非隔离型三电平逆变器漏电流抑制与中点电位平衡控制

Leakage Current Suppression and Balance Control of Neutral Point Potential for Three-level Transformerless Inverter

针对中点钳位型三电平逆变器在光伏并网系统中存在的漏电流和中点电位不平衡的问题,文中对漏电流产生的机理和影响中点电位的因素进行了分析。针对已有调制策略存在的不足,在已有调制策略的基础上,对传统调制策略下的调制扇区进行重新划分,并在此基础上选择合适的开关序列,得到一种新型的大中小矢量调制策略。文中所提调制策略的共模电压变化幅值低、直流电压利用率高、输出电压的总谐波畸变率低,且能够对中点电位进行有效控制。最后,通过仿真和实验,将所提策略与传统调制策略在漏电流抑制和中点电位控制等方面进行对比,验证了所提调制策略的有效性。

In view of the leakage current and the imbalance of the neutral point potential of the neutral point clamped(NPC)threelevel inverter in the grid-connected photovoltaic system,the mechanism of the leakage current and the factors affecting the neutral point potential are analyzed in this paper.Aiming at the shortcomings of existing modulation strategies,based on the existing modulation strategy,the modulation sector with the traditional modulation strategy is re-divided.On this basis,suitable switching sequences are selected,and a new type of large medium and small vector modulation strategy is obtained.The modulation strategy proposed in the paper has low variation amplitude of common-mode voltage,high variation amplitude of DC voltage,low total harmonic distortion ratio of the output voltage,and it can effectively control the neutral point potential.Finally,through simulation and experiments,the proposed strategy is compared with the traditional modulation strategy in terms of leakage current suppression and neutral point potential control,and the effectiveness of the proposed modulation strategy is verified.