State feedback Robust H_∞controller for Transient Stability Enhancement of VSC-HVDC Transmission Systems

摘要

In this work, a robust and nonlinear control strategy are investigated in a power system inter connected with a VSC-HVDC system. The controller design is based on the Hoo control methodologies to deal with the nonlinearities introduced by requirements to power flow and line voltage. First, the steady state mathematical model of the VSC-HVDC system is developed and the relationship between the controlling variables is investigated. By use of H_∞.control theory,constant DC voltage controller and constant AC voltage controller are designed. A robust H_∞ control has been proposed to provide voltage support by means of reactive control at both ends; to damp out power oscillations and improve transient stability by controlling either active or reactive power, and to control the power flow through the HVDC link. The proposed control scheme is tested under several system disturbances like change in frequency at both ends , faults on the converter and inverter buses and change in short circuit ratio . Based upon the time domain simulations in MATLAB/SIMULINK environment, the proposed controller is tested and its better performance is shown compare with the PI controller whose gains are optimized with Genetic Algorithim Technique.