Phase-Shifted Carrier-Based Synchronized Sinusoidal PWM Techniques for a Cascaded H-Bridge Multilevel Inverter

This paper analyzes synchronization strategy for cascaded H-bridge multilevel inverter (CHBMLI) topologies with a carrier-based sinusoidal phase-shifted pulse width modulation (PSPWM) technique. In the PSPWM technique, a separate carrier is used for each H-bridge (HB). The carriers are generally phase shifted from each other by π/x rad (x = No. of HBs) for unipolar PWM. With the carrier frequency being an integer (odd/even) multiple of the fundamental frequency, it is observed that the positions of zero crossings of the carriers with respect to the zero crossings of voltage references play an important role for maintaining quarter-wave symmetry among multilevel inverter pole voltage waveforms. This paper analytically shows the conditions for half-wave symmetry and quarter-wave symmetry and experimentally verifies those conditions for the PSPWM technique with a five-level CHBMLI laboratory prototype.