Power systems are nonlinear multidimensional and multichannel complex objects. There are some structure and parameter uncertainties in power systems. For uncertainties compensation are used robust and adaptive control methods. The sliding mode control theory is one type of the robust control theories, which can obtain low sensitivity to object parameters changes. Therefore, new approach of nonlinear sliding mode control theory is shown in this paper. It's called synergetic sliding mode control. Here is described the procedure of synergetic sliding mode control for nonlinearly controlled objects. Proposed procedure is based on aggregated regulators analytical design (ARAD) method -the basic method of synergetic control theory. Application of this theory has been reviewed for synthesis of synchronous generator (SC) excitation nonlinear robust control law. Robustness and control performance of the proposed method are examined by numerical simulations.