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.