Unified Distributed Control for DC Microgrid Operating Modes

This paper proposes a unified distributed control strategy for DC microgrid operating modes, without bus voltage signaling or mode detection mechanisms that are normally required for decentralized control strategies. The proposed control strategy is based on the novel integration of distributed controllers for energy balancing between DC microgrid energy storage systems with distributed controllers used to regulate the average DC microgrid bus voltage, and a new method for controlling the grid connected rectifier that maintains the distributed control structure. Under the proposed control strategy, seamless mode transitions are achieved between qualitatively different operating modes, namely, 1) grid connected operation with the rectifier providing load balancing, 2) grid connected operation with the rectifier charging the energy storage systems, and 3) islanded operation. In all operating modes, the average DC microgrid bus voltage is regulated to the microgrid voltage reference, and the energy storage systems are controlled independently of the operating mode to achieve and maintain a balanced energy level. Simulations are presented demonstrating the performance of the proposed control strategy for a 380 VDC datacenter with intermittent photovoltaic generation and communication delays expected from a WiFi control network implementation.