Transactions of China Electrotechnical Society 2024 No. 7 Items and Abstract

Transactions of China Electrotechnical Society is a comprehensive academic journal in the field of electrical engineering sponsored by the China Electrotechnical Society, reporting international and domestic leading academic and scientific research achievements in basic theoretical research and engineering application. Ma Weiming, academician of the Chinese Academy of Engineering, is the director of the editorial board of the Journal and the editor-in-chief of the journal.

Electrotechnical theory

Ultra-low field magnetic resonance knee orthogonal receiving coil design

Authors: Wan Xi, He Wei, Shen Sheng, Xu Zheng

Abstract:The RF receiving coil is a key component in the magnetic resonance imaging (MRI) system, which is used to detect changing magnetic fields, and its performance directly affects the quality of the image. The ultra-low field MRI RF receiver coil operates at a lower frequency, and its impedance characteristics are different from those of traditional clinical MRI RF receiver coils. Theoretically, the signal-to-noise ratio (SNR) of an orthogonal receive coil can be improved by up to 41% compared to a single-channel coil. Compared with array coils, orthogonal receiving coils can achieve good imaging results with lower cost and design complexity. Therefore, an orthogonal receiving coil for knee joint (50.4 mT) system for ultra-low field MRI (50.4 mT) system was studied, which consists of a saddle coil and a Helmholtz coil.

Firstly, the support structure and size of the coil were determined, and the optimal size of the saddle and Helmholtz coils was determined by calculating the efficiency of the single-turn receiving coil and the inhomogeneity of the magnetic field. Then, the AC resistance of the coil was measured to evaluate the SNR of different turns of the coil, and it was found that the AC resistance increased significantly with the increase of the number of turns, so that the SNR first increased and then decreased with the increase of the number of turns of the coil. Finally, the optimal number of turns of the two coils was obtained, and the orthogonal receiving coil was fabricated, and the performance of the orthogonal receiving coil was evaluated by imaging the CuSO4∙5H2O body membrane and the knee joint in vivo. In body membrane and in vivo knee imaging, the orthogonal receiving coil maximized the image SNR by about 33.5% and 30.9% compared with the single-channel coil, respectively.

Calculation of loss of rotary electromagnetic coupler in wireless charging system and hot spot temperature study

Authors: Cheng Zhiyuan, Song Xiaoyi, Wu Xiaoting, Gui Zihang, Li Dongdong

Abstract:Electromagnetic coupler is the core component of wireless power transfer (WPT) technology, and its operating temperature determines the stability and service life of the system. In order to avoid the cumbersome acquisition process of a large number of experimental data, a three-dimensional electromagnetic field simulation model considering the influence of turn spacing and temperature caused by insulation on material properties is established by using the transient electromagnetic-thermal flow field bidirectional indirect coupling method, and then the electromagnetic loss calculation results are coupled into the heat flow field as a load and the corresponding relationship is established to realize the calculation of hot spot temperature.

The simulation and experimental results show that the maximum error between the hot spot temperature and the measured value of the physical model is 5.15%, and the temperature rise distribution law obtained by the simulation can accurately show the actual situation, verify the rationality of the physical simulation model, and provide a basis for the heat dissipation design of the rotary electromagnetic coupler, which has certain guiding significance in engineering application.

An arcing discharge model of resistive intrinsically safe circuit based on functional data analysis algorithm

Authors: Zhu Ran, Xu Liwen, Meng Qinghai

Abstract:Different from inductive and capacitive intrinsically safe circuits, the arc discharge waveforms of resistive intrinsically safe circuits cannot be accurately described because there are three types, and the imperfect description of the intrinsic safety criteria of resistive circuits will lead to the recurrence of explosion accidents under actual operating conditions. In this regard, the discharge process and waveform characteristics of resistive intrinsically safe circuits are first considered, and based on the functional data analysis regression algorithm, a high-dimensional, strongly correlated parameter, Then, the model is used to simulate the discharge process of resistive circuits and a classification method of arc discharge waveform is proposed, which finds that under the condition of specific circuit parameters, when the normal working current of the circuit is ≤0.15A or I≥0.6A, the arc discharge basically presents a typical discharge form. Finally, a spark discharge test platform is built to verify the feasibility of the arc model and the accuracy of the prediction effect.

