Electric Power

Methodology for Calculating VRE Equivalent Feed-In Tariff Based on System Cost and Its Application

ZHANG Yunzhou, CHEN Ning, HUANG Bibin, WANG Caixia, LI Jiangtao

2022, 55(2): 1-8. DOI: 10.11930/j.issn.1004-9649.202112074

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Consuming VRE (variable renewable energy) must rely on regulatory and supporting power sources such as thermal power unit and pumped storage as well as the support of power grids. As a result, the investment and operation cost of conventional power units and power grids ( i.e, the system cost of VRE) are increased. However, the system cost has not been considered in the existing domestic economic evaluation indicators of VRE, which is not conducive to the effective allocation of the system costs and enhancing the internal enthusiasm of each entity to promote the consumption of VRE. This paper puts forward the conception of VRE equivalent feed-in tariff and the calculation methodology of system cost. An idea for allocating the system cost is proposed based on the equivalent feed-in tariff. The calculation results of typical provinces show that the VRE equivalent feed-in tariff is still higher than the benchmark price of coal-fired plant during 2020-2025, which is hard for utilization of renewable energy in state-set price. The proposed system cost allocating mechanism can stimulate the inner motivation of each entity to promote the consumption of VRE and help realize the high-quality development of renewable energy.

Research on Operational Benefit Improvement Strategy of Optical Storage Power Station Based on Genetic Ant Colony Algorithm

CAO Yaqi, ZHAO Bo, WANG Lijie, LI Xiangjun, GAO Binheng

2022, 55(2): 9-18. DOI: 10.11930/j.issn.1004-9649.202101001

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This article takes the grid-connected optical storage regional power grid as the research object, and starts the research with the full use of the flexible regulation role of the energy storage system and the improvement of the system operation economy. On the basis of considering the cost of electricity, a control strategy for real-time adjustment of the BESS operating state is proposed, and an optimization model is established with the goal of maximizing net income, minimizing total cost, and extracting electricity from the large grid. The genetic-ant colony algorithm of the penalty function solves the optimization model, and analyzes the investment income of the grid-connected optical storage system from the perspective of investors. Finally, through the simulation analysis of actual data in a certain area of Jiangsu, the optimization control strategy of "photovoltaic and energy storage" in this area and the results of economic benefit analysis are given to verify the feasibility of this model and algorithm.

Optimal Control Strategy for Energy Storage Power Station in Primary Frequency Regulation of Power Grid

ZHANG Jiacheng, XIA Xiangyang, DENG Zihao, CHEN Guiquan

2022, 55(2): 19-27. DOI: 10.11930/j.issn.1004-9649.202102028

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In order to achieve accurate and fast primary frequency regulation of power grid without compromising the safety of the participating energy storage system, this paper proposes an energy storage assisted frequency modulation adaptive optimization control strategy considering both the State of Charge (SOC) and State of Health (SOH) in response to the demand of real power generation due to the system frequency deviation. According to the real-time status of the energy storage unit, the optimal switching plan is determined for multiple groups of energy storage units participating in the primary frequency modulation of the power grid. In the early stage of frequency change, depending on their health status, multiple groups of energy storage units should coordinate their output together to reduce frequency deviation. During the frequency recovery stage, the health status and charging state of each storage unit is taking into account individually so as to ensure the performance of energy storage frequency modulation while keeping each energy storage unit in a healthy operating state. In this way both the safety and economy of the energy storage system are improved. Finally, a primary frequency modulation model of the regional power grid was built, and the effectiveness of the strategy was verified by step and continuous disturbance testing.

Waste Heat Recovery and Utilization of Advanced Compressed Air Energy Storage System

WEN Xiankui, LI Xiang, DENG Tongtian, ZHONG Jingliang, WANG Suobin, LIU Shi

2022, 55(2): 28-34. DOI: 10.11930/j.issn.1004-9649.202011118

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Compressed air energy storage is a kind of energy storage technology that has developed rapidly in recent years, which can realize energy storage and release. In order to avoid heat loss during the operation of the system, a method to recover and utilize the waste heat of the system exhaust gas and the heat exchange working fluid is proposed. On the basis of the original heat recovery system, a low expansion ratio expander is added. The converter absorbs the waste heat of the working fluid and enters the expander to do work to increase the output power of the expansion unit and improve the system efficiency. By using Aspen Plus software to establish a four-stage advanced compressed air energy storage system model under steady-state conditions for simulation. The influence of the these two factors on the system efficiency and output power is explored by changing the expander exhaust pressure and the regulator valve outlet pressure, The simulation results show that the method increases the total output power of the advanced compressed air system and improves the system efficiency.

