DC Voltage Variation Based Autonomous Control of DC Microgrids

System control for dc microgrids with variable generations and energy storage is proposed in this paper. An autonomous three-level control strategy is proposed for dc microgrids with selective slack terminal(s) assigned to each operation level. The system operational status is acknowledged via the common dc voltage and the transitions between different operational levels are triggered by its variation. A four-terminal sample dc microgrid system with a grid-connected voltage-source converter, a wind turbine, an energy storage system, and dc loads are established and a specific control scheme is outlined to demonstrate the proposed strategy during various operating conditions, such as load step, generation fluctuation, islanding, grid reconnection, load shedding, and generation curtailment. The control strategy and the specific scheme are validated by experimental results conducted on a prototype dc microgrid system.