To ensure the safety of new energy vehicles during the entire period of use, it is necessary to conduct health monitoring for the full life cycle of lithium-ion batteries. Aimed at the low learning rate due to the small capacity of training data set for the remaining useful life (RUL) prediction model based on neural network and the duplicate collinearity of the extreme learning machine(ELM) method, a method for augmenting the training data set is proposed. In addition, based on the improved ELM, an RUL prediction model for the full life cycle of lithium-ion battery is built. First, the early operation data of battery is extracted to formulate health factors, and the Akima interpolation method is used to augment the amount of training data. Then, the salp swarm algorithm is used to improve the ELM network, and the RUL prediction model for the full life cycle of lithium battery is established. Finally, the NASA battery data set is used to validate the model. Experimental results show that the proposed method for augmenting the training data capacity is effective, the capacity tracking capability of the RUL prediction model in full life cycle is strong, and the prediction error is small.

The magnetic leakage from an indoor air-core reactor leads to problems such as serious nearby electromagnetic pollution and heat generation by metal equipment. To solve these problems, based on the ANSYS finite element simulation platform, the indoor air-core reactor and its surrounding ancillary facilities and building structure of a 500 kV substation are modeled in three dimensions, and the building roof is equipped with a shielding plate. Through the optimization analysis of shielding materials, thickness and gap width, a scheme is formulated to improve the electromagnetic environment surrounding the indoor reactor. Simulation results show that the magnetic induction intensity of the steel structure can be effectively reduced by adding a shielding plate which is overlapped by 3 mm thick aluminum plates above the steel beam. The temperature change of the reactor during its operation meets the insulation heat resistance requirement for the air-core reactor. The edge section temperature of the shielding device is higher, with a peak of 53.26 °C. The average temperature of surrounding buildings and facilities increases by about 5-10 °C, which meets the requirements of safe operation.

The converter with constant-power control in a flexible DC distribution system has characteristics of constant-power load, which will reduce the system damping and adversely affect the system stability. To address this problem, a superconducting magnetic energy storage (SMES) device is introduced to improve the system stability. A feed-back control model of the flexible DC distribution system is derived, and the effect of constant-power load characteris-tics of the converter on system stability is investigated by frequency-domain analysis. Combined with a mathematical model and frequency-domain analysis, it is also pointed out that the SMES device can improve the system stability by introducing positive damping to grid and increasing the phase margin of the system's open-loop transfer function at the shear frequency. To prevent over-high voltage at both ends of the superconducting magnet, the DC/DC converter which connects the SMES device with the DC distribution network needs to have certain voltage regulation performance. Therefore, the SMES device with a modular multilevel DC/DC converter (DC-MMC) is studied, which can adjust the number of sub-modules flexibly to set the voltage ratio of the converter. Moreover, the DC-MMC can control the voltage at both ends of the superconducting magnet while realizing a bidirectional flow of energy in the converter, thus protect-ing storage device. The feasibility and effectiveness of the SMES device with DC-MMC in improving the stability of flex-ible DC distribution system is verified by time-domain simula-tion waveforms.

A single-phase transformerless inverter for photovoltaic power generation is proposed, which has a common ground between its input and output and thus eliminates the common-mode current in the photovoltaic system. Meanwhile, its voltage gain is higher than that of the traditional single-phase quasi-Z-source inverter. In addition, the use of thin film capacitor makes the inverter more reliable and prolongs its service life. The working principle of this inverter is also analyzed in detail. Finally, a 140 W prototype was built, and results verified the correctness of the proposed inverter topology and the effectiveness of the control strategy in islanding and grid-connected operation modes.

In view of the high fluctuation and randomness of wind turbine output, which affects the safe and stable operation of power system as well as the accuracy of wind power prediction, a wind power prediction method based on the fluctuation characteristics of wind power is proposed. First, the fluctuation characteristics of wind power are analyzed in terms of time scale and unit scale, and the appropriate wind power data is selected for wind power prediction. Then, a wind turbine short-term power prediction model based on least squares-support vector machine (LS-SVM) is established. The adaptive variational mode decomposition (AVMD) is used to decompose the wind power data to achieve frequency division, and the improved particle swarm optimization(IPSO) is used to optimize the model parameters affecting the re-gression prediction in the LS-SVM model. Experimental results show that the prediction model has strong adaptability, and the effectiveness of the prediction method can be proved by prediction error evaluation indexes.