Robust Game Optimization Scheduling Method for User-Side Distributed Energy Storage

LIN Zhenfeng, ZHENG Changbao, RUI Tao, HU Cungang

2022, 55(2): 35-43,114. DOI: 10.11930/j.issn.1004-9649.202012085

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Aiming at the economic scheduling problem of the system under multi-agent energy trading mechanism in open electricity market, this paper proposes a robust game optimization scheduling method for user-side distributed energy storage based on cooperative game theory. The purpose of this method is to coordinate the energy interaction between distribution network and users. By finding the equilibrium point of the game model, the optimal user-side energy storage scheduling strategy is formulated, so as to improve the new energy consumption level and economic benefits of the system. Secondly, in order to reduce the influence of source and load uncertainty on the system economy in the actual dispatching operation process, robust optimization theory is used to deal with the uncertain factors. Finally, an example is given to verify the effectiveness of the proposed optimal scheduling method to improve the photovoltaic energy consumption level and reduce the operation cost of market entity.

Massive Data Processing Method for Battery Energy Storage Power Stations Based on Rough Sets

CHEN Juan, HUI Dong, FAN Maosong, HU Juan, CHU Yongjin

2022, 55(2): 44-50,208. DOI: 10.11930/j.issn.1004-9649.202102047

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During the operation of energy storage power stations with lithium-ion batteries, huge amounts of uploaded data and high-frequency data sampling increase the difficulty of online real-time evaluation. How to extract and compress effective data and ensure the fidelity of the compressed data has become the main content of preprocessing in data mining. Given the above problems, the attributes of the data from a battery cluster are first reduced by the method using rough set theory. The battery cluster is selected from the energy storage power station under a specific working condition. Then, according to the $ 2\sigma $ principle of normal distribution, the attribute values are divided on the basis of binary logic, and the battery cells are classified into frequent detection objects and infrequent detection objects, which reduces the amount of data processed online. Finally, the data of the same battery cluster under different working conditions in 20 days are taken to verify the effectiveness of the processing method.

A Real-Time Co-simulation Platform for Power CPS Based on Multi-component Parallel Architecture

WAN Keting, LU Lingxia, YU Miao, QI Donglian

2022, 55(2): 51-61. DOI: 10.11930/j.issn.1004-9649.202108089

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For power cyber-physical system (CPS) formed by integration of traditional power systems and advanced information technology, the coupling between the power system on the physical side and the communication network on the information side are continuously deepened. which leads to increasingly serious power system failures caused by communication problems such as network failures and malicious attacks, and the traditional simulation methods are no longer suitable for simulating and analyzing such scenarios. Based on an analysis of the state of the art in power CPS simulation technology, the embedded control components and penetration testing components are designed with mainstream real-time simulation tools. Based on the multi-component parallel architecture, a real-time co-simulation platform with multiple real-time simulation modes is designed for power CPS, and the overall architecture and component operating mechanism are discussed in detail. At last, the testing cases covering a variety of simulation scenarios are proposed, and the simulation results have verified the effectiveness and accuracy of the platform. This platform can satisfy the real-time simulation requirements of the power CPS for main operating scenarios, and can support the functions of multi-terminal communication and penetration testing.

