非隔离型三电平并网逆变器的输出滤波器优化设计

将非隔离型三电平并网逆变器的LCL滤波器电容公共点直接引回直流侧中点,可以有效减小漏电流,但同时也会导致桥臂电流有效值增大且易发生共模谐振,降低了逆变器效率和稳定性。对于诸如光伏并网发电场合,建立了非隔离型三电平并网逆变器的共模和差模等效模型,在此基础上分析上述问题的产生机理,并提出一种基于共模差模解耦的输出滤波器设计方案。该方案首先在结构上将滤波电容分为并联的两部分,仅将其中容值较小的电容公共点引回直流侧中点以降低共模和差模滤波回路之间的参数耦合程度;其次在分析逆变器桥臂电流纹波和输出共模源频谱分布的基础上,给出所提滤波器的参数设计原则。最后,通过一台5kW三相三电平逆变器样机对所提滤波器优化设计方案进行实验验证,结果表明所提方案在满足并网标准和漏电流抑制要求的同时,能够有效提高系统稳定性和效率。

Optimized Design of Output Filter for Transformerless Three-level Grid-connected Inverter

Linking the capacitor neutral point of LCL filter for transformerless three-level inverter back to the DC midpoint directly has an advantage of leakage current reduction. But it also brings large current virtual value and common-mode resonance of bridge-side current, which leads to the reduction of the system efficiency and stability. For occasions such as the grid-connected photovoltaic power generation, the common-mode and differential-mode models of three-level grid-connected inverter are developed. Based on the models, the mechanism of the two problems is analysed and an optimized design scheme is proposed. In the scheme, the capacitor of LCL filter is divided into two parts and the neutral point of the smaller one is linked to the DC midpoint, which reduces the parameter coupling degree between the common-mode and differential-mode circuits. Then, the design principles of the filter parameters are proposed based on bridge-side current ripple and common-mode voltage source spectrum analysis. Finally, an optimized design scheme of the proposed filter is verified by a prototype 5 kW three-phase three-level inverter,, the results showing that the proposed method is able to satisfy the integration standards and inhibition requirements of the leakage current while improving the system efficiency and stability.