Dynamic model of sodium sulphur battery for application in microgrids

Nowadays, in addition to a tendency to the use of renewable energy sources, there is also the tendency to operate these units in a decentralized manner so that they are able, if necessary, to work independently or in isolation from the rest of the power system. These systems are called microgrids (MGs). When using renewable energy sources, mainly based on solar radiation or wind, the problem is mainly the fluctuating and intermittent nature of these resources. In the case of MGs, this problem is particularly critical given the need of the ability to work in isolation. To operate MGs safely, a combination of several types of generators and also energy storage should be used to maintain the balance of active power. Among the new storage systems, sodium sulphur batteries (NAS) are considered suitable to perform various security tasks in MG. NAS batteries have a high energy and power density per unit volume and they can also provide energy in both the short and long range. However, the disadvantage of these batteries is that there are few models that genuinely represent their dynamic behavior. For a proper study of the security of MGs using NAS battery, it is necessary to identify their dynamic performance with an accurate model. This paper presents the detailed modeling and dynamic simulation of a NAS battery storage for use in MGs. It also describes the power conditioning system (DSTATCOM) used to connect the NAS battery with the MG and the control strategy. Finally, a NAS battery model was implemented in the environment of MATLAB/Simulink, and then tested in a microgrid system.