With an increased permeability of distributed wind power and photovoltaic in low voltage distribution networks, a plurality of microgrid may coexist in a regional distribution network. This is attracting wide attention in microgrid technologies that contain energy mutual and coordinated control. This paper studies the multi-microgrid, including the typical features of the multi-microgrid and topology structures, multi-microgrid energy management and optimal scheduling method, multimicrogrid multi coordinated control strategy, multi-microgrid multi-confguration operation mode.

In view of the low reliability of power supply in rural distribution network and the problem of voltage overrun and power flow reversal caused by large-scale distributed photovoltaic access under the policy of photovoltaic poverty alleviation, a coordinated control method of optical storage based on Virtual Substation mode is proposed. Combining with the actual engineering case of Yinglixiang distribution network in Hebei Province, the steady-state performance of the system under different operation schemes, such as voltage level and network loss, is analyzed. The effectiveness of the proposed method to improve the reliability of rural distribution network is verifed by Monte Carlo simulation.

With the development of active distribution network, demand response, as an important adjustable resource, is introduced into the distribution network system to ensure the safe, stable and economic operation of the distribution network system under the combined action of distributed generation, energy storage and other equipment. However, the uncertainty of the external environment in the response process and the uncertainty of the price demand curve make the demand response have greater uncertainty in the current system. A scheduling optimization model of active distribution network considering demand response uncertainty is proposed in this paper, aiming to minimize the operating cost. This paper focus on the analysis of two different types of demand response:incentive-based demand response and price-sensitive demand response, whose influence of uncertainty on costs is also considered. And the model is linearized by piecewise linearization. Finally, rationality and effectiveness of the proposed model are verified with modified 33 node system.

With the deepening reform of the electricity market in the retail side, it is of great signifcance to study the direct electricity trading on the distribution side with the participation of multimicrogrids. In this paper, a Nash bargaining model based on cooperative game theory is proposed to deal with the direct electricity transaction between multi-microgrid and load aggregator, taking the optimal beneft of each participant under the traditional transaction mode as the disagreement point of bargaining, so that the participants of the game can obtain Pareto optimal beneft. The model is a non-linear and non-convex problem, which is diffcult to solve directly. Therefore, it is divided it into two sub-problems:solving payment and maximizing alliance benefts. In order to protect the privacy of each agent, the maximizing alliance benefits uses alternating direction method of multiplier to solve the distributed optimization problem. In the process of solving the model, only the expected transaction power is exchanged between the two parties. The simulation results show that the model can effectively improve the operational effciency of both sides of the transaction.

When the voltage type droop control strategy is adopted in a distributed energy storage system for a DC distribution network, the degree of coupling between all the distributed energy storage units becomes very high, which is easily affected by the impedance of the line, and hence poor effect of current sharing. This paper proposes a current type droop control strategy, analyses the calculation method of key control parameters, and the decoupling of the line impedance between all the units of the distributed energy storage system. The experimental results verify the effectiveness of the proposed control strategy.

This paper proposes a distributed optimization dispatch strategy for an isolated microgrid (MG) using a multi-a gent system (MAS). The isolated MG consists of suppliers, consumers and energy storage operators which are considered as agents. Based on the self-interest motivation market, a real-time price mechanism is proposed to optimize energy supply and demand, aiming to maximize the social welfare of each agent in the isolated MG. To achieve market equilibrium among all agents in the isolated MG, an asynchronous alternating direction method of multipliers (ADMM) algorithm is designed to provide market clearing price and solve power balance, where each agent only needs to exchange a small amount of information with its neighboring agents. Simulation results demonstrate the validity of the proposed strategy.

