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Coordinated Control Strategy for Sending-End Converters in Wind-Integrated Real Bipolar MMC-HVDC Systems
LI Botong, LIN Mengyuan, ZHENG Guanghui, DONG Yuejin, LIU Yichao
Electric Power Construction ›› 2026, Vol. 47 ›› Issue (2) : 14-27.
PDF(2524 KB)
PDF(2524 KB)
Coordinated Control Strategy for Sending-End Converters in Wind-Integrated Real Bipolar MMC-HVDC Systems
[Objective] Modular multilevel converter based high voltage direct current （MMC-HVDC） technology with a real bipolar connection is one of the mainstream technical solutions for efficient grid connection and cross-regional consumption of large-scale islanded wind farms. It has been widely adopted in HVDC projects such as Zhangbei and Rudong in Jiangsu. However，the control strategy for the sending-end positive and negative pole converters faces the dual challenge of balancing bipolar transmission power and providing stable voltage support for the wind farm. To address this，a grid-forming coordinated control strategy for bipolar converters is proposed，which combines an active power-frequency boost scheme with a reactive power-voltage droop scheme. [Methods] The coupling mechanism among active power，phase，and frequency at the sending-end bipolar converters is analyzed. An active power-frequency boost control strategy is established，clarifying the power balance and frequency coordination of bipolar converter under wind power fluctuation and the adaptive regulation mechanism under capacity-limited conditions. The coupling relationship between the voltage and reactive power of the sending end converters and wind farm is revealed. A reactive power-voltage droop control strategy with capacity and active power constraints is established. The coordinated stability mechanism of AC bus voltage under reactive power fluctuation is investigated. [Results] Simulation results demonstrate that the proposed strategy can effectively maintain dynamic power balance between the bipolar converters and provide stable voltage and frequency support for the AC system under various conditions，including system power fluctuations and single-pole capacity limitations. [Conclusions] The grid-forming coordinated control strategy proposed can effectively address the core challenges of power balance and voltage and frequency support for the sending-end bipolar converters in islanded wind farm MMC-HVDC systems under complex operating conditions，thereby improving the operation stability of the system.
islanded wind farm / modular multilevel converter based high voltage direct current （MMC-HVDC） / sending-end bipolar converters / active power-frequency rise control / reactive power-voltage droop control / coordinated control strategy
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Because DC system usually adopts overhead line for DC transmission, its failure rate is high. When a single-pole short-circuit grounding fault occurs in the system, the unbalanced power of the fault pole can be transferred to the non-fault pole through the real-bipolar wiring mode. The unbalanced power can be divided into self-absorption and collaborative absorption according to the power margin of the converter station. For the self-absorption situation, fault ride-through can be realized by power transfer between sending end bipolar converter stations. For the situation of collaborative absorption, the coordinated control strategies between converter station and energy dissipation resistance are designed. Considering the limited input time of energy dissipation resistance, unbalanced power in DC System is reduced by sub-sequent generator cutting. Finally, the effectiveness of the proposed control strategy is verified in PSCAD. The simulation results show that the strategy can effectively avoid the expansion of fault range and ensure the safe operation of the system. |
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