As power lithium-ion batteries play a key role in the electric vehicle industry, ensuring their working reliability has become a research hotspot at present. In this paper, the materials and manufacturing processes of lithium-ion batteries are reviewed. The battery state estimation and remaining useful life prediction methods are summarized in detail, and the advantages and disadvantages of these methods are discussed. From the perspective of battery management system, the relevant knowledges of equalization management system and thermal management system are sorted out in turn. From the perspective of electric vehicle hybrid energy storage system, the performance degradation mechanism under actual working conditions and the relevant technologies are elaborated upon. Finally, the status quo of key technologies related to the reliability of power lithium-ion batteries used in electric vehicles is summarized from four aspects, and the development possibilities in the future are forecasted.

A shutdown strategy for a low-cost hybrid DC converter based on diode rectifier is studied. The shut-down process of the auxiliary converter is divided into an energy feedback stage and an energy dissipation stage. At the energy feedback stage, part of the energy stored in the capacitors of sub-modules is fed back to grid through the DC transmission line under the active control. At the energy dissipation stage, the resonant capacitor and the capacitors of sub-modules are discharged in sequence through a discharging resistor. The calculation methods for the discharging cur-rent, capacitance voltage, and discharging time are derived, and the design method for the discharging resistor is also given. The capacitors of the auxiliary converter can be discharged quickly and efficiently under the proposed shutdown strategy without a high-voltage and large-capacity discharging resistor, which is conducive to the realization in engineer-ing projects. Finally, a simulation model is constructed in Matlab/Simulink, and the validity of the shutdown strategy is verified by simulation results.

Aimed at the problem of DC voltage fluctuations caused by load switching, power fluctuations and dou-ble-frequency injection in DC microgrids, a dynamic compensation control strategy for a Buck-type bidirectional DC-DC converter based on model predictive control (MPC) is proposed. First, the corresponding discrete state space matrix is es-tablished, and the input current is used as the disturbance. Second, the model-based inner-loop current predictive control and outer-loop voltage control of the Buck-type bidirectional DC-DC converter is designed. Third, a dynamic compensa-tion control structure based on a residual generator is designed for the current disturbance, and the dynamic compensa-tion controller Q(z) is solved. At the same time, the recursive least squares algorithm is used for parameter identification to reduce the influence of model uncertainty on the dynamic compensation control strategy. Finally, a comparative ex-periment was designed on the PSCAD/EMTDC simulation platform to verify the effectiveness of the proposed control strategy. Experimental results show that the compensation control structure can effectively solve the problem of DC bus voltage fluctuations and enhance the robustness of the entire system without changing the original predictive control.

A design method for small and medium-power DC/DC converters suitable for low-orbit commercial aerospace is given in this paper. A synchronous rectifier flyback topology and surface mounted devices are adopted, which can meet the demands for common single-and multi-output DC/DC converters applied in aerospace, with advantages of low cost, high performance, high reliability, and mass production. To further improve the conversion efficiency and power density, gallium nitride(GaN) FETs are also used. In addition, the losses of main power devices in the topology under different operating conditions are calculated and compared. Finally, a DC/DC converter with a wide range of input voltage (23-47 V) and output of 5 V and 30 W was built for verification.

The state-of-charge (SOC) balance control of series-connected lithium batteries is of significance to the improvement of battery life. In this paper, a hybrid SOC equalization scheme based on active-passive equalization is proposed against the SOC discreteness of a lithium battery cell, in which the topology of the active equalizer is realized by a multi-winding flyback converter, and the passive equalizer consists of a resistor and a switch connected in parallel at both ends of the cell. The operating principle for the hybrid SOC equalizer is analyzed in detail, and the effect of SOC discreteness on equalization speed is discussed in terms of control strategy. The standard deviation representing the degree of discreteness and the coefficient representing the reasons of discreteness are introduced to realize the fast equalization of SOC under different discrete conditions. The topology of the proposed hybrid equalizer and the corresponding control scheme can optimize energy consumption and balancing speed, and experimental results verify the feasibility of theoretical analysis.