电力电子主导的交直流混联电网振荡分析与评估

Oscillation Analysis and Evaluation of the Power Electronics-dominated Hybrid AC/DC Grid

电力电子变流器主导的交直流混联电网极易产生各类振荡问题,为了对其进行有效的抑制和预防,需对系统进行全面的振荡分析与评估。对此,频域模态分析法(frequencydomain modal analysis,FMA)作为振荡诊断的有效工具,已成功应用于电力电子变流器主导的交流电网中。然而,FMA在对交直流混联电网振荡的评估中存在一定局限,即无法准确刻画广域/局域振荡特性。为此,该文结合FMA和对角占优理论,提出一种面向交直流混联电网的振荡分析与评估方法,能够准确反映广域/局域振荡特性,并获取振荡源、振荡传播以及振荡阻断等信息。首先,揭示交直流系统特有的局域振荡现象及其形成机理。其次,建立振荡评估指标体系,包括谐振模式指标、节点/支路/回路振荡指标和广域–局域振荡指标。最后,在MATLAB/Simulink平台上搭建一个风电场经多端柔直送出的测试系统,通过仿真分析验证上述振荡评估方法的有效性,所得振荡相关信息能够指导系统镇定方案的制定。

The power electronics-dominated hybrid AC/DC grid has been suffering from various oscillation problems.To effectively suppress such oscillation issues,it is necessary to carry out a comprehensive analysis and evaluation of the system oscillation.In this respect,the frequency-domain modal analysis(FMA)method has been widely applied in the oscillation analysis of the power electronics-dominated AC grid.However,as will be revealed in this paper,there exist some limitations in the FMA when applied to the hybrid AC/DC grid,i.e.,inability to accurately characterize the wide-/local-area oscillations.Therefore,based on the FMA and diagonal dominance theory,this paper proposes an oscillation evaluation method for the hybrid AC/DC grid,by which the wide-/local-area oscillations can be well characterized and information like oscillation source,propagation and intercepting can be obtained.Firstly,the unique local-area oscillation phenomenon of the hybrid AC/DC grid is revealed as well as its formation mechanism.Secondly,the oscillation evaluation indices system is established,including oscillation mode index,node/branch/loop oscillation index and wide-/local-area oscillation index.At last,a multi-terminal HVDC transmission test system connected with large-scale wind farms is built in MATLAB/Simulink to validate the proposed evaluation method,where the oscillation relevant information obtained can guide the system stabilization plan-making.