Abstract: The observer-based fuzzy H_∞ controller design problem was considered for steam valve opening of multi-machine power systems which is consisting of turbo-generators. Firstly， T-S fuzzy model was used to establish the model for multi-machine power systems. Because sometimes the measurable state variables of actual power systems may not be used as the premise variables of the fuzzy rules， the observer-based conditions were derived to guarantee the H_∞ performance. However， the conditions are not based on the linear matrix inequalities (LMIs)， which can only be solved by a two-step method. Then the LMIs-based conditions by only one step were proposed， in which the conservativeness of the conditions was reduced. Finally， the T-S fuzzy model was established for the steam valve opening of two-machine infinite bus power systems with local linearization method， and effectiveness of the proposed controller design was verified by the simulation results.

Key words: nonlinear multi-machine power systems, fuzzy observer-based controller, LMIs, H_∞ performance, steam valve opening