This paper presents the design of a robust fixedââ?¬Âorder HâË?ž controller to damp out the interââ?¬Âarea\noscillations and to enhance the stability of the power system. The proposed HâË?ž approach is based\non shaping the openââ?¬Âloop transfer function in the Nyquist diagram through minimizing the quadââ?¬Â\nratic error between the actual and the desired open loop transfer functions in the frequency doââ?¬Â\nmain under linear constraints that guarantee robustness and stability. The proposed approach is\nrobust with respect to multiââ?¬Âmodel uncertainty closedââ?¬Âloop sensitivity functions in the Nyquist\ndiagram through the constraints on their infinity norm. The HâË?ž constraints are linearized with the\nhelp of a desired openââ?¬Âloop transfer function. The controller is designed using the convex optimiââ?¬Â\nzation techniques in which the difference between the openââ?¬Âloop transfer function and the desired\none is minimized. The twoââ?¬Âarea fourââ?¬Âmachine test system is selected to evaluate the performance\nof the designed controller under different load conditions as well as different levels of wind peneââ?¬Â\ntrations.
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