This paper analyzes the transient voltage stability of the dual-source DC power system. The system’s equivalent model is first established. Subsequently, the effect mechanisms of line parameters and voltage-source rectifiers’ current control inner loops on the system’s transient voltage instability are investigated. It indicates that these factors reduce the power supply capacity of the source, increasing the risk of transient instability in the system. Then, considering the influence of fault depths, the influence of different large disturbances on the transient voltage stability is investigated. Furthermore, the critical cutting voltage and critical cutting time for DC power systems are determined and then validated on the MATLAB R2023b/Simulink platform. Finally, based on the mixed potential function theory, the impact of system parameter variations on stability boundaries is analyzed quantitatively. Simulation verification is conducted on the MATLAB R2023b/Simulink platform, and experimental verification is conducted on the RT-LAB Hardware-in-the-Loop platform. The results of the quantitative analysis and experiments corroborate the conclusions drawn from the mechanistic analysis, underscoring the critical role of line parameters and converter control parameters in the system’s transient voltage stability.

With the growing integration of renewable energy sources into power grids, the risks of oscillation caused by interactions between grid-tied inverters and the grids are becoming increasingly prominent. Although existing studies have made significant progress in inverter modeling and oscillatory stability analysis, most of them do not sufficiently consider complex mirror frequency coupling effects (MFCE) under unbalanced operating conditions, leading to unreliable models and erroneous stability analysis results. To address this inadequacy, this work develops a novel sequence impedance modeling scheme that can be widely applied to unbalanced operating conditions. In particular, taking a representative type of grid-forming inverter for instance, i.e., droop-controlled inverter (DCI), a single-input single-output sequence impedance modeling method based on harmonic linearization (HL) is proposed to comprehensively model both a given DCI and the connected grid. By accounting for multifrequency interactions within the DCI, this method captures MFCE and unbalanced factors, leading to a more accurate impedance model. Further, the dominant factors influencing system stability are identified with a combination of normalized sensitivity analysis and proportional weighting. Finally, the detailed impacts of these dominant factors on system stability margin under three typical unbalanced operating conditions are analyzed through the Bode criterion. The effectiveness and reliability of the whole scheme proposed in this work are validated on the constructed grid-connected droop-controlled experimental platform.

The submarine DC power system is prone to largesignal instability due to extreme operation conditions, potentially causing failures in submarine observation networks. Consequently, it's essential to investigate the system's physical mechanism behind large-signal instability and develop effective stability enhancement strategies. Firstly, a large-signal model of the submarine DC power system is established in this paper. Then, the intrinsic instability mechanisms are revealed by analyzing the nonlinear behavior of the source and load in the system. Subsequently, based on mixed potential function theory, the large-signal stability criterion of the system is defined by incorporating both physical characteristics and control dynamics, and factors that influence the large-signal stability boundary of the system are analyzed. It reveals that maintaining the voltage transfer ratio of the submarine converter at 1 is crucial for stability, based on which, a frequency compensation-based stability enhancement method is proposed. This method optimizes the control loop structure of the submarine converter, significantly improving the system's robustness against large disturbances. Finally, Simulink simulations are carried out to validate the stability analysis results and the stability enhancement strategy under large disturbances.

Due to extreme operational conditions, submarine DC power systems are prone to large-signal instability. Therefore, it’s essential to investigate the underlying physical mechanisms and develop effective stabilization strategies. This paper first establishes a large-signal model of the submarine DC power system. Incorporating the physical characteristics and control dynamics in the system, the large-signal stability boundary is defined by using the mixed potential function method, and key factors influencing the stability boundary are identified. Subsequently, the instability mechanisms, along with the effect mechanisms of these key factors’ variations on large-signal stability, are further analyzed based on the model of source-side and load-side power interactions. The analysis indicates that suppressing the transient reduction in the voltage conversion ratio of the submarine converter is critical to maintaining stability. Motivated by this insight, a switching frequency compensation strategy is proposed, and it demonstrates improved disturbance-rejection performance compared with conventional approaches. Finally, simulations and hardware-in-the-loop experiments are conducted to validate the stability analysis results and the effectiveness of the stability enhancement strategy under large disturbances.