Power Systems & Integrated Energy

Stochastic power flow acceleration algorithm for distribution network based on inter-regional scenario equivalence

Authors: Li Junhui, Zhao Hanjie, Zhu Xingxu, Guo Qi, Li Cuiping

Abstract:In order to solve the problem of low computational efficiency caused by the need to simulate a large number of node power injection in the stochastic power flow algorithm of distribution network, a stochastic power flow acceleration algorithm of distribution network based on inter-regional scenario equivalence is proposed.

Firstly, starting from the topological connection law of the distribution network, the influence of node power injection on power flow in other regions in each region is converted into the influence on boundary quantity, and a multi-region power flow model based on boundary quantity is establishedThe E 118 node test system conducts a case analysis, which verifies the accuracy of the proposed method, and the proposed method can significantly improve the computational efficiency.

Analysis of the influence mechanism of grid connection of direct-drive wind farm on the shafting torsional vibration of thermal power units caused by DC transmission

Authors: Gao Benfeng, Dong Hanxiao, Lu Yajun, Zhong Qidi

Abstract:The subsynchronous interaction between thermal power units and high-voltage direct current transmission (LCC-HVDC) of commutation converters in the grid will cause the shafting torsional vibration (SSTI) of thermal power units, while the influence and mechanism of direct drive wind farm (DDWF) connected to the LCC-HVDC transmitter on the damping characteristics of SSTI have not yet been clarified, and relevant research needs to be carried out. In order to solve the above problems, a small signal model is established based on the modular modeling method based on the transmission system of DDWF and thermal power bundled through LCC-HVDC, and the influence of DDWF access and parameter changes on the SSTI damping of thermal power units caused by LCC-HVDC is analyzed by using the eigenvalue method.

The results show that DDWF and thermal power units share the power fluctuation of LCC-HVDC, weaken the subsynchronous interaction between thermal power units and LCC-HVDC, thereby increasing SSTI damping and reducing the risk of SSTI. When the wind speed increases, the SSTI damping increases, when the electrical distance between the DDWF and the LCC-HVDC rectifier station increases, the SSTI damping decreases, and when the LCC-HVDC rectifier side changes from constant current control to constant power control, or the inverter side changes from constant voltage control to constant shutdown angle control, the SSTI damping decreases. Based on the PSCAD/EMTDC platform, the time domain simulation is carried out to verify the correctness of the eigenvalue analysis and mechanism analysis.

Subsynchronous oscillation suppression strategy of grid-constructed direct-drive permanent magnet synchronous wind turbine with UDE additional damping branch

Authors: Chen Jian, Ren Yongfeng, Meng Qingtian, Xue Yu, He Jinwei

Abstract:In order to solve the problem of subsynchronous oscillation of grid-based direct-drive permanent magnet synchronous wind turbines under weak power grid, an additional damping branch oscillation suppression strategy based on Uncertainty and Disturbance Estimator (UDE) is proposed. Secondly, the influence of voltage-current double closed-loop control on the subsynchronous oscillation of the grid-side direct-drive permanent magnet synchronous wind turbine under the weak grid is deeply analyzed, and the oscillation suppression strategy of the UDE additional damping branch introduced into the current loop is proposed, and the filtering bandwidth idea is used to estimate the system disturbance based on the additional damping control of UDE, and the damping support is realized by dynamic voltage compensation, which can effectively suppress the subsynchronous oscillation and improve the robustness of the systemThe effectiveness of the boosted oscillation suppression method is verified by time-domain simulation.

