Coordinated Approach of DC Bus and Battery SoC Signaling for the Automated Control of DC-DC Converters involved in PV-BES based Off-Grid DC Microgrid

Droop control is one of the most frequently used primary control methods that use only local information for managing multiple distributed energy resources (DERs), including battery energy storage (BES). Conventionally controlling BES based on droop and DC bus signaling (DBS) control may sometimes lead to its deep discharge. Thus, to overcome the issue, this paper presents an automated primary coordinated control strategy for the optimum utilization of available DERs for off-grid DC microgrid (MG) applications to supply critical and non-critical loads. The improved control strategy utilizes both DC bus signaling (DBS) and state of charge (SoC)-based droop control strategy to generate appropriate DC link voltage references that need to be controlled by a BES interface via bidirectional DC-DC converter. The generated DC link voltage reference varies between the preset upper and lower limits during the entire operating range. Further, the developed DC link voltage range is subdivided into different operational bands, namely the normal operation (NO) band, safety operation (SO) band, and critical operation (CO) band. As per the operating band of the network, an appropriate control strategy for BES via DC-DC converter is devised to prevent deep discharge. The proposed control method has been validated through MATLAB/Simulink and a real-time simulator (OPAL-RT OP4510) for DC MG networks sourced with photovoltaic (PV) and BES.