Large-scale distributed power supply, energy storage and electric vehicles are distributed into the distribution network, resulting in frequent bidirectional overrun of power supply voltage at the user side, power flow reversal at the station area, harmonic overrun and other issues, which have a signifcant impact on the power quality, operation economy and reliability of distribution network. A new micro-grid confguration method for low-voltage distribution transformer area is presented. The technical framework, functional framework and control objectives of the micro-grid oriented to lowvoltage distribution transformer area are systematically described. A two-stage coordinated control model based on the micro-grid is established. Through the coordinated control and optimal dispatch of the micro-grid, the optimal grid-connected and effcient generation of distributed generation are realized. The validity of the method and model is validated by the simulation calculation of typical microgrid.

According to To address the general power supply problem in the low-voltage distribution area, based on the analysis of the application mode of the energy storage system in the multi-target scenario, and considering the alternative benefts of energy storage to the grid investment, the typical capacity of the modular energy storage system suitable for the low-voltage distribution area is proposed based on the analysis of the application mode of the energy storage system in the multi-target scenario. The configuration and structure of the energy storage system is designed. By choosing In a typical low-voltage distribution area, the practical application is carried out. Testing and operating results of the energy storage system show that the proposed design for low-voltage distribution area application has strong practicality and promotion value.

This paper proposed an energy system for the integration of renewable energy with energy storage in a frigid plateau region. The system was intended for an isolated residential community with heating and power demands, which includes wind, photovoltaic, and hydroelectric power generation, trough solar collector, heat storage unit, electrical energy storage unit and an integrated control unit for achieving a high effciency in the utilization of renewable energy. An optimization method based on the genetic algorithm was established for the proposed system, aimed at fnding a confguration with optimal economics. Besides, a real-time energy management strategy, which took into account the performances of components, was proposed to ensure an effective operation of the system. A case study was then conducted to minimize the annualized cost of the system. The results showed the feasibility of the energy management strategy.

The inadequate peak shaving capacity of power grid and the serious problem of wind abandonment restrict the expansion of wind power generation scale in China. It is a trend to solve a large number of wind abandonment problems in China by allocating heat storage to participate in wind power peak shaving and changing the traditional restriction mode of "fxing electricity by heat". It is of great signifcance to study the heat transfer process in the electro thermal energy storage device for improving the effciency of the electro thermal energy storage device. For the phenomena of flow, heat transfer and stress in solid electric regenerator, a three-dimensional coupled heat transfer mathematical model of heat-fluid-solid is established. The fluid-solid coupled heat transfer model is used to transform the heat flow boundary which is diffcult to determine into the internal boundary of the system. The distribution of temperature feld and stress feld in solid electric regenerator is analyzed, and the effects of three different porosity and wire arrangement on temperature distribution uniformity and deformation of regenerator were compared The research results have certain reference value for improving the effciency of solid electric heat storage device and peak shaving of power grid.

The mathematical model for the dual-stage converter topology is established. First, the influence of neutral-point voltage fluctuation of DC capacitor on the output of the converter is analyzed based on this model. Then the influence mechanism of unbalanced output current and harmonic current on DC capacitor neutral-point voltage is studied. Furthermore, the suppression control strategy of AC output voltage unbalance and zero-sequence harmonic under unbalanced and non-linear loads is proposed. Finally, a simulation model of MATLAB and a 80 kW experimental prototype are established to validate the control strategy theoretically. The simulation and experimental results proof the effectiveness of the control strategy.

It is urgent to develop environmental friendly and sustainable large energy storage devices with superior performances. Conventional lithium-ion batteries based on transition metal oxide limited by their low theoretical specifc capacity and structure cannot meet the demand of future energy storage system. The development and application of new types of Li-organic materials, Li-S, Li-O₂, flow battery and other batteries system will become the main focus of future energy systems. Especially, the conjugated carbonyl compounds with the merits of high theoretical capacity, flexible structure, fne redox property and green sustainability are potential energy storage materials for future. Calix[4] quinone (C₂₈H₁₆O₈, C4Q) is a quinone derivative of Calix[4] arene, with a high theoretical capacity of 446 mA·h/g, which is signifcantly higher than that of traditional inorganic electrode materials. C4Q contains four p-quinone units linked by four methylene groups, the carbonyl groups are not sterically encumbered, hence the eight active centers are capable for reversible electrode reactions. Furthermore, the molecular structure of C4Q very stable and hardly decomposes in the electrochemical processes. More importantly, it is not limited to the reaction system theoretically by virtue of the electron transfer reaction, so it can be used as electrode materials for lithium, sodium, zinc and magnesium plasma batteries. In this paper, the applications of C4Q and its modifcation strategies are summarized.

