A Novel Control Method Based on Droop for Cooperation of Flywheel and Battery Energy Storage Systems in Islanded Microgrids

Recently, microgrids (MGs) have provided different advantages for electrical power systems, but they have created some challenges too. One of the most important challenges is the stability of the MG in islanded operations. To overcome this challenge, energy storage systems (ESSs) can play an effective role. On the other hand, each ESS has distinct characteristics that make them suitable for specific applications in the MG. The suitable cooperation among them can ensure reliable operation of the MG. Moreover, it affects the operation of ESSs and their lifetime. In this paper, cooperation between two types of ESSs (flywheel and battery) is studied. The flywheel ESS, which has high power density, is used during MG transient responses, and the battery ESS responds to long-term load changes. A new control method, based on droop equations, is proposed for each ESS unit. Then, the genetic algorithm is used to obtain the optimal controller coefficients. The simulation results show suitable cooperation between ESS units and stable operation of the MG. Finally, to analyze the proposed method's impact on the stability, a root locus analysis is presented.