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Over the past few decades, global electricity production increased steadily and has reached 25,592 TWh by the end of 2017. With rapid development of hydro power, solar power, and wind power, the proportion of renewable energy in all energy sources rises remarkable, achieving 24.8% in 2017. However, renewable energy cannot replace all traditional fossil fuels due to the intrinsic intermittence and fluctuation.

The AC and DC system of flexible substation have been applied in the project, and it is imperative to study the protection scheme. Based on the basic structure of the AC and DC system of flexible substation, the partitioned and layered protection scheme are proposed. Both the component-level and the station-level protection configuration schemes are proposed. Based on two flexible substations connected to the grid, the fault recovery strategy is proposed, and the fault recovery processes of 10kV AC line fault and ± 10kV DC line fault of two flexible substations are simulated and analyzed. The simulation results are consistent with the proposed strategy. The proposed fault recovery strategy has reference significance for the device or system composed of converter interconnections in multiple operating states.

The equipment composition, networking form and functional characteristics of the flexible substation are different from the conventional substation and intelligent substation, and its protection has special characteristics. Based on the project of flexible substation, this paper proposes a three-layer protection system framework of in-situ protection, substation-area protection and wide-area protection for flexible substation, and analyzes the basic performance of protection reliability, selectivity and speed. The research results show that the proposed flexible substation protection system framework is reasonable and feasible, and it can be used as reference for the future design of the protection system structure in the smart grid and global energy Internet construction.

In this paper, Na2CO3-K2CO3 / MgO phase change composite was coated on the surface of glass by spray plating, which solved the problem of absorbing moisture and pulverizing of molten salt / MgO phase change thermal storage material in high humidity environment, and reduced the absorbing moisture and pulverizing rate from 31% to 19% without affecting the latent heat of phase change thermal storage material.

Molten salt is a type of material for high temperature thermal energy storage. The thermophysical property, thermostability, and corrosion performance of molten salt are the main points of interest in thermal energy storage field. How to further broaden the usage temperature range of molten salt, develop more molten salts with low melting points, and optimize the thermal conductivity and viscosity of materials has been widely concerned by researchers. Recently, thermal storage technology of molten salt has been applied to the field of concentrating solar power. The thermophysical property, and corrosive performance of molten salt are very important for the large-scale preparation and application of molten salt materials. Based on the classification of molten salt materials, this paper reviews the thermophysical properties of some common molten salts (carbonate, chloride, nitrate, polybasic salt, etc.), and summarizes the current research progress of improving its thermophysical properties. Moreover, the corrosive performance of several types of commonly used molten salts in thermal energy storage applications is analyzed. Besides, some corrosion protection technologies are proposed according to the current application of molten salt and the corrosion mechanism. Finally, the development trend of the application of molten salt in the field of heat storage is prospected.

In this work, Na2CO3-K2CO3/MgO composites with MgO serving as supporting material and Na2CO3-K2CO3 eutectic salt acting as thermal absorbing materials were prepared by the form-stable technique. Besides, the possible effects of Cu, Fe and Al on the thermal properties of the composite were investigated. The thermal properties including phase composition, latent heat and thermal conductivity, etc. were measured using X-ray diffraction, differential scanning calorimetry, thermal constant analyzer and thermogravimetric analysis, etc. The X-ray diffraction results show that Na2CO3-K2CO3 and MgO have good chemical compatibility. The differential scanning calorimetry results show that the melting point of the Na2CO3-K2CO3/MgO composites is 707.5°C and its enthalpy of fusion is 67.98J/g. The thermal constants analyzer results indicate that the addition of metal powder can improve the thermal conductivity of the sample, but the increase rate is not obvious because of its oxidation in the air, some even reduce the thermal conductivity.

The development and application status of the key performance testing technology of heat storage materials in the application process are reviewed. According to the practical application requirements in terms of heat storage capacity, heat exchange capacity, material strength, service life, etc., the key performances of thermal storage materials that need to be focused on are sorted out, and the relevant testing techniques for each performance are sorted out and summarized. The specific test methods applicable to high-temperature heat storage materials are analyzed, and the related test technologies and evaluation methods for future heat storage materials are prospected.

Based on the temperature change and thermal storage processes of PCM phase change energy storage unit, the PCM channel number of which is 39, the plate spacing is 0.01 m, the air channel is 40 with its plate spacing of 0.003 m, and the unit length is total of 1.62 m. MATLAB solution about the above PCM energy storage unit was performed according to the model and physical property data, and the numerical simulation was carried out by using Fluent software. The theoretical calculation and numerical simulation were compared and analyzed. It is found that only in the case of smaller or larger flow rate working conditions, the solution results of MATLAB for the increase rate of the average temperature of the phase change material inside the system is quite different from the FLUENT simulation result; the comparison of the phase change process degree of advancement is found that at a higher flow rate, the difference between the two results is small, but the difference is larger when the flow rate is smaller; the comparison result of the PCM liquid rate is different under the small flow rate condition. However, the comparative analysis of heat storage shows that the maximum error does not exceed 10%. It can be seen that the flow rate conditions in the model and working conditions are the obvious factors affecting the two results, but the calculation and simulation results can more accurately describe the heat storage characteristics of the PCM phase change energy storage unit, which was calculated in nearly 90% ranges of working conditions, which can prove that the results of MATLAB and FLUENT are consistent.