Hydrated salt-based phase change materials have several advantages including moderate phase transition temperatures, high thermal conductivity, high latent heat and low prices, and hence a potential for a broad range of applications. Such materials, however, often come across problems including supercooling, phase separation and poor cycling stability, which limit their practical applications. One way to resolve the problems are the combination of the hydrated salts with other materials to form composites. This has been proven highly effective. Recent years also see researchers to use composite phase change materials as a mean to improve thermal properties of the phase change materials, including phase transition temperature, thermal conductivity and latent heat etc. This paper summaries recent progress in the area.

Short circuit in lithium ion battery is the main cause of thermal runaway, the proper safety additives can prevent the thermal runaway. A positive temperature coeffcient material (PANI-PEW) was prepared by polymering amount of PANI particles on the surface of PEW. The morphology and conductivity of PANI-PEW, the electrochemical performance of LiFePO₄ batteries with PANI-PEW were tested at room temperature and 120℃. The results showed as follow:the conductivity of PANIPEW was 1.08×10^-3 S/m at room temperature and its resistant increased rapidly during 90~120℃. It had little effect on the impedance and cycling performance when PANI-PEW introduced into LiFePO₄ battery at 0.5 C and 1 C. But the impedance of LiFePO₄ battery with 15% PANI-PEW increased rapidly and the frst specifc capacity only was 35.3mA·h/g after the LiFePO₄ electrode with 15% PANI-PEW was treated at 120℃ for 1 min, even after the 12th cycle, the specifc capacity closed to 0. This study indicate that the PANI-PEW is an excellent PTC composite and improved the safety performance of LiFePO₄ battery at 120℃.

Ceramic composite separators are used widely in the feld of power lithium-ion battery and have a direct effect on electrical performance. Six kinds of commercialized polyethylene terephthalate (PET)/ceramic and polyolefin/ceramic composite separator are selected and their corresponding morphology, contact angle, air permeability and electrolyte uptake are investigated. Lithium nickel cobalt manganese oxide/graphite pouch cell of 2 A·h were fabricated with these ceramic composite separators. And the resistance, capacity, self-discharge, AC impedance, rate capability, cycle life and high-temperature float charge performance are characterized. Due to the small and uniform size (0.2~0.5 μm) of coated ceramic particles, high electrolyte uptake (2.0 mg·cm^-2), low air permeability[72 s·(100 mL)^-1] and resistance (4.65 mΩ) for 2# PET/ceramic separator, the prepared lithiumion battery exhibits best comprehensive performance with excellent rate capability of 94.9% capacity retention from 1C to 10C, outstanding cycle life of 102% capacity retention after 500 cycles at 5C and high capacity retention of 90.4% for the floating charge at 65℃ after 1000 h.

Tin oxides have attracted much attention as a negative material for lithium-ion batteries due to its high theoretical specific capacity and low cost. In this work, taking tin tetrachloride pentahydrate as tin source and graphene oxide (GO)/C₆H₁₂O₆ as carbon source, the composite of SnO₂ dispersed into amorphous carbon has been synthesized by hydrolysis and carbonization in large scale. The composite structure and morphology of the products are characterized, and the electrochemical properties of the product are analyzed by electrochemical tests. SnO₂ nanoparticles are homogeneously dispersed in the matrix of amorphous carbon. After 100 cycles, the discharge capacity of the composite is 541 mA·h·g^-1. Amorphous carbon can effectively suppress the volume change of SnO₂ particles during charging/discharging, and improves the conductivity of the composites and the cyclic stability. It leads to an improved electrochemical properties.