Dynamic grouping of induction motors taking into account the effects of LVRT

Authors: Pan Xueping, Wang Weikang, Chen Haidong, Sun Xiaorong, Guo Jinpeng

Abstract:With the large-scale and extensive integration of new energy into the grid, its influence on the dynamic equivalent modeling of induction motors is worth paying attention to. In this paper, a new method for dynamic grouping of induction motors in new energy power systems is proposed. The interaction between the induction motor and the power grid is analyzed, and it is proposed that the dynamic equivalence accuracy of the induction motor can be improved by considering the dynamic similarity of the voltage at the machine end on the basis of the existing grouping based on the dynamic similarity of the induction motor. For the high proportion of new energy power systems, it is found that there are new energy units near the induction motors, and when some new energy units enter low voltage ride-through (LVRT) during the fault period, the dynamic characteristics of these induction motors are significantly different. Therefore, a dynamic grouping method considering the voltage drop depth of the induction motor port in the new energy power system is proposed.

The analysis of the examples shows that the grouping method proposed in this paper taking into account the dynamic similarity of the port voltage of the induction motor and the depth of the port voltage drop has high equivalence accuracy and strong adaptability.

Double-layer optimization of frequency modulation power of fire-multi-storage system based on ensemble empirical mode decomposition and multi-objective genetic algorithm

Authors: Li Cuiping, Si Wenbo, Li Junhui, Yan Gangui, Jia Chen

Abstract:In order to solve the problem of multiple energy storage power stations distributed in different network nodes of the regional power grid participating in the frequency modulation power dispatching of the power grid, a two-layer optimization strategy for frequency modulation power of the fire-multiple storage system based on Ensemble Empirical Mode Decomposition (EEMD) and Multi-objective Genetic Algorithm (MOGA) is proposed. The strategy consists of an optimization layer for the power modulation of thermal storage and an optimization layer for the frequency modulation power of a multi-energy storage power station: the upper layer takes into account the respective advantages and remaining frequency modulation capacity of the thermal and storage resources, constructs an optimal allocation model of the thermal and storage frequency modulation power, and introduces the adaptive weight coefficient of the frequency modulation cost and state of charge (SOC) in the lower layer, and completes the distribution of the frequency modulation power among the multi-energy storage power stations with the lowest frequency modulation cost and SOC equilibrium as the optimization goals.

The simulation results show that the proposed strategy can improve the frequency modulation effect of the regional power grid and reduce the frequency modulation cost, and control the frequency modulation cost and SOC of multiple energy storage power stations in a balanced manner, which can prevent the energy storage power stations with good economy from being on the edge of SOC out-of-limit for a long time, and improve the enthusiasm and sustainability of energy storage power stations to participate in frequency regulation.

Considering the low-carbon economic dispatch of carbon capture power plants with flexible adjustment of wind power ramp-up

Authors: Han Li, Wang Chong, Yu Xiaojiao, Yu Hongbo, Wang Xiaojing

Abstract:In order to achieve the "dual carbon" goal, the use of renewable energy such as wind power is the fundamental way to reduce carbon emissions, and carbon capture power plants are the direct means to reduce carbon emissions. However, wind power has inherent volatility, and the sudden rise and fall of wind power will affect the "electricity-carbon coupling" characteristics of carbon capture power plants, which will have an adverse impact on the carbon capture effect. The liquid storage tank can approximately store and release energy by increasing or decreasing the amount of its own solution, which provides the possibility to solve the above problems.

In this paper, a mathematical model of carbon capture power plant is first constructed, the correlation between the storage and discharge energy brought by the storage tank and the energy consumption of carbon capture equipment by increasing or decreasing the amount of solution is analyzed, and the two-way adjustment ability of the storage tank is studied. The power system of high-carbon power plants and wind farms is simulated to prove the effectiveness of the proposed method.

