Droop-based Control Strategy to operate a DC Nanogrid under the Net Zero Energy Concept

This work presents a droop-based control strategy for a dc nanogrid designed to operate under the Net Zero Energy (NZE) concept, enabling seamless transitions between grid-connected and islanded modes. The nanogrid integrates photovoltaic (PV) generation, a fast electric vehicle charging station (EVSE), and a battery energy storage system (BESS) into a $700~$V dc bus interfacing with the ac grid via a bidirectional three-phase AC-DC converter. An isolated DC-DC converter establishes a secondary $48~$V dc bus for powering dc loads. An energy management system (EMS) defines an optimal day-ahead power dispatch for the BESS to meet NZE objectives. At the primary control level, a modified power-to-voltage droop strategy ensures accurate power tracking and parallel operation with the AC-DC converter. This approach enables continuous voltage regulation of the main bus under instantaneous power imbalances caused by schedule deviations or operational mode transitions. Additionally, the proposed strategy eliminates the need for secondary control or high-bandwidth communication. The system is validated through hardware-in-the-loop (HIL) simulations using the Typhoon HIL 604 platform, with the control strategy implemented on a DSP. Real-time simulation results confirm stable performance under various operating conditions, including transitions between modes.