# CoSimulating Communication Networks and Electrical System for Performance Evaluation in Smart Grid
## 2 Related Work  
There have been a few research studies to verify the impact of the networking system in the smart grid. In this section, we introduce the previous achievements in smart grid cosimulation research domain, and analyze the differences between the OOCoSim and the existing studies. The work in [10] is a novel attempt which tries to integrate power and communication simulation. In the paper, authors propose EPOCHS platform which includes PSCAD/EMTDC simulators for the electromagnetic transient simulation, PSLF for the power system simulation, and NS-2 for the communication infrastructure. The challenging issue in the work is a synchronization since the PSLF simulator performs typical continuous-time transient simulation in power system and the NS-2 is a discrete event simulator. To address the issue, authors employed time-step based synchronization, in which each simulator performs simulation independently and is suspended at certain synchronization points. However, in the method, events between the synchronization points are ignored or buffered, and it can cause accumulated simulation errors [11]. The errors can be reduced by introducing small size of synchronization step, but it has trade-off with simulation speed. Moreover, using NS-2 as a network simulator is an inappropriate option since it has simplified lower layer models including physical layer models. In smart grid, the wireless channel conditions are harsher than those of typical wireless environments [12; 13], therefore, using NS-2 as a network simulator for the smart grid simulation can cause inaccurate results. In [14], multi-agent system based simulator was introduced to simulate dynamic control in smart city. In the simulator, the software agents try to create the dynamic behavior of devices that perform monitoring, controlling, and producing electrical energy, and the created behavior is simulated  
Figure 1: The conceptual representation of the proposed cosimulation. to generate various results (for example, power demand over time). However, in the simulator, consideration of the network system, which can make the critical influence on the smart city system, was excluded. Since the network system is very important infrastructure of the smart city that can create the serious impact on the system, inclusion of the network system is required to generate more realistic simulation results. In [15], open source based simulation method was proposed. NS-2 and OpenDSS were employed to simulate the smart grid scenario. They designed an application scenario in which electrical energy in energy storage units is dispatched to prevent voltage drop when the solar ramping phenomenon is occurred. The dispatch command is transmitted to each storage units through IEEE 802.11 based multi-hop network system. Through the NS-2 simulator, the arrival time of the dispatch command is simulated, and then the information is merged into the OpenDSS simulation script. Through the proposed cosimulation, the designed application scenario was successfully simulated, and the simulation results let us know that voltage drop in solar ramping phenomenon can be successfully compensated through the energy storage units. However, since the simulation operates on different platforms (Linux platform for NS-2 and Windows platform for OpenDSS), the dynamic and controllable cosimulation cannot be achieved. For example, simulation of an application which adjusts transmission power of the dispatch command based on the voltage dropping level requires repeated re-simulation of the NS-2 simulator since the voltage dropping level is a dynamic value; therefore, the value cannot be considered in the NS-2 simulation phase. To simulate such applications which require more complicated combination of the two systems, the dynamic and controllable cosimulation should be employed. In [11; 16], authors proposed GECO, a cosimulation frame work with PSLF and NS-2 simulator for WAMS (Wide Area Measurement System).