It is very important to accurately identify the critical nodes of the power grid for its safe and stable operation. In this paper, a method for identifying the critical nodes of the power grid based on the improved entropy weight method (IEWM) is proposed, and the IEWM corrects issues with the information overlap between evaluation indices and inconsistency between the entropy weight (EW) and entropy value (EV). First, considering the power grid topology and operating conditions, structural factor evaluation indices and state factor evaluation indices are established. On this basis, the IEWM is used to assign weights to nodes with different voltage levels, which strengthens the consideration of node voltage levels in the identification method of critical nodes and makes the results more accurate and effective. Simulation experiments of IEEE 30-bus and IEEE 118-bus systems verify the accuracy of the critical node identification method proposed in this paper.

This study proposes a multitype electrolytic collaborative hydrogen production model for optimizing the capacity configuration of renewable energy off grid hydrogen production systems. The electrolytic hydrogen production process utilizes the synergistic electrolysis of an alkaline electrolyzer (AEL) and proton exchange membrane electrolyzer (PEMEL), fully leveraging the advantages of the low cost of the AEL and strong regulation characteristics of the PEMEL. For the convenience of the optimization solution, the article constructs a mixed linear optimization model that considers the constraints during system operation, with the objective function of minimizing total costs while meeting industrial production requirements. Gurobi is used for the optimal solution to obtain the optimal configuration of a renewable energy off grid hydrogen production system. By comparing and analyzing the optimal configuration under conventional load and high-load conditions, it is concluded that collaborative electrolysis has advantages in improving resource consumption and reducing hydrogen production costs. This is of great significance for optimizing the capacity configuration of off grid hydrogen production systems and improving the overall economic benefits of the system.

This paper proposes a generalized design method of extended state observer (ESO) based nonsingular terminal sliding mode (NTSM) control for voltage source converter (VSC) station. The non-linear loads and external disturbances and parameter perturbations of the converter station are considered as external disturbances which are bounded. The ESO is designed to reject the external disturbances which include not only the unmeasured system states but also the modeling uncertainties. At the same time, the non-singular terminal sliding mode control method based on ESO is proposed to solve the problems of slow dynamic response of output voltage and high waveform distortion rate in converter station. The proposed control method is validated through numerical simulation shows a closed-loop dynamics and better transient performance, and the controller can effectively suppress the differential peak values of active power, reactive power and DC voltage in the initial stage of system start-up. Under conditions of non-singularity of the controller, the influence of system disturbances in the chattering of the controller is effectively eliminated and the robust performance of the system is enhanced.