Establishing accurate power battery model is one of the key issues in the development of battery management system (BMS). Battery has strong non-linear characteristics, and its model parameters vary with various factors. In battery model parameter identifcation, the more variable factors are considered, the more accurate the identification results are, but the running speed of the model will be reduced, which will affect its practical application. Among all kinds of variable factors, state of charge (SOC) has the most significant impact on battery model parameters. Identifcation and application of battery model parameters under different SOC will improve the accuracy of battery model while maintaining good real-time performance. In this paper, the secondorder RC equivalent circuit model is used for power lithium batteries. The rebound voltage data of batteries under different SOC conditions are obtained through experiments. The least square ftting method is used to identify the model parameters under different SOC conditions. Furthermore, a real-time simulation model of model parameters varying with SOC is built, and the model is simulated and verifed by experiments. The results show that the model has high accuracy and realtime performance.

The accurate estimation of SOC is very important for improving the dynamic performance and energy utilization efficiency of batteries. In the estimation process, the inaccuracy of model parameters and the uncertainty of system noise will greatly affect the results. In order to reduce the influence of model parameter identifcation and system noise on the SOC estimation accuracy, this paper adopts the second-order RC equivalent circuit model combined with the adaptive extended kalman filter algorithm (AEKF) to estimate the SOC of lithium batteries. In order to reduce the estimation error caused by parameter identifcation, the least square method with forgetting factoris used to identify the model parameters online. AEKF can correct the system and process noise, so as to reduce the impact of noise on SOC estimation. At last, EKF and AEKF are used for SOC estimation respectively and their errors are compared. The results show that joint AEKF and least square parameter online identifcation has higher accuracy and better adaptability.

To solve the problems of high energy consumption and lag in heat dissipation of power batteries of electric vehicles, a control strategy of air cooling for power batteries based on minimum energy consumption is proposed. The strategy predicts the future temperature rise of power battery according to the working conditions which is predicted by vehicle navigation system. On the premise of meeting the heat dissipation requirement of power battery, the optimal objective is to minimize the energy consumption of fan, the sectional dynamic programming algorithm is applied to determining the starting time and optimal wind speed of fan in the future section. Taking the combined working conditions of ARB02, HWFET and UDDSHDV with slope information as test conditions, the hardwarein-the-loop test for the accuracy of predicting the future temperature rise of power battery is carried out. The maximum difference between the real-time road condition test temperature and the test temperature in predicting working conditions is 0.3℃, the maximum deviation rate is 0.7%. Fluent simulation results are compared with the other two control strategies, The results show that under the control strategy, the temperature of power battery is always within 40℃, and the maximum temperature difference of battery pack is 1.1℃; the energy consumption of fan is 77.2% of that of the control strategy of fan opening in the whole process, and 53.7% of that of fan based on temperature control strategy. The strategy can effectively control the temperature of power battery and minimize the energy consumption of fan.

Modifed carbon nanotubes were prepared by through acid oxidation and ball milling before combined with stearic acid to prepare a composite phase change material. X-ray diffraction results showed that the ball milling treatment damaged the structure of the carbon nanotubes, whereas no changes occurred to the phase of the carbon nanotubes after oxidation with the mixed acid. Infrared spectroscopic analyses indicated that the ball milling treatment and mixed acid oxidation gave a purifying effect on the carbon nanotubes, and the acidifed carbon nanotubes exhibited functional groups such as hydroxyl groups and carbonyl groups, contributing to the dispersion of the carbon nanotubes. The scanning electron microscopic analyses suggested that the dispersibility of the modified carbon nanotubes in stearic acid was acidified carbon nanotubes > ball-milled carbon nanotubes > carbon nanotubes. The thermal conductivity results also agreed with this above order, indicating that the dispersion of carbon nanotubes increased the thermal conductivity of stearic acid.