Exploring the Evolution Mechanism and Active Defense of Cross-Domain Cascading Failures in New Type Power System

LIU Yihan, WANG Yufei

2022, 55(2): 62-72,81. DOI: 10.11930/j.issn.1004-9649.202110081

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The new type power system realizes the extensive interconnection of new energy sources and diversified loads, as well as the dynamic interaction of cyber flow and energy flow, but it also faces more and more serious security threats. The attackers can launch cyber attacks to cause a series of spatiotemporal coordinated power faults at multiple power nodes, forming cross-domain cascading failures (CDCF), and undermining the stable running of new type power system. In this context, the evolution and active defense mechanism of CDCF are studied. Firstly, the coupling security risks of new type power system are analyzed based on the system architecture and running characteristics. After that, an event-driven analysis is carried out on the whole attack process of CDCF caused by the attackers, and a CDCF mathematical model is established. Finally, the active defense process of CDCF is analyzed from the defenders’ perspective. A CDCF active defense mode is proposed considering the characteristics of new type power system, and a decision-making model for the optimal active defense scheme is established to provide the technical solution for CDCA active defense.

A Security Evaluation Method for Cyber Physical Distribution System Considering Influence of Information Failure

LI Xiao, XU Jianbing, LI Manli, NI Ming, TONG Heqin

2022, 55(2): 73-81. DOI: 10.11930/j.issn.1004-9649.202109039

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Information failure events caused by natural faults or cyber attacks will affect the fault handling process of distribution network, leading to the expansion of power outage area and extension of power outage time. In order to quantify the impact of information failure on the security of the cyber physical distribution system, a CPS security evaluation framework of distribution network is firstly established, which clarifies the content and process of security evaluation. Secondly, a mathematical model is built for distribution network fault recovery with the minimized load loss power as the objective function, and the optimal switch action strategy under power failure is obtained. And then an analysis is made of the impact of information failure faults, which occur in the process of fault location, isolation and recovery, on the fault handling business, and the security evaluation indicators under the cyber-physical combination faults are calculated. Finally, the key combination faults set and the key power/information equipment which have the largest impact on the cyber physical distribution system are obtained. The simulation results based on a 62-node distribution network have verified the effectiveness and rationality of the proposed method.

Non-intrusive Industrial Load Identification Based on Random Forest Algorithm and Steady-State Waveform

WANG Jian, YI Shuhui, LIU Junjie, LIU Jian

2022, 55(2): 82-89. DOI: 10.11930/j.issn.1004-9649.202109026

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Non-intrusive industrial load identification can accurately acquire the operation situations of each load in the plant, which is beneficial to the demand-side intelligent power management. The identification method for industrial load is complicated and difficult to implement due to the difficulty in collecting transient data for modeling and the demand for high-precision measuring equipment. Aiming at this situation, a non-intrusive industrial load identification method is proposed using random forest algorithm and steady state waveform. Firstly, the steady state waveform is extracted by monitoring the power state change of the industrial load through the event, and the characteristic data of the steady state waveform of the single load current is constructed according to the difference of the current waveform caused by different performance of the industrial load. Then, by using the high-dimensional data of the steady-state waveform as the sample data, the bootstrap sampling method and the CART algorithm in the random forest algorithm are used to generate multiple decision trees. Finally, the industrial load types are identified by voting multiple decision trees. The actual operating load data of a factory is used as the sample data for simulation, and the effectiveness and rapidity of the proposed identification algorithm are verified with simulation. The simulation results show that the accuracy rate of the proposed identification algorithm is more than 99% with the identification time of 3.36 s, which is much higher than the accuracy rate of 63.8% and the identification time of 6.15 s of the Bayesian identification algorithm. Therefore, the proposed identification algorithm can effectively realize the non-intrusive industrial load identification.

Deconvolution Beamforming Algorithm Based Abnormal Noise Fault Identification of Dry-Type Transformer

BAO Hailong, SHAO Yuying, WANG Xiao, PENG Peng, YUAN Guogang, ZHUANG Beini

2022, 55(2): 90-97. DOI: 10.11930/j.issn.1004-9649.202004162

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To improve the accuracy of the conventional beamforming location algorithm, the deconvolution beamforming algorithm is proposed for the abnormal noise fault identification of dry-type transformer. The basic principle of deconvolution beamforming algorithm is analyzed, and its applicability to the dry-type transformer abnormal-noise fault identification is verified. A dry-type transformer fault identification method based on the accurate location of abnormal-noise is studied, where the feature recognition of voice print is considered. The concept of "the energy ratio of high-frequency characteristic peak" is firstly proposed to quantify the severity of mechanical abnormal noise. Finally, experimental test and field verification validate the effectiveness and accuracy of the proposed method.

