A Simple Carrier-Based PWM Method For Three-Phase Four-Leg Inverters Considering All Four Pole Voltages Simultaneously

Complexity of the three-dimensional space vector PWM (3D-SVM) algorithm can be reduced using an equivalent carrier-based continuous PWM method. However, since the neutral-phase voltage was neglected in determining the zero-sequence voltage of the PWM, it introduces an error for an imbalance case, increases complexity of the algorithm, and is inconsistent with the carrier-based PWM for the three-leg inverter. This paper proposes a new and natural standpoint for the carrier-based PWM of the four-leg inverter, by considering all pole voltages including that of the neutral phase simultaneously in the determination of zero-sequence voltage. This new viewpoint renders the full consistency between the PWM methods for the three- and four-leg inverters. It can generate both continuous and discontinuous PWM easily in the same manner as is done for the three-leg inverter. The connection between the discontinuous PWM and the 3D- SVM is also clarified.