Accurate modeling of high-impedance ground faults based on dynamic resistive series

Authors: Zhong Yihan, Deng Feng, Shi Hongfei, Xu Fan, Li Xinyu

Abstract:The existing high-resistance grounding fault models lack a physical explanation of the whole process of fault development, and it is difficult to accurately simulate the nonlinear characteristics of the fault. Based on the field recording data, the physical process of high-impedance grounding faults is studied in depth, and it is concluded that the nonlinear distortion of the fault current waveform comes from two aspects: the nonlinearity caused by the breakdown of the air gap and the nonlinearity of the grounding medium itself. Accordingly, the fault resistance of high-impedance grounding fault is composed of arc resistance and grounding resistance in series, and a new model of high-impedance grounding fault based on dynamic resistance series connection is established.

Firstly, the Thomson principle is used to analyze the generation of dynamic arc in the breakdown process of air medium, and the fault point exponential arc model is established; then, the dispersion process of fault current in the soil is studied, and the expression of the change of ground resistance with fault current is solved in combination with the change law of soil resistivity, and the grounding resistance model is established; finally, the two are connected in series in PSCAD to build a new model of high-impedance grounding fault, combined with the field fault data and compared with other models, it is verified that the proposed model can more accurately characterize the nonlinear characteristics of high-impedance grounding faults under different grounding media, and provides more accurate data support for the subsequent research on the identification of high-impedance grounding faults。

A lifeform electric shock fault identification method with multi-feature optimization selection under unbalanced small samples

Authors: Gao Wei, Rao Junmin, Quan Shengxin, Guo Moufa

Abstract:In order to solve the problem that the existing residual current protection devices cannot effectively identify electric shock accidents, a method for identifying electric shock faults in living organisms with multi-feature optimal selection under unbalanced small samples is proposed. Firstly, the variational autoencoder (VAE) was used to multiply the small sample data of the electrocution of the living body to achieve the equilibrium of positive and negative samples, and then 23 eigenquantities that could reflect the dynamic change characteristics of the waveform were extracted in the time domain, and the Gaussian kernel Fisher discriminant analysis (GKFDA) and the maximum information coefficient (MIC) method were used to select the optimal expression feature group.

Experimental results show that the proposed method can train an excellent classification model by using an unbalanced small-sample electric shock dataset, with a diagnostic accuracy of 98.75% and a diagnosis time of only 1.33 ms. Its excellent performance combined with the design of online incremental learning classifier makes the model have the ability to learn new knowledge and has excellent engineering application prospects.

A line mode traveling wave line selection method for distribution network based on the boundary characteristics of high-frequency filtering of substation

Authors: Wu Yuqi, Li Zhengtian, Lin Xiangning, Huang Zixin, Li Zhao

Abstract:Inspired by the high-frequency filtering effect of bus shunt capacitors on the linear mode traveling wave, this paper proposes a line selection method based on the zero-mode traveling wave design method based on the zero-mode traveling wave design method.

Firstly, the research confirms that the line boundary of the intelligent substation composed of electronic voltage transformer, metal oxide arrester and stray capacitance of the rest of the bus equipment has strong high-frequency filtering characteristics, and its refractive attenuation effect on the line mode traveling wave lays a foundation for the design of the subsequent line selection method. The EMTDC simulation platform verifies the effectiveness, sensitivity and reliability of the proposed line selection method, which uses the line mode traveling wave as the selected modulus, which provides a new idea for solving the problem of fault line selection.

Elastic recovery strategy of district-tunnel power supply system based on DC line interconnection

Authors: Kong Huiwen, Ma Jing, Cheng Peng, Jia Limin

Abstract:Under the "dual carbon" goal, the integrated power supply scenarios of energy and transportation represented by photovoltaic carports and photovoltaic tunnels in service areas are gradually popularized, which makes the district-tunnel power supply system with open form and scattered layout more vulnerable in the face of extreme disasters or man-made attacks. Therefore, an elastic recovery strategy for district-tunnel power supply system based on DC line interconnection is proposed. According to the pre-disaster renovation and resilience reinforcement plan for DC lines.

