基于附加改进有源滤波器的柔性直流输电系统高频振荡抑制策略

High Frequency Oscillation Suppression Strategy for Flexible HVDC System Based on Improved Active Filter

模块化多电平换流器型柔性直流输电系统(MMC-HVDC)的高频振荡现象是由控制链路延时导致的负阻尼特征与交流系统阻抗相互作用而引发的。目前大部分高频振荡抑制策略在抑制高频振荡的同时易引起中低频段的振荡。建立了包含链路延时环节的MMC高频阻抗数学模型以及交流系统高频阻抗数学模型,分析高频振荡现象产生的机理。由此提出在内环控制中的电压前馈环节附加改进有源滤波器的高频振荡抑制策略,详细设计了滤波器的控制参数,并与电压前馈环节仅附加带阻滤波器的抑制策略进行比较。最后通过电磁暂态仿真验证了该抑制策略不会影响系统稳定运行,可在有效抑制高频振荡的同时避免激发其它频段的振荡现象。

The high-frequency oscillation(HFO)phenomenon in modular multilevel converter based high voltage direct current(MMC-HVDC)system is caused by the interaction between AC system impedance and negative damping characteristics induced by the control link delay.At present,most of HFO suppression strategies are easy to cause oscillation in the middle and low frequency band while suppressing HFO.To solve the above problems,this paper establishes the mathematical models of MMC high frequency impedance including link delay and AC system high frequency impedance,and analyzes the mechanism of HFO.Furthermore,the HFO suppression strategy is proposed to add the improved active filter to the voltage feed-forward link in the inner loop control.The control parameters of the filter are designed and compared with the suppression strategy adding a band-stop filter to the voltage feedforward link.Finally,the electromagnetic transient simulation verifies that the suppression strategy will not affect the stable operation of the system,but can effectively suppress the HFO while avoiding the oscillation of other frequency bands.