Abstract
Interest in DC microgrids is rapidly increasing along with the improvement of DC power technology because of its advantages. To support the integration process of DC microgrids with the existing AC utility grids, the form of hybrid AC/DC microgrids is considered for higher power conversion efficiency, lower component cost and better power quality. In the system, AC and DC portions are connected through interlink bidirectional AC/DC converters (IC) with a proper control system and power management. In the stand-alone operation mode of AC/DC hybrid microgrids, the control of power injection through the IC is crucial in order to maintain the system security. This paper mainly deals with a coordination control strategy of IC and a battery energy storage system (BESS) converter under stand-alone operation. A coordinated control strategy for the IC, which considers the state of charge (SOC) level of BESS and the load shedding scheme as the last resort, is proposed to obtain better power sharing between AC and DC subgrids. The scheme will be tested with a hybrid AC/DC microgrid, using the tool of the PSCAD/EMTDC software.
Highlights
The increasing penetration of dispersed energy resources (DERs) in distribution systems has improved microgrids’ implementation
The proposed coordination control strategy between the interlink bidirectional AC/DC converters (IC) and battery energy storage system (BESS) converters can facilitate a smooth transition of the power transfer between AC and DC subgrids in stand-alone mode for secure operation, using the available resources and the last resort action of load shedding within the feasible operational region of BESS
The objective of the IC controller is to regulate the frequency of the AC subgrid and the bus voltage of the DC subgrid by the control of the active power injection via the IC
Summary
The increasing penetration of dispersed energy resources (DERs) in distribution systems has improved microgrids’ implementation. Power generations from various DERs, such as photovoltaic systems, are DC power, so are modern electrical loads and energy storage systems Those DC technologies are integrated with the existing AC systems through converters, which would expend more component costs and increase power losses. Operating the microgrid in stand-alone mode would lead to more challenges, when the imbalance of generation and consumption happen because of flexible load and DERs. Various droop control methods have been proposed to maintain the system stability by sharing power between AC and DC subgrids, as in [11]. In this circumstance, the weak portion of the microgrid might experience the severe degradation of system security. The proposed coordination control strategy between the IC and BESS converters can facilitate a smooth transition of the power transfer between AC and DC subgrids in stand-alone mode for secure operation, using the available resources and the last resort action of load shedding within the feasible operational region of BESS
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