Communication-Free Grid-Supportive Control of Converter-Based ZIP Loads in DC Microgrids

In recent years, DC microgrids have garnered significant attention due to their superior capability in integrating renewable energy sources. However, the predominance of renewables in these systems introduces increased uncertainty in power generation, thereby elevating the risk of load loss. While the integration of energy storage systems is widely regarded as the primary solution to mitigate this issue, load-side grid support has also been proposed as a viable alternative strategy. This paper proposes a communication-free grid-supportive load (GSL) controller for converter-based constant-impedance/current/power (ZIP) loads, enabling local voltage support using only bus-voltage measurements. First, a unified control strategy is introduced that dynamically adjusts the load-side voltage reference via a saturation-plus-hysteresis mechanism, ensuring device safety while enabling grid support. Second, an energy-based restoration scheme is proposed that tracks cumulative power deviations and smoothly returns the load to nominal operation, avoiding rebound transients. Finally, the concept is experimentally validated on a 700V, 14kW DC microgrid. Under a 4 kW load step, the proposed scheme reduces the voltage dip by 12.9% and prevents converter shutdown when the battery reaches its power limit, outperforming a conventional PI-controlled system. The results demonstrate that local, device-embedded control of ZIP loads can deliver effective grid support without requiring communication or additional energy storage.