Analysis About the Effect of Dielectric Film Surface Residual Charge on Vibration of Filter Capacitor Core

WANG Shuai, LI Lin, CUI Jianye, ZHAO Shousheng, ZHANG Pengning, WANG Yaqi, HE Qiang

2022, 55(2): 98-107,151. DOI: 10.11930/j.issn.1004-9649.202004193

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The noise of filter power capacitor in high voltage direct current (HVDC) converters is becoming increasingly prominent. Thus, the vibration mechanism of capacitor should be further investigated to provide theoretical reference for noise reduction measures. In this regard, two main goals are to study the residual charge density on the surface of dielectric film inside the capacitor and its effect on the vibration of the capacitor core. Therefore, the residual charge density is measured by means of electrostatic probe and charge inversion, and the probability statistical law of the electric force of electrode plate with the residual charge distributing randomly is calculated and analyzed. Finally, the vibration acceleration of capacitor is obtained through Electric Field-Mechanical Force-Vibration coupling simulation and the results are validated by experiment. The results indicate that the residual charge density of films mainly distributes between ?10^?4 and 10^?4C/m². When a single-frequency excitation is applied, the force and vibration spectrum contains not only the double-frequency component but also the base-frequency component, which aggravates the imbalance of force on internal electrode plate.

Corona Characteristics and Series Optimization of Fittings for 1 000 kV UHV Transmission Lines

NIU Haijun, ZHANG Xuesong, QUAN Shanshan, LIU Shengchun, SI Jiajun

2022, 55(2): 108-114. DOI: 10.11930/j.issn.1004-9649.202105030

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The common corona problems of fittings for ultra high voltage alternating current transmission lines are analyzed based on the field test results of the Zhebei-Fuzhou 1000 kV UHV AC transmission line. According to the technical parameters of 1000 kV UHV AC transmission lines, structure design optimization is carried out for fittings such as suspension string, tension string, the grading and shielding ring of rigid jumper string based on the design, manufacture, construction and operation experience of 1000 kV UHV AC transmission line fittings in China. The optimization effect of the fittings is further verified through the full scale test of corona and noise of the suspension strings.

Weight Analysis of Lightning Disaster Factors and High Risk Tower Identification for ±1 100 kV Jiquan Line

REN Hua, LI Jian, MI Xiao, GU Shanqiang, WANG Jian, WU Min, CAO Wei, ZHANG Rui

2022, 55(2): 115-124. DOI: 10.11930/j.issn.1004-9649.202107064

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Lightning disaster factors for transmission lines mainly include lightning parameters, landforms, insulation configuration and earth resistance, but their weight values for lightning risk are hard to be obtained for a certain transmission line. In this paper, an in-depth analysis is made of the lightning disaster factors for the ±1 100 kV Jiquan line. By using the analytic hierarchy process for lightning disaster risk evaluation, the weight of each disaster factor is obtained through calculating their membership and establishing judgment matrices. The results show that lightning density, lightning current amplitude and protection angle are main disaster factors with high weight values for lightning risk, and their weight values are 0.420, 0.247, 0.147 respectively. Based on the disaster factors with high weight values, the aggregation analysis method is used to identify the towers with high lightning risks, which has provided a important basis for formulating lightning protection strategy for Jiquan Line. Compared with the differential lightning risk evaluation on every tower, the proposed method in this paper can rapidly identify the towers with high risk of lightning, thus significantly reducing the tedious work. This method is applicable to lightning risk evaluation for the transmission lines with long distance or for a large number of transmission lines.

