Superconducting magnetic energy storage (SMES) units can be used to enhance the stability of power systems. The key to make good use of the SMES units is to design effective controllers. This paper presents a number of results on the analysis and control of multi-machine power systems with such units via Hamiltonian function method. It has been shown that the multi-machine power systems with SMES units can be made to be a port-controlled Hamiltonian (PCH) system by using a state feedback control, and that the stability of the resulting system can be established. Furthermore, this paper proposes a novel energy-based adaptive L-2 disturbance attenuation control scheme for the multimachine systems with SMES units. The control scheme is a decentralized one and consists of two parts: one is an L-2 disturbance attenuation excitation controller for the generators, and the other is an adaptive L-2 disturbance attenuation controller for the SMES units. Simulations on a six-machine system with one SMES unit show that the proposed control scheme is very effective. (c) 2006 Elsevier Ltd. All rights reserved.