Modeling and analysis on the voltage-mediated flexibility control of a low-voltage DC building energy system

The use of direct current (DC) bus voltage as a unified control signal for flexibility control has raised significant attention in low-voltage DC building energy systems, with advantages in coordinating diverse flexible resources for demand response. However, while DC bus signaling simplifies system-wide control, existing research lacks clear transient stability boundaries and dynamic interaction models under high flexible load penetration, leading to risks of voltage instability during load or source fluctuations. To bridge this gap, a simulation model of a flexible low-voltage DC (FLVDC) system is developed in MATLAB/Simulink refined to the device level, where the 750 V high-level bus voltage serves as the sole control signal to regulate device operations. The analysis framework tests stability boundaries and transient responses, including overshoot, and settling time of bus voltage and grid power dynamics under source and load steps. Validation through two real-world scenarios demonstrates that the FLVDC system achieves flexible demand response by adjusting device power consumption based on voltage-mediated control. Key findings show that the small-scale scenario features a broader stable voltage range but inferior transient performance compared to the large-scale one with more sources and loads. Droop control is shown to reduce overshoot and settling time, while rigid control provides a fixed reference value without fluctuation with grid power. Under voltage-mediated control, the FLVDC system can provide 309 W/V grid flexibility in small-scale scenario from 550 V to 1020 V and 2309 W/V in large-scale scenario from 650 V to 825 V. The simulation model can provide building operators with a feasible tool to verify system design and optimize control strategies.