A Power Flow Control Strategy for Hybrid Control Architecture of DC Microgrid under Unreliable Grid Connection Considering Electricity Price Constraint

This paper presents a power flow control strategy for a hybrid control architecture of the DC microgrid (DCMG) system under an unreliable grid connection considering the constraint of electricity price. To overcome the limitation of the existing schemes, a hybrid control architecture which combines the centralized control and distributed control is applied to control DCMG. By using the hybrid control approach, a more optimal and reliable DCMG system can be constructed even though a fault occurs in the grid or a central controller (CC). The power flow control strategy for the hybrid DCMG control architecture also takes the constraint of electricity price into account for the purpose of minimizing the electricity cost. In the proposed hybrid control, the high bandwidth communication (HBC) link is used in the centralized control to connect the CC with DCMG power agents. On the other hand, the low bandwidth communication (LBC) link is employed to constitute the distributed control. A small size of data is used to exchange the information fast between the agents and CC, or between each agent and its neighbors, which increases the reliability and robustness of the DCMG system in case of a fault in the communication link of the centralized control. A DCMG system with 400-V rated DC-link voltage which consists of a wind power agent, a battery agent, a grid agent, a load agent, and a CC is constructed in this study by using three power converters based on 32-bit floating point digital signal processor (DSP) TMS320F28335 controller. Various simulation and experimental results prove that the proposed scheme improves the system stability and robustness even in the presence of a fault in the communication link of the centralized control. In addition, the proposed scheme is capable of maintaining the DC-link voltage stably at the nominal value without severe transients both in the centralized control and distributed control, as well as both in the grid-connected case and islanded case. Finally, the scalability of the DCMG system is tested by adding and removing additional wind power agent and battery agent during a certain period.