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RSS2023 Vol. 10, No. 5
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2023, 10(5): 1-1.
Abstract:
The new power system is an important component of the new energy system and a key carrier for achieving the "carbon peak and neutrality" goal. The Rreport to the 20th National Congress of the Communist Party of China emphasizes that it is necessary to accelerate the planning and construction of a new energy system to ensure energy security. The construction of an advanced DC transmission system that is digitalized, informatized and intelligent plays an important role in promoting the evolution of the traditional energy system towards a clean, low-carbon, safe, and efficient new power system. The period covered by the 14th Five-Year Plan is a critical window period for achieving the carbon peak goal as well as an opportunity period for promoting the construction of a new energy supply and consumption system based on large-scale wind and photovoltaic power bases, with stable, safe and reliable UHV transmission and transformation as the carrier. Currently, the construction of the new power system has made phased progress, but the large-scale reliable transmission and efficient utilization of new energy still face multiple challenges such as optimizing the network of the sending end system, enabling long-distance VSC-HVDC transmission, and ensuring stable operation of the receiving end system.In this context, Southern Energy Construction planned a special topic on "DC transmission technology for new power system construction", closely tracking the relevant hotspots and industry dynamics in the field of new power system construction and advanced DC transmission technology in China. We sincerely invite frontline teachers from universities and frontline engineers and R & D personnel from enterprises to share the latest research findings and industry dynamics. Through the collision of sparks of thought in this issue, we hope to provide valuable ideas for the high-quality and sustainable development of China's DC transmission technology.We would like to express our sincere gratitude to the authors, peer reviewing experts and readers for their support of this special topic. We hope that the publication of this special topic can provide a valuable reference for experts and scholars who are concerned and engaged in related research, thereby promoting the rapid development of basic theories and key technologies in the field of DC transmission. Introduction to Special Editors-in-Chief Dr. Yuan Zhiyong is a professor-level senior engineer and the director of HVDC Transmission & Power Electronics Technology Institute of CSG Electric Power Research Institute Co., Ltd. He has been engaged in research and engineering practice in the fields of DC transmission and smart grid technology for a long time. He has participated in the complete design of several HVDC and UHVDC transmission projects, as well as multiple projects under The National Key R & D Program of China. He has also worked as a postdoctoral fellow at Virginia Tech and The University of Tennessee in the United States. He currently serves as a member of multiple standardization organizations including the Electricity Quality and Flexible Transmission Standards Committee in the power industry and the Distribution System Standards Committee in the energy industry. He has received multiple awards such as the First Prize of the Mechanical Industry Science and Technology Award and the First Prize of the China Electric Power Innovation Award, published more than 30 SCI/EI papers and holds more than 10 licensed invention patents. Currently , Dr. Yuan Zhiyong is leading a team to engage in research and development and engineering applications in various fields, including new energy DC transmission systems, high-power power electronics technology, MVDC and LVDC distribution systems, and new energy storage technologies.Sun Potao is an associate professor at the School of Electrical Engineering, Chongqing University. He holds a doctoral degree and is a doctoral supervisor. He has been selected for the "Youth Talent Promotion Project" of the Chinese Society for Electrical Engineering and the "Chongqing Talent • Youth Top Talent Plan." He has served as the organizing committee chairman, publishing committee chairman, and session chairman for multiple international conferences including IEEE ICHVE, IEEE ICEMPE, and ISH. He once served as an Associate Editor/Editorial Board Member of WSEAS Trans. Power Syst. journal. He is currently a youth member of the CIGRE China National Committee, and a member/secretary of the IEEE P3196 International Standards Working Group. In the past five years, Sun Potao has undertaken three projects funded by the National Natural Science Foundation of China, one subproject of the National Key R & D Program, one pre-research project funded by the Equipment Development Department of the Central Military Commission, one project funded by China Postdoctoral Science Foundation, and one special project funded by the Chongqing Postdoctoral Fund. He has participated as a lead researcher in one key project funded by the National Natural Science Foundation of China and two projects under the 973 Program. Sun Potao has published over 40 papers, including over 30 papers published by him in the capacity of first author/corresponding author in SCI journals such as Chem Eng. J., Adv. Sci, ACS Appl. Mater. Inner., Appl. Phys. Lett., and IEEE Trans. He has also applied for and been granted more than 10 licensed invention patents. In addition, he has guided university students to win six provincial and ministerial gold awards and one silver award in the “Internet+” Undergraduate Innovation and Entrepreneurship Competition. He has also received the Winning Prize of the National Postdoctoral Innovation and Entrepreneurship Competition.