Secondly, based on the multi-level classification strategy of the important weight of the fault load, the objective function of fault recovery is constructed with the goal of maximizing the recovery amount of the important load and minimizing the additional loss of the system, so as to ensure the maximum elastic recovery of the system based on scarce distributed energy resources after the occurrence of extreme disastersFinally, the effectiveness of the proposed strategy is verified by the simulation of the improved IEEE 123-node distribution network covering the area-tunnel power supply system.

Short-term load prediction of multi-user in station area based on spatio-temporal attention mechanism

Authors: Zhao Hongshan, Wu Yuchen, Wen Kaiyun, Sun Chengyan, Xue Yang

Abstract:In order to solve the problem that the traditional load prediction method that explores the temporal characteristics of a single user cannot learn the spatial correlation between users and cannot realize the common prediction of multiple users in the scenario of massive and high fluctuation user load prediction in low-voltage station area, a Transformer load prediction model based on spatio-temporal attention mechanism (STformer) is proposed to provide accurate short-term load prediction for multiple users in the station area.

Firstly, the traditional Transformer model is improved by embedding the sequence decomposition module, the autocorrelation calculation module and the spatial attention module. Among them, the sequence decomposition module can decompose the user load curve with large fluctuations into a number of relatively stable sub-series, which is helpful to better extract the time dependence and periodic factors of the load curve, the autocorrelation calculation is an improved attention mechanism, which can mine the time correlation of multiple historical contemporaneous subseries, and the spatial attention mechanism can extract the dynamic spatial correlation between multiple users in the station area. Then, the Monte Carlo random inactivation method (MC dropout) was used to extend the STformer to the probability prediction of multi-user load in the station area.

Finally, the real multi-user load dataset is used for verification, and compared with a variety of load prediction models, it is proved that the STformer model can effectively improve the accuracy and robustness of short-term multi-user load point prediction and probabilistic prediction.

Inter-provincial and intra-provincial market clearance and pricing model in the evolution process of the national unified electricity market

Authors: Chen Yi, Wang Han, Yan Zheng, Feng Kai, Liu Zijie

Abstract:In order to promote the mutual assistance of power resources in the provinces and the optimal allocation of power resources across the country, the mainland is promoting the reform of the power market in an orderly manner, and gradually realizing the coupling of the inter-provincial and intra-provincial markets and the evolution of the national unified market.

According to the different degrees of inter-provincial and intra-provincial market coupling, the evolution process is divided into three stages: hierarchical stage, loose coupling stage and tight coupling stage. Further considering the recovery of transmission charges for inter-regional, inter-provincial and intra-provincial transmission, inter-regional DC transmission lines and intra-regional AC transmission lines are charged according to the amount of electricity transmitted, and intra-provincial lines are charged according to the electricity consumption of user loads. The clearing model and pricing mechanism for different transmission fee collection methods are constructed, and the sequential clearing is adopted in the hierarchical stage, the double-layer iterative clearing is adopted in the loose coupling stage, and the unified clearing is adopted in the tight coupling stage, and the node electricity price pricing mechanism is adopted in the pricing mechanism.

Finally, the IEEE 39-node and 118-node systems are used to verify the effectiveness of the clearing model and pricing mechanism, and the influence of transmission charges on the clearing and pricing results is analyzed.

High voltage and discharge

Detection method and analysis of spatiotemporal evolution characteristics of micron-scale dust dispersion concentration under flat plate electrode

Authors: Xue Naifan, Wei Lai, Li Qingmin, Wang Yuan, Yang Ruicheng

Abstract:Micron-level dust will inevitably be generated in the production, operation and maintenance of gas-insulated fully enclosed combined electrical appliances and gas-insulated metal-enclosed transmission lines (GIS/GIL), which may be the root cause of unidentified discharge at the engineering site. In order to detect the dispersion concentration of micron-scale dust and study the spatiotemporal evolution characteristics of the concentration, the light scattering characteristics of 10000 mesh, 2000 mesh and 1000 mesh dust were analyzed, and a dust concentration detection platform based on plate electrodes was designed and built on this basis, so as to realize the quantitative detection of dust dispersion concentration.

