SVG机间谐波交互对子模块直流电压的影响分析与抑制方法

Analysis of Influence of Harmonic Interaction Between SVGs on Sub-module DC Voltage and Suppression Method

为确保风电区域网内动态无功合理分布和电压达标,大量静止无功发生器(static var generator,SVG)被接入风场和风场汇流站,但由于SVG机间交互作用导致的设备负交互问题也开始显现。针对此类问题,首先分析H桥级联型SVG双机拓扑结构,针对双机载波异步条件下产生的机间高次谐波电压差进行数学推导,研究高次谐波环流对SVG内H桥子模块电容直流电压动态稳定性的影响。通过对各H桥子模块电容吸收有功功率差异的推导分析,发现非特征谐波与H桥子模块直流电压失衡之间的内在联系,指出当谐波环流导致非特征次谐波越限时,将会引发各H桥模块直流电压不平衡,并且提出一种直流电压均衡控制策略来解决SVG直流电压失衡的问题,实现各H桥子模块直流电压稳定,最后通过仿真验证了理论分析和所提控制策略的正确性。

To ensure reasonable reactive power distribution and voltage regulation,a large number of static var generators(SVGs)are connected to wind farms and afflux stations.However,the issue of negative interaction caused by the interaction between SVGs emerges.Aiming at this problem,firstly,the cascaded H-bridge topology of two-parallel SVGs is analyzed.Then,inter-converter harmonic voltage difference is derived under the condition of parallel SVGs with asynchronous carriers,and the effect of higher harmonic circulation on dynamic stability of the DC voltage of the H-bridge sub-module in SVGs is studied.The intrinsic relationship between non-characteristic harmonics and DC voltage imbalance of H-bridge sub-module is found out by deriving and analyzing the difference of active powers flowing through DC capacitor.When the non-characteristic harmonics exceed limit due to harmonic circulation,H-bridge DC voltage imbalance will be induced.A DC voltage balancing strategy is proposed to solve the SVG DC voltage imbalance problem,so that the DC voltage of the H-bridge sub-module keeps stable.Finally,correctness of theoretical analysis and the proposed2 control strategy are verified with simulation.