基于独立分裂电容的非隔离型中性点箝位逆变器漏电流抑制

Leakage Current Suppression of Non-isolated Neutral-point-clamped Inverter Based on Independent Split Capacitor

为了解决非隔离型中性点箝位(neutral-point-clamped,NPC)三电平并网逆变器的漏电流问题,该文提出一种拓扑结构与调制相结合的漏电流抑制综合方案,该方案在抑制桥臂电流低频震荡、减小连接线电流和抑制漏电流方面可达到综合效果最优,同时又能控制直流母线中点电位平衡。首先,针对拓扑结构提出一种独立分裂电容(independentsplitting capacitor,ISC)结构的改进方法,该方法是一种折中处理方法,在减小漏电流的同时可以显著减小连接线电流,从传递函数的角度分析独立分裂电容值对漏电流和连接线电流的影响,并给出独立分裂电容值的理论计算公式。其次,在调制策略上采用一种基于LMZVM&LMSVM的矢量混合调制,通过减小共模电压变化率来进一步减小漏电流,并实现直流母线中点电位平衡控制。最后,通过仿真和实验对提出的ISC?LMZVM&LMSVM漏电流抑制综合方案进行验证,结果表明了该方法在漏电流抑制、减小桥臂电流低频振荡和连接线电流方面的有效性。

In order to solve the leakage current problem of non-isolated NPC three-level grid-connected inverter,a comprehensive scheme of leakage current suppression combining topology structure and modulation was proposed.This scheme has the comprehensive optimization effect in suppressing the low-frequency oscillation of the bridge arm current,reducing the link-line current and suppressing leakage current,and at the same time,it can control the neutral point potential balance of DC bus.Firstly,for the topology structure,an improved method of independent splitting capacitor(ISC)structure was proposed.This method is a compromise processing method,which can significantly reduce the link-line current while reducing the leakage current.The influence of the ISC on leakage current and the link-line current was analyzed from the point of view of transfer function,and the theoretical calculation formula of ISC value was given.Secondly,in order to further reduce the leakage current,a vector hybrid modulation based on LMZVM&LMSVM(LMZVM:Large Vector,Medium Vector and Zero Vector modulation;LMSVM:Large Vector,Medium Vector and Small Vector modulation)was adopted in the modulation strategy to further reduce the leakage current by reducing the common-mode voltage change rate,and the neutral point potential balance control of DC bus was realized.Finally,the comprehensive scheme of ISC?LMZVM&LMSVM leakage current suppression proposed was verified by simulation and experiment.The results show that the proposed method is effective in leakage current suppression,reducing the low-frequency oscillation of bridge arm current and link-line current.