Through experimental studies, the evolution law of the dispersion concentration of micron-level dust with different particle sizes and initial masses under the pressure boosting process and continuous pressure was obtained. Studies have shown that with the increase of voltage action time, the dust concentration quickly reaches a maximum and then gradually decreases. The diffuse concentration of micron-level dust will peak during the pressurization process, and a larger concentration peak will occur when the particle size of the dust decreases or the initial mass increases. In the process of dust movement, there is a special phenomenon of agglomeration, which causes serious electric field distortion and threatens the safety of air gap insulation.

The results of this paper illustrate the spatiotemporal evolution of the dispersion concentration of micron-scale metal dust, which can provide support for the monitoring and hazard assessment of micron-level metal pollutants in electrical equipment such as GIS/GIL.

Experimental and simulation study of anode melting process in high-current vacuum arc

Authors: Zhang Zaiqin, Liu Zhiyuan, Wang Chuang, Geng Yingsan, Wang Jianhua

Abstract:In the process of high-current vacuum breaking, the melting process of the anode contact under the action of electric arc greatly affects the breaking result. At present, the research on anode melting focuses on copper and copper-based alloys, and the thermal characteristics of the materials involved are limited. In order to analyze the anode melting mechanism under a larger range of physical parameters, the anodic melting experiments were carried out on four materials, namely W, Mo, Cr and Fe, and the arc magnetohydrodynamic model and the anode heat transfer model were established to simulate the melting process.

The results show that the critical melting currents of the four anode materials are 14.0, 11.9, 8.6 and 7.5 kA respectively in the high-current arcing experiment of the fixed cathode for Cu. The maximum anode temperature of the four materials occurred around 7.0 ms at the arcing time, and the error between the maximum anode temperature calculated and the melting point of the corresponding materials under the critical current was less than 150 K.

Carrier transport and thermal failure mechanism of GaAs photoconductive switch triggered by weak light

Authors: Si Xinyang, Xu Ming, Wang Wenhao, Chang Jiahao, Wang Chengjie

Abstract:The carrier transport mechanism in the form of filamentous current in a high-multiplying gallium arsenide photoconductive switch (GaAs PCSS) triggered by weak light is of great significance for the study of its transient operating characteristics and lifetime. In this paper, the physical model of GaAs PCSS is constructed based on the finite element method, and the transient output current and lattice temperature of the 1.5 μJ switch under weak light trigger are simulated and analyzed by combining the heat generation mechanism of filamentous current, and the influence of bias electric field on the output characteristics of GaAs PCSS is investigated. The photogenerated carrier transport process and damage mechanism of GaAs PCSS in high multiplication mode were studied by the transient electric field, electron concentration and lattice temperature inside the switch at different times.

The results show that the existence of high-density filamentous currents is accompanied by the generation and development of high-field domains. The higher the electric field inside the switch, the more obvious the carrier bunching phenomenon caused by the negative differential effect, and the higher the corresponding electron concentration and lattice temperature, and the maximum electric field strength and lattice temperature near the anode are 220 kV/cm and 821.92 K, respectively.

Live detection technology for insulation deterioration state of distribution cable based on harmonic components

Authors: Xu Haisong, Zhang Daning, Hu Ran, Lu Xu, Wang Anzhe, etc

Abstract:Due to the limitation of power outage maintenance of urban power grid, the harmonic current live detection technology of distribution cable is expected to become an effective supplement to the traditional offline diagnosis method, so as to improve the real-time diagnosis of the insulation state of distribution cable. In this paper, a true experimental platform for 10 kV distribution cable is built, and typical defective cables with moisture and long-term thermal aging are prepared. The magnetic flux evolution of the cable insulator under typical defects is obtained by COMSOL finite element electromagnetic simulation, and the harmonic current characteristics and statistical characteristics of the cable with typical defects are obtained through experimental tests.