2023, 10(5): 1-8.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.001
Abstract:
Introduction Due to the dense load, complex grid structure, and close electrical connections in the Guangdong power grid area, there are three major problems for a long time: the risk of large-scale power outages, the interaction between AC and DC, and the excessive short-circuit current, making it difficult to meet the needs of future power load development and flexible system regulation. Method To address the above issues, a high-performance VSC-HVDC (Voltage Source Converter-based High Voltage Direct Current) back-to-back project was constructed in the core area of Guangdong Power Grid, and a new generation of high-performance VSC-HVDC back-to-back technology was studied and adopted. The VSC-HVDC interconnection control of complex power grids, the development of highly reliable and high-performance converter valves, and the design of green and efficient converter stations were deeply studied. The upgrade of VSC-HVDC back-to-back technology was achieved. Result The project successfully achieved automatic control of asynchronous power flow, significantly reducing the link delay of the control and protection system, developed high-performance and highly reliable VSC-HVDC converter valves, and optimized the design in terms of noise reduction, loss reduction, water conservation, and other aspects of the converter station. A comprehensive perception system for the converter station was built, achieving intelligent operation and maintenance. At present, the project is running well. Conclusion The VSC-HVDC back-to-back project of Guangdong Power Grid has solved the three major stability problems faced by the multi DC feeder receiving end grid for a long time and enhanced the long-term safe and reliable power supply capacity of the Guangdong-Hong Kong-Macao Greater Bay Area.
2023, 10(5): 9-16.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.002
Abstract:
Introduction Due to its flexibility and rapid control ability, voltage source converter based high voltage direct current (VSC-HVDC) technology can be used in asynchronous grid interconnection, renewable energy grid-connection, and urban grid power supply. In this paper, the flexible and compact interconnection scheme of urban power grid is proposed to realize the interconnection and improve safety and stability of the urban power grid. Method According to the current situation of the power grid, and considering the difficulty of implementing new transmission lines in urban areas and the difficulty of controlling the construction period, the site selection and interconnection scheme were carried out from the perspective of exploiting potential of existing substations and transmission lines. The interconnection scale was determined comprehensively by combining the system requirements, the transmission capacity of the original lines, and the feasibility of capacity increase transformation. Due to the shortage of urban land, compact equipment and indoor compact layout was recommended. Result The flexible and compact back-to-back converter station is adopted to realize the interconnection, significantly reduce the short-circuit current level of the system and improve the security and stability of the urban power grid. The compact design which can save about 40% of the space is adopted to meet the need to alleviate the scarcity of urban land resources. Conclusion The compact and flexible interconnection proposed plays a good role in guiding the application of VSC-HVDC technology in urban power grid interconnection and has high reference value.
Research on the Design of Operating Condition of Multi-Resistance Superconducting DC Current Limiter
2023, 10(5): 17-23.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.003
Abstract:
Introduction The working principle of the resistive superconducting current limiter is based on the zero resistance effect of the superconductor, which is connected in series in the line and basically has no resistance during normal operation. When the circuit is short-circuited and the current exceeds the critical current, the superconductor loses excess and the resistance value increases rapidly, which plays a role in limiting the short-circuit current. So the superconducting DC (Direct Current) current limiter has little effect on the power grid when it is in normal operation. When the system short-circuit current exceeds the critical current, it will quickly limit the current value, effectively reducing the requirements for DC equipment. Based on Nan'ao ±160 kV multi-terminal VSC-HVDC (Voltage Source Converter Based High Voltage Direct Current) system, the possible operating conditions of superconducting DC current limiter are discussed, and how to realize the possible operating conditions is analyzed. Method For the five possible operating conditions, it was recommended to set disconnector to achieve automatic switching of operating conditions. Result The proposed scheme of electrical connection and compact layout is given based on the configuration of the equipment. And according to different operating conditions, the corresponding current path diagram is given. Conclusion The possible working conditions of superconducting DC current limiter and the automatic switching electrical connection and compact layout can be obtained by similar analysis for other flexible DC transmission systems.
