Amr Abdelnaeem Ismail Said
A Sequential Power Flow Algorithm for Islanded Hybrid AC/DC Microgrids
The advent of electronically based distributed generation (DG) and the radical changes in the nature of loading have promoted power distribution in a dc paradigm. On one hand, greater economies could be achieved if renewable energy resources such as wind and photovoltaic (PV) were integrated into dc rather than ac systems. On the other hand, major loads such as Plug-in electric vehicles (PEVs) represent crucial factors in future electric distribution systems. The evolving dc network will be integrable with the traditional ac network through interlinking converters, accordingly forming a new hybrid distribution paradigm. For higher system security, such hybrid networks are characterized by droop control schemes that enable overall load sharing among the installed DGs in the islanded mode.
In This seminar, a sequential power flow algorithm is proposed for hybrid ac/dc microgrids operating in the islanded mode. Unlike in grid-connected systems, variable, rather than fixed, frequency and voltage are utilized for power coordination between the ac and dc microgrids, respectively. The main challenge is to solve the power flow problem in hybrid microgrids while considering the absence of a slack bus and the coupling between the frequency and dc voltage. In the proposed algorithm, the ac power flow is solved using the Newton-Raphson (NR) method, thereby updating the ac variables and accordingly utilizing these variables in a proposed interlinking converter model for the dc problem. This sequential algorithm is iterated until convergence. Detailed time-domain simulations using PSCAD/EMTDC have validated the algorithm’s accuracy. Its robustness and computational cost are contrasted to those of conventional algorithms.