A novel communication-less fuzzy based control method to improve SOC balancing, current-sharing, and voltage restoration in a widespread DC microgrid

Abstract

DC Bus Voltage Restoration, proportional current-sharing and SOCs balancing are the leading vital challenges in the field of DC microgrids. It seems that, using communication links and a central controller will solve these problems. However, microgrids under such control system will encounter some drawbacks such as low modularity, flexibility, reliability, and high cost and complexity. Besides, using communication links and the central controller is not reasonable for widespread DC microgrids. In this paper, a novel communication-less control method is proposed. First, the voltage of units is controlled by the droop controller to ensure the system stability. Next, a unit which has the least distance from critical loads, is chosen as “sender unit”. The sender unit voltage is set such that the voltage deviation of the sender bus is reduced to zero. Then, this unit injects an AC signal to the DC bus. The frequency of AC signal is determined by a fuzzy controller based on the sender unit SOC and its current. Another fuzzy controller specifies the units’ current based on the frequency of AC signal and their SOC. The units’ current determination is done such that not only the SOCs are balanced, and the voltage deviation is reduced, but also the current is appropriately shared. As the proposed method does not rely on communication links, it is applicable on both the single-bus and multi-bus microgrids (compact and geographically dispersed). The stability analysis confirms that the proposed method is strongly stable. Simulation results prove that microgrids controlled by the proposed method has a desirable performance from the standpoint of current-sharing, SOCs equalizing, and DC bus voltage regulation.