As a major carbon emitter, how to create an effective path for low-carbon actions in the ports is extremely urgent. In view of the abundant renewable energy resources and hydrogen equipment in the ports, a multi-source output hydrogen storage coordination system in the ports is built to achieve the purpose of carbon reduction. From the perspective of multi-energy and low-carbon economic operation in the ports, an optimal operation method of multi-source output in the ports based on the optimal carbon emission flow(CEF) is proposed to take into account both carbon emission and economy. Based on the calculation method of the nodal carbon intensity of the power system, the calculation model of the carbon potential of the electric energy storage device and the electric hydrogen conversion device under the new power system is defined; Then, a multi-objective function with the lowest carbon emission and the maximum system economic benefit is established considering the influence of the charging and discharging depth and the number of cycles of the energy storage device; Finally, a non-dominated sorting genetic algorithm II (NSGA-II) is used to analyze a ports scenario integrated with new energy, electric energy storage equipment, and electric hydrogen conversion equipment. The results show that the proposed optimal operation method can effectively reduce the carbon emissions of the ports and improve the economy of the power system in the ports.

The widely used flywheel energy storage (FES) system has such advantages as high power density, no environment pollution, a long service life, a wide operating temperature range, and unlimited charging–discharging times. The flywheel array energy storage system (FAESS), which includes the multiple standardized flywheel energy storage unit (FESU), is an effective solution for obtaining large capacity and high-power energy storage. In this paper, the strategy for coordinating and controlling the charging–discharging of the FAESS is studied in depth. Firstly, a deep analysis is conducted on the loss generated during the charging–discharging process of the FESU. The results indicate that the loss is related to the charging–discharging of power. To solve the problems of over-charging, over-discharging, and overcurrent caused by traditional charging–discharging control strategies, this paper proposes a charging–discharging coordination control strategy based on the equal incremental principle (EIP). This strategy aims to minimize the total loss and establish a mathematical model of optimal coordination control with the constraints of total charging–discharging power, rated power limit, over-charging, over-discharging, and overcurrent. Based on the EIP, the optimal distribution scheme of power charging–discharging is determined. Secondly, this paper gives the specific implementation scheme of the optimal coordinated control strategy. Lastly, the charging–discharging coordinated control strategy is verified by examples. The results show that the coordinated control strategy can effectively reduce the loss during the charging–discharging process and can prevent over-charging, over-discharging, and overcurrent of the system. Overall, it has a better control effect than the existing charging–discharging control strategies.

The modular multilevel converter (MMC) is now the most attractive topology for medium and high voltage power conversion applications with several advantages over the traditional voltage source converter (VSC). However, due to a large number of sub-modules (SMs) in the MMC, system reliability is a big challenge in its practical application, where each SM may be considered as a potential point of failure. In this paper, a reliability evaluation based on the Markov model is proposed for the MMC. The failure rates of the power electronic devices and SMs are firstly analyzed. Then, the Markov model and the state transition equation of the system are built in detail. A general reliability evaluation function is established, in which the mean time to failure and reliability evaluation of the MMC with redundant SMs are also discussed. Finally, a practical direct current (DC) distribution example for reliability evaluation is analyzed, and the results verify that the reliability evaluation based on the Markov model could provide a useful reference for project design.

The analysis and calculation of the short-circuit fault current in the DC grid is of great significance to the design and configuration of the converter station and DC circuit breaker parameters. The existing flexible DC system not only includes the modular multilevel converter (MMC) converter, but also needs power equipment such as the fault current limiter and DC circuit breaker. Therefore, the system modeling and short circuit calculation of the multi-terminal DC system after adding the DC circuit breaker are also of great significance for the design of DC power system parameters and the grid troubleshooting ability. In this paper, firstly, the parameters of the four-terminal DC system of the modular multilevel converter (MMC) are simplified, and the analytical solution of the short circuit fault current of the multi-terminal DC system is given. Then, the external characteristics of the cascaded hybrid DC circuit breaker are modeled. Based on the equivalent circuit of the fault current in different stages, the short circuit calculation method of four-terminal MMC system with DC circuit breaker is obtained. This method can effectively describe the overall trend of fault current and provide the basis for the configuration of DC line protection settings and DC circuit breaker related parameters.

With the increasing proportion of renewable energy integration in port areas, the trend of replacing conventional fossil energy load with electricity and hydrogen is becoming prominent, posing challenges to the safe operation of traditional port electrical systems. To address the above issues, firstly, we propose a novel architecture for a hybrid AC-DC electric-hydrogen coupling system, improving the scheduling flexibility. Then, we propose the energy management strategy considering multi-type hydrogen load dispatching based on the system, 100% local use of renewable energy is achieved. Lastly, we propose the equipment capacity configuration optimization method based on the strategy, considering various investment and operation costs of the port electric-hydrogen coupling system, which increases the annual income by 32.5% at an additional cost of only 6.3%, indicating great improvement in the economy while ensuing renewable energy consumption. The program is implemented on the MATLAB $+$ YALMIP platform, and optimization models are solved using GUROBI. The simulation results validate the economic, low-carbon emissions and technical feasibility of the proposed system with its operation strategy and capacity configuration scheme.

As a new technology, supercapacitor can attain greater energy density than those of conventional capacitors and greater power density than those of batteries. As a result, supercapacitors may become an attractive power solution for an increasing number of applications. In this paper, after a brief introduction of supercapacitor components, a supercapacitor based ride-through system for industrial drive applications is presented. The design details are discussed and experimental results are given.