2023, 10(5): 24-33.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.004
Abstract:
Introduction Under the existing converter station reactive power compensation scheme, the synchronous condenser only provides transient reactive power support, and the AC (Alternating Current) filter undertakes steady-state reactive power compensation and adjustment tasks, with a lack of coordination scheme between the two and insufficient economy. Method On the basis of ensuring the dynamic characteristics of the synchronous condenser, based on the operating characteristics of the DC (Direct Current) sending and receiving end systems, firstly, a reactive power optimization scheme for the converter station was proposed, in which the regulator was used to replace a part of the part of the AC filter capacity with the regulator, and both participated in steady state reactive power compensation. Ubsequently, a two-layer reactive power adjustment strategy for the converter station was proposed according to the sequence of actions. The first layer of reactive power adjustment was undertaken by the synchronous condenser, which was realized by adjusting the output within the range of steady state operation. The second layer of reactive power adjustment was started after the first layer of reactive power adjustment, and the AC filters were switched on group by group for reactive power adjustment until the reactive power adjustment requirement of the converter station was reached. Finally, a LCC-HVDC (Line-Commutated Converter High Voltage Direct Current) system simulation model was built in PSCAD for simulation verification. Result The simulation results show that the reactive power compensation scheme and the two-layer reactive power adjustment strategy proposed can optimize the number of AC filter configuration groups in the converter station, reduce the frequency of AC filter switching in the converter station. Conclusion The proposed scheme achieves optimization of the existing LCC-HVDC converter station reactive power compensation scheme and reactive power adjustment strategy.
2023, 10(5): 34-40.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.005
Abstract:
Introduction With the continuous improvement of the strategic position of clean energy, more and more new energy power generation equipment is connected to the power grid, but its power quality is unstable, which has a great impact on the AC (Alternating-Current) transmission grid. Flexible DC (Direct-Current) transmission networks can effectively isolate AC and the DC networks, and have good development prospects. The key component of flexible DC power transmission is the converter valve. The key component of flexible DC power transmission is the converter valve with fully controlled IGBT components as the core. Therefore, the safe and stable operation of IGBT (Insulate-Gate Bipolar Transistor) components plays an important role in the stability of the entire flexible DC system. In order to improve the safety and operational stability of IGBT components, it is necessary to control their operating current and voltage to avoid overcurrent and overvoltage damage. At the same time, it is necessary to control the temperature and humidity of the environment, equipment corrosion resistance to improve operating conditions. Method Therefore, both internal and external strategies were adopted. Starting resistors, reactors, lightning arresters, etc. were installed internally to control the current and voltage of the circuit. Externally, air conditioners were set, the room tightness was improved, and equipment anti-corrosion treatment was equipped to ensure a good working environment. Result By configuring starting resistors, reactors, lightning arresters and other facilities in the internal circuit, the circuit current and voltage are limited, and then the overcurrent multiple and overvoltage multiple acting on the IGBT components are controlled under extreme conditions. By controlling the temperature and humidity of the room where the IGBT is located and the corrosion resistance of the equipment, a suitable environment is provided for the operation of the IGBT components, which is helpful to improve the safety and operational reliability of the IGBT components. Conclusion Flexible DC transmission can well solve the power transmission problem of new energy power generation facilities with poor power quality. And by optimizing the internal strategy of the flexible DC transmission system circuit and the external strategy to improve the suitability of the operating environment of the IGBT components, the safety and operational reliability of the IGBT components and even the entire flexible direct current system are improved.
2023, 10(5): 41-49.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.006
Abstract:
Introduction In response to the pain points of the operation and maintenance of the converter station, the design methods of the three-dimensional digitization and intelligent operation system are proposed, and the actual application is performed in the project. Method Firstly, the overall architecture, technical architecture, data architecture and functional modules of the system were explained, and by using digital twin technology, operation and maintenance services such as intelligent inspection, intelligent operation, and intelligent security were realized. Then the key technologies of the system were studied, including converter station modeling and refined processing, model and data fusion technology, and panoramic visualization technology, which realized the centralized operation and control of the whole site in the three-dimensional scenarios. Finally, the system was deployed at the project site, which greatly improved operation and maintenance efficiency and experience. Result The application of the system shows that the manual replacement rate of daily intelligent inspection projects reaches more than 80%, the on-site operation time can be reduced by 60%, and the operating risk management and control capabilities and safety levels are improved, saving 65% of working hours. Conclusion The three-dimensional digitalization and intelligent operation system of the converter station can effectively improve the accurate management of the equipment, and realize the cost reduction and benefit increasing of the operation and maintenance business.
