The article deals with the control problem for a large-scale nonlinear system with chaotic dynamics based on a centralized and decentralized controller structure. The control is based on the feedback principle, which makes it possible to implement in a closed system a given spectrum of Lyapunov characteristic exponents to suppress chaotic dynamics and transfer the system to stable periodic movements or to a state of equilibrium. To change the spectrum, a modal control procedure is proposed, generalized for nonlinear large-scale systems. An example of the application of this technique to suppress chaotic oscillations in a system consisting of three synchronous generators is considered. Computational experiments confirm the workability of centralized and decentralized management. The article considers the use of the proposed method for the synthesis of decentralized control through the example of a system consisting of three synchronous generators. The results of the study confirmed the suppression of chaotic oscillations and the provision of a regular mode in a closed system. The advantage of the proposed decentralized control is the reduction of computational costs for the synthesis and implementation of control systems for large-scale systems.