As the construction of new power systems, DC microgrids will become an important part of the distribution network. As AC load connecting to DC microgrids, the oscillating power will enter the DC system, which affects the power distribution of energy storage system. To solve this issue, the comprehensive principle of power distribution of distributed energy storage system was given, and a wireless power sharing method was proposed. This method takes the charge state as the “information carrier”, each energy storage unit can realize state of charge (SOC) balancing and oscillating power sharing at same time. In addition, from the perspective of equivalent output impedance, this paper gived a detailed analysis and discussion on the distribution effect of different control algorithms, which showed the proposed control algorithm could meet the requirements of the comprehensive principle. Finally, the effectiveness of the proposed distributed energy storage control strategy was validated by experiments.

Modular multilevel direct current transformer (MMDCT) provides a feasible solution to realize the efficient and stable integration of electric vehicle charging and discharging cluster into urban DC distribution network. However, there are impulse currents caused by capacitor charging and transformer inrush current in its starting process. Therefore, a fast pre-charging strategy based on compound frequency control was proposed. The independent control of direct current component and intermediate frequency component was used to realize simultaneous charging of the primary and secondary sides. The double closed-loop control was adopted in the primary side, while the variable-step phase shift peak current control was adopted in the secondary side, which solved the contradiction between charging speed and inrush current. Furthermore, a quantitative comparative analysis of various pre-charging strategies was carried out. The effectiveness and feasibility of the proposed pre-charging strategy were verified through simulation. The results show that the magnitude of the inrush current and the charging time are effectively controlled by the proposed method.

With the rapid development of renewable energy sources, virtual synchronous generators (VSG) have garnered significant attention as a key technology for enhancing the stability of power systems. However, severe power-oscillation issues are inherent to multi-VSG systems. In this study, a control strategy was investigated for a multi-VSG parallel operation. A distributed adaptive parameter method is proposed to suppress power oscillations. First, by integrating the virtual impedance, frequency rate of change, and adaptive inertia, this method effectively reduces the initial power overshoot and improves the stability and robustness of the system. Second, in the case of non-uniform communication delays in transmission line communication, an operation strategy is introduced, wherein centralized and distributed controls serve as mutual backup protection, further enhancing system reliability. Finally, the simulation results demonstrate the robustness and high delay tolerance of the method considering non-uniform communication delays, promoting the practical application of multi-VSG systems and enhancing the frequency response performance of generator clusters.

Objectives In response to the impact of the bandwidth of the current inner loop PI controller on the stability of the grid connected system of direct drive wind turbines under the background of weak electricity network, which leads to the induction of sub synchronous oscillation (SSO) phenomenon, a linear active disturbance rejection control (LADRC) was proposed to replace the current inner loop PI controller with an improved linear state error feedback control law (LSEF) to suppress SSO. Methods Firstly, the LSEF of the LADRC controller was improved, and the tracking errors and anti-interference capabilities were studied. Moreover, an impedance model for the system considering frequency coupling effects was developed, and the Nyquist criterion was employed to assess the impact of line impedance values on the stability of the grid-connected converter system. Finally, the analysis and validation were performed using PSCAD/EMTDC simulation software. Results Compared with traditional LADRC, the improved LADRC can reduce the DC side voltage fluctuation range by 85% and the active power fluctuation range by 89%. Conclusions Compared with traditional LADRC controllers, improved LADRC controllers can better reduce the range of power fluctuations, DC side voltage fluctuations, and tracking errors.