In this paper, the novel three-dimensional space vector modulation (3DSVM) under d.c. variation is proposed for controlling the 3-leg center-split inverter. Different from the conventional 2-Dimentional SVM, the zero vectors can not only reduce the switching losses by optimizing the switching sequences but also compensate the neutral line current in the novel 3DSVM. However, the dc voltage variation affects the origin or reference point along with the zero-axis, which is considered as the most important operation issues of the three-leg center-split inverter. The 3DSVM under d.c. variation is achieved, which can maintain the output performance when the d.c. voltage unbalance occurs. And the d.c. voltage variation limitation is also discussed. A 3-leg center-split inverter prototype is implemented and used as a shunt power quality compensator for three-phase four-wire system. Simulation and experimental results are given to validate the effectiveness of the proposed control strategy.