2023, 10(5): 50-56.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.007
Abstract:
Introduction With the rapid development of AC/DC distribution networks and distributed generation technology, the role of DC microgrids in distribution networks is becoming increasingly important and will become an important component of future distribution networks. Due to the small coverage area and low line impedance of the DC microgrid, when an inter pole short circuit fault occurs, the fault current increases rapidly and has a large amplitude, which can reach more than 10 times the rated working current. This makes it difficult to set the protection of DC microgrids and requires high equipment selection, which restricts the rapid development of DC microgrids. Method In response to the above issues, taking the DC microgrid as the research object, starting from the working principle of inter pole faults in the DC microgrid, the fault characteristics on the DC side of the DC microgrid were analyzed. In response to the shortcomings of existing main current limiting methods, a voltage controllable fault current controller was proposed to achieve precise control of fault current. The simulation model of DC microgrid and fault current controller was built for simulation verification. Result The simulation results show that the fault current controller can significantly reduce the fault current and achieve precise control of the fault current, making the system controllable before and after the fault without locking the protection. During steady-state operation, the fault current controller can also assist the VSC (Voltage Source Converter) in further stabilizing the DC bus voltage. Conclusion To cooperate with the normal operation of the relay protection device and avoid VSC triggering overcurrent protection blocking, it is recommended to set the fault current control range between 1~2 pu.
2023, 10(5): 57-64.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.008
Abstract:
Introduction With the rapid development of power electronic equipment and artificial intelligence and other high-tech, DC (Direct Current) system has been popularized and applied in substations. The grounding fault of the substation DC system has become an important factor affecting the safe and stable operation of the substation. Method Firstly, the DC system of the substation was introduced, and its components, typical types of DC ground faults and their adverse effects were analyzed. Then, the principle of five common DC ground fault finding strategies was emphasized. Result Based on their respective research status and application scenarios, the advantages and disadvantages of various finding strategy are compared and analyzed. Conclusion Combined with the existing problems and technical development trends, the future research directions of DC grounding fault detection at home and abroad are prospected from the perspectives of accurate fault location, complex fault identification, finding accuracy and the improvement of the endurance of portable insulation detection device.
2023, 10(5): 65-71.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.009
Abstract:
Introduction With the development of new loads, such as distributed power sources and electric vehicles, DC(Direct Current) microgrids have the advantages of fewer commutation links and lower system losses than AC(Alternating Current) microgrids, and have become the current research hotspot. Due to the small coverage of the DC microgrid and access to a large amount of distributed power sources, the fault current rises quickly with a large amplitude when inter-pole short-circuit fault occurs, making it difficult to achieve differential coordination with traditional overcurrent protection used in AC distribution networks and posing a great challenge to fault localization. Method Therefore, in response to the characteristics of fault current in DC microgrids, the method for designing overcurrent protection setting value based on the precise control value of fault current through the integration of current limiting and protection was proposed. Combined with the reasonable capacity design of each branch, it can easily achieve differential coordination and accurately locate faults. Result A corresponding DC microgrid model is built on the PSCAD/EMTDC simulation platform. The proposed protection scheme is simulated and verified, and the result shows that the scheme can correctly locate the fault point and quickly remove the fault. Conclusion The proposed protection scheme can ensure the selectivity of overcurrent, which verifies the rationality of the scheme.
2023, 10(5): 72-79.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.010
Abstract:
Introduction This article aims to study the issue of the melting capacity and reactive output capacity of the full bridge modular multi-level converter (MMC) type DC (Direct Current) melting ice device under different operating modes. Method Calculation of current AC (Alternating Current) component, DC component, rms value and peak value of bridge arm converter of full-bridge MMC type DC ice melting device, selection of number of bridge arm modules, IGBT (Insulated-Gate Bipolar Transistor) power module support capacitance calculation, bridge arm reactor inductance calculation, start-up loop resistance calculation were elaborated; The maximum reactive power output capacity of the device under the set ice melting capacity and the maximum ice melting capacity of the device under the set reactive power output capacity were analyzed in detail, and the coupling relationship and decoupling calculation between the ice melting capacity and the reactive power output capacity were explored. Result Research has shown that there is a coupling relationship between the melting capacity and reactive output capacity after the parameters of the melting device are determined. Conclusion The reason is that the bridge arm current contains both AC and DC components, and the AC component is determined by both the melting mode and reactive compensation mode, while the DC component only depends on the line melting current.
