  In networked control systems (NCS), sensing and control signals between the
plant and controllers are typically transmitted wirelessly. Thus, the time
delay plays an important role for the stability of NCS, especially with
distributed controllers. In this paper, the optimal control strategy is derived
for distributed control networks with time delays. In particular, we form the
optimal control problem as a non-cooperative linear quadratic game (LQG). Then,
the optimal control strategy of each controller is obtained that is based on
the current state and the last control strategies. The proposed optimal
distributed controller reduces to some known controllers under certain
conditions. Moreover, we illustrate the application of the proposed distributed
controller to load frequency control in power grid systems.
