Four-dimensional space vector PWM algorithm for multilevel four-leg converters

Four-leg voltage-source converters provide an effective neutral connection in three-phase systems with neutral wire. They can be applied to inverters, rectifiers or active filters to control the neutral current caused by unbalanced or nonlinear loads as well as unbalanced sources. From the modulation point of view, the four-leg converters can be considered as four-phase systems. Hence, the modulation task can be carried out with a generic multiphase modulation algorithm. Recently, a novel space vector PWM technique for multilevel multiphase voltage-source converters has been presented. The four-dimensional space vector PWM algorithm for multilevel four-leg converters presented in this paper is the result of applying such technique to a four-phase converter. Finally, the algorithm is implemented in a low-cost FPGA and it is tested with a prototype by using a five-level cascaded full-bridge inverter.