2023, 10(5): 80-86.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.011
Abstract:
Introduction The potential positive feedback of virtual inertia and damping control (VIDC) may exacerbate the interaction within the control loop, causing low-frequency oscillation of bus voltage and disrupting the stability of electric vehicle DC charging station (EVCS). Although the existing multi-timescale impedance model explains the stability mechanism of VIDC and the low-frequency oscillation mechanism of VIDC-controlled-EVCS, it is essentially a high-order transfer function, making it difficult to obtain analytical expressions for damping control strategies. Method Therefore, a detailed impedance analysis of the virtual impedance of the loop was conducted to intuitively reveal the fundamental reasons for the higher-order properties of each loop impedance. Result A closed-loop gain fitting method for the control loop was proposed through Bode diagram approximation, and a low-order impedance circuit model was established. Conclusion The effectiveness of the proposed multi-timescale impedance model is verified through Matlab/Simulation.
2023, 10(5): 87-93.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.012
Abstract:
Introduction Unlike the independent grounding electrode, shared earth electrode is connected to multiple DC (Direct Current) systems, and its parameters and operation mode need to be determined by each system connected to it. There are mutual influences between systems, and various factors need to be considered comprehensively during design. Method By using CDEGS, the mutual influence factors and laws between the two grounding electrodes were analyzed, especially the mutual influence between the deep well grounding electrode and the vertical grounding electrode. Then the influence on the step potential with the same polarity operation and different polarity operation when multiple grounding electrodes operate and share at the same time in the actual scenario was studied. Result The simulation results show that the degree of interaction between grounding electrodes changes with the change of soil resistivity characteristics and the distance between electrodes. The influence of deep well grounding electrode on vertical grounding electrode is different from that of vertical grounding electrode. Conclusion The general law of interaction between vertical grounding electrode and deep-well grounding electrode is studied in this paper, which can provide theoretical and technical support for the scheme of shared grounding electrode, and opens up new ideas for the design of grounding electrode in the future.
2023, 10(5): 94-105.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.013
Abstract:
Introduction As an important thrust of China's "new infrastructure", internet data centers have ushered in opportunities for vigorous development and become new areas of energy use, putting forward higher requirements for the power supply level and capacity of the local distribution network. The innovative application of flexible transmission and distribution technology and key equipment makes the power supply and distribution system more intelligent, more flexible and more reliable, and more able to cope with the challenges brought by the large proportion of DC loads and concentrated high-load energy loads such as Internet data centers, and realize the construction and operation of Internet data centers more low-carbon, more efficient, more reliable and more economical. Method Firstly, the basic load requirements of Internet data center were discussed, the overall classification and performance requirements of internet data centers were analyzed. The application of flexible technology in distribution network was studied, with a focus on analyzing and comparing three types of technical routes: "rectification distribution, DC distribution, and AC-DC hybrid power supply and distribution". Result The paper provides provides tailored solutions for issues related to system reliability, stability, power quality, power efficiency and acceptance of new energy. Conclusion By summarizing the existing research results, flexible transmission and distribution technology is regarded as the core technology of building internet data center. Targeted data center control scheme should be studied from different aspects such as device and algorithms. After summarizing the research results of different aspects, the paper also looks forward to the practice and popularization of head-to-head transmission and distribution technology in internet data center.
