Simulation of the power grid including numerous microgrids (MGs) with complex and detailed model (DM) is very time-consuming. Nevertheless, these kinds of simulations are vital for power engineers and utilities to analyze the impact of dynamic interconnections among MGs and the power grid. In this paper, an electrical equivalent model (EM) including electrical components, such as an equivalent solid oxide fuel cell (SOFC) model, voltage source converter (VSC), and static load, is proposed for a fuel cell-based MG. The parameters of the EM are estimated to behave similar to the DM of the MG in different scenarios and operating points. The parameter estimation procedure is conducted using genetic algorithm. The IEEE 9-Bus transmission system is considered as the main grid, while the IEEE 33-Bus distribution system is considered as the grid-connected MG. Three SOFCs of different size and dynamic parameters are connected through VSCs to the MG. Different scenarios of active and reactive power changes are simulated, and results of the EM and DM are compared, to demonstrate the accuracy of the determined EM.KEYWORDS equivalent model, microgrid, parameter estimation, SOFC
| INTRODUCTIONRecently, the need for high quality and reliable power along with emission concerns has drawn the attentions to the renewable distributed generations (DGs). 1 At first, the conventional passive distribution systems were transformed to active ones with integration of different types of DGs. In the next step, the concept of the microgrid (MG) was formed and defined as a low voltage distribution system containing DGs, electrical and thermal loads, which all operate together under a common control system. This control system provides the ability of operating in grid-connected and islanded modes compared to active distribution systems (ADSs). 2 Fuel cells (FCs) have always been a promising DC source for MGs in literature. Many researches have been conducted on MGs considering different types of FCs as the source of DC side. For instance, for stability assessment and real-time applications, a simplified dynamic model for a gridconnected FC power plant has been presented in Hatziadoniu et al 3 and Resrepo et al. 4 Authors have presented the control and modeling of a proton exchange membrane FC as a DG in Wang et al 5 and Karami et al. 6 Fuel cell-based DGs have been considered as DGs in islanded MGs for frequency regulation in previous studies. 7-9 Among different types of FCs, solid oxide fuel cell (SOFC) is one of the most attractive ones in MGs due to its low emissions and high energy efficiency. 10 In Sedighisigarchi and Feliachi, 11,12 a comprehensive nonlinear dynamic model of SOFC has been developed for transient stability analysis and enhancement. Mathematical modeling of a grid-connected SOFC power plant for small-signal stability studies has been presented in Wenjuan et al. 13 The mathematical modeling of SOFC will be briefly explained in Section 2.Besides the well-known advantages of MGs, there are some concerns that should be analy...