Transformer Fault Diagnosis Method Based on DCAE-KSSELM

HAO Lingling, ZHU Yongli, WANG Yongzheng

2022, 55(2): 125-130. DOI: 10.11930/j.issn.1004-9649.202111003

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In order to make full use of the large number of unlabeled samples generated during transformer fault and improve the accuracy of fault diagnosis, an innovative fault diagnosis method is proposed based on the combination of deep contractive autoencoder (DCAE) and kernel semi-supervised extreme learning machines (KSSELM). First, the unlabeled samples are used to train the DCAE network layer by layer and initialize the network parameters. Then the labeled samples are used to fine-tune the network parameters.Finally, the labeled samples and unlabeled samples are used as the inputs of the hybrid network of DCAE-KSSELM to make the fault diagnosis. The experimental results show that the proposed hybrid model has good stability, high fault diagnosis accuracy and strong robustness.

Photovoltaic Global Maximum Power Tracking Based on Improved Dragonfly Algorithm

XUE Fei, MA Xin, TIAN Bei, WU Hui

2022, 55(2): 131-137. DOI: 10.11930/j.issn.1004-9649.202010137

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A multi-peak phenomenon can be observed on the power-voltage (P-U) characteristic curve of a photovoltaic (PV) array under partially shaded conditions (PSCs). In this case, conventional maximum power point tracking (MPPT) algorithms tend to fall into local extremums, and swarm intelligence algorithms would spend much time in tracking. Thus, this paper proposes an improved MPPT algorithm based on the dragonfly algorithm (DA) and the perturbation and observation (P & O) algorithm. The convergence rate and global search ability of the algorithm are improved by optimizing particle roles and introducing the Lévy flight model. With the P & O algorithm, the concept of population density is put forward and an optimal local search strategy is formulated to modify the population search efficiency and precision. Finally, comparisons with the P & O algorithm, particle swarm optimization (PSO) algorithm, and the original DA through simulation verify the validity of the proposed algorithm.

Joint Clearing Model of Day-Ahead Energy Market and Down Regulation Service Market for Accommodation of Renewable Energy

ZHANG Mingli, ZHANG Na, WU Zhikai, GAO Jing, XU Xilin, LI Jian, LV Quan

2022, 55(2): 138-144. DOI: 10.11930/j.issn.1004-9649.202101059

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In the background of the integrated market operation of the day-ahead energy trading and deep regulation service trading in Northeast China, a joint clearing model of the two market is established. The objective function of the model is to minimum the sum of the generation cost, start-up cost, and deep regulation compensation cost of thermal power units, as well as the compensation cost for renewable energy curtailment. It is subjective to the system power balance constraint, reserve constraint, and the operation boundaries of thermal power units and renewable energy generation. It realizes the global optimality for the two markets under the premise of priority consumption for renewable energy generation. It pre-clears the energy market and then re-clears the joint market. The numerical simulation shows that the joint market clearing problem can be solved within acceptable time.

Hybrid Power Generation System to Promote New Energy Consumption

YANG Kun, SUN Lei, FANG Chaoyun, ZHANG Yi

2022, 55(2): 145-151. DOI: 10.11930/j.issn.1004-9649.202105111

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Solar power is increasing day by day, and the scheduling and controllability of the previous single photovoltaic power generation system running on the grid are insufficient. A new hybrid power generation system is proposed to improve the sensitivity of scheduling. The system includes wind farms, photovoltaic power plants, solar thermal power plants and electric heaters. The electric heater is mainly to convert the excess wind and light energy into heat energy and store it in the heat storage tank of the solar power plant. By using the good scheduling and controllability of the heat storage thermal power station, it improves the rotating reserve and climbing capacity of the system, reduces the randomness and uncertainty of the scenery output, so as to improve the consumption of new energy. In order to maximize the net income of the system, the model is established to maximize the system profit under technical constraints, and the influence of the hybrid power generation system on the new energy consumption under different climate conditions is studied.

LVRT Reactive Current Index of Renewable Units Based on the Constraints of Transient Voltage

LIU Hui, WANG Kuo

2022, 55(2): 152-158. DOI: 10.11930/j.issn.1004-9649.202111041

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The renewable power gathering system often presents the characteristics of a weak AC grid. And the voltage fluctuates greatly during the failure process. The problem of renewable units being turned-off due to low voltage and transient overvoltage is prominent. This paper establishes the voltage-current relationship of the renewable power gathering system. Considering the safety constraints of low voltage and transient overvoltage, we gives the LVRT reactive current index requirements for the renewable units through theoretical derivation. Then, the renewable power gathering system is classified according to the short circuit ratio (SCR), and for systems with different SCRs, differentiated LVRT reactive current index requirements are given.