2023, 10(5): 106-115.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.014
Abstract:
Introduction Lithium iron phosphate battery storage power plants are an important basis for new power systems to consume large-scale new energy, however, the thermal runaway of battery cells seriously threatens the operational safety of storage power plants. It is important to conduct real-time monitoring and scientific warning of local overheating in storage power plants. Method In this work, a thermal microcapsule with the ability to sense overheating temperature and produce colour changes was prepared and added in appropriate amounts to an epoxy resin matrix to form a composite insulating material with the characteristics of sensing external overheating temperature fields. Result Test results show that the colour of the prepared thermosensitive microcapsule/epoxy insulating temperature indication coating can change sensitively with external temperature changes, with a sudden colour change occurring at around 60 °C. When the doping mass fraction of the thermosensitive microcapsules is 0.25%, the insulation strength and dielectric properties of the composite coating are comparable to those of the pure epoxy resin material, maintaining good intrinsic electrical properties. Conclusion The thermosensitive colour-changing composite insulation coating proposed in the study can visibly change the temperature of the external local overheating state, providing a new technical route for the application of thermal runaway warning in energy storage power plants, which has certain engineering application value.
2023, 10(5): 116-128.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.015
Abstract:
Introduction The galloping of transmission lines will lead to trip, worn hardware, broken insulator string, damaged tower-arm and other accidents. In serious cases, collapsed tower accidents may occur. Therefore, it is very meaningful to establish the galloping model of transmission lines and analyze its galloping. Method Classic and cutting-edge literature at home and abroad was systematically studied, and the research status about bending stiffness, aerodynamic coefficient, numerical simulation, and the analytic method of galloping equations was comprehensively summarized. The advantages and disadvantages of existing research was analyzed, and the development trend of transmission lines galloping topics was summarized here. Result The relevant results will have high reference value for the development of iced transmission lines galloping in China. Conclusion At this stage, the research of iced transmission lines galloping has made certain progress and conclusions, but there are still many challenges and problems to be solved.
2023, 10(5): 129-138.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.016
Abstract:
Introduction The rapid development of VSC-HVDC provides practical support for MMC (Modular Multi-Level Converter) topology. Takes a half bridge MMC converter as an example, the relationship between steady-state capacitor voltage fluctuation, harmonic interaction, and bridge arm switching function of MMC is studied in order to provide theoretical support for MMC system design and control strategy. Method By establishing analytical expressions for the sub module capacitor voltage and bridge arm switch function, the mathematical approximate expressions for the energy fluctuation and capacitor voltage fluctuation of the upper and lower bridge arms of the MMC converter were obtained. Furthermore, the distribution law of harmonics in the upper and lower bridge arms current, AC (Alternating Current ) valve side, and DC (Direct Current) side, as well as the positive and negative sequence relationship of inter phase circulation were studied. Based on the harmonic formula, an estimation method for the secondary circulation was obtained; Furthermore, the variable comparison method was used to study the relationship between the switching function of the bridge arm and the voltage of the submodule capacitance with the valve side power factor and the size of the submodule capacitance. Finally, a detailed PSCAD/EMTDC model was built based on actual engineering parameters, and a consistency comparison between theoretical analysis and offline simulation was conducted. Result The research has shown that the inter phase circulating current of MMC only contains even harmonics, with 6k+2 circulating currents exhibiting negative sequence, 6k+4 circulating currents exhibiting positive sequence, and 6k circulating currents exhibiting zero sequence characteristics. At the same time, under steady-state conditions, the AC voltage and current flow at the outlet of MMC valve side only contains odd harmonics, while the DC voltage and current flow at MMC DC side only contains even harmonics, and at the power factor angle φ<0, the peak value of the bridge arm switch function will be greater than 1, and the peak voltage fluctuation of the module capacitor at low power factor is greater than that at high power factor. Conclusion Based on this, we can select and design capacitor for MMC inverters and carry out the transient stability strategies, also, master the operational characteristics of MMC topology through theoretical analysis.
2023, 10(5): 139-148.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.017
Abstract:
Introduction Low-frequency alternating current power transmission technology has attracted wide attention. Although its theoretical research continues to go deeper, there are still many problems to be solved before its engineering implementation in large-capacity long-distance offshore wind power transmission scenarios. The development and selection of offshore low-frequency main transformer is one of such problems. Method Based on the detailed description of the structure and working principle of the low-frequency alternating current transmission system for offshore wind power, the low-frequency operation characteristics of the offshore main transformer were analyzed. Result If the transformer is transformed by increasing the core section and winding turns, the weight, volume and total loss of the low-frequency transformer will be increased greatly, which will have a great impact on the economy of the overall transmission scheme of offshore wind power and the load and layout of offshore step-up station. It is necessary to study the miniaturization, light weight and low loss design of offshore low-frequency transformer. Conclusion The key transformation technologies of offshore low-frequency transformer are discussed in detail. In the aspect of transformer core, the research and development of high-performance oriented silicon steel sheet with high magnetic density or low loss is the most concerned low-frequency transformer transformation technology. With the offshore advantages, the design of water cooling mode and intelligently monitored transformer cooling mode can also optimize the overall quality and volume of transformer. Ester high ignition point insulated oil transformer has the advantages of biodegradability, inflammability and high reliability of oil, which means that it is more suitable for offshore low-frequency transformer compared with the conventional mineral oil transformer. The future development of the above key technologies is expected to provide reference for the development and application of large-capacity and high-voltage class offshore low-frequency transformer, so as to promote the engineering practice of low-frequency technology in the field of large-capacity long-range offshore wind power transmission.
