LCC-MTDC系统换流器直流改进三脉动谐波模型研究

Advanced three-pulse harmonic models of converters of LCC-MTDC systems

基于电网换相换流器的多端直流(LCC-MTDC)输电系统是未来的发展方向。直流滤波器设计的优劣极大地依赖于LCC直流谐波模型的准确性。LCC-MTDC系统中各换流器的谐波相互渗透、互相影响,对换流器直流谐波模型提出了更高的要求。本文采用分段线性法,对换流阀在每个周期中的全过程进行机理分析,进而形成改进三脉动谐波模型的电压和电感模型,因此改进三脉动谐波模型能够准确地反映交流系统不对称及背景谐波的影响。以并联三端LCC-MTDC系统为例,通过与PSCAD/EMTDC仿真结果进行比较,验证了本文所提换流器直流谐波模型具有更好的计算准确性。

The multi-terminal direct current(MTDC)transmission system is the development trends in HVDC technology.In order to design DC filters reasonably and effectively,an accurate harmonic model of converter need to be established.Since 3-pulse harmonic model can only be applied in symmetrical system without considering the effect of background harmonics,the model is not accurate enough to be used in HVDC transmission project.For above reasons,this paper proposes an advanced 3-pulse harmonic model which can apply in the asymmetric system.The advanced model has the same topology as 3-pulse harmonic model,but the influence on asymmetric factors and background harmonics of 3-pulse harmonic voltage source and 3-pulse inductance are taken into account.Finally,taking Three Gorges-Changzhou HVDC transmission project as an example,through the compare of simulation in PSCAD/EMTDC demonstrate the correctness of the advanced 3-pulse harmonic model.