On this basis, a method for analyzing the deterioration degree of distribution cable based on LASSO regression analysis was constructed by using the harmonic feature data, and a defect type identification method based on cluster analysis was further proposed. The results show that the 3rd, 4th, 5th and 11th harmonics of harmonic current of distribution cable are closely related to the deterioration state of the cable. The recognition accuracy of the model combining principal component analysis (PCA) data dimensionality reduction and expectation maximization cluster analysis can reach up to 75.64% when used to identify the state of moisture and normal cables. The live detection method and evaluation method proposed in this paper can effectively check for high-risk cables with latent defects.

Anti-icing method and field test of wire rime based on dual-pass shape memory effect of memory alloy

Authors: Zeng Wei, Jiang Xingliang, Yang Guolin, Pan Bichen, Zhang Zhijin

Abstract:Transmission line icing seriously threatens the safe operation of power system, and scholars at home and abroad have carried out a lot of research on the methods of inhibiting wire icing. Based on the two-way shape memory effect of shape memory alloy maintaining different shapes at different temperatures, a method of arranging shape memory alloy on the surface of the conductor is proposed, and the shape change is used to change the electric field strength on the surface of the conductor to suppress the icing of the conductor, so as to realize the non-manual intervention anti-icing of the transmission line without power interruption. A three-dimensional model of the shape memory alloy wire was established, and the electric field on the surface was simulated and analyzed.

The results show that the electric field strength on the surface of the wire increases gradually with the increase of the deformation of the shape memory alloy. The cylindrical aluminum strips bent upwards at both ends were used to replace the shape memory alloy after the shape change, and the LGJ-150/25 wire surface was arranged on the surface of the LGJ-150/25 wire, and the natural icing experiment was carried out in the field at the National Field Scientific Observation and Research Station of Energy Equipment Safety in Xuefeng Mountain, Chongqing University. The experimental results show that the aluminum strips placed on the surface of the wire instead of the deformed memory alloy can inhibit the rime icing of the wire, and the effect is the best when the initial surface electric field strength of the wire is 10 kV/cm, and the icing quality and thickness are reduced by 57.1% and 48.7%, respectively.

A new cable defect diagnosis method based on reflection coefficient and kernel function

Authors: Rao Xianjie, Xu Zhonglin, Liu Xiangyu, Guan Huifang, Zhou Kai

Abstract:In order to solve the problems of poor defect location effect and difficulty in judging defect types in the existing cable local defect detection methods, a new cable defect diagnosis method based on Reflection Coefficient Spectroscopy (RCS) was proposed. Firstly, the RCS mathematical model of the cable route with local defects is established by using the distribution parameter model of the cable line, and according to the RCS mathematical model, a reasonable kernel function is determined, and a new defect diagnosis function based on RCS is designed. Then, the feasibility and accuracy of the method were tested by modeling and simulation of different types and severity of cable line defects, and finally, local defects were designed on coaxial cable and 10 kV power cable, and the real cable defects were diagnosed and analyzed by this method.

The simulation and measurement results show that the method can accurately locate the defects in the cable route, and can accurately judge the type and severity of the defects, which shows the practicability of the method and has high practical engineering value.

Power storage and application

Research progress on the influencing mechanism and optimization strategy of polypropylene-based thin-film energy storage

Authors: Zhang Chuansheng, Ren Chengyan, Huang Bangdou, Xing Zhaoliang, etc

Abstract:Biaxially oriented polypropylene (BOPP) film is widely used in film capacitors because of its good insulation, low loss, and self-healing properties after metallization. At present, BOPP film capacitors are also facing problems such as low energy storage density per unit volume and poor high-temperature performance, which cannot meet the development trend of equipment intensification and miniaturization, and it is urgent to carry out research on the improvement of polypropylene-based film energy storage density.

