Impact of Dead-band Time on the Harmonic Spectrum of Power Converters

Power electronic (PE) converters suffer from a topological disadvantage as they often employ two series-connected switches within a common leg of a converter. These two switches have a complementary role i.e. when one switch is ON, the other must be OFF otherwise a short circuit will result with impending risks for the switches and power supply. This condition must be respected at all times - during steady-state and transient switching periods. Although modern PE switches are very fast switching, their speed is not infinite. And, in practice, a suitable dead-band time is required with any pulse width modulation (PWM) technique to prevent the occurrence of a short circuit between two switches in a common leg. A larger dead-band time enhances the security of operation of the switches (converter) but at the expense of additional harmonics and lower efficiency. This paper investigates the impact of dead-band time on the harmonic spectrum for a single-phase H-bridge converter for low/medium voltage applications and cascaded H-bridge (CHB) multilevel converter for medium/high voltage applications.