Molten salts has been used an a regenerative working medium for solar thermal power because of their good heat transfer ability, high working temperature and temperature range, low system pressure and favorable economics. Non-uniform heating process, however, often results in temperature difference between solid heating surface and the heat transfer fluid, leading to the buoyancy effect and hence mixed convection. Heat conduction through the solid tube wall is likely to exert an effect on the mixed convective heat transfer. This paper numerically studies this effect, specifically the mixed convection process of a molten salt heated by a horizontal square tube surface under a non-uniform heating condition. The wall thickness was considered in the study. The relationship between various dimensionless numbers was analyzed. The results were compared with the flow pattern diagram and classical correlations. The results showed that there was buoyancy effect in the non-uniform heating process with the core zone located near the heating wall and the shape of the core zone changing with the increased flow distance. The Nu number increases with the increase of Re number and Ri number, and Nu_x decreases frst before rises with the depth of flow distance.Compared with the numerical simulation results for a zero wall thermal conductivity, the shape of the mainstream core region was more uniform, the local Nu_x was higher and the rising position was earlier, and the flow and heat transfer characteristics were consistent. The simulation results were in good agreement with the classical correlation.

The Mg-Cu alloys were studied using the molecular dynamics approach with an embedded atom method (EAM). The thermal properties and microstructure of different Mg-Cu alloys were investigated. The melting temperature and enthalpy were studied based on the energy-temperature curve and the C_p-temperature curve. The results showed that, with the growth of Cu content, the melting point of Mg-Cu alloys decreased frst and then increased, and the melting enthalpy increased first and then decreased. With the increase of Cu content, the density and specific heat capacity decreased, and the thermal conductivity increased. We simulated the microstructure of Mg-Cu alloy at the room temperature. The results showed that the interaction between different atoms in Mg-Cu alloy was stronger, which was benefcial to the formation of α+Mg₂Cu eutectic structure. The simulation results also confrmed that the α+Mg₂Cu eutectic was a major factor affecting the melting enthalpy and thermal conductivity of the Mg-Cu alloy.

In this paper, the energy and power characteristics of a flywheel energy storage system are analyzed. Current flywheel energy storage systems could store approximately 0.5-100 kW·h energy and discharge at a rate of 2-3000 kW. Here a design of a 100kW·h flywheel is proposed. By using a low speed steel flywheel rotor with a stress limit of 800 MPa, the energy density could reach 13-18W·h/kg. With such a stress level, however, the size of the flywheel could reach the meter scale, making it difficult to manufacture. To overcome such a challenge, a multi-disc axial connection structure design was proposed. The high-speed composite flywheel rotor was designed with 3 or 4 thin cylinders made from winding fber reinforced composite considering the radial stress optimization. Stress analyses indicated that both the 3-layer flywheel at a speed of 9000 r/min and the 4-layer flywheel at a speed of 15000 r/min would meet the structural strength requirements with an energy density at 50-70 W·h/kg.

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 2969 papers online from Apr. 01, 2019 to May 31, 2019. 100 of them were selected to be highlighted. Layered oxide including Li-rich oxides and high voltage spinel cathode materials are still under extensive investigations for studying Li+ intercalationdeintercalation mechanism and evolution of surface structure, and the influences of doping, coating and interface modifications on their cycling performances. Large efforts were devoted to Si based composite anode materials for optimizing the composite material, electrode and electrolyte. The cycling properties of metallic lithium electrode are improved by using different kinds of surface cover layer. Sulfde and halide containing sulfde based solid state electrolyte and solid state batteries are drawn large attentions. Additives to liquid electrolytes are investigated for improving the cycling performance and coulombic efficiency of high voltage spinel and Ni-rich oxide cathodes. The cathode of Li-S battery is investigated for optimizing its kinetic and cycling performances. In-situ technologies are used to analyze the structural evolution of cathode materials and the fading of solid state batteries and theoretical work covers the kinetics, SEI, the cell fading mechanism.