In this paper, the polarization and breakdown mechanisms affecting the characteristics of dielectric energy storage are introduced, which provides a necessary theoretical basis for the development of modification schemes. Secondly, a variety of unfavorable factors and key challenges caused by the existing industrial production process are carefully discussed, and the intervention point is found for the combination of modification scheme and production practice, and the existing control methods, such as matrix control, structural design optimization and surface modification, etc., are deeply excavated, the advantages and disadvantages of inorganic and organic component doping, "sandwich" structure, functional layer deposition and grafting are analyzed, and novel methods such as quantum size effect control are summarized. Finally, from the perspective of industrial production, a high-efficiency and low-cost modification method is proposed, the corresponding mechanism is discussed, and the future research focus is summarized and prospected.

State-of-charge estimation of lithium-ion battery based on observation equation reconstruction filtering algorithm

Authors: Huang Kai, Sun Kai, Guo Yongfang, Wang Zipeng, Li Senmao

Abstract:The accuracy of the observation equation in the filtering algorithm plays a decisive role in the battery state evaluation. However, due to the influence of temperature, operating current and state of charge (SOC), even if the battery model with high accuracy is used, there is still a large error between the output value of the observed equation and the actual voltage in the Extended Kalman Filter (EKF) algorithm, that is, a large amount of new information is generated.

In this paper, an Enhanced Extended Kalman Filter (E-EKF) algorithm based on the recombination of observational equations is proposed. The core idea of the algorithm is to reorganize the observation equation by using the error correction strategy with temperature, SOC and current adaptability, so as to reduce the new information in the algorithm and improve the accuracy of SOC estimation. The performance of the E-EKF algorithm was verified by using two typical operating conditions at different temperatures. The experimental results show that the algorithm can adapt to different temperatures and working conditions, and has high SOC estimation accuracy.

Battery peak power estimation method based on multi-time-scale double-extended Kalman filter

Authors: Li Qiang, Zhang Kaixuan, Yuan Wenwen, Xu Yahan, Yang Ruixin, etc

Abstract:Power battery is the technical bottleneck of electric vehicles, and the high-precision estimation of its state has always been a technical difficulty in the industry, and the inaccurate state estimation is easy to cause potential safety hazards and accelerate the aging of the power battery system. However, the characteristics of power batteries such as the inevitable decay of each use, time-varying nonlinearity, and environmental sensitivity make it extremely challenging to accurately estimate their state in real time.

In order to solve the problem of peak power estimation of lithium-ion power batteries, a Dual Extended Kalman Filter (DEKF) algorithm based on multi-time scale sliding window is proposed, and the model parameter library is updated based on the peak power test results, and the slow time-varying estimation of parameters is realized. The evaluation index shows that the verification results show that the proposed algorithm can accurately estimate the battery parameters and power state in the whole life and full power range of the power battery, and the voltage error is less than 40 mV.

Efficiency optimization of multi-stack proton exchange membrane electrolysis hydrogen production system based on power-temperature adaptive control

Authors: Han Pengfei, Xu Xiaoyuan, Wang Han, Yan Zheng

Abstract:With the development of renewable energy power generation and electrolysis hydrogen production technology, hydrogen production from renewable energy based on proton exchange membrane (PEM) technology will become one of the main means of hydrogen energy supply. New energy power generation is random and fluctuating, and the power allocation strategy of the existing multi-stack PEM electrolysis hydrogen production system is difficult to ensure the efficient operation of the system in the power fluctuation scenario. In this paper, the overall efficiency model of the hydrogen production system including the main energy consumption links is established, and the characteristic relationship between hydrogen production efficiency and current density and temperature is explored.

Then, according to the efficiency characteristics, an efficiency optimization strategy for multi-stack PEM electrolysis hydrogen production system based on power-temperature adaptive control was proposed, which included offline optimization and online control: the offline optimization part pre-formulated the electrolyzer power and temperature setting scheme under different total electrolysis power according to the efficiency model of the hydrogen production system, and the online control part adjusted the electrolyzer power and temperature according to the offline optimization scheme and hydrogen production power.

Finally, the actual wind power is used for case analysis, and the results show that compared with the traditional power average allocation strategy and chain allocation strategy, the efficiency optimization strategy proposed in this paper increases the hydrogen production by 6.4% and 5.7%, respectively.