Coordinated Control Strategy Based on Controllable Voltage Source-Current Source Hybrid HVDC Transmission System
Xiong Yao1, Wei Xiaoguang2, Tang Guangfu2, Jiang Taosha2, Zhang Wenwen1, Li Song2, Du Hui2, Zhang Jie2, Wang Yixuan1, Qi Lei1
1. State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing 102206 China; 2. Beijing Huairou Laboratory Beijing 101400 China
Abstract：To ensure the efficient transmission of new energy from the desert and gobi Regions, China has accelerated the construction of ultra-high voltage direct current (UHVDC) transmission corridors. A large number of UHVDC projects are being arranged, deployed and continuously promoted. The controllable voltage source-current source type hybrid DC delivery scheme not only provides frequency reference and voltage support, but also has low cost, low loss, high reliability, and no phase change failure problem, so it is more suitable for large-scale clean energy delivery scenarios with complex and changing operating conditions. However, how to improve the active support capability of the converter at the sending and receiving ends after an AC fault occurs in the hybrid DC system to ensure efficient and reliable clean energy delivery and safe and stable operation of the system is still a difficult problem that needs to be solved urgently. Firstly, a mathematical model of controllable voltage-current source hybrid DC transmission system is established to depict the DC voltage, current and power operation characteristics of the hybrid DC system under the transient steady state condition.Secondly, the reactive power of the controllable current source converter is analyzed in relation to the phase angle difference and the direct current, and then a method is proposed to improve the reactive power support capability of the hybrid DC system under the AC fault at the receiving end. Thirdly, by introducing an additional active current control module based on Δivd-ΔP slope control and an additional reactive power control module, the line overload level under the AC fault condition and the voltage drop during the fault period are effectively reduced, and the reactive power support to the receiving end grid is realized, which improves the operational performance of the hybrid DC system. Finally, the correctness and effectiveness of the proposed control strategy are verified by simulation with electromagnetic transient simulation software PSCAD/EMTDC. The proposed control strategy for two-phase short-circuit faults in the AC system at the receiving end can reduce the AC voltage dips by 30.7%, while under three-phase short-circuit faults, the instantaneous value of the AC voltage can be improved by 45.5% compared with the traditional control strategy, which improves the active support capability of the converter at the receiving end, and then reduces the probability of the occurrence of the safety risk accidents of the power grid. The following conclusions can be drawn: (1) The reactive power emitted by the CSC converter at the receiving end is increased by reducing the phase angle difference during the fault period or by appropriately adjusting the line load level. (2) The proposed control strategy can actively support the AC and DC side voltages of the receiving end under the fault condition, realizing the reactive power support to the receiving end power grid. (3) Compared with the LCC-CSC system, the controllable voltage source-current source hybrid DC transmission system has strong weak-system access capability,better fault and fault recovery characteristics, which can be used as a topology scheme for large-scale clean energy transmission via UHVDC system.
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2025, Vol. 40 
