Modeling and stability analysis of AC and DC microgrids

There has been a significant improvement in Micro grid Technology to utilize the local distributed sources and also to minimize the transmission losses. In certain cases of power blackouts they serve as main sources of power for some emergency loads. Traditionally A.C grids are preferred over DC grids to transmit power over long distances even though there are many problems associated with A.C grids such as frequency dip, voltage drop due to reactance, charging currents, leakage currents, low power factor problems, skin effect, Ferranti effect etc. because the voltages can be easily stepped up or stepped down using transformers. Whereas in D.C grid systems voltage conversion accounts for switching losses and equipment costs But at the micro grid level the supply voltages are low, and most of the sources are DC. The Rapid development in power semiconductor technology makes it possible to convert voltages in DC with low cost and reduced power losses. Most of the problems associated with A.C grid can also be overcome by moving to D.C grid.AC and DC microgrid models were developed in MATLAB/SIMULINK environment and the stability and transient analysis is performed during faults and sudden load variations on both microgrids in real time using OPAL-RT real time digital simulator. Effects of weak main grid on stability of both microgrids have been analyzed.