Distributed Predefined-Time Droop-Free Unified Control Scheme for Parallel Energy Storage Units in All-Electric Aircraft Onboard DC Microgrid

In all-electric aircraft (AEA), onboard DC microgrids with parallel energy storage units (ESUs) often suffer from state-of-charge (SoC) imbalance, inaccurate current distribution, and DC bus voltage instability—threatening system safety and performance. This paper proposes a distributed droop-free unified control scheme based on predefined-time (PdT) control theory, addressing these challenges through two main components. First, a distributed PdT consensus observer allows each ESU to locally estimate global average values within user-defined timeframe by exchanging information only with neighboring units. Second, a PdT droop-free unified controller simultaneously achieves precise SoC-based current allocation and stable bus voltage regulation—without relying on droop coefficients or multiple secondary loops. Simulation results under communication delays, controller input noise, and network scalability conditions demonstrate that the proposed method restores bus voltage and synchronizes control variables within a predefined time. Compared to enhanced droop-based strategies, it reduces bus voltage fluctuation by up to 80.8%, and significantly improves SoC balancing speed and current distribution accuracy. Hardware-in-the-loop experiments on the Starsim platform validate the method's real-time performance and robustness under load transients and fault conditions. Overall, the proposed scheme offers a scalable, low-complexity solution for reliable coordination control in AEA microgrids with multiple ESUs.