# CoSimulating Communication Networks and Electrical System for Performance Evaluation in Smart Grid
## 1 Introduction
Another challenge is that the smart grid is a mixture of large and complex systems. Therefore, we cannot build a precise cosimulation tool by extending an individual simulation tool for a single system. For example, if we employ a single network simulator which has an extension for the power system, the large scale of the power system might be simplified, so unrealistic assumptions would be introduced. Therefore, integrating independent simulators of each system would be a favorable choice for simulating smart grid. Figure 1 shows the conceptual representation of the proposed cosimulation. The application model defines the control policies, algorithms, and functions, which receive current states of the power system and event signal, and then decide the next states. The transmission of the event signals and control messages can be simulated through the network simulation. As the network simulation is invoked, the network-side information is retrieved by the application model in the context of the cosimulation. Similarly, control policies are applied to the power system simulation, and the new states information are reported to the application model. Moreover, meaningful results of the smart grid application are generated by the power system simulation, which can verify the impact of the application. Based on the conceptual representation of the cosimulation, we propose a novel cosimulation work for the smart grid applications, called OOCoSim, which stands for OPNET [8] and OpenDSS [9] cosimulation. Since both OPNET and OpenDSS have large scalability, various applications in the future smart grid can be implemented and simulated in OOCoSim. Moreover, both OPNET and OpenDSS can operate simultaneously on the same platform (Windows platform), dynamic and organic simulation can be achieved. In the future smart grid, complex applications which require dedicated interaction, such as deciding the amount of adjustment of power system state based on the network performance, would be introduced. Such complex application can be modeled and simulated in OOCoSim, since OOCoSim utilizes and manages the live simulations of OPNET and OpenDSS. However, to manage the live simulations of OPNET and OpenDSS, a scheduling scheme which performs synchronization between the events of the power system and the network system is required. To solve the synchronization issue, we devised global time management scheme which has rollback mechanism to reflect the events from the network system to the global event scheduler. To verify the proposed OOCoSim and provide a guideline to model the smart grid application, we designed a simulation study of the demand response application. The application model of the demand response is introduced and the results generated by OOCoSim are discussed in a later section. Through the simulation study, the impact of the underlying network infrastructure of the demand response application would be analyzed. The remainder of this paper is organized as follows. We first introduce some related work in Section 2. Then, a blueprint of OOCoSim and its implementation are presented in Section 3. In Section 4, we describe a model of the smart grid application. We present a simulation model and a set of simulation results that OOCoSim produces in Section 5. Finally, we conclude the paper in Section 6.