The traditional power grid system was constructed in a centralized and radial topology where power is generated and delivered from one end to the other. Conventional methods for unidirectional power flow analysis will no longer be effective to control renewable energy sources implemented at the consumption sector efficiently; new strategies are called for to facilitate the bidirectional flow incurred by power production of the distributed energy resource units. The transformation will require intelligent distribution automation by means of decentralized power management as well as information and communications technologies to actualize smart grid modernization. In this paper, we design autonomous distribution networks that take scalability into account by dividing the legacy distribution network into a set of subnetworks. We tackle the power flow and power balance issues individually in parallel to optimize the global distribution operation by our proposed power-control method. Meanwhile, we propose an overlay multi-tier communications infrastructure for the underlying power network to analyze the traffic of data information and control message required for associated power flow operation. Based on the proposed schemes, we show that we can potentially improve the utilization of renewable energy production and achieve data traffic reduction under decentralized operations as compared to legacy centralized management.