. The thesis mainly focusses on the state feedback controller design. In this thesis designing of a state feedback H∞ controller with structural constraints. With the main ideology of considering the load disturbances, And those disturbances are considered through the dynamic modeling of the ZIP load (which is not in the literature). And the formulation of performance channel with respect to the load disturbance in nominal load power is a challenging task that has been proposed in this thesis. The design of the small signal model of the power system with generator unit, transmission line and load is required for the design of the wide area controller. The generator unit includes the generator, turbine, exciter, speed governing system and PSS model. The small signal modeling of the load is performed for the ZIP load model. The study for damping of the interarea oscillations caused in the subsystems connected by tieline for load disturbances utilizing LQR control as well as H∞ control techniques. The state feedback gain matrix is determined using the LQR control optimization, it considers the entire set of state variables as inputs. Whereas in the case of H∞ optimization the states which are given as the input to the controller can be choosed such that a structural contraint on the state feedback gain from H∞ control can be imposed by choosing the required states as inputs to the controller. A 68-bus, 16- machine system is used for the case study. MATLAB/Simulink environment is used for statespace model design, the controller design and the time-domain analysis of the modeled controllers. H∞ control is used to design a state feedback matrix with structural constraints involved

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