Nose-to-Tail Modulation of Three-Phase 12 N Switching-Cells Inverter for Zero Common Mode Voltage

Aiming at a class of transformerless three-phase dc/ac inverters with N times of 12 switching-cells, this letter proposes a novel nose-to-tail modulation (NTM) method, which can realize zero common-mode voltage (CMV). The NTM algorithm places the driving pulses nose-to-tail of the six conversion units in the upper/lower arm, so as to realize the same number of units put into the upper and lower arms at any time. In addition, a dead-time compensation scheme achieving the elimination of narrow pulse CMV caused by dead time is also proposed for NTM. As a result, the zero CMV can be achieved. Although the proposed NTM slightly increases the modulation complexity, it is of great significance in CMV sensitive systems, such as grid-tied and motor drive systems. The effectiveness of the proposal is verified by experiments.