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The outbreak of multiple disaster sites during the coronavirus disease 2019 (COVID-19) pandemic has presented challenges due to varying access time intensity, population density, and medical resources at each site. To address these issues, this study focuses on 13 districts and counties in Wuhan, China. The importance of each research area is analyzed using the improved PageRank and TOPSIS algorithms to determine the optimal site selection plan. Additionally, a particle swarm algorithm is used to construct an emergency material dispatching model that targets both distribution and site selection costs to solve the multi-distribution center dispatching problem. The results suggest that constructing 10 distribution centers can satisfy the demand for epidemic prevention and control in Wuhan city while saving costs associated with site selection and material distribution. Compared to the previous optimal solution, the distribution and site selection costs under the optimal solution decreased by 27.9% and 17.82%, respectively. This approach can serve as a basis for dispatching emergency materials during public health emergencies.

The More Electric Aircraft (MEA) stands for the direction of aviation development in the new era, and the reliability of power systems on the MEA has attracted widespread attention. Based on the characteristics of MEA power systems, an equivalent method of electrical topology structure is presented in this article, and evaluation method is proposed which shows the reliability of the overall system with the reliability of specific nodes. Firstly, electrical topology structure of a MEA power system is converted into a network node diagram according to the proposed equivalent method. Then, the minimal path sets of specific nodes are obtained by the adjacent matrix algorithm, and the low-order minimal cut sets of disjointed are obtained. After that, the actual failure rate of components is converted to node failure rate, and the reliability of the overall system is evaluated by operational reliability indexes of specific nodes. Finally, taking the MEA A380 as an example, this paper compares and analyzes the reliability of AC loads, DC loads, and key loads to verify the validity and feasibility of the proposed evaluation method. This evaluation system can predict the weak points existing in the MEA power system, as well as providing theoretical support for maintenance schedule.

Large signal stability means that a system can be a transition to a new stable state without losing synchronism after a large disturbance. The large signal stability problem brought by large capacity electrical loads in ac/dc independent power system is prominent, which seriously affects the dynamic security of the system. In view of modeling characteristics of ac/dc system, a generalized state space average large signal modeling method for the ac/dc independent power system in dq-coordinates is proposed. A large signal model of the ac/dc independent power system is constructed, which includes generators, inverter units, rectifying units, and dc/dc converters. The simulation results indicate that the large signal model constructed in this paper can accurately reflect the dynamic characteristics of the system under large disturbances, such as startup and sudden change in load, which is helpful to understand and improve the dynamic performance of the system under large disturbance. Furthermore, with feasibility and effectiveness, the large signal model provides convenience and possibility for the theoretical analysis of large signal stability of ac/dc independent power systems in the future.

Minimal cut sets are the basis of reliability analysis using analytical techniques. At the present stage, minimal cut sets are mainly obtained by dealing with minimal path sets, which involves cumbersome steps and slower operational speed. The speed of reliability analysis is limited by that of calculating minimal cut sets. In consideration of the characteristics of microgrid, a hierarchical approach for fast calculating minimal cut sets is proposed in this paper. Firstly, an equivalent principle is proposed to convert topology structure into network node diagram; then grades of nodes are designated based on their original connection and the breadth-first search approach; afterwards, root-leaf matrices and selected matrix are created to specify the direction and order of the search. Next, all possible combinations of minimal cut sets are vertically traversed out by replacing root nodes with leaf nodes to achieve a more rapid access to minimal cut sets. Finally, taking the electrical structure of type A380 more electric aircraft as an example, mainstream methods are compared to show the correctness and advantage of our proposed method.

PV system integration with VSC-HVDC technology has been significantly developed in the past decades. The photovoltaic DC boost integration and grid-connected system (PV-HVDC) is composed of DC boost converter and modular multi-level converter(MMC). Input-parallel and output-series(IPOS) connected DC/DC converter is adapted to increase the output voltage of PV plants. As there are multiple operation modes of the system, the DC/DC converter should be controlled coordinately to assure stable operation of system. A communication-less coordinated control strategy that the DC boost converter can switches the control mode according to the variation of DC bus voltage is proposed in this paper. When the error between the DC bus voltage and the rated value exceeds the dead zone, DC boost switches to constant output voltage mode, and the stability of DC bus voltage can be maintained. In addition, an output voltage sharing control strategy is designed for the IPOS connected converter to achieve coordinated and stable operation between sub modules. The proposed control strategy is evaluated based on time-domain simulation studies in PSCAD using a 1MW PV-HVDC system. The results show that the proposed strategy enables the stable operation of the system in various conditions.

Under grid contingencies, voltage source converters (VSC) under traditional control scheme can experience significant instabilities for power control as well as DC voltage regulations, especially under unbalanced grid voltage with the presence of double line-frequency disturbances. This paper proposes an Automatic-coordinated Transitioning Control (ATC) Scheme to enable control mode transitioning for Modular Multilevel Converter (MMC) based photovoltaic (PV) Medium-Voltage DC (PV-MVDC) system. The proposed ATC has two control objectives under grid unbalance: 1. to fully regulate MVDC bus voltage without significant ripples; 2. to provide flexible & stable power control for the grid-side MMC. To achieve so, on the detection of grid unbalance the ATC scheme transits the DC voltage regulation mode of grid-side MMC to the power control mode with negative sequence loops for grid power support provision; on the detection of MVDC bus voltage variation, the ATC transit the maximum power point tracking mode of the DC/DC boost converter to the DC bus voltage regulation mode for maintaining the power balance in the MVDC network. The proposed ATC scheme is validated by a detailed PV-MVDC model simulated by PSCAD/EMTDC, and its effectiveness in achieving DC voltage stability and AC power control flexibility under grid unbalance is verified.

In Constant speed constant frequency (CSCF) AC power supply system, generator output constant frequency and constant voltage AC power by connecting engine with constant speed transmission device (CSD). However, CSCF has many disadvantages, such as complex structure, heavy weight, high cost and low energy conversion efficiency. By eliminating CSD in CSCF and taking output voltage and output frequency as feedback quantities, this paper proposes a dual excitation control method to achieve the same effect as CSCF power source. From the perspective of engineering applications, this improved method can greatly reduce the weight of aviation power generation system. It has a simple structure and can cut down the cost of power system operation and maintenance. Simulation results show that the method of dual excitation control presented in this paper is effective, and it also provides a new idea for the improvement in aviation power generation system.