SoC-based Real-Time Simulation of MMC Electromagnetic Transient

YOU Guangzeng, SONG Zhao, GUI Zihang, LI Lingfang, ZHU Xinchun, SHU Dewu

2022, 55(2): 159-165,189. DOI: 10.11930/j.issn.1004-9649.202011104

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With the rapid emergence and profound penetration of modular multilevel converters (MMC) in power system, the real-time simulation technology of electromagnetic transient (EMT) becomes very important. In order to realize the real-time simulation of the MMC-based flexible HVDC system, a real-time System-on-Chip (SoC) simulation model is proposed for MMC, which is applicable to field programmable gate arrays(FPGA). Based on this EMT model, the MMC arm is made equivalent to one Thevenin’s circuit, which keeps the number of nodes unchangeable when MMC level varies, thus greatly accelerating the simulation process. This method can not only suppress the numerical oscillation under faults, but also realize the real-time simulation of multiple sub-modules. The PSCAD simulation results have verified the accuracy and efficiency of the proposed model and corresponding calculation method, and the dynamics of both sub-module level and system level can be reflected accurately and efficiently.

Coordinated Control of DC Microgrid System Based on Bus Voltage Stratification

LIN Qiyou, JIANG Wenliang, LI Yuanyuan, WANG Dongdong, MOU Sinan

2022, 55(2): 166-171,180. DOI: 10.11930/j.issn.1004-9649.202012071

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In a DC microgrid system, distributed units are usually connected to the DC bus in a decentralized manner, and distributed power sources and loads are easily affected by the external environment, which degrades the bus voltage stability of the DC microgrid. In order to solve this problem, a coordinated control strategy for DC microgrid system based on bus voltage stratification is proposed in this paper. The strategy builds a DC microgrid system structure mainly based on photovoltaic power generation, and then divides the bus voltage into five levels. Under the corresponding operation mode of each level, the operation mode and the control strategy are studied. Finally, the effectiveness of the proposed control strategy in suppressing the fluctuation of the system bus voltage is verified when the fluctuation of the photovoltaic power generation and the load is caused by the change of environmental factors.

Direct Power Model Predictive Control Method for DC-Side Sensor-Less Single-Phase Cascaded H-Bridges Photovoltaic Inverters

ZHANG Xi, MAO Yipeng, YU Le, YANG Hao

2022, 55(2): 172-180. DOI: 10.11930/j.issn.1004-9649.202005068

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In order to reduce the complexity of photovoltaic generation system, a direct power model predictive control method suitable for DC-side sensor-less photovoltaic inverters is presented in this paper. Based on the idea of serial calculation, each H-bridge is considered as a single inverter. In the meantime, when the optimal modulation function is being calculated for each H-bridge, the DC-side capacitor voltage of each H-bridge is reconstructed using the increment of output voltage of inverters. In addition, a term about the error of capacitor voltage is embedded into the optimal modulation function to keep capacitors’ voltages balance. After building a system model through Matlab/Simulink, the performance of the presented method is verified.

Measurement and Comparison of Magnetic Properties of 0.10 mm and 0.23 mm Oriented Silicon Steel under Different Operating Conditions

LIU Yang, GONG Xuehai, CHEN Xin, HAN Yu, YANG Fuyao, MA Guang, GAO Jie

2022, 55(2): 181-189. DOI: 10.11930/j.issn.1004-9649.202006198

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Different types of oriented silicon steels exhibit different magnetic properties in complicated power electronic equipment operating conditions. For the sake of accurate selection of oriented silicon steel type, the magnetic characteristics of 0.10 mm ultra-thin oriented silicon steel and 0.23 mm ordinary thickness oriented silicon steel were measured under different operating conditions based on the medium frequency Epstein Frame. The magnetic characteristics of two types of oriented silicon steels are revealed. According to the performance under different frequency sinusoidal magnetization, PWM pulse magnetization and special pulse magnetization conditions, the selection suggestions of oriented silicon steel under different operating conditions are given, which provides data support for the design of power electronic equipment.