2023, 10(5): 149-156.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.018
Abstract:
Introduction The correct topology information recorded by the power supply department can help the staff monitor the power grid information, analyze the faults, and optimize the operation of the power grid to meet the needs of lean and intelligent management of low-voltage distribution networks. At present, the addition of various new types of electricity-using equipment and users has caused the low-voltage distribution network structure to show a continuous change in characteristics, and the line maintenance cost is greatly increased. Method Therefore, the identification method of low-voltage distribution network attribution relationship based on density clustering was proposed. First, the effective voltage data collected by smart meters were extracted to generate a high-dimensional time-series voltage matrix. Then, the t-distributed Stochastic Neighbor Embedding algorithm (t-SNE) and Density-Based Spatial Clustering of Applications with Noise algorithm (DBSCAN) were applied to cluster the voltage data to achieve identification of low-voltage distribution network attribution relationship. Finally, the actual data of a low-voltage distribution network in Sanya City, Hainan Province were analyzed, and the proposed method is compared with other mainstream topology identification methods. Result The analysis results show that the proposed method can achieve more than 95% of identification accuracy, which is higher than other mainstream topology identification methods. Conclusion The proposed method is effective and advantageous in solving such problems, and can provide reference for practical engineering applications and offer a different research idea in the field of topology identification of low-voltage distribution network.
2023, 10(5): 157-165.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.019
Abstract:
Introduction The application of UPFC (Unified Power Flow Controller) is to increase the transmission capacity of key sections, which mainly through the injection of a certain series voltage into the system and therefore divert the power flow of target line. Method Focusing on the key transmission sections, the regional power grid was divided into the transmission network, the interconnection network and the internal network based on their function, then the Gaussian elimination method was used to equalize the system network into a two-channel constant power exchange system. On this basis, based on the energy conservation principle, the phasor method was applied to provide phasor graph of the voltage, power angle, impedance, and active power relationship between the UPFC branch and the equivalent branch before and after the UPFC was put into operation, respectively, for the stand-alone infinity system and the constant power exchange system. The classical power transfer function was used to deduced the UPFC injection voltage and series converter capacity calculation formula. Result The calculation method is simple and practical, especially suitable for power system planning and design stage. Conclusion The above method is applied to the calculation of Shenzhen power grid example, and compared with the simulation results of PSCAD, the validity and practicability of the method are verified.
2023, 10(5): 166-173.
doi: 10.16516/j.gedi.issn2095-8676.2023.05.020
Abstract:
Introduction With the development of new energy, the influence of new energy uncertainty and time characteristics on power grid is increasing day by day. Traditional new energy indexes are difficult to describe the interaction between power grid and new energy. It is necessary to establish evaluation system and index to quantify the impact of new energy on power grid. Method Construct the evaluation system from multi-dimensional and multi-scale and establish new energy output characteristic index, electric quantity characteristic index, peak regulation characteristic index and flexibility demand index to analyze the new energy output characteristics, the relationship between new energy output and electric quantity, the influence of new energy on peak regulation and the influence of new energy fluctuation on power grid at critical moments. Typical scene features were mined by applying indexes from different time scales such as year, season, month, day and hour. Result All kinds of indexes of the evaluation system has been calculated by taking the actual wind power, PV power and load in a certain area as an example. The results show quantitatively the influence of regional new energy on power grid and its distribution characteristics at different time scales. The engineering practicability of the proposed index system is verified. Conclusion The proposed index calculation method is quick and simple and the physical meaning of indexes is clear and intuitive and helpful to guide the planning and dispatching of new energy.
