SHE-PWM switching strategies for active neutral point clamped multilevel converters

The main drawback of the diode neutral-point-clamped (NPC) converter is the unequal loss distribution among the semiconductor devices which confines the maximum output power and the switching frequency. To address this drawback, switching state redundancy is required to evenly distribute the losses and can be achieved differently as the level of the converter changes. For instance, the three-level active NPC (3L-ANPC) converter has switching state redundancy and is derived from the 3L-NPC converter by adding an anti-parallel switch to the clamping diodes; in the 4L-ANPC converter, the combination of a 2L converter and a 3L-ANPC converter is used; in a 5L-ANPC converter, the combination of the 3L-ANPC and 3L-flying capacitor (FC) converter is advantageous. The paper discusses selective-harmonic-elimination (SHE) pulse-width-modulation (PWM) strategies for the above mentioned converters and explains how loss distribution can be achieved.