The photovoltaic power generation and active filter (PV-AF) system can realize photovoltaic grid-connected power regulation, and meanwhile it can also improve the power quality of power grid effectively. The four-leg grid-connected inverter has successfully been used in the three-phase four-wire system. In this paper, a three-dimensional space vector pulse width modulation (3D-SVPWM) method based on the gh$\gamma $ coordinate system for a four-leg inverter has been proposed. As the switching vectors of the four-leg inverter are in the three-dimensional space, it is difficult to realize the complex modulation process. In order to simplify the modulation process, the reference vector is placed into gh$\gamma $ coordinates in the proposed modulation strategy, and then the vectors are selected and the duration times are acquired directly by a group of intermediate variables, which could be obtained by linear transformation of the coordinates. As the intermediate variables are used, the modulation can be easily implemented by the proposed modulation strategy without excessive mathematical calculations. The simulation and experimental results all confirmed the validity and effectiveness of this strategy.

The photovoltaic power generation and active filter (PV-AF) system can realize photovoltaic grid-connected power regulation, and meanwhile it can also improve the power quality of power grid effectively. The four-leg grid-connected inverter has successfully been used in the three-phase four-wire system. In this paper, a three-dimensional space vector pulse width modulation (3D-SVPWM) method based on the gh$\gamma $ coordinate system for a four-leg inverter has been proposed. As the switching vectors of the four-leg inverter are in the three-dimensional space, it is difficult to realize the complex modulation process. In order to simplify the modulation process, the reference vector is placed into gh$\gamma $ coordinates in the proposed modulation strategy, and then the vectors are selected and the duration times are acquired directly by a group of intermediate variables, which could be obtained by linear transformation of the coordinates. As the intermediate variables are used, the modulation can be easily implemented by the proposed modulation strategy without excessive mathematical calculations. The simulation and experimental results all confirmed the validity and effectiveness of this strategy.