Three-dimensional space vector modulation for four-leg voltage-source converters

Four-leg voltage-source converters can effectively provide the neutral connection in three-phase four-wire systems. They can be used in inverter, rectifier, and active filter applications to handle the neutral current caused by the unbalanced and/or nonlinear load or unbalanced source. In this paper, three-dimensional (3-D) space vector modulation (SVM) schemes are proposed for controlling the four-leg voltage-source converters. Important issues for 3-D SVM, such as definition of 3-D vectors, identification of adjacent switching vectors in the 3-D space, and switching vector sequencing schemes and comparisons are addressed. The proposed 3-D SVM is a superset of the traditional two-dimensional (2-D) SVM, and thus it inherits all the merits of the traditional 2-D SVM. A 100 kW 5 kHz four-leg inverter and a 20 kHz four-leg rectifier prototypes are built and controlled by the proposed 3-D SVM. Experimental results are presented to validate the effectiveness of the 3-D SVM.