Flexible Control Structure for Enhancement of Scalability in DC Microgrids

In this article, a new control structure is proposed to improve the scalability of dc microgrids. Because conventional control structures require implementation of higher control level, subsystems that do not include them cannot be added in a microgrid. However, there are many subsystems in the field that do not support higher control level, which hinders microgrid scalability. For such subsystems to perform these functions, their local controller should be modified, which requires a lot of time and economic effort. In this article, by adding a new controller that performs higher control level without changing the local controller of subsystems, a structure to expand the scalability of a dc microgrid is proposed. The proposed flexible control structure consists of a local controller of subsystems, a flexible controller that performs higher control level, and microgrid central controller. A new communication network is required between local controller and flexible controller. However, due to a communication delay, the overall system stability is reduced. Therefore, problems related to the additional communication network were analyzed and a compensator was designed to overcome these issues. Through the flexible control structure, a subsystem that does not support higher control level can be added to dc microgrid.