Robust Current-Sensorless Discrete-Time Sliding-Mode Control for On-Board Three-Phase UPS Systems

On-board three-phase two-level uninterruptible power supply systems serve as vital energy interfaces, ensuring high-fidelity power distribution for critical payloads in heavy-duty unmanned aerial vehicles. Therefore, this paper introduces a robust current-sensorless discrete-time sliding-mode control (DSMC) strategy in the stationary αβ frame to simplify the system structure while maintaining high-quality dynamic voltage performance. A discrete-time extended-state observer (DESO) is implemented to precisely estimate the filter capacitor current, effectively addressing the voltage regulation issues stemming from load fluctuations and the absence of sensors. Furthermore, the DESO-based current estimate is incorporated as feedforward compensation into the DSMC architecture to significantly bolster the disturbance rejection and fault-tolerance capabilities of system. The simulation results verify that the proposed method outperforms typical cascaded proportional–resonant control, delivering superior voltage tracking accuracy and robust performance. Specifically, compared to the typical cascaded strategy, the proposed method reduces the steady-state RMS voltage tracking error by approximately 1.5 V across all load types, and decreases the THD by 0.08% under balanced loads and 0.15% under nonlinear loads.