应对柔性直流电网线路故障的混合型MMC直流电压目标预设控制

DC Voltage Target Predetermined Control of Hybrid MMC to Handle Line Fault of Overhead DC Grid

随着国内外基于混合型模块化多电平换流器(modular multilevel converter,MMC)的架空线柔性直流输电工程的建设,研究其直流故障穿越控制技术将具备较大的工程应用价值。为减小故障电流峰值,且加快故障清除后直流电网功率恢复速度,提出一种适用于混合型MMC的直流电压目标预设控制策略。其充分利用了混合型MMC的宽范围直流电压输出能力,通过预先设定的直流电压目标控制曲线,优化直流电压站在直流故障发生后的暂态特性。进一步研究直流电压目标预设控制的基本原理与具体实现方式。针对直流电压目标预设控制分别在两端柔性直流输电系统以及直流电网中的应用,讨论故障期间电压站直流电压预设指令值的选取方法,分析比较不同直流电压预设控制曲线对故障后直流母线电压跌落、直流母线电流峰值以及直流功率恢复时间的影响。仿真分析表明,直流电压目标预设控制能够在一定程度上降低直流故障峰值电流,并较为明显的加快直流故障清除后直流电网功率恢复速度,具备一定的工程应用前景。

With the plan for HVDC projects based on hybrid/full-bridge modular multilevel converter(MMC),the research on DC fault ride through control of hybrid MMC is an urgent demand for engineering application.To reduce the peak value of DC fault current,and accelerate the recovery of the DC power,this paper proposed a DC voltage predetermined control for hybrid MMC.It optimized the transient characteristics of the DC voltage station after the DC fault.The fundamental principle and design method of DC voltage predetermined control were disclosed in this paper.The selection principle of DC voltage reference during the DC fault was discussed in the view of the application both in two-terminal HVDC system and DC grids.The influence of different DC voltage predetermined curves on the drop of DC bus voltage,the peak of DC current,and the recovery of DC power transmission were analyzed.Simulation analysis shows that the DC voltage predetermined control can reduce the peak value of DC fault current to a certain extent,and significantly accelerate the DC power recovery after DC fault,which has certain engineering application prospects.