Primary Control Operation Modes in Islanded Hybrid ac/dc Microgrids

Hybrid ac/dc microgrids are an interesting solution in order to improve the quality of the energy delivered by the electric grid. Typically a hierarchically configured control strategy is adopted, where primary level strategies perform the power control of devices connected to the microgrid. This paper analyzes and compares in simulation five operation modes of primary control strategies in islanded hybrid ac/dc microgrids. The results show that the use of multiple grid-forming units in the ac and dc network of the microgrid requires lower-size energy storage devices and the reliability of the microgrid is improved. The power management of the interface converter between networks is highlighted for improving the performance of the microgrid when different variations of frequency and voltage take place. It is shown that by applying a slightly higher control level strategy to this converter, power variations are shared among all the grid-forming devices and therefore voltage and frequency deviations are balanced.