Control Strategy and Test of Offshore Wind Flexible Low Frequency Transmission Converter
Gao Shilong1,2, Chen Wu3, Yang Yong2, Wang Jialong2, Zhao Haixi3
1. School of Cyber Science and Engineering Southeast University Nanjing 210096 China; 2. State Grid Economic and Technological Research Institute Co. Ltd Beijing 102209 China; 3. School of Electrical Engineering Southeast University Nanjing 210096 China
Abstract：As a useful supplement to power frequency AC transmission and DC transmission, flexible low-frequency transmission can be applied to scenarios such as medium and long-distance offshore wind power transmission, onshore new energy collection and transmission, power flow evacuation in DC landing areas, multi Island interconnection and cable urban power supply, and long-distance transmission in remote areas. In the offshore wind power grid connected system, the low-frequency transmission technology can overcome the problem of large proportion of capacitive reactive power consumption when the traditional AC transmission is carried out through the submarine cable for long-distance transmission, and realize the advantages of long-distance power transmission without the need for offshore converter station, so it is very suitable for the application of offshore wind power grid connected system. Modular multilevel matrix converter (M3C) has important application prospects in offshore wind power scenarios due to its advantages of low output harmonic content and high equivalent switching frequency. Compared with modular multilevel converter (MMC), M3C converter uses 9 H-bridge cascaded bridges to form a matrix structure, which has complex structure, and each bridge arm bears the peak voltage of I/F and low frequency, and the control strategy is complex. Firstly, based on the working principle and mathematical model of M3C converter, this paper proposes the operation control strategy of M3C converter, including power frequency side control and low frequency side control. The power side control is divided into power module voltage control (power side outer loop control) and current side control. The low frequency side control is divided into low frequency side power side outer loop control and current side control; Aiming at the complex characteristics of voltage fluctuation of low-frequency converter M3C converter module and the requirements of bridge arm circulation control, a new voltage balancing and bridge arm circulation control strategy is designed. Secondly, this paper puts forward the design scheme of M3C converter, bridge arm reactor and valve control system of offshore wind power flexible low-frequency converter, and develops a 10KV 10MW water-cooled offshore wind power low-frequency converter based on M3C converter. Finally, the whole machine operation test system was built to carry out the sequence control active soft start and power module voltage balancing test, inverter de locking and whole machine test, and inverter reactive power test. The test shows that the low-frequency transmission converter of offshore wind power meets the requirements of practical application, and provides reference for engineering application design. Flexible low-frequency power transmission has the advantages of low line charging power, zero crossing interruption, variable voltage and so on, and can directly output low-frequency power by using wind turbines without offshore converter platform. It is one of the ways of efficient collection and transmission of large-scale new energy. In the future, the typical application scenarios of flexible low-frequency technology will be further expanded, and the low-frequency networking planning, design and engineering application of large-scale offshore wind power systems will be carried out by taking advantage of the flexible networking of low-frequency systems .
高仕龙, 陈武, 杨勇, 王加龙, 赵海熙. 海上风电柔性低频输电换流器控制策略及试验[J]. 电工技术学报, 2024, 39(zk1): 77-94.
Gao Shilong, Chen Wu, Yang Yong, Wang Jialong, Zhao Haixi. Control Strategy and Test of Offshore Wind Flexible Low Frequency Transmission Converter. Transactions of China Electrotechnical Society, 2024, 39(zk1): 77-94.
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2024, Vol. 39 
