A novel Linear Matrices Inequality (LMI) based H2/H∞ output feedback controller for power system with large disturbances in different load conditions is presented in this paper. Unlike normal H-norm based controller design methods, the regional pole constraints are used to enhance the system performance, and two redefined lemmas are applied for the output feedback controller. Oscillations caused by different kinds of large disturbances are analysed by comparing the performances of the proposed power system stabilizer (PSS), normal H2 PSS, and conventional PSS (CPSS). For the wind turbine, disturbances caused by various kinds of wind conditions are taken into consideration. Because of the strong self-damping ability, the performance of the proposed PSS is compared with CPSS and the case of no PSS. The simulation and experiments are evaluated on a benchmark single machine infinite bus (SMIB) system and a novel double-fed induction generator (DFIG) wind turbine model. The H2/H∞ robust control guarantees the damping performance for large disturbances and its robustness is better than that of other PSSs.