受端电网故障下真双极柔性直流输电系统电压协同控制方法  

A Voltage Collaborative Control Method for Symmetrical Bipolar MMC-HVDC under the Receiving-End Grid Fault

作　　者：熊俊 甘文风 陈愚 陈柏汗 于乐 XIONG Jun;GAN Wenfeng;CHEN Yu;CHEN Baihan;YU Le(Southwest Branch of State Grid Corporation of China,Chengdu 610041,Sichuan,China)

机构地区：[1]国家电网有限公司西南分部,四川成都610041

出　　处：《电网与清洁能源》2024年第5期32-41,51,共11页Power System and Clean Energy

基　　金：国家电网有限公司科技项目(SGSW0000DDKZZXJS2200080)。

摘　　要：盈余功率积累可能诱发基于模块化多电平换流器的高压柔性直流输电系统(high-voltage direct current based on the modular multilevel converter,MMC-HVDC)过压闭锁,乃至引发海上风电场机组失步或受端电网低频减载。现有降压或升频等直流电压控制方法仅针对伪双极接线,缺乏讨论不同控制模式的换流器间协同原则;且控制参考值未能自适应受端电网的故障严重程度,导致海上风电场有功功率调节过量。该文基于受端电网故障下MMC-HVDC平均值模型,解析了海上正负极换流器和风电场的功率耦合特性,提出了交流母线电压控制极换流器平衡换流站间有功功率,有功和无功功率控制极换流站抑制极间不平衡的协同原理。通过解析海上风电场在交流母线电压控制极换流器降压作用下的功率外特性,提出了恰好避免直流电压越限的临界交流母线电压计算方法。通过解析使得受端换流站有功电流受限的交流母线电压作为启动门槛,提出了受端电网故障下真双极MMC-HVDC电压协同控制方法。理论分析和仿真结果表明,所提方法令海上正负极换流器分别运行于临界交流母线电压和抑制极间不平衡的有功功率,可在避免直流电压越限的前提下,最大限度提升MMC-HVDC在受端电网故障工况下的有功功率传输能力。Surplus power accumulation may induce over-voltage blocking of high-voltage direct current based on the modular multilevel converter(MMC-HVDC),which may even lead to the tripping of offshore wind farms or low-frequency load shedding of the receiving-end grid.The existing DC voltage control methods,such as voltage or frequency modulation,are only for pseudo-bipolar,which lack discussions on the principle of coordination between converters with different control modes.In addition,the control reference value fails to adapt to the fault severity of the receiving-end grid,which leads to the over-regulation of active power in offshore wind farms.To this end,this paper analyzes the power coupling characteristics of offshore positive and negative converters and wind farms based on the MMC-HVDC average model under receiving-end grid faults and proposes the coordination principle of balancing the active power between converters based on the converter with a fixed AC bus voltage vector,and suppressing the inter-pole imbalance based on the converter with a fixed active and reactive power.By analyzing the power external characteristics of offshore wind farms under the effect of the converter with a fixed AC bus voltage vector voltage reduction,a critical AC bus voltage calculation method is proposed to avoid DC overvoltage precisely.By analyzing the AC bus voltage that makes the active current of the receiving-end converter limited as the startup threshold,the cooperative voltage control method for symmetrical bipolar MMC-HVDC under receiving-end grid fault is proposed.Theoretical analysis and simulation results show that the proposed method enables the positive and negative converters of the offshore end converter to operate at the critical AC bus voltage and the active power that suppresses the inter-pole imbalance,which can maximize the power transfer capability of MMC-HVDC under the fault condition of the receiving-end grid while avoiding the DC voltage overrun.

关 键 词：真双极 柔性直流输电系统 交流故障 协同控制 直流电压 

分 类 号：TM46[电气工程—电器]