- In this paper we present a module-based modeling of electrical power grids. Each (group of) component(s) is defined as a module and its dynamics is represented in terms of its local variables and the interconnection variables between the module and the system network. Therefore, it is possible to specify the performance sub-objectives of each module for a given range of variations in interaction variables and to ensure that the local sub-objectives are met through local sensing and actuation. The specifications are implemented through an interactive cyber-based protocol between the local modules and the network operator. The network operator defines bounds on the interaction variables. Individual modules, in turn, adjust their own local control to meet local performance specifications for the given bounds on the interaction variables. Sufficient conditions on network properties are derived under which this interactive protocol between the network operation and the modules converges to a system-wide stable operation. The proposed interactive protocol could be used for incorporating into future electric power grids high penetration of distributed generation resources, and this is illustrated on a simple example. 2008 IEEE.