Realization of a five-level NPC inverter using carrier phase-shift technique

This paper presents a theoretical study and experimental results of using phase-shift technique to dilate the output spectrum of a five-level neutral-point-clamped (NPC) pulse width modulated (PWM) H-bridge inverter. It is shown that the output spectrum can be made to consist of the multiple of the fourth order cross-modulated harmonics with appropriate phase-shift combination. The spectrum dilation offers an advantage of reducing both the number and magnitudes of the low-order signal harmonics without increasing the carrier frequency which will inevitably increase the switching loss. Experimental results obtained from a proof-of-concept prototype with a 10 kHz triangular carrier and 200 Hz sinusoidal modulating signal confirm the superior features of the proposed scheme.