A Unidirectional Hierarchical Control Structure with Zero Power Sharing Error for Hybrid AC/DC Microgrid

The desire for decreasing the stress on the individual AC and DC sources motivates accurate load sharing in Hybrid AC/DC microgrids (HMGs). The conventional hierarchical control scheme suffers from error in active power sharing among the DC sources and inaccurate reactive power sharing in the AC microgrid, which result from the local property of voltage. To circumvent this issue, a unidirectional hierarchical control scheme, which employs a combination of central and local secondary controllers is proposed in this paper. For each of the DC and AC microgrids, the central secondary controller eliminates the voltage/frequency deviations through a common control signal, which is broadcasted to the sources and interlink converter (IC). In addition, the DC and AC PCC voltages are broadcasted to the sources and IC. The local secondary controller (power sharing correction unit) of each source alters the central secondary control signal based on the PCC voltage. By incorporation of the PCC voltage in the droop characteristics of the sources and the control loop of IC, the error in active/reactive power sharing is eliminated. The stability of the proposed scheme is analyzed through small signal analysis. Simulation and experimental results are presented to validate the proposed control method.