Theoretical Study on Large-scale Microgrids and their Equivalent Modelling

Load flow analysis can produce accurate voltage profile and power generation from each distributed generator in large-scale microgrids. Nevertheless, its application is limited to balanced or nearly balanced condition. For unbalanced operation, it is still indispensable to use modelling approach to examine their steady-state response, transient response, and stability under both balanced and unbalanced conditions. In this paper, the equivalent model of the PV panel-based generation is introduced to replace the detailed circuits for studying more complex microgrids in the modelling. To duplicate the functions of using multiple Texas Instrument 28377s or 28379x for controlling each inverter, multi-rate modelling in Simulink has been conducted. Moreover, a new formulation for the load flow analysis and voltage profile calculation is given, based on which the analytical solutions have been reached. It is found that the results from the analytical approach are very close to those from the multi-rate modelling. This validates the effectiveness of two different approaches. Furthermore, the influence of shunt capacitor in the LCL filter and software filters has been investigated.