Hysteresis Parameter Identification of J-A Model Current Transformer Based on Improved Whale Algorithm

LI Yilun, ZHANG Yishu, SONG Guang

2022, 55(2): 190-199. DOI: 10.11930/j.issn.1004-9649.202004178

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The accurate and rapid identification of model parameters is crucial to the simulation of the hysteresis characteristics of current transformer cores based on the J-A hysteresis model. With regard to the difficulties in measuring the input and output of the existing J-A model parameters in addition to the slow convergence speed and low accuracy of the extraction method, a parameter extraction method of the ψ-i JA hysteresis model based on the improved whale algorithm is proposed in this paper. The model is established in terms of flux linkage and current instead of flux density and magnetic field. The parameters are extracted using an improved whale algorithm with adaptive adjustment of weights and search strategies. By taking advantage of the proposed method, particle swarm algorithm, and whale algorithm respectively, the hysteresis curves of P-type current transformer and PR-type current transformer are identified and compared. The result comparison shows that the improved whale algorithm has higher accuracy and fewer iterations, such that the high efficiency of the proposed method is verified.

Heat-Treatment Optimizing Study on Soft Magnetic Properties of FeCuNbSiB Nanocrystalline Alloys

DONG Bangshao, ZHOU Shaoxiong, ZHI Qizheng, XING Yanxing, YANG Fuyao, QIAO Guangyao, HAN Yu

2022, 55(2): 200-208. DOI: 10.11930/j.issn.1004-9649.202007232

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This job was focused on the annealing technique of large-size nanocrystalline core with height of 50 mm, to meet the low core loss requirement of large-size nanocrystalline core used in large-capacity high-frequency transformer. Two typical nanocrystalline alloys, Fe_73.5Cu₁Nb₃Si_15.5B₇ and Fe_73.5Cu₁Nb₃Si_13.5B₉ ribbons (hereinafter referred to as B₇ and B₉) with the width of 50 mm, were selected to investigate the influence of annealing temperatures (330~600℃) on their soft magnetic properties and core losses. The experimental results were demonstrated that B₇ and B₉ alloys probably started to crystallize as early as annealed at 420 ℃, which is much lower temperature than the widely-held at 500 ℃. The two alloys were obtained the lowest core losses by being annealed at 550℃ and 580℃, respectively. However, they showed the highest permeability and the lowest coercivity when annealed at 500℃ and 550℃, respectively. The core losses of B₇ alloy was continued to reduce through by transversal field annealing, and the lowest value of P_cm(0.5T/20k) was 7.3W/kg, which is the lowest as far as we know. According to the measured data, the core losses of nanocrystalline magnetic core can be described by $ {P}_{{\rm{cm}}}=0.5{f}^{1.42}{{B}_{{\rm{m}}}}^{2.27} $ in fractional method, and has been confirmed by experimental results.

Dielectric and Hydrophobic Properties of Modified Magnesium Oxide/Epoxy Resin Composites

PANG Xianhai, JIA Boyan, CHEN Zhijie, GU Chaomin, ZHAO Lihua, REN Junwen

2022, 55(2): 209-216. DOI: 10.11930/j.issn.1004-9649.202107105

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To improve the electrical and hydrophobic properties of epoxy resins in switchgear equipment，the magnesium oxide nanoparticles (nMgO) are modified with silane coupling agent (KH560) and fluorinated silane coupling agent respectively, and characterized by FT-IR and XPS. And the epoxy composites of different concentrations (5%, 10%, 15% and 20%) are prepared with solution blending method, and characterized by testing dielectric constant, dielectric loss, conductivity and contact angle. The results show that the introduction of fluorine element can reduce the surface energy of the composites, and the hydrophobicity of the epoxy composites is significantly improved with the increase of the doping content, reaching 114° at 20 wt.%. The electrical properties of the epoxy composites all meet the requirements for the use of electrical equipment, with the dielectric loss being lower than the level of epoxy resin and the resistivity being higher than that of epoxy resin.

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